Amiga 500 sudden death

Hi,

First of all let me thank you in advance any advise / help that could be provided

I'm a owner of a Amiga 500 Rock Lobster Rev. 6A which arrived to me in pretty bad shape.
It had a 512K ram expansion on the trapdoor charged with a Varta battery which was not replaced in about 25 years. We all know what happens when those little bombs do not receive some maintenance...

Anyway, the damage wasn't so severe and only affected the cooper traces of the RAM expansion, so I was able to remove all the leaked acid and even save the memory expansion!
The 500 motherboard was not affected, but in a second detailed inspection I spotted some corrosion on some IC legs: Denise, CPU, Gary,... which was cleaned pretty well and the continuity test with a multimeter didn't reveal any problem.

So, having done this the A500 was fully functional and I was enjoying it for about 2 weeks.
One day, being playing Sensible Soccer, the image disappeared all in a sudden and since then I've been unable to revive it.
When turned on, only the power led turns on, no image (no video signal) and no disk spin.
Tested the PSU voltages and those were fine, however I had a backup PSU and tried too: same result.

Did a complete swap of all custom ICs (and CPU, except Fat Agnus) with another Rev5 working mobo and the result was the same. The ICs on the other mobo proved to work fine.

Took out Fat Agnus and cleaned the contacts (2 pins had some corrosion). Same result.

So I finally opted to use the oscilloscope and found that 68K CPU pin 15 did not have any CLK signal.
Cheked that osc gave the correct 28,9Mhz signal, which arrived to U33.

So, what might be preventing the CPU to have any CLK signal?

Thank you.

[Dipski]

Check Pin 38 on Agnus to see if it's generating the 7MHz, if it's there and not at the CPU you've got a failed component somewhere inbetween, if the 7MHz isn't there either it's not being generated or a component has failed (grounding it for example).