Yusynth vc panner wiring

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Re: Yusynth vc panner wiring

Post by Paul Cooper »

Well done on some good fault finding there. I have looked at what you have found and there is a missing trace on the ground connection to U1 from the inputs connector ground pad. Yet another problem with YuSynth PCBs I'm sorry to say. We only manufacture the PCBs to YuSynth original gerber files.

It's an easy fix, you just need ground the trace you highlighted in red. Here is one way with a link on the underside of the PCB but feel free to ground it anyway you find easiest. I have just checked a build I did many years ago and sure enough, I had put a link in there but failed to remember to document it on our website which I shall do now.
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Re: Yusynth vc panner wiring

Post by dummyplugconspiracy »

This is the best news I have heard in weeks. THANK YOU! I knew I wasn't going mad. And as my fault-finding has improved I refused to believe I was still missing something as physical/visible as a point of continuity. But it's still not natural for me to assume the board is the problem - I'm much more likely to blame my assembly. I will give this a shot tonight. THANKS!!!
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Re: Yusynth vc panner wiring

Post by dummyplugconspiracy »

This thing is sooooo close to ready. Output stage is all behaving perfectly. Channels 2-4 also working great. Channel 1 isn't. I only get left channel. When pan is centered I hear medium volume left. When pan is left I hear louder left. When pan is right I hear nothing. I'm slightly worried since I believe this was the same behavior I noted before determining I had a failed LM13700 chip. I sourced a few chips locally and installed it tonight with good results. So either my channel 1 problem has nothing to do with the chip, or my channel 1 problem fries LM13700 chips. I think I can rule out the pots and wiring. Everything is doing its job, there's just no right channel making it to the output. I'll examine the schematic tomorrow, but any advice in the meantime?
Thanks!
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Re: Yusynth vc panner wiring

Post by dummyplugconspiracy »

Began tracking the channel 1 problem tonight. Started with sine wave on input 1. I tracked it thru until U103b pin 13. Somewhere between R124 and pin 13 sine wave goes away and doesn't reappear. I checked R125 and R126 for voltage to make sure they were grounded properly and they read 0V.

I swapped the U103 chip with a new one. Usually this module reads about .11 on my power supply. When I fired it up it jumped to .15 and hit .17 before I was able to switch it back off. The module smelled of hot plastic. And though the module was face down at the time, I'm pretty sure I heard the click of the VU meters pinning. I powered it back on and advanced current slowly. It leveled off at .11 this time but the damage was done and channel 1 still doesn't work. I presume I fried another chip. But I'm still not 100% sure it was the U103 chip. First time around the problem followed the chip so I assumed that was the issue. But in fact channel 1 itself is the issue and it kills chips. Maybe not just U103. I haven't had time to keep probing back to the others. But as I mentioned in an earlier post, channel 1 does pan, does accept cv, does input, does control input level, does affect the VU meters, and does output. Just only left channel content - right channel is missing. That points to U103 I think. Or maybe Q101?

I did compare voltage between working channel 2 and bad channel 1,but only after the incident. On U103 I got this:

Bad Channel 1 u103
Pin 13 = 0v
Pin 14 = 14.46v
Pin 15= 0v
Pin 16 = -14.2v

Good channel 2 u203
Pin 13 = 0v
Pin 14 = 14.46v
Pin 15= 0v
Pin 16 = -1.16v this is not a match

Also R122 reads -0.32
R222 reads -6.93v

I also checked Q101 vs Q102 and got:
Q101 = -0.32 / -0.94 / -0.32
Q102 = -6.93 / -1.04 / -0.47
Also not a match.

That's as far as I had time to go. Since I'm pretty sure my problem is related to power supply voltage damaging components, it seems like we can eliminate some things. I checked all wiring and inspected soldering and it all looks fine. I also used impedance to make sure grounds were reaching ground and so far they all work. Were there any undocumented board trace errors on this one? What do I try next?

Thanks!
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Paul Cooper
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Re: Yusynth vc panner wiring

Post by Paul Cooper »

Some of your measurements do not make sense and I do not have a module here but do these tests:

1. Remove U103 and do not replace for these tests
2. Put your +/- 5V sine wave into channel 1 with the level pot at 100%
3. Check you can see the sine wave on pins 1 & 7 of U102
4. Check you can see the sine wave on pins 4 & 13 of U103 socket. It will be at a greatly reduce amplitude of +/- 50mV
5. Measure the voltage on 2, 3, 14, 15 of U103 socket
6. Make sure you have 4V on the wiper of trimmer T101
6. Measure the voltage at pins 1 & 14 of U101 with the pan pot of channel 1 at fully cw and fully ccw rotations
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Re: Yusynth vc panner wiring

Post by dummyplugconspiracy »

Missed a day over here, but hopefully I will see a response before the weekend now that I took these tests:

Using the 5V sine wive with pan pot centered and channel level at full. I don't believe it matters where master level was set, but I left it at about 75% to stay consistent with my other tests.

