Troubleshooting a MIDI Verb ii

[jasonallenh]

So, I've had one of these for a long time, and I've always liked it. Now, my dear old friend has gone and crapped himself.  :'(

Symptoms- Some effects still work (delay), some do not (Reverbs, flanges). The effects that are not working all come with a maxed out overload LED. When selecting any reverb program, I get a high pitched squeal sort of like feedback or an oscillation. When I select a chorus or flange, I get crunchy distorted nothingness. In all cases, the input signal will pass just fine, and the mix control will let you blend in as much disappointment as you could bear to hear.

First things first- YES, I am using the 9VAC adapter (the original, in fact). I measured it for fun, and it's floating around 10VAC unloaded. I checked the regulators as well- this uses a pair of 78/79 12s for +/- 12V, and both are giving me reasonably correct voltages. There is also a 7805 that is also reading what you would expect it to...

So now what???? I am afraid that in my limited knowlege, if I reach the digital components, I won't really know what to look for anymore 

Also, is it possible that the filter caps could be bad enough that they aren't supporting the rest of the circuit enough? None of them appear to have blown (these don't have the creases on the top, so I'm wondering if they could be blown from underneath). I wonder if it's worth recapping it anyway (mine is from 1987), but I'd like to know whether the regulators could have good enough output but not enough juice "in storage" to not allow the unit to function properly.

Aside from that, my next step is to look up the pinouts of each ic, DAC, ADC, and DSP chip and see if the V-Ins all look good....

How am I doing? Any suggestions?

 

[analogguru]

Before you do anything else:
Move the "Mix"-potentiometer 50 times from left to right (and back) and check if the problem persists.

 

[jasonallenh]

That sounds crazy. I'll try it. 

 

[kooma]

If your power rails are ok, then I would check any interconnection cables and (if IC's are mounted in sockets)
bad connections/oxidation in them..

 

[JohnRoberts]

So, I've had one of these for a long time, and I've always liked it. Now, my dear old friend has gone and crapped himself.  :'(

Symptoms- Some effects still work (delay), some do not (Reverbs, flanges). The effects that are not working all come with a maxed out overload LED. When selecting any reverb program, I get a high pitched squeal sort of like feedback or an oscillation. When I select a chorus or flange, I get crunchy distorted nothingness. In all cases, the input signal will pass just fine, and the mix control will let you blend in as much disappointment as you could bear to hear.

First things first- YES, I am using the 9VAC adapter (the original, in fact). I measured it for fun, and it's floating around 10VAC unloaded. I checked the regulators as well- this uses a pair of 78/79 12s for +/- 12V, and both are giving me reasonably correct voltages. There is also a 7805 that is also reading what you would expect it to...

So now what???? I am afraid that in my limited knowlege, if I reach the digital components, I won't really know what to look for anymore 

Also, is it possible that the filter caps could be bad enough that they aren't supporting the rest of the circuit enough? None of them appear to have blown (these don't have the creases on the top, so I'm wondering if they could be blown from underneath). I wonder if it's worth recapping it anyway (mine is from 1987), but I'd like to know whether the regulators could have good enough output but not enough juice "in storage" to not allow the unit to function properly.

Aside from that, my next step is to look up the pinouts of each ic, DAC, ADC, and DSP chip and see if the V-Ins all look good....

How am I doing? Any suggestions?

It's difficult with digital paths that generally work or they don't. So I would look for something on the analog side of the circuit. If something like recirculation is done on the analog side a bad solder connection on a pot leg could affect that.

Simple delay just uses a single digital path, while chorus and flange mix wet with dry audio stems.

Recheck solder connections, perhaps a faulty pot.

JR

 

[jasonallenh]

Power Rails are good, I removed all the ICs and ribbon connectors- no dice.

Did the mix pot exercise thing- no dice.

I'll start the process of reheating all the joints and see how that goes.

Thanks for the help so far, everyone =)

=jh=