Getting to the bottom of things or clean until there is nothing left to clean

So with a new (old) espresso machine comes a lot of responsibility cleaning.  Unfortunately one finds that just because someone says they cleaned a machine or that they say it has a problem with a pump does NOT mean that is true.  I’ve found that just because I take everything apart and soak it in cleaners and sanitizers and sometimes even hit it with a steam cleaner or some other method does not mean that someone else did.

After finding that something was shorting out I googled for things that cause this and the most likely scenario was that the heater was shorting out.  If you google “repair espresso heater element” or something similar you are likely to find one of two articles posted at Orphan Espresso about how to repair a heater element that has been damaged by water leaks.  In those articles they tell you to disconnect the power leads and get in between the metal of the boiler and the various parts of the heater element.  You will find a center metal element wrapped in various materials such as ceramic, other metal bits, and some sorts of resin/epoxy like material or other insulating things.  What happens is over the years the material cracks and breaks down and absorbs water like a sponge into all the nooks and other broken bits.

To repair this you have to test the metal boiler to element to prove there is a short with a resistance check using a multi-meter.  If a reading between the metal body and the heater element connection shows continuity then you have a short.  If you look around the wire and probe it with a fine metal pick you will probably see the material start to crumble and flake out.  You will need to dig out all of the material that will come free scraping and digging until it seems solid.  You will STILL have a short after this.  Depending on how adventurous you want to be you have two possible options.  If you have a heat gun you can start off there and possibly get lucky.

Previously I had been remodeling a house and used a heat gun to help speed up drying certain paint touch ups and for removing paint from woodwork.  I had picked up a heat gun from Home Depot to do this and had used this one linked from Amazon below:

Wagner Digital Heat Gun HT3500

You don’t really want to set it more than about 500 degrees and only want to hold it a few inches away waving it around somewhat quickly not lingering directly on it for more than a couple seconds. After a few minutes check it again with the meter. After about 10 minutes of warming it up repeatedly it should dry out and show no connectivity.  If it continues to show connectivity keep heating it up some more but if it never gets any better you might need to replace the heater.  The article on Orphan suggests removing the heater from the boiler and baking it,.  Depending on the age and “standardness” of your boiler you might not want to take it apart due to possibly having problems finding new gaskets.

In my case this is a non-standard machine.  If the gasket was damaged when taking it apart I’d have more difficulty finding a replacement.  I may still need to do this but for now the boiler wasn’t leaking around that area so I didn’t want to risk it.  Obviously you will need to try to drain the boiler and any water tanks before tipping your machine over to get to the heater parts if they are not available on the top or sides.

When I flipped the machine over I had a plate.


After removing the bolts and taking off the plate I saw evidence of rust on the contacts.  Obviously water had come from somewhere at some point and got into the heater parts and clearly rusted the connectors.


I went to an automotive parts store and purchased a clear liquid that removes rust.  You want something that eats the rust off and converts it.  Not something that converts the rust where it is and builds new layers.  Usually the kind that removes it and converts is somewhat clear or yellowish.  The one I used was “pH neutral” and thus not an acid.  You should probably try to find something like that.  The ones that are milky white or bluish are binders that convert the rust into a crusty black later bonded to the surface should not be used because it might cause issues with the electricity and the connector.

To rebuild the insulator around the heater I had to use a non-conductive high temperature epoxy.  I also used an insulator paint to cover the replaced epoxy.  When it was done it looked like this (I just painted over the end  more than was probably necessary but it’s not exactly easy to paint the insulator in sometimes).


To seal it I used a tube of epoxy putty from Amazon:

Rectorseal EP-200

They have a larger tube that is the same material in case you use epoxy more regularly than I do. The 200 number on the end has to do with the size. an EP-400 is the bigger version of the EP-200 (2 ounce vs 4 ounce). This epoxy is NSF certified for food/drinking water contact and is safe for 500 degree Fahrenheit contact. You have to let the epoxy cure for at least an hour before painting it. I tested the multimeter readings after installing the epoxy. It shows a short until the epoxy is cured. The epoxy hardens in just under 15 minutes. I used some tools for working with moulding clay for making decorative beads and figures to push the epoxy down into the gap and smooth it off.

