Would appreciate help - vintage Ibanez FL9 flanger has no effect - SOLVED

[DangerousBeans]

So I bought a 1984 FL9 from John Grimsley at Supersonicmods 6 years ago, it had been refurbed and has worked beautifully until now. Well, except perhaps a slight volume boost, which didn't seem to be there originally but crept in over the years - but that could simply be the changes in my set-up, it didn't bother me too much.

Me: I'm not an electronics expert but I'm ok with a soldering iron, I manage to fix most things with a combination of Google and a very basic understanding of which components do what, and I've built a couple of BYOC pedals. I have a multimeter and a signal probe but no oscilloscope.

A few weeks ago, the pedal stopped working. As in, it sounded different - there was something there, but it just didn't sound like a flanger any more. I had a look inside and couldn't see anything obviously wrong like loose wires or blown capacitors. I found the hard-to-read service manual (http://www.mojotronics.com/images/FL9.pdf) and decided my problem was I had no effect, there was definitely a sweep going on. And when I came back to it another day - the sweep had gone, but the effect was definitely there - turning the knobs changed the sound as expected, it just didn't sweep. It seemed to me like a solder joint gone wrong, so I went round and re-soldered everything. After this, there was no effect whatsoever. The LED comes on but there is no change in sound when the pedal is engaged, not even the slightest click or change in sound as it switches, the sound is clean and continuous. Could I have short circuited somewhere? I cannot find where. Or burned a chip? My soldering iron is 18W, not too powerful. Could it be that the switch is now just switching the LED and not the rest of the circuit? How do I test that?

The service manual confused me a bit (specifically, where are CP1, CP2, etc?). However, I found on this forum, armndry had heroically redrawn and improved the circuit diagram (http://www.diystompboxes.com/smfforum/index.php?action=printpage;topic=106490.0). So I have measured the voltages on each of the ICs and they are all not far from being right - the ones which should be 5V are 4.89, running off a Visual Sound 1Spot which is putting out 9.45V.

My next move would be to replace the most likely culprits - the two orange 47uF caps, and the ICs (going to add sockets just to be on the safe side), but even though ordering the components will cost only a few pounds, it feels wrong doing it by trial and error, especially since the voltage readings seem to be ok. And after typing all this, it just occurred to me to measure the voltages with the effect off - and they are exactly the same as when the effect is on.

Thanks for reading this far and if anyone has any pointers, I would be very grateful!

[anotherjim]

My first suspects would be the control pots. On any old FX they are the moving parts with the most wear and tear and could easily explain permanent or intermittent loss of signal and sweep. Test resistance from pot wipers (centre wire) to each end at different settings.

If you look at the test point chart in the manual, there is CP14 that's different volts for on and off. Cathode of D103 somewhere near the middle of the board.

[DangerousBeans]

Thanks for the reply.

I tested the pots, they seem ok.

Good spot on D103 - that was on my list to check when I gave up on it last night, and I forgot it this morning. Yes, it is showing a difference on and off: 7.89V on, 0.68V off. So I guess the switching is working at least.

[armdnrdy]

I would audio probe the circuit to see where the signal stops. Also, check to see if the LFO is oscillating and that the clock is working correctly.

[DangerousBeans]

Cheers, armdnrdy! I've traced the signal as far as pin 3 on IC104, it's going in there but isn't coming out at the other pins.

Your redrawn diagram and the labelled photo have helped a lot - the scans of the original just made my eyes hurt. So I'm guessing 104 is one chip to replace. How do I check the LFO and the clock?

[armdnrdy]

Okay...
if the clock isn't working, the signal will not pass. If the BBD is bad the signal will not pass. So..check a few things to determine the problem.

You can check the LFO at pin 7 of IC3B, or at the wiper (lug 2) of the Width control. Your meter should be connected from these points to ground.

To check the clock, set all of the controls CCW. With your meter switched to Frequency mode, check the clock at pins 2 or 4 of IC5.
You should get a reading around 40KHz. Once again....the reading is taken with your meter probes from the aforementioned clock IC pins to ground.

[DangerousBeans]

Ok, looks like my first guess was correct, and the simple answers are often the right ones, and most problems are down to human error...

While I was checking the frequencies, I spotted a tiny, microscopic trail of solder that shouldn't have been there, between two connections on IC105. Melted it off... and I've got my flanger back! It sounds as good as ever   

So yes - it must have been a dead joint somewhere that broke the effect, re-flowing the solder was the solution - but I should have been a bit more bloody careful.

I hope this thread is of use to someone in the future. Thank you for your help!