01 March 2024, 17:38 | #1 |
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A500 rev6a extra 512K not detected
Hi,
I'm trying to fix an A500 6a which has 1MB on board. The extra 512K is not factory and was added before I got this machine. The issue is - only 512K chip is detected, the extra 512K is not seen at all, either a chip or slow-mem. I traced all tracks and found no connectivity issues, a quick test with a logic-probe shows activity on address/data/cas/ras on the added RAM ICs. When attempting to write to memory locations where this RAM should be (using AmigaTestKit), I immediately get a garbled screen and then a hard crash. I replaced both Agnus and Gary without change in behavior. Since 512K chip is usable (and passes AmigaTestKit memory tests), I assume that U34 and U35 are probably ok. Any advice on what to check next? Thanks! |
01 March 2024, 17:55 | #2 |
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clean the connector/purchase another memory expansion to to see if works, they are cheap today
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01 March 2024, 18:20 | #3 |
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01 March 2024, 18:47 | #4 |
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The additional RAM could still be faulty. I had an expansion RAM that seemed to test okay on ATK but would crash when used (opposite to how yours is causing issues)!
There is a way to piggyback on RAM to test which might be faulty which might be an option to isolate faulty one. |
01 March 2024, 19:02 | #5 |
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04 March 2024, 14:59 | #6 |
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Issue was fixed.
It ended up being a missing ground on Gary _EXRAM pin, which prevented the additional RAM from being detected. Essentially, JP7A pads 2,3 must be shorted and not 'left in the air' as some tutorials suggest. |
04 March 2024, 15:40 | #7 |
ex. demoscener "Bigmama"
Join Date: Jun 2012
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_EXRAM has a pull up, so if you leave the jumper floating, you explicitly say no to expansion ram.
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