Advice wanted Amiga A500 power issue

[gksonnier]

I recently acquired and Amiga 500 through E-Bay.  It came with only the main unit.  No PSU or anything else included.  It was sold for parts or repair.  I was able to put together a PSU using the ATX hack.  I do have correct voltages (+12V, -12V, 5V) at the Amiga connector.  I also checked the connector to make sure I didn't have a short.  The issue I am seeing is as follows:

When I attempt to power up the Amiga, the CAPS LOCK key will do a quick flash, then turn off.  The ATX PSU will then stop working all together.  I have to unplug the PSU from the Amiga and plug it back in to get the PSU to power up again.  If I disconnect the 5V lead and power it up, the ATX PSU does continue to run.  Obviously the Amiga will not start like this.  I also took it a step further by hooking up the 5V side (both +5 and Ground) to a separate power source.  Once I power up the 5V side, the ATX PSU will shut down again.  Another thing I notice that when this happens, if I unplug the power lead to the ATX PSU, then pull and replace the connector on the Amiga, the PSU fan will briefly spin.  It is like there is a capacitor somewhere discharging. 

I have also reseated all chips on the board.  The motherboard appears in perfect condition.  The battery has been removed from the expansion board and shows no evidence of prior leaking.  I also tried booting without the expansion board, floppy drive, and even keyboard.  All three produced the same result. 

I am afraid I may have a bad motherboard.  I am unsure what to check next.  This is an Amiga 500 Rev 5.  Any help would be greatly appreciated!  I really look forward to getting this computer working.  I had one of these years ago, and regretted letting it go. 

Thanks in advance!

[gksonnier]

Really appreciate the reply, thank you!  I did uncover another detail through my investigation.  On a hunch, I wanted to check for ground at the power connector.  The pin that should be 5V is shorted to ground.  This explains the behavior with my ATX PSU.  I tried another PSU (before testing for ground at the power connector) which also did not work.  As for the power LED, it does not light at all.  I did pull all chips one by one to test further.  I see no physical signs of corrosion or damage, but did not check with a microscope or anything like that. 

I will continue to troubleshoot.  I imagine I may have a shorted capacitor or an issue with a chip/socket as you mentioned.  I may go ahead an find extra chips to have something to swap and test. 

Again, thanks for your reply.  It has been years since I have owned an Amiga 500.  I really want to get this one going again. 

[gksonnier]

Appreciate the response about possible shorted RAM.  I am still working on this.  Haven't solved it yet, but haven't given up either.  I think I may have to remove the RAM to really test it.  I may go ahead and socket those so that they can easily be replaced in the future.  Thanks again for the reply!  I really hope I can get this thing going again. 

[gksonnier]

That is a good idea.  I will try that when I get home.  Thanks for the reply!