I picked up the tools from Michael’s (a craft supply chain) and paid way more (4-6 times) for it than the Amazon price:

11 piece Clay Tool Set

After it curing for an hour I then used an insulator varnish that I also picked up from Amazon:

MG Chemicals 4228 Red GLPT Insulating Varnish, 55 ml Bottle

The more commonly recommended insulator paint is something called Glyptal. Finding that might be possibly for you but I was not able to find it or anything like it nearby. I’m pretty sure the GLPT in the description is in reference to Glpytal. It is a strong insulator once dried and seals out moisture and is able to withstand a bit over 300 degrees Fahrenheit worth of heat. Glyptal has the same basic properties.

After letting it dry I found the same test results with the multimeter showing the short repaired. I used the heat gun to hurry up the drying so I could test the multimeter reading. I let the entire thing sit 24 hours before turning the heater on for testing.

Prior to working on the heater I tried cleaning the machine.  I had to remove the dispersion screen/bolt but the first screw driver I used was too small.  I found that the only screwdriver that worked well was a HUGE 5/8 inch wide flat screw driver.



Once I did that with the correct screwdriver I found that the item did not seem like it had ever been cleaned because it never looked like it had been removed before my attempt.  It looked like this inside where the water comes in against the back side of the screen.



Looking at the underside I saw evidence that the 8 outlets for the dispersion bolt were blocked.  Only 3 clearly had a strong water path etched in the gunk left in the machine due to it not being cleaned.



After a good cleaning the dispersion screen/bolt looked like this:


The area behind the dispersion screen looked like this:


The following day I started up the machine and the heater did stay on and the whole system cycled through heating, steaming, and dispensing.  Pressure looked a little low until I ran some TSP through the system diluted in water.  After a few minutes of flushing the cleaner into the tank suddenly huge blobs of espresso grinds started squirting out of the machine and all of the water was dark dark brown.  Several gallons of water through the system later it came out clear-ish and I moved on to other cleaning solutions.  Following the brown water and espresso grind mixtures I found the pressure in the machine drastically improved.  I would say it was the difference of a trickle vs it gushing out once the brown had gone away.

As a result of the above I spent $362 for the machine on eBay.  I bought a $3.81 tube of epoxy putty and $10.33 for the insulator paint.  The rest of the items were pretty much optional and technically I only used about $0.10 worth of any of them.  So skipping the tools since I will likely still use them for other things or already had them – I spent $376.14 for this espresso machine.  Add to that about $15 worth of gas to drive to and from where I picked up the machine.

Pretty on the outside and ugly on the inside prototype

So I’ve been busy doing a bunch of computer maintenance and looking into other things I’ve neglected while building the roaster so it’s been a bit slow.  I decided I wanted to start gluing corners together and drilling some holes to see how the case goes together so I can eventually get back to fixing the issues with the roast controller case.  Over the past several weeks I soldered together all of the boards, made wiring harnesses and figured out a bunch of “oops” moves I had made designing things when I got rushed for time.

Turns out I was not able to get stand offs locally in the sizes I had wanted so the heights are all screwed up where I placed holes on the outside surfaces.  I also forgot to specifically allocate power for the exhaust fan in the original design BUT I did have “Spare” pins allocated. The fan I ordered also was not the right size for the hole template I had used (Inside fan dimension vs outside screw / case dimension)… neither of them were actually labeled right the way every other fan I have is sized.

So with everything screwed or harnessed in place this is what I have for the Arduino…

The Arduino wired for Coffee Roaster control

It is a MEGA2560 mounted on a Crib for Arduino.  On top is an Ethernet Shield w/ microSD slot.  Then I used a variety of crimped headers to connect to some of the pins on the MEGA and on the ethernet shield.  I have twenty five lines in the bundle going to the Arduino.  I had some spare 10 strand cables from a project at Halloween and no 25 strand cables to use so I used one of those cable wraps to keep the all together after connecting DB25 to one end and header pins to the other.  Once the lid for the crib for Arduino is in place it then connects to the back of the enclosure.

Wiring Harness connecting to the back of the controller enclosure

As you may notice the sockets I was using for connecting the power out are the type that snap in.  The majority of these will not snap into most laser cut plastic sheets and instead are designed for aluminum cases.  The plug to the right on the other hand screws in.  These work great with a variety of thicker locations.  The fan was originally going to be on the inside with a wire cover on the outside but with the wrong size fan hole in use I had the wrong cover to fit the fans that I had that would fit the hole.

For the DB25 connectors it turned out good that I had decided to use a cut out pattern  that had the holes on the side for the anchoring hex nuts rather than just having them cut out so that I could mount them to the socket and anchor the connector.  Since the stand offs were too short they don’t allow me to anchor the PCBs to the bottom plate.  Instead I had to screw them to the back plate using normal screws and with the burnt circles on the laser cut work I had to use some washers too to keep it sturdy.  This is what the back plate looks like.

