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I have had a non-functioning Mini Me board sitting around for a while and decided to finally try to find out what is wrong with it. I have 2 successful builds bookending this failed build and I have a request from a friend for his own Mini Me now that he has heard it. So, as much as I hate troubleshooting I figured I would try to get this one working before ordering parts to just build another one. So with all that, and apologizing for my lack on knowledge in most of the technical aspects, here are a couple of questions…
1. Are there any sample voltages for using the 3207 chip (specifically the pinout)? I looked on the old build document and found the ones for the 3007. My assumption is the other 3 IC voltages are still the same and all of mine check out at a reasonable range (as well as the transistors). Should the voltages for the 3007/3207 be roughly the same but just a different pinout? If so, I have several that seem out of range. Ignoring the pinouts, I had 2 with 0v, one with a little over 8v, 2 with a little over 4v but the other 3 had around 7.4v. So, given that I am using the 3207, should these voltages be an area of concern / something to target?
2. Using the old build document I audio probed the circuit and found I was not getting any signal at bottom of R17 and R19. So I checked IC1 and I was not getting any signal on pins 5 or 6 but I was getting signal on 1,3 and 7. I was also getting signal downstream but low volume with no effect. So, taking a wild guess after staring at the schematic, it seemed like it was getting the dry signal into IC1 but no chorus signal so I tried to trace back from that portion of IC1. And again, I am not very knowledgeable on the technical side…but my understanding is that the LM358 may be working as an LFO to control the 4047 which in turn controls the 3207 to add the chorus effect to the signal coming from IC1 and then being sent back into IC1? Anyway, what I found is that I had no signal in the path from the 3207 to IC1 (R10, R11, C10, etc. anything in that part of the schematic). So, I checked the 3207 and the only place I was getting any signal was pin 3…which seems to be the input (from IC1). So, with all that guessing and possible nonsense, is it possible that I have a bad chip? Or does all this (and above voltages) point to it as a likely culprit?
Did not intend to write this much…I guess the main point of this rambling is that if the chip is a likely cause of the issue, I would throw an extra one in with my order for another Mini Me board. I much prefer building to troubleshooting! I spend a lot of time up front trying to avoid the need to troubleshoot…measuring each component on the DMM as I populate the board and double check against the BOM multiple times, etc. I have gone through all the basic trouble shooting stuff on this like checking all the solder joints and reflowing the ones that looked questionable and even some that didn’t. I also opened up my working Mini Me and compared all the components and they looked good / matched.
Thanks in advance to anyone who takes the time to read this and might have some input.
I’ve never used the MN3207 in this circuit what I do know is internally it’s the same circuit with the main difference being one is PMOS, MN3007 the other NMOS MN3207 meaning one requires negative power 3007 the other positive
So for this circuit I’d expect voltages would be similar
List what voltages you get by pin number
The first thing I would do is check the BBD
jumpers are correct and have good solder joints I’d also compare the voltages on the empty socket and check D4 voltages
Basically check everything you can to see whether the 3207 is faulty or not
Check all the +9v and VB points on the schematic
You are correct regarding the LFO and the clock pulse coming from the 4047 so again you can see you’d expect the same voltage on pins 10 and 11 of the 4047 and pins 2 and 6 of the 3207 then as you say output from pins 7 and 8 up to IC1B where it’s mixed with the clean from R14
It could be something prior to the 3207 causing your fault so it’s just a case of checking everything from the information you have eg is the trimmer working correctly what voltage do you get Q1 base would let you know so you’ve more or less found your problem area you just need to make sure everything up to that point is good
Weirdly enough I quite enjoy debugging you learn a lot from it for future builds
I usually print the schematic and mark it off as I check everything I rarely swap components out just in case some error I’ve made blew it in the first place
But you’re definitely using the right approach now all you need to do is try and enjoy beating it when you find and fix it just keep saying you ain’t beating me mini me!
Billy – thanks for the reply! I did a little more checking based on your suggestions but it seems that the scrap piece of paper I was using to record my readings has disappeared. I think the root cause of that issue i can figure out…I have 2 young kids. I hope I have some time to dig back into this over the weekend. Everything I was checking seemed good as far as the +9v and VB and also checked continuity to ground in most places. Everything I had checked seemed to make sense.
I will go back and redo and get the exact readings posted this weekend. I also hedged my bets and ordered another 3207 just in case…had an order I was placing anyway. But I will take your advice and finish trouble shooting in case it was something I screwed up that ruined the 3207 in the first place.
Thanks again.
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