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Old 09 November 2019, 21:44   #1
Pietro.tiberi
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A2K Black Screen

Hi,
I'm trying to restore an amiga 2000 rev.6.2 mobo.
I'm using a new ATX PCU (J300 set covering 2-3). The PSU if fine.
Voltage on CPU is 4.94 (pin14-16).

The CPU is OK (tested on another a2k)
S-video output to Monitor is ...black?

Any hints?

KR

Pietro
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Old 09 November 2019, 23:43   #2
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Did you change the jumper setting on J300? ATX PSU won't have the 'tick' signal
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Old 10 November 2019, 01:28   #3
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yes I did...

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Old 10 November 2019, 12:12   #4
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The jumper is correctly set covering position 2-3 but still black screen.
can you suggest me a next check?

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Old 10 November 2019, 13:34   #5
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I would check the CPU socket and the traces underneath it, that's where leakage from the battery usually destroys first.
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Old 10 November 2019, 15:53   #6
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should I remove the socket or a visual inspection + multimeter memory check could be enough?

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Old 10 November 2019, 16:44   #7
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continuity check..i mean

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Old 10 November 2019, 17:30   #8
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i found a possible broken track from pin 6 of 68000. Schematics say Pin6 go to AS_ ? can you tell me where is it? i'm not able to find it?

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Old 10 November 2019, 18:17   #9
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I found the following connections do _AS signal:

1) CPU to U101 (FatAgnus) pin 24
2) CPU to U102 (Gary) pin 13
3) CPU to U800 (Buster) pin 36
4) CPU to U605 pin 9
5) CPU to Co-Processore socket pin 74

Connection 5 tested OK...now checking other connections.
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Old 10 November 2019, 18:44   #10
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Sorry my fault. CPU pin6 is connected via track in the bottom side. All connection tested ok. CPU Pin 7 is the one connected via the up side (the one in the picture) of the modo.
I tested connection CPU pin7 to Buster, Gary and U606...all OK. So no issue with that track.

Now I don't know what to test...can someone help?
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Old 10 November 2019, 19:15   #11
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an additional info: when I switch on the board the video signal is detected via Video port and the Monitor show black screen....when I switch it off the video say no signal

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Old 10 November 2019, 19:39   #12
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When you turn on the machine the power light should come on dim, then brighten up. Does this happen?
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Old 10 November 2019, 19:56   #13
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Check CPU reset and halt pin state.

Reset should not be active (except temporarily at powerup/keyboard reset) and halt should stay inactive. If halt activates, it means CPU double faulted which usually means it can't access ROM/RAM properly.

Check also all data, address and control pins between CPU and ROM (and Gary).

Agnus generates blank PAL/NTSC signal at powerup, even if almost everything else is broken.
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Old 16 November 2019, 17:17   #14
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RST (pin18) is High (4.90 v). HLT (pin17) is LOW (47 mV). I measured both using pin16 as Ground.
So it looks like that CPU is in Reset state. Can you suggest how to proceed?

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Old 16 November 2019, 18:23   #15
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_RST and _HLT are active low, so what you are describing (RST (pin18) is High (4.90 v). HLT (pin17) is LOW (47 mV)) means that something is asserting _HLT low.

Have you got anything connected to the Zorro slots?

Have you reseated Gary (and cleaned the socket pins); tried a known working; or tested that Gary in another A2000/A500?

Make sure you also clean the CPU pins and socket.

Actually clean all the socketed chip pins and sockets. From the looks of your pictures there seem to be a lot of corrosion which needs to be cleaned up first.
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Old 16 November 2019, 18:37   #16
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Ok thanks. No boards connected...the modo in on a desk connected to Power supply only.

I've reseated CPU and ROM only. Now i'm going to clean everything with Ipopropanol Alchol. I also cleaned all cantacts (CPU&ROM). I'm waiting the isopropilic alchol will evaporate totally.

After I'll try to reseat Gary if needed...

Thanks a lot...i'll keep you posted
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Old 16 November 2019, 19:11   #17
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Gary cleaned and resesed (i don't have another modo to test it)

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Old 16 November 2019, 19:18   #18
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Rom cleaned...

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Old 16 November 2019, 19:19   #19
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cpu socket cleaned

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Old 16 November 2019, 19:22   #20
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Gary

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