Rear Panel of controller

This panel includes – One non-filtered switched 15Amp Power Entry module, 2 snap in 15 amp convenience plugs, 1 5VDC fan, 2 DB-25.  The left one is the main guts for the LCD, TRIAC control, potentiometers, thermocouple, and a variety of other sensors.  The right includes all the non-essential stuff for backlighting all the buttons on the button pad and a few other things including spare wiring.  You cna see just a screw on the right since it was relatively intact and so it won’t block the DB25 plug being used.  The right DB25 has washers and screws in place.  These are primarily used to attached the PCB in place attached to the back side.

Next up is the inside view of the electronics area:

Rear View of the Back Panel

Rear view of the back panel.  I need to shrink up the crimp connectors around the wire  (they shrink like heat shrink tubing but is actually much firmer).  Also the connector on the right side (the switched power entry module) should have the screws more securely fastened with nuts and washers but this is mainly just a test to ensure it all fits together and then allow me to focus on some programming for a while to see if I can get more working and develop menus etc.  The clear acrylic bar is used to anchor the corners better.  I need to change the locations of the screws since I could not find screws the size I wanted without spending way too much for large quantities of them on the internet and having them shipped to me etc.  The thermocouple board on the right had the same issue with the stand offs so it is just floating loose in there right now.  I need to find somewhere to get the Omron thermocouple sockets where I dont need to order them by the 1000s since it looks like Ryan McLaughlin has stopped selling things on his site when they (used to) have problems getting the newer MAXIM thermocouple chip.  They’re all over the place now but he hasn’t restarted his store up so I don’t know the deal there.

Here is the view down into the enclosure from above:

Top view into enclosure

With the cover on:

Front panel installed on enclosure

Front panel running

Front Panel Running

When I send it back out again for a new case I hope to have a different board to install that will be switching the smaller breakout boards being designed onto the circuit board as well as add a power supply and possibly having an arduino board mated on top of the circuit board perhaps to bring more of the electronics inside.  I might want to try to get a Digilent board perhaps to try converting to it as a transition between Arduino and PIC32 before I completely switch to a dedicated PIC32.

I’ve also been looking at possibly creating a dedicated PC application to communicate with it directly via USB and over ethernet.  I am toying around with the “QT/QML” language but havent gotten too far with it.  I may just go back to Processing though.

FreshRoast SR500 Teardown – Part 3

Continuing the series of taking a Fresh Roast SR500 apart leads us to the internal heat / air mechanisms.  At this stage you have reached the components critical to any modifications of your roaster.  I’m updating this post in December with photos taken back in October when I stripped the roaster down the rest of the way and began building my modifications.

Part 1 we started with the external screws to gain access to the internals.  In Part 2 we separated the electronics between the high and low voltage and then lifted the high voltage board out with the heater/fan.  This left us here:

Heater / Fan and Power board assembly

We have now reached the point where we unplug the old roaster boards and start looking at attaching alternate controls.  At this point you are going to separate the metal connectors from the board (assuming you are replacing any of these parts or modifying it in some way)  You will have a black plastic cover from the top, a metal cone underneath that funnels the hot air towards the vented top, and a black plastic pan with a fan sticking to the bottom.  The pan will have three screws.  You see one of the locations to the left side and another to the right.  The third one is not visible in this photo due to it being on the back side of everything you see.  If you remove the phillips screws from these locations it will allow the top plastic piece to be separated.  The top metal piece is sandwiches between these plastic pieces and held in place with the screws mentioned above.  The metal piece is sealed to the heater mechanisms inside the bottom black plastic pan using silicone sealant.

Once you lift the top covers off and break the silicone seal you see this:

and this:

The fan is firmly connected to the bottom and up into the blades.  The fan is a straight sheet of metal leading from the middle out to the edges with a flat disc on top.  It is not apparently simple to separate and seems quite “stuck” in place.  The middle “axle”/hub of the fan does not appear to have an obvious way to disconnect it though I’m sure there is a way to do so.

Looking back at the heating area you will see the bimetallic switch and a temperature sensitive fuse.

