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Hello All,
Finally got around to assembling the Mini-Me PCB (v2020) I picked up last year, and also decided to add one of the roto-tone boards for my first combo build. After getting it working, really happy how this turned out (thanks Wilkie!!) and also feel like I’ve learned a few things.
But one item that I’m trying to figure out is how I managed to char the 47 ohm resistor in the R31 position (photo below). I don’t think I got too close with the iron, but unfortunately I didn’t take any photos prior to boxing it up. When I initially plugged it in and stepped on the footswitch I was greeted with silence… got sound in bypass so figured I had at least part of the offboard wiring correct. Looked over the board and sure enough I had IC4 (the LM358) installed upside down. Pulled it out of the socket, reoriented and it fired right up. Lovely thick chorus!
The circuit seems to function now without issue, but would it be recommended that I replace R31 with a fresh resistor? Looking at the schematic, it becomes apparent that I really need to properly learn how to read one… but also that R31 possibly has something to do with regulating the amount of current (please excuse my dum-dum talk here if I’ve stated the obvious… or if I’m way off base). Would starting it up with the LM358 in backwards have pulled too much power and fried it? Or would there have likely been another cause?
Thanks for any guidance!
Upon close examination, I believe that you placed a resistor in the board at the position for D5 which is a 1N5817 that is used for reverse polarity protection. It fried because it overheated due to the current flow. Please remove it and replace with the diode or, at least, a jumper.
Ok.. although I was working with the Mini-Me 2020 version build doc (https://guitarpcb.com/wp-content/uploads/2018/06/Mini-Me-2020-Build-Document.pdf), which does not have a D5, but rather R31 (47 ohm) in that position. Prior to assembly I had gone through all of the MM version docs to confirm it matched the PCB layout/illustration.
If I were to place a 1n5817 at R31 on the 2020 version, would it rectify the problem and still function?
Yes. Identify the pad for the resistor that has continuity with the +9V pads. That will be the pad for the diode ANODE. The CATHODE (with the black stripe) will solder to the other pad.
Sorry, I looked at the 2021 schematic and board first. But the R31 is replaced by a diode on the newer layout.
Here to help.
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