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Offline TmaxElectronicsTopic starter

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trouble with A2000 repair after leaking battery
« on: April 25, 2023, 12:00:02 AM »
Hey all,

I have just gotten my hands onto a collection of amigas that also included an a2000 with battery damage. I have removed the battery and fixed all connections, but the board is still dead (mostly stuck at the green screen, sometimes its yellow).
All connections test fine when measuring continuity with my multimeter from the CPU to U101 (Fat Agnus), so I don't think there's a problem with those.

I have also tried using a debug rom (V1.21), which outputs the following (and every 100 runs or so it also detects errors with the UDS/LDS test):

Quote
Garbage before this text was binary numbers: 1, 2, 4, 8, 16, 32, 64, 128, 240, 15, 170 and 85
To help you find biterrors to paula. Now starting normal startuptext etc
Amiga DiagROM V1.2.1 - 16-Jul-20  - By John (Chucky/The Gang) Hertell


Testing if serial loopbackadapter is installed: <> NOT DETECTED
- Parallel Code $ff - Start of ROM, CPU Seems somewhat alive
    Checking status of mousebuttons for different startups:

    Set all Interrupt enablebits (INTENA $dff09a) to Disabled: Done
    Set all Interrupt requestbits (INTREQ $dff09c) to Disabled: Done
    Set all DMA enablebits (DMACON $dff096) to Disabled: Done

Testing if OVL is working: OK
- Parallel Code $fe - Test UDS/LDS line
  - Test of writing word $FFFF to $400 OK
  - Test of writing word $00FF to $400 OK
  - Test of writing word $FF00 to $400 OK
  - Test of writing word $0000 to $400 OK
  - Test of writing byte (even) $ff to $400 OK
  - Test of writing byte (odd) $ff to $401 OK
- Parallel Code $fd - Start of chipmemdetection

Addr $00058400   OK  Number of 32K blocks found: $0B
Startaddr: $00000400  Endaddr: $00057FFF
  - Fastmemcheck skipped as we found chipmem
- Parallel Code $fb - Memorydetection done

  Using $00044CEA as start of workmem (Base)

- Parallel Code $fa - Starting to use detected memory
m0n;

After the "- Parallel Code $fa..." it sometimes hangs, and sometimes just prints random junk.

The only real concerning part of the test I see is "Startaddr: $00000400  Endaddr: $00057FFF". I assume Endaddr should be something more like $000FFFFF?
This number is also different between different runs of the debug loop.

I have looked around the board with my oscilloscope too, but found nothing obvisouly out of the ordinary.

Has anybody got some ideas or tips as to how i can get the machine up and running again?

P.S. it's not a problem with any of the chips, I have swapped every single one over to a spare A500 and everything works fine there.
 

Offline TmaxElectronicsTopic starter

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Re: trouble with A2000 repair after leaking battery
« Reply #1 on: August 17, 2023, 12:55:52 AM »
So nobody has any ideas? :/
 

Offline scuzzb494

Re: trouble with A2000 repair after leaking battery
« Reply #2 on: August 17, 2023, 02:53:47 AM »
Spread the legs on the main CPU chip it may not be making a proper conection with the socket. I had a real problem with a bad battery leak and four of the spring socket receivers were cracked. I didn't give up and cleaned both the chip and the socket. I then very gently spread the legs on the chip wider so that it really made a connection. That worked. I have had similar issues with a Gary on an A500Plus and a Denise on an A3000.

https://www.scuzzscink.com/amiga/scuzzblog_february21/scuzzblogdfebruary21_2501.htm

Worked for me anyway.

Offline TmaxElectronicsTopic starter

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Re: trouble with A2000 repair after leaking battery
« Reply #3 on: August 18, 2023, 11:51:03 AM »
I changed the socket of the cpu as well as that of the rom, still doesn't seem to make a difference :/
 

Offline RetroNinja

Re: trouble with A2000 repair after leaking battery
« Reply #4 on: August 18, 2023, 11:40:41 PM »
Sorry, I'm not clear on what you've checked so far.

Did you continuity check the traces between the CPU and the ROM? The battery damage may have eaten up some of those traces. Can you take some pics of the area and upload them? Also, there are some main/thick power traces (not sure if + or -) between the battery and the CPU that get damaged a lot when batts go bad. What condition are they in? Lastly double check the new sockets - any solder bridges between pins?

I'll put $1 on the CPU to ROM traces.
 

Offline Castellen

Re: trouble with A2000 repair after leaking battery
« Reply #5 on: August 19, 2023, 01:31:07 AM »
The output above from DiagROM has the same symptoms of a memory address error.  I'd suggest using the new DiagROM v1.3 which now has the ability to test for and report address errors: https://www.diagrom.com/index.php/download/

The common problems that can cause memory address errors on the A2000 are either typically one or more bad DRAMs, or bad/intermittent contacts in the PLCC84 (Agnus) IC socket.  I've seen plenty of socket defects despite the socket appearing to be OK, so if in doubt, replace it.