In the center there are two bolts/nuts .  These anchor the top part of the funnel to the heater coil.  You will notice 4 spots that look like staples above.  These are how several supports made of the same material that the fuse and switch are riveted to.  There is a metal ring holding this all in place with a “washer” made out of the same material again.  This material is a high temperature material often used in heat guns, hair dryers, and popcorn poppers.  It is designed not to burn and to cool off quickly.  There is no point in disconnecting the nuts  you see and you are likely to damage something in the process when you try.  Immediately under the center part is a small heater coil that connects to the fan.  This coil always generates heat whether the system is on or in “cool”.  It is used to lower the voltage from 120 volts to somewhere close to around 20 volts DC using resistance and the resulting energy given off by the coil.  The remaining electricity leads out from the system to the “black box” rectifier on the bottom of the fan motor.  The outer coil is on the opposite side of the slit and continues all the way around providing the majority of the heat.  You can see the outer cool quite clearly in the photo below.

In the photo above and below you clearly see the temperature fuse.  This device is called a ThermoDisc Microtemp thermal cutoff.  There is a PDF that discusses the features of this particular device  It also has a diagram of the inner mechanisms that make this work.

It is a Thermodisc G4A01216C 216*C Cutoff.  Once the red stuff melts (at 216 degrees Celcius) there is a spring inside that is released and it mashes the wire outside of the housing and no longer makes contact to allow the electric to flow.  Once it fails the only way to repair it is to bypass it or to put a new one in.  Since the mechanisms are anchored with a rivet they are not the easiest to source and replace but it is possible to do.

The last mechanism is a Klixon YS10 46b-s x9ab.  This is a Klixon YS10 Series 150*C Beryllium Copper Arm, Standard Length Terminal (31.5).  Normally once it triggers at 150 Celcius it then has to cool before it works again.  The reset is set to 90 degrees normally and some models has a different offset.  YS10 specifies the type, 46 is the temperature (150 degrees) b specifies Beryllium Copper (the bimetalic switch material) -s for standard.  In the X9ab position this would possibly be where a different temperature reset amount would be specified.  It does not clarify the numbers used there.  It appeared in the PDF linked above as (XX) in the part number.  This MIGHT be that it needs a 9 degree temperature drop on the switch before it engages again assuming it uses an X as a place holder rather than using a 0.  Since it is not in parentheses this might simply be some sort of a plant number or production date rather than a temperature offset.



Many modifiers like to disconnect both the fuse and the bi-metallic switch.  I do not advise this unless you are absolutely sure what you are doing.  If you wish to use the center heat coil separately or with the main coil together this is up to you.  You will need to disconnect the white wire that leads to the fan by prying open the brass clip (under the heat shrink) and supplying your own transformer to around 20 volts AC to independently control the fan.

At the moment I’ve been using an Arduino to control a Q4015L5 triac with a MOC3052 and a H11AA1 as a zero crossing detector. There are two triacs each used to separately power the fan and the heat circuits. Each side’s gate is triggered with a MOC3052 opto-isolator by a single pin on the Arduino to a resistor through the moc’s infrared led and on to the ground pin. The H11AA1 works the opposite way triggering a led on the high voltage side and it measures the fall of the 60hz sine wave of US electric.  Each fall signals the Arduino on another pin that is connected to a hardware interrupt on the processor. The interrupt sequence compares the fan and heat potentiometers to a map and then uses the lookup value to set the length of a processor timer. The timer then comes back and fires the fan or heat pin that fires the MOC3052 linking the triac and connecting power from the input side.

I disconnected the white wire from the fan and routed it with the primary heater coil so that they both run at the same time. On the fan side I connected it to a transformer from Radioshack that outputs 25VAC. This appears to adequately run the fan and delivers more air flow than normal due to the fan being “overdriven” from it’s normal voltages. While this is not good for long term use this could be useful if properly triggered in the programming for cooling and drying or initial heat up. In other words turn heat on at 70%. Start fan at 120% Gradually drop fan to 100%. Increase heat to 100% while dropping fan to 60%. Etc…

While running the system from a variac and through a watt/amp monitor I found the fan consuming approximately 50 watts at the original 100% air flow on through the new maximum around 70 watts for a 125 to 130% flow rate. Once I turned on the heater I found the original wattage level use set at 80 to 85% heat and what seemed like a normal heat output felt by hand in front of the output. Lately I had been getting around 1520 watts with momentary flutters up to 1580 at high and full fan before bypassing the controls. Now at 100% it was showing upper 1600 to 1750 watts for the brief few seconds before I turned it down.

I’m pretty certain this is not designed to run like this and would likely melt something if left to run this way on it’s own without some sort of “safety” override in the programming. What I would expect to be necessary is to mandate original 100% air flow before the heat can be turned past the usual level and the fan cannot be lowered until a specific number of seconds after the heat is dropped to a normal number. Additionally there should be a limit on the duration of this heat overdrive. This would be used to help drive the roast in a way many home roasters like to use to try reserving some heat until towards the end to drive it to second crack or some other nuance.

