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Hi all,
I've got a M1 that came to me with a shorted tantalum and a blackened R80 which were both on the 5V rail (DAC board) which were causing intermittent audio dropouts.

Power supply voltages were also a bit low so I replaced all the power supply capacitors (electrolytic only) and the voltages came back to normal.

I screwed the instrument back cover and went on to test it hoping it was an easy fix but while the audio dropouts have vanished I get intermittent freezes when I hit the keys and sometimes random freezes even If I don't touch anything.
The freezes are mostly related to (normal) force applied in either the keyboard or the panel so I totally disconnected the keyboard but it's not that.
Next suspect I guess would be the DAC board again because that's where damage has been done but I'm not entirely sure about the mainboard since a freeze would indicate a "higher" prorioty fault than just the audio path.
At least that's what I think right now.

I checked if anything is touching the chassis, but there isn't anything apparently shorting and the whole assembly is pretty much standard so there's not much to odo wrong there I guess.

Anybody has any ideas what might be causing these freezes?

The problem with this machine is that there are many areas that are just black boxes for me (customs ICs) so that along with its size and mechanical assembly makes it quite difficult to work on.

Hi belzrebuth,

to me it sounds as if there's a kind of loose connection somewhere. I suggest to check the solder joints that you have been working on and carefully resolder them if in doubt.

You can take a wooden stick, a pencil or a screwdriver's plastic handle and slightly knock onto the pcb(s) and/or some larger capacitors/connectors/IC's etc. to find out if the behaviour changes in any way...

Its fault was the flex connector connecting the DAC board and main board.
One of the pins has been detached from the plastic end of the connector and maybe the previous owner or else had applied force trying to insert it so that pin has bent.
I can't explain why it was intermittent because the pin was almost certainly wasn't in place when I disconnected the flex ribbon.
Anyways, it seems to work fine now!

Ah ok,

glad you solved the issue - thanks for coming back with the solution

Best,
Michael