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Old 19 November 2013, 13:56   #1
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A500 Revision 3 Repair

I'm looking for some help restoring an A500 back to life. It's an early model (revision 3 without the X1 crystal).

The resistor at EMI406 appears to be bad, I will replace it and see what happens...

Power LED comes on, then after several seconds it might go out, or the disk drive LED might come on (without the drive actually spinning). This is random.
Caps lock light comes on normally and can be toggled.
There's no video output at all.
No disk activity.

Components verified to be in working condition by testing in another A500:
Kickstart ROM
Floppy drive

During testing I noticed that Denise was not warming up at all, so I took out my multimeter and I'm only measuring between 0V and 1V on Denise and the ICs surrounding it. The voltage does not fluctuate constantly, but it might be 1V and then drop to 0.1V after plugging in the composite cable. Other components like the CPU and floppy drive are being supplied with 5V. I understood that A500s are not known for cap problems, but are the larger caps C401/C402 a likely cause for this? Is there anything else I should be checking?

Any help is greatly appreciated!

Last edited by Druon; 24 November 2013 at 09:48.
Old 21 November 2013, 09:26   #2
Precious & fragile things

Join Date: Feb 2009
Location: Victoria, Australia
Posts: 1,945
Many of the Amiga computers I have in for repair are showing signs of cracked joints around the larger chips, Kickstart / 68000 etc. I don't know if the early rev of A500 boards have most or all of the chips socketted but those too can cause issues. Look for bent pins on any socketted chips ( got an A4000 at the moment that had one socketted chip with one pin bent but making contact )

You may also have a grounding issue with your wall socket where you are seeing variations in voltage or a broken wire in the PSU loom.
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Old 21 November 2013, 10:02   #3
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Join Date: Mar 2004
Location: finland
Posts: 1,466
After all very sturdy stuff - I yesterday launched my A500T with Blizzard 2060 etc after two years of no use. Worked straight away - after I connected a tube monitor because all RTG modes were tube trimmed and far away from what a LCD can display. So, a 23 years old mobo kicking a$$...
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