ADA Flanger isn't passing signal

[nbabmf]

I bought one off Craigslist today and something is not definitely right.  It's not passing signal.  When I turn the amp way up, I can hear the swoosh (noise) and twisting the knobs adjusts the parameters as they should.  That tells me that at least a portion of the circuit works as it should.

I've looked the board over and I don't SEE any bad solder joints.  I will probably reflow them all just to be safe.  I want to probe the circuit, but with that AC power going to it... I'm a little skittish about sticking my hands in there to find where the signal stops.  Do you have any pointers?  Now, the bypass works fine... so some logic and my limited knowledge of electronics seems to say that the signal is stopping after the input jack and switch, but somewhere before the SWOOSHY part haha.

I really appreciate whatever help you guys can offer.

[andrew_k]

I've looked the board over and I don't SEE any bad solder joints.  I will probably reflow them all just to needlessly expose the components to high temperatures.

dude...

[Paul Marossy]

I've repaired a few of those. When I had a unit that was not passing a signal, the culprits so far have been either a faulty IC chip or the FET in the noise gate section. They're not easy to repair, but it can be done. This is a time when an audio probe is really helpful.

[oldschoolanalog]

Put down the soldering iron and step away from the potentially valuable (sonic & $$ value); when fixed properly; vintage effect.
If you don't want to, or have the slightest doubt about working around AC then DON"T!!! You only have one life...
Besides, to really troubleshoot it you'll have to get access to the component side of the board. This requires disassembly of the unit (you will need access to the trimpots to calibrate it).
Please think this through a bit more before potentially compounding problems. The fix might be something very simple.
To quote andrew_k:
"Dude..."

[Paul Marossy]

Good points, oldschoolanalog.

If you don't want to tackle this yourself, I can repair it for you, nbabmf. Send me a PM if you're interested.

[fpaul]

If the ICs are in sockets pull them out and put them back in.  Unplug it first and I don't think you will die.  If you clip the audio probe to ground and probe the ICs using only one hand I also don't think you will die, just say away from the ac lines and the filter caps.

If you DO die, I am not responsible blah, blah, blah.

[Paul Marossy]

The IC are in sockets. I've tried pulling them out and putting them back in. That never worked in any of the units I have worked on.

[nbabmf]

Okay, plenty of "oh shit- don't touch it" in here.  Has anyone successfully repaired one?  If so, what was wrong with it?

[andrew_k]

Has anyone successfully repaired one?  If so, what was wrong with it?

The first line of Paul's first reply was "I've repaired a few of those".
You're wise to be cautious of mains voltage. But if your plan of attack is just to resolder all the parts then you shouldn't be attempting to repair this valuable vintage effect.
Don't let your ego get in the way, you might very well end up with an effect that works even less than it does now...

[fpaul]

I've heard of the IC thing working on some effects but probably a long shot.  Easy to try though.  A better idea would be just try to calibrate it.  When I calibrated my clone it wouldn't pass sound if the trims are out of whack.

I really don't see the harm of audioprobing it before paying shipping/repair costs either.

[nbabmf]

Oops, I must have missed that.  Thankfully, I don't have much of an ego when it comes to this stuff... I am just an amateur who still has a lot to learn.  So I will heed the warning to stay away from it with the soldering iron unless I find a component that must be replaced.

Most, if not all, of the IC's are socketed so hopefully it's something I can just pop out and pop a new one in.  Like I said before, there's some ambient noise being processed by the effect but not guitar signal, so I imagine the problem is in the input stage somewhere.  Is my reasoning sound?

I tend to be a little paranoid around AC mains, but if I can probe safely, I will.  I can set my keyboard to loop a demo song as I go through the signal path.  What about calibration though?  I know most of the the information on a Moosapotamus site (http://moosapotamus.net/IDEAS/ADAflanger/ADAflanger.html) applies to the SAD1024 version, but I imagine the calibration procedure would be similar.  I don't have a frequency counter so how would I do that?

[fpaul]

I didn't mean put in new IC's, just put the old one back in.  I think the idea is it cleans the contacts.  If you have new ones you could try that too.

Moose's site has the calibration for the original unit as well as the modification for the new version.  Actually I had to read about a hundred post to find out the frequencies are double in the new version.

I had to borrow a frequency counter for mine, couldn't even get close without it.  I set the rest by ear.  But the main one to just get sound going for me wasn't the two frequency trimmers or the enhance, it was one of the other two.  Sorry I don't remember which one right now.

Just remember where the trimmers are initially and you can always put them back like they were.

[nbabmf]

Update!

There IS guitar signal, but it's very faint... about as quiet as the noise on this "studio quiet" unit.  I had to crank the amp way up to hear it.  I played with the knobs some more and it's got to be something regarding signal strength.  I thought maybe I was just a moron and had the noise gate all the way up or something, but nope... it's legitimately wonky.

[Paul Marossy]

Update!

