A600 repair advice - Page 3

BennehBoy · 13 May 2021, 23:12

Kinda wishing I had a thermal camera.

BennehBoy · 14 May 2021, 14:35

I've gone over the board with my USB microscope can't see any bad connections or bridges, cleaned any gunk/electrolyte, and reflowed anything that looked even vaguely suspect.

Result being no change.

I then had a really good look at the electrolytics, and this may just be me but C408 (part of video power circuit) looks a little bulged...

I know I had real problems with the ground plane for this cap, so maybe I've managed to cook it slightly.

I'll replace it and see where that goes.

BennehBoy · 14 May 2021, 16:15

Pulled the cap, it was reading ~150uF low but ESR was fine.

Substituted another cap in that was closer to tolerance but no change.

BennehBoy · 14 May 2021, 16:39

On a hunch I powered my A500 by the ATX supply, and only get 4.4V at the floppy connector.

Using any of the 3 Amiga supplies I get 4.9V.

Swapping back to the a600 I now get 4.9v with the Amiga supplies - so probably cured something with the rework also.

RMB & floppy still not working, but also there's another clue, some gfx artefacts on screen - I hadn't noticed these before because I was using the composite out, and an RGB lead turned up today....

So, conclusion is that this isn't supply voltage but a signalling issue or fault introduced by the expansion on some of the lines not related to the extra memory.

I might just bite the bullet and but a modern 1mb expansion and see if that solves the problem.

BennehBoy · 14 May 2021, 16:43

Screenshot... looks to repeat at a fixed pixel spacing, address line issue? EDIT, it's every 16 pixels - 40 occurrences across 640 pixel wide screen.

BennehBoy · 19 May 2021, 15:37

8mb mem expansion arrived (608 mini) and works fine, fired up a game and I only have RH channel audio.

So, will take it apart again and re-inspect my repairs.

BennehBoy · 19 May 2021, 19:11

Fixed, R322 was bad.

Only had an 0805 replacement.

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13 May 2021, 23:12	#41
BennehBoy Registered User Join Date: Apr 2021 Location: England Posts: 58	Kinda wishing I had a thermal camera.

14 May 2021, 14:35	#42
BennehBoy Registered User Join Date: Apr 2021 Location: England Posts: 58	I've gone over the board with my USB microscope can't see any bad connections or bridges, cleaned any gunk/electrolyte, and reflowed anything that looked even vaguely suspect. Result being no change. I then had a really good look at the electrolytics, and this may just be me but C408 (part of video power circuit) looks a little bulged... I know I had real problems with the ground plane for this cap, so maybe I've managed to cook it slightly. I'll replace it and see where that goes.

14 May 2021, 16:15	#43
BennehBoy Registered User Join Date: Apr 2021 Location: England Posts: 58	Pulled the cap, it was reading ~150uF low but ESR was fine. Substituted another cap in that was closer to tolerance but no change.

14 May 2021, 16:39	#44
BennehBoy Registered User Join Date: Apr 2021 Location: England Posts: 58	On a hunch I powered my A500 by the ATX supply, and only get 4.4V at the floppy connector. Using any of the 3 Amiga supplies I get 4.9V. Swapping back to the a600 I now get 4.9v with the Amiga supplies - so probably cured something with the rework also. RMB & floppy still not working, but also there's another clue, some gfx artefacts on screen - I hadn't noticed these before because I was using the composite out, and an RGB lead turned up today.... So, conclusion is that this isn't supply voltage but a signalling issue or fault introduced by the expansion on some of the lines not related to the extra memory. I might just bite the bullet and but a modern 1mb expansion and see if that solves the problem.

14 May 2021, 16:43	#45
BennehBoy Registered User Join Date: Apr 2021 Location: England Posts: 58	Screenshot... looks to repeat at a fixed pixel spacing, address line issue? EDIT, it's every 16 pixels - 40 occurrences across 640 pixel wide screen.

19 May 2021, 15:37	#46
BennehBoy Registered User Join Date: Apr 2021 Location: England Posts: 58	8mb mem expansion arrived (608 mini) and works fine, fired up a game and I only have RH channel audio. So, will take it apart again and re-inspect my repairs.

19 May 2021, 19:11	#47
BennehBoy Registered User Join Date: Apr 2021 Location: England Posts: 58	Fixed, R322 was bad. Only had an 0805 replacement.

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