Need Help With A New ADA Flanger Problem

[Paul Marossy]

I have another ADA Flanger in for some repairs. The owner messed up the bypass switch somehow, so I replaced it for him. But it's acting like it is on bypass mode all the time (I am sure that the switch is connected correctly, BTW). It sounds like it's trying to do something immediately after power up, but then it stops and sounds like it's in bypass mode again. None of the controls really do anything in this state, but it was fully functional  momentarily with a test signal at various frequencies. When I plugged my guitar into it, it wasn't working again. I'm a little baffled by this behaviour.

The last one I had to work on was just flat out dead, but it came to life after replacing a few of the IC chips whcih were apparently bad. I think it's another case of a bad IC chip, or maybe a bad cap in the power supply (or both). Any second opinions/suggestions?

[Paul Marossy]

Progress Report:

I measured voltages, all the chips are getting power. So, I replaced IC-1, IC-2, IC-3 & IC-4 to start with. Still acting the same way.

The interesting thing is that I when I pulled IC-5 (CD4007UBE) and IC-6 (CD4047BE) from their sockets, left them out for a minute and then put them back in, the circuit sounded like it was functioning like it is supposed to. That is until I unplugged the test signal and tried it with my guitar, then it's back to the same weird behavior.

So, at this point, my main suspects appear to be IC-5 and/or IC-6. I think I'll replace those and see what happens...

[Zben3129]

I would check for bad caps in suspect areas. Intermittent function like that could be due to charge up/down type things.

Zach

[Paul Marossy]

I would check for bad caps in suspect areas. Intermittent function like that could be due to charge up/down type things.

Zach

OK, will do. Thanks.

[oskar]

Maybee it should have been another switch. NC instead of NO or vice versa.

[Paul Marossy]

Maybee it should have been another switch. NC instead of NO or vice versa.

Good suggestion, but it uses a simple SPDT switch. Nothing special there. It's basically wired like the old wahs where the circuit is always connected to the input, but it doesn't load the guitar down in bypass mode like the old wahs did.

[Paul Marossy]

One other sort of odd thing: The main power filter supply cap (470uF/35V electrolytic) just before the 15V regulator gets a little warm after being powered up for a few minutes. Is that normal? It doesn't seem normal to me.

All of the IC chips seem to be getting a steady voltage, but I am wondering what affect a bad filter cap would have on the whole circuit. It doesn't seem like it would be a big deal since there is a voltage regulator between that cap and the circuitry. Or would it? Hmm...

[Zben3129]

Might be worth replacing, as the dielectric might be on the go, but I doubt that is causing the problem. If that cap was bad the circuit would probably just be noisy from poor filtering.

Zach

[Paul Marossy]

Might be worth replacing, as the dielectric might be on the go, but I doubt that is causing the problem. If that cap was bad the circuit would probably just be noisy from poor filtering.

Zach

Well, it's not really noisy at all, but it might be worth replacing it as a preventative maintanence measure.

[george]

if it's warm it's passing current so I would replace it ASAP, because electros can actually short out.   I once brought an Ibanez CS-505 back to life by replacing the PS rail decoupling cap.  It was shorted out between V+ and ground and when I checked the cap it was 0 ohms.

I also had to replace the 12V regulator because the shorted out filter cap had taken the regulator with it.

[Paul Marossy]

if it's warm it's passing current so I would replace it ASAP, because electros can actually short out.   I once brought an Ibanez CS-505 back to life by replacing the PS rail decoupling cap.  It was shorted out between V+ and ground and when I checked the cap it was 0 ohms.

I also had to replace the 12V regulator because the shorted out filter cap had taken the regulator with it.

Hmm... I ought to replace it then. I'd hate to see that go out an whatever else it might take out with it.

[george]

I think a cap that's any part of the power supply that is getting warm is a bad sign ... if it comes before the regulator it's a filter cap that's doing a bad job of filtering (ie smoothing out the rectifed AC waveform) if it comes after then there's AC from the regulator or it's passing DC and starting to short out.

I remember reading somewhere around here that any electro that's more than 25 years should be replaced (i'm assuming it's that old) ... ah here it is:

http://www.geofex.com/fxdebug/geriatric.htm

as note 5 says - "Just do it"   

[Paul Marossy]

I think a cap that's any part of the power supply that is getting warm is a bad sign ... if it comes before the regulator it's a filter cap that's doing a bad job of filtering (ie smoothing out the rectifed AC waveform) if it comes after then there's AC from the regulator or it's passing DC and starting to short out.