There IS guitar signal, but it's very faint... about as quiet as the noise on this "studio quiet" unit.  I had to crank the amp way up to hear it.  I played with the knobs some more and it's got to be something regarding signal strength.  I thought maybe I was just a moron and had the noise gate all the way up or something, but nope... it's legitimately wonky.

I had one on my bench once that was behaving the exact same way. IIRC, it was the FET in the noise gate that was bad. In that case, since the FET used in these units are vitually unobtainable, I used the closest substitute I could find. I got it to work again.

The ADA Flangers are a pain in the rear to work on, but they're not that dangerous. There's just one corner of the PCB where the transformer is that you need to be mindful of.

You could try the trimpot suggestion, but in my experience, fiddling with those had zero effect on producing a functioning unit.

[nbabmf]

I had one on my bench once that was behaving the exact same way. IIRC, it was the FET in the noise gate that was bad. In that case, since the FET used in these units are vitually unobtainable, I used the closest substitute I could find. I got it to work again.g with those had zero effect on producing a functioning unit.

The LS4393?  Yeah, I'm not finding it.  What did you use as a substitute?

[Paul Marossy]

Yeah, the LS4393. It has a black dome top with a white band around it. IIRC, it's very near to the large electrolytic filter cap.

I think that I used a 2N4393 in its place. It's supposed to be a direct replacement, but I have found that it's not quite the same as the original. 

[nbabmf]

Looking at the board solder side up, the pins of the JFET are oriented:

A
B
C

I set my multimeter to diode test and put the red (positive) probe on A.  B and C both read 684 (no beep).  A few minutes ago, they read 850-870 but that drop could just be from sticking the probes on them at random until I figured out the pins (maybe?).  Negative on A will read "1." for open circuit with the positive probe on B or C.  Looks like A is the gate while B and C share the negative, so one is the source and the other is the drain.  I'm not sure which is which.  So... is this a bum part or should I be checking elsewhere?  I still haven't mustered the courage to plug the pedal into the wall and probe the IC's...

[oldschoolanalog]

At some point you will have to plug in the AC cord to properly troubleshoot & calibrate it.
This is a fact there is no getting around. Do this carefully & post some V's.
That will allow folks to really help you with this.

[Paul Marossy]

At some point you will have to plug in the AC cord to properly troubleshoot & calibrate it.
This is a fact there is no getting around. Do this carefully & post some V's.
That will allow folks to really help you with this.

Yep, it's a must - you have to plug it in and give us some info in order to make some progress on this. You also need to know how to read (and understand) schematics enough to know how to trace the audio signal thru the circuit in order to figure out what the problem might be.

[nbabmf]

Okay, I had some time and probed all the IC's.  I couldn't find the schematic for the MN3010 version, so I'll just name the IC's by part number.

728 612163-1
P1 - 30.2
P2 - 7.7
P3 - 27.1
P4 - 33.1
P5 - 31.3
P6 - 27.2
P7 - 30.1
P8 - fluctuated ~15-19
P9 - 15.9
P10 - 15.5
P11 - 0
P12 - 8.3
P13 - 8.6
P14 - 4.5

MC1458P
P1 - fluctuated ~6-25
P2 - 15.3
P3 - fluctuated ~10-25
P4 - 0
P5 - 14.4
P6 - 16
P7 - fluctuated ~9-23
P8 - 33

RC3403A
P1 - 31.4
P2 - 29.5
P3 - 9.8
P4 - 32.8
P5 - 15.3
P6 - 0
P7 - 17.9
P8 - 31.4
P9 - 30.8
P10 - 30.5
P11 - 0
P12 - 25.2
P13 - 29.2
P14 - 29.2

LM343N
P1 - 10.6
P2 - 10.6
P3 - 9.9
P4 - 32.8
P5 - 31.2
P6 - 27
P7 - 31.2
P8 - 30.5
P9 - 27.9
P10 - 31.2
P11 - 0
P12 - 14.7
P13 - 31.2
P14 - 31.2

CD4007UBE
P1 - 0
P2 - 0
P3 - 0
P4 - 0
P5 - 0
P6 - 0
P7 - 0
P8 - 0
P9 - 0
P10 - fluctuated 15-19
P11 - 16.5
P12 - 0.1
P13 - 33.3
P14 - 33.5

CD4047BE
P1 - 33.1
P2 - 0.1
P3 - 18.5
P4 - 33.3
P5 - 33.3
P6 - 33.3
P7 - 0
P8 - 0
P9 - 0
P10 - 16.5
P11 - 16.5
P12 - 0
P13 - 33.3
P14 - 33.3

MN3010

P1 - 32.5
P2 - 16.5
P3 - 17.9
P4 - 1.5
P5 - 17.9
P6 - 16.4
P7 - 0
P8 - 19.5
P9 - 19.5
P10 - 16.5
P11 - 0
P12 - 16.5
P13 - 19.4
P14 - 19.6

Wow.  My fingers are tired!