This should be thought of as some sort of reserved “afterburners” to a skilled pilot used only when necessary or someone pushing a nitrous injection button on a race car or turning on some super charger.

Once heat has been disabled it clearly cools off much faster than before. As of 10/10/11 I’m waiting to more firmly mount all the controls and switch to the new potentiometers before testing a roast. I also have a few buttons for start/stop and a microSD logger to setup first before I start this because I want to track thermocouple readings vs each of the percent settings etc so I can review it later after my first test. If anyone has a way I can sense the wattage use and feed it to the Arduino too please let me know. I’ve seen a few very LARGE devices intended for whole house sensing but I’m looking for something small….

FreshRoast SR500 Teardown – Part 2

Welcome to Part 2 of the FreshRoast SR500 Teardown. In Part 1 you saw the basic steps to open the SR500 properly. This article will explain how to continue a teardown a FreshRoast SR500 roaster into the various components and probably give insight to similar pieces in a SR300 as well. If you are looking to modify an SR500 the following content will be the best starting point for understanding what makes your roaster work as it sits. It will include technical information about the components that make the SR500 work. Part three will begin to make suggestions of where modifications will need to take place if you wish to split fan and heater control to external dimmers, VARIAC devices, or otherwise control your SR500 with a Microchip PIC, Arduino, or other microcontroller or PID controller device.

This article was made possible by having purchased a spare SR500 base that can be completely broken down and tested upon. I will be using this base to interface to my roasting computer.

You should refer to Part 1 if you need assistance opening the roaster. Most people should be able to open the roaster without the first guide but it is a good idea to review it briefly to become familiar with what you are getting yourself into and deciding if you are up to it getting inside. Most of the connections are very “coarse” and use through hole parts.

For my project I am going to be using surface mount parts which requires a bit more skill. There are many options out there so if you are looking to simply use something like a 20×4 character LCD you can probably find a way to do this without the surface mount parts. If you want to continue with a graphical LCD like I am you will likely need to learn about more advanced methods of soldering.

If you are unsure you should research and contact a “Maker” or “HackerSpace” club in your area. Examples of such include NoiseBridge in San Francisco. There are plenty of other groups throughout the USA as well as in many European countries. The closest one for me is about 3 hours away unfortunately so I’ve had to resort to figuring most of these things out on my own. Coffee roaster computers are a pretty popular thing out there so you can probably find other reference material out there.

Most of these groups offer classes in soldering as well as often having capabilities to help design/build enclosures, mill parts, create circuit boards, and have shared equipment for laser cutting, CNC milling, 3D printing and many other systems. Not all groups have these amenities and many require you to demonstrate a level of mastery, take classes, or otherwise “wait for time slots” on the items of interest. Hackspaces normally charge a monthly membership to participate and use the facilities but usually have forums, IRC channels, and other such things where you can find out more information before you commit to driving for a visit.

Removing the inner parts of a FreshRoast SR500 Coffee Roaster

You will need:

  • A small phillips screwdriver.
  • A SR500 Base with the bottom removed (SR300 may be similar except for changes to the microcontroller board)
  • A baggie or small tray to hold screws
  • A clean area to work
  • Optional: Items to label the wires removed. This should be done as you unplug each wire so there is no confusion.
  • Recommended: Needle-nose pliers to grasp some of the flat connectors and pulling them from the circuit board.

Step 1: Unplug your SR500 from the wall and remove bottom as described in Part 1.

FreshRoast SR500 Interior

Step 2: Identify the high voltage power wires inside the case leading from the main black wall power cable and detach them (N and L1)

It is absolutely critical that you have unplugged the power before performing this step or you will be electrocuted.

The wires you need to remove are labeled N in the middle of the board and L1 on the JP2 side lower down on the board. Normally this would be Neutral (N) and Load (L1). Normally in most North American electrical devices you would not label things L1 and L2 unless you intended to have an L3 for three phase electric or were enumerating your loads. Since the wall plugs into one of the L’s and the other goes to the actual load this seems a little odd but I can follow the reason. Regardless, both will need to be removed to lift the circuit board and heater system up out of the enclosure. You should use the needle nose pliers to grasp the connector and pull it up. Grasp it by the metal and not the wire. Pulling by the wire will rip it out of the connector requiring it to be replaced with crimpers and appropriate ends. You should try to support the board so that pulling the ends do not put additional stress than is necessary.

