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| Recapped Macintosh Classic's screen wobbles when cold |
Posted by: goerz on 2022-03-20 10:14:54
I have a Macintosh Classic that a few months after recapping (and replacing diodes DP3 DP4, the optocoupler, and the TDA4605 chip) started exhibiting a wobbling in the lower bottom of the screen. The wobbling disappears gradually (line by line, from top to bottom) as the Mac warms up, taking from 30 to 60 seconds. Once the Mac is warmed up, it does not appear again, and the screen remains rock solid. The wobbling does not appear at every startup, only when the computer hasn't been used for a few hours (hence my idea that the issue is connected with the temperature of the components. The issue is also linked to this specific analog board: when swapping it with another one (also recapped), I cannot replicate the issue. Has anyone ever had this problem? Should I just ignore it, or is the analog board failing?
Thanks,
goerz |
Posted by: Johnnya101 on 2022-03-20 10:26:01
Definitely something on its way out. I'm sure someone on here will know exactly what... |
Posted by: AndiS on 2022-03-20 15:08:05
I had a wobbly Classic screen (but on the top, not the bottom) that was caused by a too low voltage on the 5V rail. I replaced the trimmer on the Analog Board to fix it.
Your issue does sound different, but it would not hurt to check the voltage after a cold start. This can be done from the external floppy port. Pin 6 is the 5V rail, pin 7 is the 12V rail. Ground can be found at pin 1.
Maybe this can help to track down the issue. |
Posted by: goerz on 2022-03-21 16:07:15
Thank you for your replies. I measured the voltage after a cold start and it seems fine to me (5.046V and 12.18V). It remains almost the same once the Macintosh warms up and the screen issue disappears. |
Posted by: joshc on 2022-03-21 18:10:44
Check for cracked/weak solder joints on the AB is where I'd start. |
Posted by: AndiS on 2022-03-21 22:58:51
I always measure voltages first, because it can be done without opening the case. But they do look fine indeed, so solder joints are a good thing to check next. Then its components |
Posted by: techknight on 2022-03-23 07:22:10
This is a perfect situation to grab yourself a can of freeze spray.
While its warmed up, hit each component one at a time with a can of freeze spray and see if the behavior returns. Whichever component returns the behavior is the bad one.
Start with diodes/transistors. |
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