The firmware on the CHMRO-420/CHM-420/BRTRO-420 Reflow Oven is very poorly implemented. It doesn't adhere to profiles correctly, nor does it have any real form of PID control. In addition to this, the thermocouple interface is quite noisy and is wildly out of spec most of the time, making this machine almost completely useless when you want consistent results. This mod fixes all this and more with a simple hardware and software modification.

This oven has a few unique features over the popular T-962 oven, which makes it slightly more desirable if you don't mind the higher cost:

• an internal convection fan built in.
• a fume exhaust system which you can vent outside.
• insulation and thermal tape is actually decent, so it doesn't give of nasty smells during operation.
• overall build quality is much better.

However, unlike the Unified Engineering mods to the T-692, the BRTRO-420 is slightly more difficult to modify, mostly due to the unobtainium build chain for its microcontroller, along with a few other design issues such as a poor and noisy thermocouple interface. So the decision was made to spin up a mod board that can be soldered to the bottom of the existing controller. This mod board is based on the ATSAMC21 which is a native 5V ARM processor, so it works well with the existing interfaces, without requiring level conversion.

This mod board is designed to be pretty simple to install. It just needs to be soldered onto the bottom of the PCB using the existing through hole leads (it's naturally keyed, so it's difficult to get wrong). You may need to remove some solder from the existing joints or bend some leads into the right spot to get it to fit. It doesn't have to sit flush though, just make electrical contact. You also need to short the W1 jumper on the top of the existing controller board to disable the original microcontroller (DO NOT RUN the modded controller without this jumper in place). The boards come pre-installed with a custom Arduino bootloader and the latest firmware release.

IMPORTANT: This product requires the modification of hazardous live mains voltage equipment. Understand the risks of doing so before purchasing and modifying your device. Also note that incorrect firmware can also pose a fire risk, do not modify the firmware or use alternative reflow firmware without understanding the implications of doing so.

The mod includes longer screws to mount (the thicker part of) the board as well as a jumper and header (in case the board isn't populated with one) for the W1 pins. Optionally you can also obtain new thermocouple terminals if you prefer not to desolder the existing ones as well as a fan shim which reduces chassis fan noise. These are shown in the gallery above.

Please see the GitHub repo for more information about installation. This documentation is a bit rough as this is a limited run, but if there's anything a bit unclear please don't hesitate to get in touch.