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Power Supply takes a while to reach full output voltage


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The Macintosh Classic I've been working on is now done. All the large electrolytic caps on the analogue board and the caps on the logic board were all replaced. Voltages measure stable and within spec from the floppy disk port. C2 on the CRT neck board was also replaced.

 

However I've noticed that when the computer is left switched off for a long period of time, the voltage readings are very low, the screen is the wrong shape, it shakes violently and there's a chequerboard pattern. If you wait, the voltage eventually creeps up and it boots (but the memory check takes a while), wait even longer and the screen eventually returns to the correct shape and stops shaking.

 

Anyone know what could cause such an issue?

 

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Posted (edited)

You know, I think I meant to replace that and never got around to it (partly because I couldn't find it since it's one of the small ones). I'll open the case tomorrow and test the diode.

 

EDIT: Wait, no, the giant one with the heat sink. Why did I think one of the little ones? Yes, there was a lot of gunk around that area of the board and it'll absolutely be that diode I forgot to replace. I'll remind myself to order a part tomorrow.

Edited by benanderson89
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