A friend of mine has a smoker, who’s front panel circuit recently gave up the ghost. He bought a new one that he thought was compatible but sadly it had an incompatible connector. When I asked him about the symptoms, he said that it couldn’t set the temperature anymore. It was pretty clear on closer inspection that the likely culprit was a mechanical fault on the “set temp” button.

I believe the model of the smoker is “Masterbuilt MB20071117” or something very similar, and the replacement he bought was a “Digital Control Panel Kit Replacement” that seems to be compatible based on the amazon listing… clearly not though, one review even complains “20071117 is a 4 prong connector. This panel has a 2 [and] 5 prong connectors and is not compatible.”

Anyways, here I sit in my lab with a peculiar Masterbuilt smoker panel, and a not so compatible clone. 

Busted Buttons

Probing the buttons… I’ve never seen buttons this busted. Scraping away the oxidation I can’t even get a consistent “short” when the button is depressed. All my measurements are in the MΩ range.

Clearly then this is the issue… I have some replacements, but they’re all the shorter style. Alternatively, I could raid parts from the “replacement” new board. Neither of these methods sounds very fun. The boards are covered in conformal coating that can be a pain to solder through.

Alternatively, I could check the circuits and see if I can make the replacement work. This seems more fun so I’ll take this path...

Spider Man Pointing Meme

They’re the same board. It looks like the fab house maybe took some liberties with the copper pours and tooling holes, but other than that (and the extra pin on the connector!) the two circuits are identical. 

Gerbers are largely the same, even the silkscreen and ref designators are identical. The only immediate thing that jumps out is C02 doesn’t use a capacitor on the old board… weird. Other than that there’s the following BOM value changes.

Note 1 – Wasn’t sure if 1015 or 5101. Measure in circuit as 5.09k so I’ll guess the latter.

The good news is the 4^th pin isn’t used anywhere. The bad news, they completely changed the wiring so we’ll need to do some pin pulling. Lastly, the confusing news, why is C02 a resistor on our new board?

I’m not too sure what the 2 remaining pins do on the connector. One is power, another is ground and then the remaining 2 go to the IC. One through this CR filter, the other just through a 10k. There’s also that 2wire bundle (black and yellow) that seems to have the same CR filter (now including the 5.1k PD). 

My best guess is they’re clock and data lines. Maybe the designer wanted to soften the edges of the signal. (I later realized that one of those signals was for an analog input from a temprature sensor).

Power Up

Lets power the thing up cuz I’m curious. The name on the IC has been removed so I can’t get any help there…. Just by looking at the circuit it seems like the white wire is ground, leaving red as the likely culprit for VCC. I set a low current limit at 3V3, and saw nothing. But the board came to life around 3.7V with a short beep.

When I try to probe the signal connected to C02 (looking for activity maybe), I put the panel into some error mode “EAA1”. Looking into it, it seems to be related to the “smoker's ambient temperature sensor reading too low of a temperature”. The error state latches until you power cycle it.

Ok lets treat it like an input then… I wired it up to my function generator and applied 500mV and powered up the device. Its maximum range is 300’C @3.46V. If the voltage on this pin drops below ~100mV or so it’ll cause the device to go into an ERROR state. At this point you’ll need to reboot the device to get it out of this state. WhAt A gOoD fEaTuRe!!!

Here’s a quick demo of the front panel, and its annoying error state. The new board behaves the same.

Fixing The Thing

Well, I’ve had my fun, time to fix it. The easiest solution is to swap the 4-pin connector onto the new board (since I now know they're functionally identical). Here’s the finished repair… it looks the same… -_-

If you find yourself with one of these incompatible replacements, but don’t have a 4-pin connector to solder, you could try to rewire the 5-pin connector to match the 4-pin version… Here’s the differences.

If you’re holding the 5pin connector with the tab pointing towards you, the pattern should be rewired from left to right as; Blue/Signal – White/GND – Black/Signal – Red/Vcc.

Anyways, repair done, and I gained a new 7 segment display for my scrap bin… if I have any issues plugging this into the Masterbuilt smoker I’ll update the post, else assume it went smoothly.