Yellow Magic (very) quiet output

Hey, I’ve searched all the forums but I haven’t found a similar question…
I built a yellow magic shruthi kit, and although I thought it went very smoothly there is almost no output on the board - it is only noticeable after boosting the levels very high. I went through the troubleshooting guide on the filter page ( All the power points are working as they should, however all the audio chain points (the numbers) AFTER the first one (mixer output) are extremely quiet. Point two is barely audibly, the others not at all. I have checked all the resistors, transistors, and capacitors and I haven’t noticed anything wrong although I suppose I could have missed one… I have also replaced the TL074 and TL072 in that row but I don’t have any LM13700s to replace the other two chips. It seems as though the signals dies in the filter right? Is it just the LM13700s that I have to replace?

and photos of the circuit boards? you may have a bad joint or have missed a solder point .( Ive done that once ., little dab of solder and all fixed!)

sure… I have gone over the board a couple of times but I haven’t found anything. I’m not the best solderer(?) in the world but I have done my share of circuits and circuit design

quiet output sounds like a resistor value might be too high no? maybe I’ll go check the values again

Nice jacks!
Your resistors look plausible on first look

hah! an old ebay special. I couldn’t find anything wrong with the resistors either, and I went through everything else again. That pretty much leaves the LM13700s right?

I forgot to mention but I did a bad thing and connected a PSU with the wrong polarity the first time I connected it, it doesn’t seem to have done any damage to the power circuit which I would assume would be the first thing fried - it seems to have a reverse polarity diode too

There are a few points on the PCB that look like they could use more solder. Basically, anything that doesn’t look like a small volcano could take a little more.

hmmm I don’t think that’s it… maybe it’s the picture angle but I don’t see any that need reflowing. I guess I could go over them again though

It looked like pin 3, or 4 or 5 of the V2164 could use some as it looked flat with just the socket leg in the middle. Better go get my MBP notebook so I can sketch a little on top of your photo.

ah yes thanks, I see them now, and now that I look there’s a couple on the first LM13700 that could use a little more too. I’ll redo those when I get a chance - I lost the tip to my soldering iron (long story)
I’m not sure that’s the issue though as my troubleshooting suggests the sound never makes it through the filter section, whereas that is the delay chip - I’ll report back when I’ve checked it though

One possibility, are you sure about the orientation of your transistors? When I was building my first SMR4 I had a full bag of 390x that had to be flipped in order to work. It was a moment of sweat when it first did not work. Since then I always check orientation when I buy a hundred.

you mean the pinout could be reversed? that would explain why another board I built at the same time isn’t working either, and by not working I mean the output is also very quiet. I probably should have seen the similarities…

yes mine had to be turned around 180°
just a guess, always hope for an easy fix

so… how do you check for pinouts? They are all what look like TO-92 PNP transistors, don’t they have a pre-determined pinout? I used different transistors in my other build so I doubt that’s related

I went over most of the joints on the board which hasn’t seemed to make a difference

it depends from manufacturer apparently, maybe even just a bad run and sold cheaper to retailer for that reason. I’m not sure where I got mine from but if you can’t identify the manufacturer from the print you can’t judge from datasheet.

How to find out: You can use a multimeter that has the Hfe option to check for PNP or NPN. It will also give you the pinout.

ah okay, that’s pretty easy… what should the pinout be though? is it this?:

anyone? I tested other PNPs in the same batch and they worked just fine

That seems to be the standard pinout which mine have too at the moment. Best is to check for polarity on a multi meter. Or easy: If the problem indeed is the orientation of the 3906 it should appear only in one direction and work the other way around.
Otherwise it’s something else, it was just a thought anyway.

Yeah I meant I tested the polarity of others in that batch and they came out the same. If that’s the correct polarity then it doesn’t seem like that’s the issue at this point

thanks though it was a good thought but I’m still stumped. I’ve replaced all the ICs except for the 13700s which I don’t have spares of, and gone over all the solder points a few times, checked the caps, resistors, transistors, PSU…