Jumper settings and advice for Alcomp A504 4meg 2meg ram expansion for A500 or A2000

snowpile79 · 15 July 2021, 21:24

Hello! I have an Alcomp A504 2meg (or upgradable to 4meg) ram card that typically fits in a cpu slot for an A500 but you can use it in an A2000 or 1000 as well (I suppose). Picture attached. I did troubleshoot and fix one of the SN74LS245 tri-state bus transceivers (one of the socketed chips on the board) which restored the card to full functionality when only 2megs of ram are installed on the board (its default from the factory config I guess). I purchased the 1bitx1meg ram chips to upgrade it to 4meg. If I put all the chips in the card red screens saying the expansion card is bad. If I pull the old 2megs of ram and put the new ram in its place (in the same sockets) the card works fine and I even ran ram tests on both sets of 2megs of ram no issues. I put all the ram back in after cleaning the sockets and still either get a red screen saying expansion card 5/1 is bad (the ram card) or I get a yellow screen. If you look at the picture I upload I have circled the jumper pins. The two pins towards the bottom (when looking at the picture) are both ground therefore my belief is any jumpers I install should go from the bottom ground pin to the upper pin. I have tried jumpers in both positions. If I install a jumper vertically on the right the card completely disables and does not show up/is not auto detected at all (this seems like a ram disable jumper although all doc I can find on this card says there is no ram disable option). Installing a jumper in the left vertical position just causes either a red expansion card bad error or a yellow screen. You will see in the pictures that I have started replacing some of the sockets that wouldnt allow ram chips to fully seat. I'm not positive if that will fix it and will continue to work on it regardless. For 2meg to work no jumpers must be installed but with no jumpers and 4meg installed currently I get a red screen with bad expansion card error or a yellow screen and endless reboot so I'm missing something and adding jumpers to the headers doesnt result in any success. Maybe someone out there has a 4meg version of this card and can tell me what their jumpers are set at so at least I can set those properly and continue with troubleshooting or maybe replacing the questionable sockets will work. Thanks for any info.

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snowpile79 · 15 July 2021, 21:26

Oh the rows of chips labeled with a zero are bank 0 and are the banks that work with 2megs of ram. The moment I fill banks 1 with compatible known working/tested ram chips the card errors as explained regardless of what I do.

snowpile79 · 26 July 2021, 16:34

Just reporting back to possibly help others with this card in the future.

As explained before there is a 4 post jumper block in the center of the card.

This info: http://amiga.resource.cx/exp/a504 is not entirely correct. I found that if you install a jumper in the top jumper block (install it across the pins horizontally) it will disable the card.

If you install a jumper on the bottom jumper block horizontally then that puts the card in 4megabyte mode (you have to populate all the chips).

If there is NO jumper on the bottom block that puts the card in 2meg mode.

At any rate I have confirmed these settings although my card wont work in 4meg mode. If I populate the top most row of ram chips the amiga yellow screens OR guru's. I believe the PAL chip that generates the CAS for that row is possibly faulty or theres another logic chip faulty. Still looking into it I'm guessing theres nobody out there who has been able to dump the PAL or even tried. It works in 2meg mode though. Anyways I'll keep poking at it.

snowpile79 · 26 July 2021, 16:35

I just noticed my picture is rotated to the right 90 degrees. When I say "jumper block on the top" you have to rotate my picture back left 90 degrees and look at it from that point of view.

Quote:

Originally Posted by snowpile79

Just reporting back to possibly help others with this card in the future.

As explained before there is a 4 post jumper block in the center of the card.

This info: http://amiga.resource.cx/exp/a504 is not entirely correct. I found that if you install a jumper in the top jumper block (install it across the pins horizontally) it will disable the card.

If you install a jumper on the bottom jumper block horizontally then that puts the card in 4megabyte mode (you have to populate all the chips).

If there is NO jumper on the bottom block that puts the card in 2meg mode.

At any rate I have confirmed these settings although my card wont work in 4meg mode. If I populate the top most row of ram chips the amiga yellow screens OR guru's. I believe the PAL chip that generates the CAS for that row is possibly faulty or theres another logic chip faulty. Still looking into it I'm guessing theres nobody out there who has been able to dump the PAL or even tried. It works in 2meg mode though. Anyways I'll keep poking at it.

15 July 2021, 21:24	#1
snowpile79 Registered User Join Date: Jan 2018 Location: Hancock Posts: 48	Jumper settings and advice for Alcomp A504 4meg 2meg ram expansion for A500 or A2000 Hello! I have an Alcomp A504 2meg (or upgradable to 4meg) ram card that typically fits in a cpu slot for an A500 but you can use it in an A2000 or 1000 as well (I suppose). Picture attached. I did troubleshoot and fix one of the SN74LS245 tri-state bus transceivers (one of the socketed chips on the board) which restored the card to full functionality when only 2megs of ram are installed on the board (its default from the factory config I guess). I purchased the 1bitx1meg ram chips to upgrade it to 4meg. If I put all the chips in the card red screens saying the expansion card is bad. If I pull the old 2megs of ram and put the new ram in its place (in the same sockets) the card works fine and I even ran ram tests on both sets of 2megs of ram no issues. I put all the ram back in after cleaning the sockets and still either get a red screen saying expansion card 5/1 is bad (the ram card) or I get a yellow screen. If you look at the picture I upload I have circled the jumper pins. The two pins towards the bottom (when looking at the picture) are both ground therefore my belief is any jumpers I install should go from the bottom ground pin to the upper pin. I have tried jumpers in both positions. If I install a jumper vertically on the right the card completely disables and does not show up/is not auto detected at all (this seems like a ram disable jumper although all doc I can find on this card says there is no ram disable option). Installing a jumper in the left vertical position just causes either a red expansion card bad error or a yellow screen. You will see in the pictures that I have started replacing some of the sockets that wouldnt allow ram chips to fully seat. I'm not positive if that will fix it and will continue to work on it regardless. For 2meg to work no jumpers must be installed but with no jumpers and 4meg installed currently I get a red screen with bad expansion card error or a yellow screen and endless reboot so I'm missing something and adding jumpers to the headers doesnt result in any success. Maybe someone out there has a 4meg version of this card and can tell me what their jumpers are set at so at least I can set those properly and continue with troubleshooting or maybe replacing the questionable sockets will work. Thanks for any info.

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15 July 2021, 21:26	#2
snowpile79 Registered User Join Date: Jan 2018 Location: Hancock Posts: 48	Oh the rows of chips labeled with a zero are bank 0 and are the banks that work with 2megs of ram. The moment I fill banks 1 with compatible known working/tested ram chips the card errors as explained regardless of what I do.

26 July 2021, 16:34	#3
snowpile79 Registered User Join Date: Jan 2018 Location: Hancock Posts: 48	Just reporting back to possibly help others with this card in the future. As explained before there is a 4 post jumper block in the center of the card. This info: http://amiga.resource.cx/exp/a504 is not entirely correct. I found that if you install a jumper in the top jumper block (install it across the pins horizontally) it will disable the card. If you install a jumper on the bottom jumper block horizontally then that puts the card in 4megabyte mode (you have to populate all the chips). If there is NO jumper on the bottom block that puts the card in 2meg mode. At any rate I have confirmed these settings although my card wont work in 4meg mode. If I populate the top most row of ram chips the amiga yellow screens OR guru's. I believe the PAL chip that generates the CAS for that row is possibly faulty or theres another logic chip faulty. Still looking into it I'm guessing theres nobody out there who has been able to dump the PAL or even tried. It works in 2meg mode though. Anyways I'll keep poking at it.

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