Broken Ibanez SS-20 Session Man II

[OosterhoutW]

Dear DIYstompboxes-hero's,

I am aware that i'm new to the forum. I was redirected here by Brian Wampler from Wamplerpedals.

I have purchased an Ibanez SS-20 Session Man II some time ago, and now the delay circuit isn't switching on anymore.

This is a giant problem for me, since I really care about this pedal (I used it on an album track).

I' m not shy of repairing pedals or guitars (basically all musical instruments) but this one has left me in shambles. The circuit is an absolute maze. Considering it's functions that doesn't surprise me.

The biggest problem, however, is that there are no schematics online. I've asked the Ibanez customer support and their pedal luthier also doesn't have a schematic. Since the pedal is so incredibly complicated I have no clue where to start.

The problem is that the delay circuit is continuosly bypassed somehow. The distortion is working fine, and when the pedal is in both series and parallel position the distortion is hearable. When I checked the trimpots inside the pedal (for the delay lvl and amount of repeats) they were turned up fully. I measured both of the trimpots and they were working perfectly fine. Now I stumbled upon 3!! more trimpots (numbers 103 and 203  on the larger PCB, and 502 on the smaller PCB) which arent mentioned in the manual. I have no idea what they do and i'm reluctant on moving them.

I was hoping you could help me figure out what the problem is, either by bringing to attention how the circuit works and/or with a schematic that gives an overview. I suspect a bad resistor or a bad chip, since the delay circuit is only bypassed.

Please leave a reply in any case, if you could help or not. Thanks in advance!

Wouter van Oosterhout. (16-02-2023)

Important developments (23-02-2023)
- I've contacted the following people/company's for info or help: Ibanez japan, Ibanez USA, Robert Keeley, JHS Pedals, Fromel Electronics, Walrus Audio, Brian Wampler, and Alchemy Audio. It was Brian Wampler who redirected me to DIYstompboxes and FreeStompBoxes.
- I've contacted Ibanez Japan and USA for the schematic, but they could only send me the service manual (included as PDF in this post). I also measured the MN3207 and MN3102 chips (their voltage readings are in the picture). I measured these chips according to the trouble-shooting part in the service manual, but couldn't detect any faults in them. Maybe you are able to?
- Ibanez Japan has assured me not to touch the "extra" trimpots as described in the story above, as they are set to a specific default in the factory. I haven't done so either way (they didn't describe their functions though...)

[OosterhoutW]

I just noticed only the first page of the service manual is uploaded, as a picture. I'm not sure how to fix that...

[ElectricDruid]

The diagram on the front is quite helpful, but if you could put the PDF up online somewhere so we can have a look, that'd be very useful.

Have you got some photos of the board?

The overall scheme of the delay part looks pretty standard: pre-emphasis (op-amp, I expect), compressor (570/571), filter (another op-amp? could be transistor), BBD (MN-series, the clue is the associated clock chip), another filter, then the other half of the 570 set up as an expander, and then out to the mixer.

The first step would be to work out which chips on the PCB are doing which parts of that process, and check the outputs of each one to see how far the signal gets. We've had one or two examples recently where the 570 compander was the culprit, so that's a possibility.

[OosterhoutW]

Hello! I made some screenshots. Hopefully this helps. It contains a sort of x-ray picture of the front and back of the pedal!

Thanks for your help. So much!

Also: in reply to my questions Walrus Audio suspected a blown BBD-chip (but I can't discern that), and Robert Keeley replied by suggesting it might be a blown FET-bypass (I recently repaired an Ibz SD9 Sonic Distortion with two blown FET-transistors. The bypass didn't work with that pedal either, but when bypassed it still let through some sound (a very low dB overdriven/distorted sound).

Hopefully you can provide more assistance, since I really don't understand it all that much still...!

Cheers

[ElectricDruid]

Hello! I made some screenshots. Hopefully this helps. It contains a sort of x-ray picture of the front and back of the pedal!

Thanks. Those don't really add a great deal. Pity. Oh well, onwards!

Also: in reply to my questions Walrus Audio suspected a blown BBD-chip (but I can't discern that)

That's possible. That's an easy one to check, because you can fairly easily find the BBD, and then you can check for signal coming out of its output pins.

Robert Keeley replied by suggesting it might be a blown FET-bypass

It's a good suggestion in general, because they are a common failure. However, in this case that's not possible because the FET bypass is after the mixer, and you said that the Distortion stage worked ok in Parallel mode. That implies that the mixer and the effect FET are both working.

Hopefully you can provide more assistance, since I really don't understand it all that much still...!

Well, I'm making educated guesses only, I'm afraid. There isn't much to go on. Can you read IC markings on those PCB images in the service manual document? Or is there any parts list or something? We could really do with working out which parts do which functions, and then where those are. Otherwise we have to trace it out on the board, which is error-prone and pretty tiresome!

Could you take a nice big bright picture of the circuit board in your pedal please?

[OosterhoutW]

Hello! Here! I made as good of a couple of pictures as I could make. Don't be alarmed by the complexity of this beauty... but be alarmed...

Oh and: I don't have a way of measuring sinusses, because I only have a digital multimeter. Hopefully this won't be necessary to assess the problem.

The BBD chip is the MN3207 chip, and the MN3102 is some kind of oscillation chip (I don't fully understand it's function).

Hopefully you can get us going again!

PS. As you can see it uses a 10 band white cable to connect the main circuit board with the control circuit board (my biggest question about the split of them is what the chip on the control board is for...). Did I tell you there were 2 PCB's in this pedal?!?!?

[digi2t]

Wow! Just checked around the net, and these are commanding some stupid high prices for a pedal that many love to hate. 

Two PCB's in these is the norm. A main board with the bulk of the circuit, and the daughter board for the pots, LED's, and sometimes ancillary parts for some of the controls. Generally, ribbon cables connecting the two. I did find a close up shot of the main board over at mirosol's site, but these boards are usually so densely packed, that reading values... fugget about it.

Most times, tracing through the audio side with an audio probe will quickly reveal where the bobo is, but without a schematic, the degree of difficulty increases greatly. Not impossible, but tougher.

If you're really in a bind, I could look it over, and trace it out for posterity at the same time. One more for the library. PM me if you're interested.

PS. I wonder what the diff is between the SS10 and SS20???

[OosterhoutW]

Hello!

Like I said, I dont have an audio probe, but I might be able to find one soon.

Im just wondering: considering the nature of the problem, it has to be in the delay part of the circuit somewhere, absolutely 0 delay-audio. Most problems are typical, not? A broken transistor would emulate different problems than a broken BBD chip...!

I live in The Netherlands as well, so getting the pedal over to you might be a bit hard...