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Old 17 June 2020, 05:54   #1
cbmeeks
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Another Amiga 2000 black screen

I'm trying to restore my Amiga 2000 REV4.1 board.


It had corrosion from the Varta battery. I have repaired two traces but I'm wondering if there might be more damage. Here is what I've done so far:


1) Replaced CPU, Agnus, Denise, Gary with known working components


2) Pulled corroded CPU socket and replaced with new socket (machine socket)


3) Pulled corroded ROM socket and replaced with new dual-wipe socket.


4) Tested that CPU has connection on every pin to *somewhere* else. In other words, each CPU pin has continuity to various places like the ROM, CPU edge connector, etc.


5) Tested voltages on PSU. Everything checks fine. Only suspects are +12v shows as +11.7v and -12v shows as -11.48v. That is with a load on the PSU. Not sure if those values are "close enough" or not.


6) Tick signal registers a solid 60.0Hz from the PSU directly (checked pin 14).


7) Pulled RP900, RP901, RP100 and RP101 and confirmed each resistor was correct value (and cleaned corrosion around pads).



Many of the vias and pins around the CPU and as far as the RAM are dingy but seem to still have continuity. Although, I haven't tested every variation.


Last time I remember this working was 20+ years ago. And I could be wrong about that. Been in storage all this time. :-(


What's next?


I have an oscilloscope so I will probably start testing frequencies too. Maybe check for activity on the buses.


Any advice would be appreciated. BTW, I don't have any floppy or LED's hooked up at the moment. Just motherboard, monochrome composite and PSU.


Thanks!
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Old 18 June 2020, 06:33   #2
cbmeeks
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SUCCESS!!!


I finally put the scope on it and noticed that the address bus and data bus were held high.


I also tested the reset and clock which both appeared OK.


So then I toned out every address and data pin from the CPU to the ROM and noticed that I must have missed one. D5. So another bodge wire later and behold!


This unit originally had WB1.2 so I swapped out the ROM with a spare 500 so now it's running WB1.3.


After 20+ years this Amiga breathes again. There could be other faults...but I'm excited all the same.


Next step is to remove the slot edge connector next to the CPU. I don't have any cards for it and there is some green corrosion on the pins. I figured I can remove that and clean the pads underneath. I don't imagine it will be that hard finding a replacement.
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Old 18 June 2020, 09:19   #3
dalek
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Yay - so satisfying to get a working system after all that troubleshooting and repair
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Old 18 June 2020, 11:27   #4
Vypr
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Quote:
Originally Posted by cbmeeks View Post
SUCCESS!!!


I finally put the scope on it and noticed that the address bus and data bus were held high.


I also tested the reset and clock which both appeared OK.


So then I toned out every address and data pin from the CPU to the ROM and noticed that I must have missed one. D5. So another bodge wire later and behold!


This unit originally had WB1.2 so I swapped out the ROM with a spare 500 so now it's running WB1.3.


After 20+ years this Amiga breathes again. There could be other faults...but I'm excited all the same.


Next step is to remove the slot edge connector next to the CPU. I don't have any cards for it and there is some green corrosion on the pins. I figured I can remove that and clean the pads underneath. I don't imagine it will be that hard finding a replacement.

Great to hear you found the problem. Regarding the edge connector, it won;t be that easy to find an 86 pin card edge connector and they are not easy to come by.
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Old 18 June 2020, 13:25   #5
DigitalKeeper
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Thumbs up

Nice work!

And it's the right & first way to do - check all Socket's for contact Problem's and then, check if the CPU are stuck at _HLT and/or _RST Line - check Traces

In most cases (99%) ya find a broken trace

Another Amiga Back to Life!

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Old 18 June 2020, 19:16   #6
cbmeeks
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Originally Posted by Vypr View Post
Great to hear you found the problem. Regarding the edge connector, it won;t be that easy to find an 86 pin card edge connector and they are not easy to come by.



I'm afraid you are correct on this one. I cannot find one on Mouser. They have an 86 pin edge connector but the spacing is not the same and it has flanges.


Anyone know where I can source one? I thought about seeing if I could repair the one I got. It might be salvageable. Just don't like the idea of reusing it.


I'm glad I pulled it...take a look at what I found under it.
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Old 18 June 2020, 21:53   #7
jasonsbeer
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Quote:
Originally Posted by cbmeeks View Post
I'm afraid you are correct on this one. I cannot find one on Mouser. They have an 86 pin edge connector but the spacing is not the same and it has flanges..
Mouser part # 571-1-5530843-0

Mouser does not have the part defined correctly, but that's the correct part number.

Here you go...digikey has them. Part #A144213-ND.

https://www.digikey.com/products/en?keywords=A144213-ND

Last edited by jasonsbeer; 19 June 2020 at 00:36.
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Old 19 June 2020, 05:24   #8
cbmeeks
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Awesome!!


Thanks!
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