ASV envelope problems

[eljay]

I have the following issues with my ASV envelopes.

1) ENV1 appears to work correctly modulating VCO2 FM and VCO2 PWM but the ENV1 depth pot doesn't do anything to modulate the filter. An input to the ENV Accent doesn't appear to do anything either.

2)Apart from the attack and sustain pots on ENV2 which seem to be OK, the Decay and Release pots seem to have a limited if any effect.

I'm not sure if I've disturbed something during my recent pitch CV mods or just exposed a problem that was already there. I tracked through the schematic and changed the OPA2134 at U12 as this seemed a possible common component, no change. I checked all main board resistors and found an error with R14, this was changed from 10k to 12K, no change. All other functions, oscillators etc seem to working OK, everything calibrated correctly. I'm a bit stuck.

[Synthbuilder]

ENV1 appears to work correctly modulating VCO2 FM and VCO2 PWM but the ENV1 depth pot doesn't do anything to modulate the filter.

Can you scope the output voltage at pin 7 U12? If so, you should be able to see the envelope here when triggered.

If not, then check the voltage across R161. It should be around 5V. If not, the problem could be either R161 or R158. If it's 0V then it could be a short under HDR3 (between pins 5 and 3) on either the main board or socket board. Or a problem with the IDC interconnect.

If all is well there, then check the output voltage on pin 7 U4 on the main board. This should be +5V. If not check soldering around U4, R10 and R11.

If that is all OK, then it may be worth replacing U8.

Apart from the attack and sustain pots on ENV2 which seem to be OK, the Decay and Release pots seem to have a limited if any effect.

Swap U24 and U25. If the problem now moves to ENV1 then it's probably the AS3310 chip.

[eljay]

I have changed U8, no change. I did measure 0V across R161 but I also measured 10V across R158 (VREF?). Pins 5 and 3 are shorted together but they are all connected to GND so I thought that should be expected, the schematic shows all odd pins on HDR3 connected to ground. I made a new IDC cable for HDR3, no change. I didn't find 5V on Pin6 of HDR 3 on the main board which I was expecting. I measured the resistance of R161 in circuit and got 11k. I measured continuity between R158 and R161.

I swapped the AS3310 chips, no change. I did establish that if I use the LFO to modulate the ENV Accent input at the same time as adjusting Env1 that the ENV1 depth pot does have an effect on the filter but not in a usable sense.

[Synthbuilder]

I did measure 0V across R161 but I also measured 10V across R158 (VREF?).

That's your problem.

Pins 5 and 3 are shorted together but they are all connected to GND ....

Sorry my fault I meant pins 5 and 6. So you were looking in the right place when you...

I didn't find 5V on Pin6 of HDR 3 on the main board which I was expecting.

This indeed is the problem. We now need to find out why. You mentioned that R161 was reading 11K and that you had 10V across R158. If this is the case the problem is not that the voltage is being pulled down by a short but that the current is not being supplied by R158. I'm guessing that either R158 is not what it should be, eg. 1M instead of 10K, or that it's busted.

I swapped the AS3310 chips, no change.

Look again at the resistors feeding the decay and release control pins of U24. That is R156, R130, R162, and R144.

[eljay]

Fixed!! Hurrah!

I changed R158, it appeared to have blown, the resistor value rings indicated it was the correct value. There is now 5V across R161 and the Env1 Depth Pot works as expected.

I checked R156, R130, R162 and R144. R156 and R162 indicated the correct value of 39K but were blown, once changed ENV2 is now working as expected.

Why have these problems occurred? I also found a couple of dodgy crimp terminal connections (Molex) in the power leads (the cable came out when I tugged on them) which I replaced but whether these had caused a problem I don't know, I replaced them anyway. I'd seen no problems whilst calibrating the module and it was on for some time.

Many thanks Tony for your guidance and support, I have to say it wouldn't have occurred to me that resistors could become faulty.

[Synthbuilder]

I have to say it wouldn't have occurred to me that resistors could become faulty.

They very rarely do without some sort of large current going through them. But that hasn't happened here as the resistor would almost certainly have shown some visible signs of burn out. And since all the resistors are of fairly large values, even if you strapped them across both power rails they still wouldn't have died.

My guess is that either they have been damaged when the leads were bent, or that they were poorly made. Where did you get them? Buying any components from any source other than reputable sellers always carries a risk of duff components. I got some vactrols the other day as part of a kit from a supposedly reputable supplier. Both of them were clearly fakes as the device enclosure wasn't marked for polarity and had holes to let the light in. And the quad op-amp that came with the kit was also counterfeit.

[eljay]

I guess it's just a bit of bad luck. I've got the vast majority of my resistors for 60+ modules from bitsbox and I have not had any other problems that I am aware of. The main thing is the fault has been identified and fixed thanks to your excellent diagnosis. Initial results from my new duophonic ASVs sound great and the re-calibration to work with my 5U version of Yarns has worked well.