It is ok to slide the circuit board up some as shown in the L1 photo. It will be difficult to lift the board up very far prior to removal of the N and L1 wires. Again, support the board as you use the needle-nose to pull the wires off.

N on right between 100W and JP1

N on left between 100W and JP1

L1 on Left below JP2 and MOC

L1 Removed below JP1 and MOC3043 chip

N removed

Step 2a: If desired during step 2 above or 3 below you may wish to remove the power circuit board from the PCB guides in the enclosure.

Gently slide the power board upward on both sides trying to clear the top edges. This may be difficult to do and is generally not necessary until you wish to remove L2, 100W and 1000W.

Power Board being lifted out of guides

Step 3: Remove JP1 and JP2 low voltage cables.

Both of these cables are low voltage and will come off easily when pulled. JP1 connects to the main logic board with the Atmel CPU and front control panel. JP2 connects to the Fan Speed Control potentiometer.

JP1 Removed

JP2 Removed

Step 4: Slide heater/fan assembly out while looking for the NTC sensor cable.

Do so slowly because the NTC sensor is still attached to the main logic board. Once the heater top layer begins to slide out of the enclosure you should try to find the wiring coming from the side of the heater. If you removed the circuit board from the guides pay attention to it as well so that it does not catch on anything.

NTC Sensor on Heater Enclosure

Identify the connection on the main logic board and unplug.

NTC Sensor connector

NTC Sensor unplugged

Step 5: Inspect the removed heater and power control board.

Heater / Fan and Power board assembly

You should be left with a loose middle portion of the enclosure with the main logic board still attached.

Middle Enclosure with Main Logic Board

Put it to the side and continue with the power board removal.

Step 6: Remove the 1000W, 100W and L1 cables to separate the Power Control Board.

Using the needle-nose pliers pull off the 1000W, 100W and L1 cables from the Power Control Board. This will allow replacement, modification, or other inspection to occur more easily.

As mentioned above L1 and L2 are a little odd in North American wiring but regardless the white wire is the Neutral and Black is the Load typically. Since we have 1000W and 100W and one has black and one has a white wire this continues in not complying with North American wiring standards and there are other reasons this roaster is abnormal with wiring so we will disregard this in thinking about the roaster. The 1000W connection white wire comes from a large outside heater coil and gets fed power from the L2 connection. The 100W side requires voltage to be applied to L2 and will operate both the fan and the small center heating element.

The 100W side heater to fan wire connects to the bridge rectifier on the base of the fan motor and is wired this way to use the heater coil in the middle to provide resistance to drop the voltage to a level acceptable to run the fan. The black wire side of the bridge rectifier is connected to the 100W connection on the power board creating a second complete circuit. The fan itself (after the rectifier) picks up its power on the other 2 wires once the internal mechanisms “do their thing” in that bridge rectifier. There is a capacitor jumped across the rectifier and I’m not very familiar with rectifiers and using a capacitor but I would guess this has something to do with the zero crossing and trying not to “sputter” when the power cuts out momentarily since this is DC for the motor and AC for the power source.

Alternate angle of power control board.

JP1 is labeled with J1 through J5 positions. J4 and J5 go to pins 4 and 5 on the MOC3043 chip. This is for microprocessor control of the attached devices. The board appears to have spots of solder placed on each of these that look like a “via” that someone tried to solder over but there does no appear to be a real via on this board since it appears to be a single layer board when viewed in front of a bright light. I’m not really sure why those spots are there. If someone has any ideas please pass them on and I’ll add them here.

J3 connects to the Neutral connection. J1 appears to go around the edge of the board linking to the fan potentiometer circuit and the BTA08 (Q6) trigger. J2 leads directly to the BTA16 (Q5) trigger.

Electronics and Connections Analysis

Normally in home electrical work you are required to switch the load side on or off prior to whatever object gets the power. For example you have power going to a light switch. The wire that comes out of the switch then leads to the light and then the light connects to neutral. When you flip the switch you supply load power to the switch, the light then illuminates, and then it passes the electric to neutral completing the circuit. This is typically a safety measure so that you can change light bulbs and particularly remove broken ones with the power off and not get electrocuted as well as generally being good practice in case of almost any other malfunction. This is not how the roaster is wired. If you had the ability to touch either the fan or the heater coil while it was plugged in but not running you would get electrocuted because they appear to be always live. Since they are physically enclosed it is not as important but will affect how you control the roaster.