I remember reading somewhere around here that any electro that's more than 25 years should be replaced (i'm assuming it's that old) ... ah here it is:

http://www.geofex.com/fxdebug/geriatric.htm

as note 5 says - "Just do it"   

Yeah, I read that the other day, too! I think I need to definitely replace at least the main power filter cap since it is probably twenty years old now.

[Paul Marossy]

OK, here's an update:

I replaced the CDxxxx IC chips this evening, and it's still acting the same way. If I feed it a strong signal (about 2V PTP), it sounds like it's supposed to, but when I play guitar thru it or use a weaker test signal, I get no flanging or anything that I can hear - it just sounds like it's on bypass mode. I did try replacing every IC chip on the PCB now, except for the MN3010 (which I don't have on hand). All of the controls are affecting the sound, except the Threshold control, which I assume won't do much when the circuit is being fed a continuous sine wave.

So... I have to admit that I am a little baffled by this behaviour and am not sure where to look. I mean it seems to be working, just not to where you can hear it. Any suggestions?

[oldschoolanalog]

Have you audio probed it?
Have you tried adjusting the bias trimpot?
Try these using a guitar as the signal source.
All the Best,
Dave

[Paul Marossy]

Have you audio probed it?
Have you tried adjusting the bias trimpot?
Try these using a guitar as the signal source.
All the Best,
Dave

I haven't tried audio probing it yet. Since the signal path seems to be going in some many different places, I wanted to try and narrow down the possibilities first, if possible. 

[Zben3129]

Don't have the schematic on hand so I'm not sure of the values, but I would try maybe replacing the input cap and making sure (or replacing) that the input resistor is what it should be and that damage wasn't somehow done to it, not that I can think of any way to hurt the input resistor. Sounds like you may be losing a lot of signal before it reaches the BBD, resulting in barely anything to flange. Unless the signal you get through is the same volume (or close to) the bypassed signal. If this is the case let us know as it may be key to fixing the problem.

Zach

[Paul Marossy]

Don't have the schematic on hand so I'm not sure of the values, but I would try maybe replacing the input cap and making sure (or replacing) that the input resistor is what it should be and that damage wasn't somehow done to it, not that I can think of any way to hurt the input resistor. Sounds like you may be losing a lot of signal before it reaches the BBD, resulting in barely anything to flange. Unless the signal you get through is the same volume (or close to) the bypassed signal. If this is the case let us know as it may be key to fixing the problem.

Zach

I thought of the input cap. It's just a 0.01uF ceramic cap, it looks to be OK, though.

The signal in effect mode is just slightly less strong than it is in straight thru bypass mode, but with no flanging until I feed it a pretty healthy signal. That's what makes this kind of odd to me. The last one of these I fixed, it was just completely dead in effect mode. I replaced some IC chips that I suspected might be the culprit, and that did the trick in that case. In this case, it does seem like something is preventing the signal from reaching some critical location, but I don't know exactly where that is. 

[oldschoolanalog]

Have you tried adjusting the bias trimpot?
...using a guitar as the signal source.

If that doesn't do anything...
Bite the bullet; with schematic in hand; audio probe it. Start at the input and... you know the drill  . Don't start on a part swapping binge till you hear whats going on. Or see; if you have a 'scope.
Hang in there.

[Zben3129]

Don't have the schematic on hand so I'm not sure of the values, but I would try maybe replacing the input cap and making sure (or replacing) that the input resistor is what it should be and that damage wasn't somehow done to it, not that I can think of any way to hurt the input resistor. Sounds like you may be losing a lot of signal before it reaches the BBD, resulting in barely anything to flange. Unless the signal you get through is the same volume (or close to) the bypassed signal. If this is the case let us know as it may be key to fixing the problem.

Zach

I thought of the input cap. It's just a 0.01uF ceramic cap, it looks to be OK, though.

The signal in effect mode is just slightly less strong than it is in straight thru bypass mode, but with no flanging until I feed it a pretty healthy signal. That's what makes this kind of odd to me. The last one of these I fixed, it was just completely dead in effect mode. I replaced some IC chips that I suspected might be the culprit, and that did the trick in that case. In this case, it does seem like something is preventing the signal from reaching some critical location, but I don't know exactly where that is. 

Well in that case there is probably an issue in the BBD section (past whatever input buffers, input gain stage etc. that there may be), so, yes, it is time to

Have you tried adjusting the bias trimpot?
...using a guitar as the signal source.

If that doesn't do anything...
Bite the bullet; with schematic in hand; audio probe it. Start at the input and... you know the drill  . Don't start on a part swapping binge till you hear whats going on. Or see; if you have a 'scope.
Hang in there.

Zach