exxos's Atari, Amiga & retro forum

Hi all,

I need help identifying what is wrong with my A2000. Every time I start the machine it produces a black /grey/white screen and often a black screen with horizontal red/green lines.

I have done the usual reseat/check all custom ICs, checked the traces around the processor, ROM, Agnus, Gary and RAM.

What is odd about this machine is that _RST and _HLT both often start "high". I have never seen this behavior before. Does anyone know what might be causing that?

I guess you could try the Diagrom.

However, seeing as you say that the reset line is never low points towards the reset circuit. I don't know the way the Amiga keeps the CPU in reset until everything is stabilised.

P.S. Looks like Gary is the chip controlling the reset. Try reseating the chip and cleaning the socket. I think that they're single wipe sockets which are always iffy.

My biggest problems with A2000 have always been around the battery area. The alkali leaks go under the 68000 socket (which typically does not get removed during neutralisation) and it eats at the board underneath.

I was going to suggest Diagrom as well.

stephen_usher wrote: 05 Feb 2024 21:16 I guess you could try the Diagrom.

However, seeing as you say that the reset line is never low points towards the reset circuit. I don't know the way the Amiga keeps the CPU in reset until everything is stabilised.

P.S. Looks like Gary is the chip controlling the reset. Try reseating the chip and cleaning the socket. I think that they're single wipe sockets which are always iffy.

I should have mentioned in my original post that all my testing is with the Diagrom inserted. Every so often, the machine will start with the flashing Diagrom green /red screen until it gets to the final screen of horizontal lines. However, even in those instances, HLT and RST will start high...which surely must be wrong?

alexh wrote: 05 Feb 2024 21:22 My biggest problems with A2000 have always been around the battery area. The alkali leaks go under the 68000 socket (which typically does not get removed during neutralisation) and it eats at the board underneath.

I replaced the processor socket and thoroughly cleaned that area. I did not find any damaged traces, even the usual pin 64 to via to pin 24 of the ROM is fine.

Can you look at the serial out from Diagrom. it's going to show you more info instead of guessing

I have looked at the serial output and unfortunately it doesn't reveal anything other than "no chipmem detected".
I have since removed all 8 RAM ICs, soldered sockets and used 8 known working RAM ICs. However, that odd behavior on the HLT and RST lines has remained.

If the CPU isn't being held in reset at power on all bets are off. Check to see if the Gary is correctly holding /RESET low at power on. If it's not then Gary is probably defective.

I seem to remember an "Adrian's Digital Basement" episode relatively recently where he had similar issues.

I just checked (again) and RST on Gary is held high on startup, as is HLT.
I have tested this Gary in another machine which does start correctly.