The slide switch on the front and the cool/up/down adjustments only control the (right) gate sides of the two triacs. This gate is like a light switch. Normally this is a high voltage that is triggered by an opto-isolator chip. The MOC3043 inboard does this for one of the sides while other circuits trigger the other side. The other pins of the triac are the high voltage switched side connections. Both the 100W and 1000W neutral wire connections lead to the middle triac pins of their respective sides and are then gate switched to the wall Neutral pin in the middle of the board on the left side of the triac.

The 100W side’s use of the heater coils is used to drop the voltage by resistance to the fans rather than using transformers or other devices to provide lower voltage to the fan. It is more important as a voltage control than it is as a heater. The fan being connected this way results in some heat being generated whether you are in the cool cycle or not and would vary with the fan speed. Obviously changes in heat are slightly mitigated by the air flow. To fully control the fan separately from all parts of the heater you would need to separate the white wire side and route it to neutral while supplying power separately to the fan by a transformer to control the voltage or else completely remove the bridge rectifier and control it by DC power directly. 100W of heat is not very much and is likely not much of a concern and certainly not really useful either as a reserved heat source. Watching a wattage / amp meter in real time when the fan (with small coil) is running shows about 125-150 watts of power use at full fan. The 1000W side full heater bumps wattage into the 1450 to 1520+ range when supplied a full 120VAC.

The 1000W connection white wire comes from a large outside heater coil and gets fed power from the L2 connection. If you were to separate both of these wires and plug them into wall power you would get A LOT of heat being generated. The 100W side requires voltage to be applied to L2 and will operate both the fan and the small center heating element. Both of these when plugged in separately operate normally. Together I had some issues keeping the fan running once the fan side circuit is set to full power and the heater exceeds half power but this may be due to a faulty potentiometer I was dealing with. Ultimately I wanted heat totally separate from fan so I bypassed this with a transformer entirely and have a different set of potentiometers to install soon. I also switched from neutral gate switching to load side switching.

The fan does not appear labeled with any part numbers or any indication of voltage requirements. Based upon the common construction of many other air roasters and specifically a DIY favorite, the Poppery, being almost all similar it is likely to be a 20 volt fan and runs higher than 1.5 amps at the top.

As shown in Jim West’s blog entry about modifying a poppery (not affiliated with this site nor endorsing my modifications) the use of a transformer is probably required on the fan if we separate things fully and wish to control fan alone without a lot of complicated electronics. Use of a transformer is more expensive than some of these other options but it is quick and easy. Jim’s diagram of the heat system with the labels for each connection point is identical to the FreshRoast including the safety mechanisms. Those mechanisms on the FreshRoast, however, are calibrated to higher temperatures than what is allowed on a Poppery so the FreshRoast is much like a coffee calibrated poppery.

As a result I would hesitate to agree with anyone removing any of these devices like happens with a Poppery without being absolutely certain of their choice and without building in a lot of additional mechanisms. Pay attention to the old and new schematic areas for my point about the way this is wired. Running the fan alone on a variac at lower voltages works fine. As it exceeds the 20 volts area it begins to show the constant glow of an arc spark in the motor and may arc outside (dangerously) at higher voltages. A transformer is likely to be the easiest and safest solution.

Possible SR300 Fan Speed Modification

On the rear of the “power control board” above it has a silk screen label P/N:306171. I believe this is probably going to be the same board found in the SR300. On the SR500 the socket labeled JP2 leads to wiring on the rear marked R29, R30, and D5 on the “left” side. The position for R29 has no resistor installed on a SR500 but it appears to still have jagged solder and scrape marks on mine.

I believe this is a pre-assembled board made for the SR300 that is tested this way and then forwarded to the roaster manufacturer. My guess then is it is allocated to a SR500 where the manufacturer manually removes R29 and installs it in the SR500 case connecting a potentiometer that is installed on a SR500 panel assembly.

If JP2 exists and is unused on an SR300 the R29 might be able to be removed and replaced with a potentiometer using the JP2 (or holes for it). The front panel might then be drilled and the potentiometer then gets “creatively” installed. I’m going to guess that the plastic is probably already shaped for it and possibly drilled too because it’s probably easier to just put a different gray “sticker” on top depending on the roaster being made.

No impression yet on the “brain” bits of the roaster low voltage board and if the heat switch can be adapted. I would expect this part to be unique for each roaster model unless the installed switch only gets wired to the “High” and off positions of the board and excludes the middle and low position being connected to anything.

