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YACFAB Yet Another Classic Faulty AB: continuous restart, multiple reboot


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Hey,

 

I'm not really lucky with Classic AB :(

Story short:the Mac is rebooting continuously.

 

Longer story;:

I'm restoring a Classic AB. the low voltage caps were severely leaking.

I replaced them all, so do the MOSFET which was blowing the fuse.

Given the many recommendations I found in other threads I also replaced the TDA 4605.

In the picture I marked in red the replaced parts, in green the one which tested ok (de-soldered and tested).

The voltage are very stable V5.05 BUT when I connect the MB and the CRT it behave as it follows:

initially, when cold, the screen flickers for a few seconds, than I hear the happy chime

it keeps playing the chime several times, every second or so, but less and less frequently until I'm able to see the happy face and even the desktop, but inevitably it restarts.

 

- The digital multimeter shows no drop in the voltage when it restart but I might not be fast enough: I do not have an oscilloscope for a proper signal analysis.

- I noticed that it is less prone to restart if I use an external power supply for the SCSI2SD.

Some component are unable to provide the required current load, but which one?

Where should I turn my attention?

thanks

 

140885503_Photoon02-04-21at00_21.jpg.7b78a2637465d158a052be7d3dedcfb9.jpg

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