Scary SM 124 behaviour

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pixelpusher
Posts: 57
Joined: Fri Dec 27, 2019 9:01 pm

Scary SM 124 behaviour

Post by pixelpusher » Fri Jan 03, 2020 8:21 pm

Hi,

I got a SM 124 in an auction (together with a Mega ST) and that monitor
a) isn't very bright, but works on the Mega ST it came with
b) makes the picture "jump" vertically on a another Mega, esp. when there's disc access or when the blitter is heavily used
c) doesn't work on a 1040 STF - the 1040 continously reboots after a few seconds (with either a white or black screen)

Inside of the monitor I saw that the large 100uF (400V) capacitor was a little bit bulky on the top (the other capacitors looked ok, although they certainly have aged too), so I replaced it, but that didn't fix any of the issues.

Does anyone have an idea what's going on here? I find esp. b) and c) a little bit scary ...

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Re: Scary SM 124 behaviour

Post by exxos » Fri Jan 03, 2020 8:27 pm

pixelpusher wrote:
Fri Jan 03, 2020 8:21 pm
b) makes the picture "jump" vertically on a another Mega, esp. when there's disc access or when the blitter is heavily used
Disk access issues are normally bad PSU in the machine.
pixelpusher wrote:
Fri Jan 03, 2020 8:21 pm
c) doesn't work on a 1040 STF - the 1040 continously reboots after a few seconds (with either a white or black screen)
Maybe bad mono detect connection on the socket or plug.
pixelpusher wrote:
Fri Jan 03, 2020 8:21 pm
Inside of the monitor I saw that the large 100uF (400V) capacitor was a little bit bulky on the top (the other capacitors looked ok, although they certainly have aged too), so I replaced it, but that didn't fix any of the issues.
It is best to change aging mains caps, but the bulge is normally just the plastic on top warping over time.. if its a metal top and bulging then its likely about to go boom.
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pixelpusher
Posts: 57
Joined: Fri Dec 27, 2019 9:01 pm

Re: Scary SM 124 behaviour

Post by pixelpusher » Fri Jan 03, 2020 9:12 pm

I swapped the PSUs and checked the machines also with another SM124 and a TFT. Only this auction monitor triggers this behaviour. I'll check for cable for mono detection (I don't think that two machines suddenly have an issue with their socket - and then only when they are connected to this specific monitor)

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