FreshRoast SR500 Teardown – Part 1

This article will explain how to teardown a FreshRoast SR500 roaster and probably an SR300 as well. If you are looking to modify an SR500 the following content will be useful as well. It will include technical information about the components that make the SR500 work and suggestions of where modifications will need to take place if you wish to split fan and heater control to external dimmers, VARIAC devices, or otherwise control your SR500 with a Microchip PIC, Arduino, or other microcontroller or PID controller device.

Now that I’ve finally obtained a spare SR500 base I’m a little more comfortable with tearing down the roaster to see what is inside.  This process has confirmed my initial memory of the roaster being simple to open up.

On SweetMarias’ forum there was a question by a user that I replied to about how to open the SR500 to clean it. I made reference to the FreshRoast SR500 being pretty easy to open up to clean it out inside if you felt it had clogged in any way but did not have the ability to just pop one open nor did I have enough notes about it.  The user managed to clean his through the holes in the roaster using compressed air through the various openings due to having difficulty removing the screws and getting the bottom off.  I suspect he missed taking out the screws in the middle labeled as 7 and 8 below.

This article will be the first part explaining how to teardown a SR500 roaster and probably a SR300 as well.  If you are looking to modify an SR500 the later parts will be much more useful though everyone will need to know how to open it up to do most things.

Opening a FreshRoast SR500 Coffee Roaster

You will need:

  • A phillips screwdriver.
  • A SR500 Base (SR300 may be similar except for changes to the microcontroller board)
  • A baggie or small tray to hold screws
  • A clean area to work
  • Optional: Vacuum and/or compressed air to clean chaff from interior of the roaster base

Step 1:  Unplug your SR500 from the wall.

There is serious electrical voltage at levels that can kill you inside the SR500. DO NOT OPEN THE ROASTER BECAUSE YOU WILL VOID YOUR WARRANTY AND YOU WILL GET ELECTROCUTED AND BURN DOWN YOUR HOUSE.  (No really…)

Step 2: Place your SR500 base in a clean work area.

Remove the roast chamber, chaff collector, and lid so that all that is left is a base.

FreshRoast SR500 Base

SR500 Control Panel

Step 3: Since you apparently do not mind getting electrocuted, burning your house down, or voiding your warranty it’s not my fault if you continue further.

When you electrocute yourself and end up dead don’t come crying to me about it…. or haunting me either. I also don’t want to hear from your spouse, parents, kids, lawyer, or the fire department either.  I will smudge stick , holy water, and exorcise this house at the drop of a hat should your “ghost” come to haunt me… don’t tempt me. By continuing further you have indicated your agreement that you are willing to get electrocuted at your own risk and void your warranty and risk burning your house down. You also agree that you will not haunt me afterwards because this is what you wanted to do at your own risk. Now that we have the formalities covered you may (if desired) continue to Step 4.

Step 4: Turn the roaster over.

FreshRoast SR500 Bottom

Step 5: Remove the 8 screws from the bottom.

FreshRoast SR500 Screws (8)

Numbered Screw positions for SR500 Roaster

Step 6: Loosen and remove the bottom plate.

The bottom plate should be VERY loose at this point and could simply fall off.  In addition be aware the top ring of the roaster will be very loose now too.

FreshRoast SR500 Bottom Plate and Screws

Step 7: Bag up your loose screws so that you do not lose them.

Better to be safe than sorry.  Store the loose screws in a tray or sandwich bag.  There will be additional screws later if you remove the micro control board later.  Also be aware

Step 8: Inspect the interior.

From top to bottom in the picture below you have AC Power cord entering the roaster base, power control board, blower fan in the middle as well as the heater assembly around the fan, and the main logic micro control board at the bottom.

To the right you have the fan potentiometer wiring leading from the round potentiometer leading to the right side of the power control board.  On the left you have the main logic board wiring leading to the middle of the power control board.  In the middle the blower fan and the heater have black and white wiring that lead to the power control board.  Out of the side of the heater assembly are two small wires that are not visible in this photo.  Those are the NTC sensor wiring.

FreshRoast SR500 Interior

Step 9:  If you are interested in cleaning the roaster you certainly can do so now.

Compressed air and/or vacuuming can be done at this time.  With a narrow crevice tool you can probably get access next to the motor in the middle.  There are many small blades as part of the blower inside the black housing shown above.  If you are more adventurous you will need to disassemble further and this will get you closer to the intake around the motor assembly.

Step 10:  Further Disassembly.

If you are disassembling the roaster further you will need to remove the power board, the lower housing from the upper housing, and disconnect the “microcontroller board” from the power board.  These will be explained in Part 2.