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Old 13 October 2019, 15:21   #1
dssence
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A500 green screen or light green issue

Hi can you help I’ve got an a500 rev6 board and I’m getting I suppose it’s a light green, and green light blinkin, I already tried to reseat angus 8372a several times, exchanged cia’s , reseated rom , and other chips. I felt some of the soldered rams were warm . this machine had an a501 installed. What I tried was to disable all the VCC supply going to all rams asto check if I still got a green screen. I disabled voltage to rams and still green screen. So what could be the issue? . Is there any jumper I need to move to enable the external a501?
Thanks
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Old 13 October 2019, 15:49   #2
AmigaHope
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Quote:
Originally Posted by dssence View Post
Hi can you help I’ve got an a500 rev6 board and I’m getting I suppose it’s a light green, and green light blinkin, I already tried to reseat angus 8372a several times, exchanged cia’s , reseated rom , and other chips. I felt some of the soldered rams were warm . this machine had an a501 installed. What I tried was to disable all the VCC supply going to all rams asto check if I still got a green screen. I disabled voltage to rams and still green screen. So what could be the issue? . Is there any jumper I need to move to enable the external a501?
Thanks
Green screen means there's a problem with the chip ram bus. Either there is a problem with the Agnus, there is a problem with the onboard memory, or there is a problem with the traces and components connecting them.

Disabling onboard chip ram will still give you a green screen as it will fail the poweron check.
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Old 13 October 2019, 17:21   #3
solarmon
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Are you saying there is an issue with the A501 ram expansion? So, without the A501 connected does the A500 will boot OK?

Or are you trying to say that the A500 had an A501 ram expansion that had battery corrosion and is now preventing the A500 from booting, even with the A501 not connected.

I'm also a bit confused with the statement: 'disabled voltage to the rams'? How did you do this?
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Old 14 October 2019, 02:25   #4
dssence
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Originally Posted by AmigaHope View Post
Green screen means there's a problem with the chip ram bus. Either there is a problem with the Agnus, there is a problem with the onboard memory, or there is a problem with the traces and components connecting them.

Disabling onboard chip ram will still give you a green screen as it will fail the poweron check.
Good thanks for taking your time to answer. Well I knew those could be the issues, but question is I've got the skills to solder the Agnus manually doing microsoldering , should I go that way .
I already used my oscilloscope to check the clock outputs from Agnus 7mhz and 28mhz and they're clean and steady. So could this be linked to bad CIA's I exchanged both and reseated them. Still same issue. Something which called my attention was after checking the green screen, if I plug the external a501 card I can see some gray screen like if it's try to initialize... So something is going on there.
I did these tests leaving pin VCC from ram's lifted. Same green screen. But again seem's like when it resets when I plug a501 I see for a second a gray I think or black screen.
Once more which traces can I check ? . I don't have any IC's to try from other places to replace agnus or replace CIa's which could be the case.. but I've got multimeter, frequency generator and scope.
Thanks again.
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Old 14 October 2019, 02:26   #5
dssence
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Originally Posted by solarmon View Post
Are you saying there is an issue with the A501 ram expansion? So, without the A501 connected does the A500 will boot OK?

Or are you trying to say that the A500 had an A501 ram expansion that had battery corrosion and is now preventing the A500 from booting, even with the A501 not connected.

I'm also a bit confused with the statement: 'disabled voltage to the rams'? How did you do this?
Again thanks for taking your time for answering. Well I tried plugging the A501 and for a brief instant like a sec I see a gray screen and then comes the light green. No it does not boot at all either way. It did have corrosion and I cleaned thoroughly but liquid didn't came inside the main pcb.
Any ideas, besides my other reply ?

Thanks again
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Old 14 October 2019, 10:34   #6
solarmon
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Originally Posted by dssence View Post
Again thanks for taking your time for answering. Well I tried plugging the A501 and for a brief instant like a sec I see a gray screen and then comes the light green. No it does not boot at all either way. It did have corrosion and I cleaned thoroughly but liquid didn't came inside the main pcb.
Any ideas, besides my other reply ?

Thanks again
I would leave the A501 disconnected until you can prove your motherboard is OK and can boot up.

A green screen means that the system can setup/configure memory - so this could either mean a RAM chip itself could be faulty; or a memory address or data line from Agnus or CPU to the RAM chips is broken somewhere. These traces can also go though (and under) some logic chips (U10 to U13, and U34, U35, U32 (on rev 8)), so these needs to be checked too.

I would leave the power going to the RAM chips, as if you remove power to it, then it will be the same as the RAM chip being 'faulty'.

You should use the following resources to check the memory address and data lines:

(Unfortunately, there is only a board view for a rev 8a A500)
http://www.amigapcb.org/

https://www.amigawiki.org/dnl/schematics/A500_R6.pdf
https://gamesx.com/wiki/lib/exe/fetc...ice_manual.pdf
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