Sammich SID 6582A problems

[theskeletonboy]

I am the owner of a White sammichSID kit that i bought from another user on the flea market a while back and I've recently been playing with the synth again. I want to make sure its in perfect working order, and I have discovered that it is not.

I have two problems with its functions:

1. When I received it, it was jumping values with the encoder as well as the up and down arrows. Is there a fix for that?

2. I also have a problem with the right chip in mine, sometimes it cuts out completely. Turning it off and back on again makes the chip start working again, but i've noticed that it has a slightly different tone than my other chip, despite being the same series. 

 

I'm capable of repairing this myself, I'm just not sure where to start to fix these issues. Can you suggest anything?

[jjonas]

With the buttons it might be a debounce problem, if "jumping values" means one press changes e.g. two steps instead of just one  (and not going all over the place). I managed to fix it like in the thread below ('Button press delay'). It involves changing the source code and compiling it, but it wasn't hard even though I had no previous experience. Could be that the encoder has a similar problem too. I don't know whether there's a parameter in the source code for that as well, but an alternative nuts-and-bolts option is just to try another encoder.

Re the chip turning off, I can't help you there, but I think it's normal that SID chips sound slightly different even if they're from the same series.

Edited October 24, 2015 by jjonas

[Katch]

I'm going to take a guess that poor solder work is probably the culprit.  It can cause both of the problems you are experiencing.

Swap test your SIDs (swap left right) if the fault follows the chip then you have a faultly SID, if it stays with the socket - refer to my first suspicion, poor solder work.

Do a visual inspection of all the solder joints - post high res photos of both sides of both boards if you can - and we can take a look.

Edited October 26, 2015 by Katch

[mrspring]

The sammich is fairly bulletproof as long as it was constructed carefully in the first place, so the controls issue would be down to physical contamination of the switches or encoder, or more likely be caused by poor construction. Has it been gigged? How about in a smoky room? Could be dirt. If it's clean and smells clean, then You need to dismantle it and examine the boards, and all the solder joints. if any of them look like they have a 'ring' in them, as in you can see a contour line in the solder blob, or look matte or just plain crappy, then think about re-flowing the join. Just heat it up with an iron so the solder melts and goes hard again. Obviously, any tarnishing on the board itself is a hint that the builder was a little sloppy, and may have used a little too much heat, or had to fix a mistake. If You see that kind of stuff, be prepared to review the build properly.

As for the SIDs sounding different - that's SIDs for you :) But, if a SID starts off from cold fine, and then goes out of tune or looses a waveform as it heats up, it's probably just faulty. You can try attaching some stick-on low-profile heatsinks to them, as in the cooler kits for the Raspberry Pi, which might swing things, but they are very far from stable even when they are "good" chips - this is why the sound so excellent when ganged as a stereo signal.

[Katch]

A good culprit to look at when you have flakey controls are the resistor networks (long thin black components on the control surface)  - these were the cause of a lot of my CS issues with my build and desoldering and reflowing was the fix.

[theskeletonboy]

Thanks everyone for you responses! JJonas i will check that out. yeah sometimes i click buttons or move the encoder and it jumps the correct single value and sometimes it jumps anywhere from 2-5 values, totally randomly. I can take a look at the source code with your forum post. 

Katch - the swap test sounds like a good idea, I have done that before with cables and other studio equipment... ill report back.

 

From the time i've had it its always been in a smoke free studio, rarely used, not plugged in when stored. The circuit boards are pretty clean, but i will take a good look around on the board to see if there's any bad solders or dust. From when i've cracked it open it seemed clean to me. I'll post photos later.

Thanks! - Skele