A500 rev6a extra 512K not detected

[UberFreak]

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!

[stx2199]

clean the connector/purchase another memory expansion to to see if works, they are cheap today

[UberFreak]

Hi,

Its not an expansion, but motherboard RAM.

Originally Posted by stx2199

clean the connector/purchase another memory expansion to to see if works, they are cheap today

[lesta_smsc]

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.

[stx2199]

Originally Posted by UberFreak

Hi,

Its not an expansion, but motherboard RAM.

yet u can purchase a memory expansion and you will get 512kb of slow memory
512k+512k is a more compatible config with old games than 1mb chip only

[UberFreak]

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.

[hooverphonique]

_EXRAM has a pull up, so if you leave the jumper floating, you explicitly say no to expansion ram.