Yekuku wrote: ↑
Mon Feb 01, 2021 9:37 pm
try these steps
1. remove slider
2. connect/solder the 2 contacts in the green circle ( OUT 2 in schematics, should be Right channel)
3. connect/solder the 2 contacts in the red cycle.( OUT 1 in schematics, should be Left channel)
if you choose to skip step 1 , set slider to full volume.
Main output should have full volume
Well I never thought I'd be posting this but the M1 is now fixed and working perfectly... what a relief!!
It turns out that it was all due to bad soldering on my part
... my technician friend came over and we methodically went through the boards with his oscilloscope, working back from the jack board until we found the source of the problem on the DA board which was a dry joint on one of the capacitor legs on the output 1 channel of the DA board.
To recap, I had no signal out of output 1, clear signal from output 2 and none from 3 and 4 (that I could tell)... we worked out that output 1 had the bad joint even though it looked OK... with a bit of wiggling, we sometimes got a signal and sometimes not and that gave us a clue... to be sure, we reflowed all the recapped capacitor connections on the DA board and when we tested it, everything came back to life. We realised that the lack of output on channel 3 and 4 must have been because of a programming error (ie. nothing was allocated to ch 3 or 4 as the main output) which meant ch 1 was broken, ch 2 was OK and ch 3 & 4 were also working but muted.
The 12V load into the 5V board didn't do any damage and he thinks that may have been because I simply switched the synth on and off without playing anything through the synth or perhaps just because I was very lucky.... the jury is still out though it makes you think that a lot of these old components are much stronger than you realise (or are stated in the service manual).
I'm pretty sure that the power board also had a dry joint as there definitely wasn't any voltage from the 5V or 12V rail when I made my first repairs many weeks ago... I reflowed those joints which fixed the problem so we figured the problem would be hiding in either the motherboard or the DA board.
Anyway - whichever way you look at it, I think I was lucky to get away without damaging the synth and after having recapped and replaced all of the switches, there's no need to open it up again so hopefully, that's the end of the story.
I just want to thank you for all of your help and advice through this... I learnt quite a lot about the synth and really appreciated your advice and interest in trying to get it working again... hopefully this drama might stay in the forum archives and help someone else out in the future... just remember to correctly and carefully label your cables and be careful of those 5V and 12V power supply cables that sit next to each other and look almost identical (and triple check your soldering!!!!)
That's enough excitement for now....