U102
pin 1 has sine
pin 7 has sine

U103
pin 4 no sine
pin 13 no sine

Wiper T101 (that's the pin at the top middle of the triangular configuration I presume) I can get it to 4V, but that trimmer is incredibly coarse and it's not easy to zero it in. I was able to hit 3.9v and 4.1v so hopefully that proves concept.

U101 with pan pot at full CW (or right panned)
pin 1 = .03v
pin14 = 0v
U101 with pan pot at full CCW (or left panned)
pin 1 = 4.25v
pin 14 = 0v
. . . this seems consistent with my problem of no right channel.

OK - what's next?
THANKS!
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Paul Cooper
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Re: Yusynth vc panner wiring

Post by Paul Cooper »

dummyplugconspiracy wrote: Fri Sep 23, 2022 9:34 am U103
pin 4 no sine
pin 13 no sine
This does not make sense, please re-check noting what I said about the amplitude at this point. Your scope should be on say 20mV/div
Paul Cooper wrote: Thu Sep 22, 2022 10:30 am U101 with pan pot at full CW (or right panned)
pin 1 = .03v
pin14 = 0v
U101 with pan pot at full CCW (or left panned)
pin 1 = 4.25v
pin 14 = 0v
Okay, so U101d pin 14 is not responding as it should. Either a duff U101 or perhaps a short between pins 12 & 13 on U101. Check for any fine solder whiskers between these two pads.
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Re: Yusynth vc panner wiring

Post by dummyplugconspiracy »

Checking U103 again - no chip installed. Pan at center.
Zoomed in to 50mv
Pin 13 and pin 4 scope traces below.

Would failed u101 or crossed pins 12/13 cause the smell and current rise and meter pinning I mentioned?

I'll inspect those pads.

Thanks!
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Pin 13 u103
Pin 13 u103
Pin 4 u103
Pin 4 u103
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Re: Yusynth vc panner wiring

Post by Paul Cooper »

Here is what I get at U102 Pins 1 & 7 the full +/-5V sine wave.
U102 Pins 1 & 7.JPG


At U103 pins 4 & 13 you should get a +/-50mV sine wave
U103 Pins 4 & 13.JPG
A short between pins 12 & 13 would not cause any damage at all to the chip. Make sure your level 1 pot is 100%, pan pot does not matter when checking U102 and U103 pins 4 & 13.

First place to check for burning is R1 and R2. Excess current due to incorrectly inserted chips can fry one or both of these resistors. YuSynth strives for single sided PCBs and as such watch out for chip orientation as the chips can be rotated 180 degrees to each other as they are on this board.
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Re: Yusynth vc panner wiring

Post by dummyplugconspiracy »

OK - I will probe around some more.

If R1 and R2 were damaged or failed all the way up at the power inlet, I would think all channels would be affected. I have channels 2-4 working perfectly. So that seems unlikely. Could those resistors be damaged and still power the rest of the channels correctly?

When you say the chips are oriented 180 degrees to each other, you mean that U101, U102, and U103 don't all have pin 1 facing top of the board, right? Not that there's variation from channel to channel. As long as the PCB is printed correctly, I am confident I installed them correctly. I will check that too, just to be safe.

THANKS
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Re: Yusynth vc panner wiring

Post by dummyplugconspiracy »

I can't believe it! R2 is absolutely burned! I can't figure out how I missed it!! Unless it only became visible on the third try. I suppose that could explain it.

Ok I can replace it. But do I need to check anything else before I test? Am I going to blow something else if I replace it and power up again? Something made it blow .... I guess incorrectly inserted chip is most likely. I'll inspect all solder points again and give it a try tomorrow. Thanks !!
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Re: Yusynth vc panner wiring

Post by dummyplugconspiracy »

Success!!

Replaced the R2, tested power. Put chip back in, tested again. All clear. Channel 1 working. Trimmed it up and installed. What a relief! Now I just have to wire it into my patchbay.
Thanks!!
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Re: Yusynth vc panner wiring

Post by dummyplugconspiracy »

One final thing. I noticed some inconsistency in the master 10k log duplex pot. Probably from all the desoldering and resoldering. It's not the wires or the pins. Something sandwiched inside there is shorting unless I squeeze the top and bottom levels slightly. I just placed a large order that won't ship for a few weeks due to a back order. What's the best way to order a replacement 7300-320 and insure that it ships with the rest of that order? Just place a new order and notate the heck out of it?

Thanks!
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