Repair Notes: A600 white screen

Repair notes are an occasional series of (fairly!) quick fixes to common issues. Hopefully, if Google bought you here then you might find this useful, it might even solve your problem!

An A600 arrived onto the workbench with the usual signs of needing a recap – black screen, capslock light on. The cause is often C612 (the 10uF electrolytic can towards the right side of the board) leaking and ceasing to perform as a capacitor – it may boot after a few minutes, but a quick proof is to remove this capacitor and to see if the machine boots normally. This cause and effect on the 600 is well documented.

In this case, however, removing C612 it did not completely fix the issue. The symptoms changed, but were now:

  • The screen moves through the Kickstart sequence – dark grey, light grey, but then gets stuck on white. No purple insert floppy screen appears.
  • Capslock responds at first to presses but then stops after 12-15 presses.
  • DiagROM appears to boot, but most tests (memory, audio, CIA, IRQs) crash and the graphics tests is has a weird background effect. And then crashes.

There was clear signs of corrosion around C306, another 10uF closer to the centre of the board. This smoothes AVREF so isn’t anything that should stop the machine booting, but the leakage is pretty bad so let’s start probing around nearby.

It doesn’t take long to find that R309 – the large 1 ohm resistor, isn’t connected to VCC as it should be. This feeds 5V to Paula, and Paula is responsible for most of those things that were crashing DiagROM. I think we have our issue! The VCC via is underneath D576 directly above, so let’s lift that off and….. ewww. Yes, that’ll be the issue. We’re starving Paula of power, which is in turn crashing Kickstart.

Via cleaned, continuity restored with some wire either side, and soldermask applied. Components replaced, and the machine is now booting to Kickstart so the recap continues.

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