Amiga 500+ only sees 512kb Ram

02 February 2018, 10:14

Hi,
I have a acid damged 500+ that I have cleaned and is now booting and working. (replaced U10, U12 and U13)
Only thing that is not working is the RAM. It only sees 512kb, also if I add extra memory in the expansion port. It makes no different.

I have tested traces U10-U13, U5 and other places.
But what can curse this? I find it very strange.. As it "works". Any help is very much appreciated :-)

Daedalus · 02 February 2018, 10:35

The memory is discovered during boot by probing the chip RAM at increasing addresses until an error occurs, which indicates that no RAM is fitted there. Once it finds this point, it stops looking for chip RAM, so it won't find any in the expansion region (1-2MB). If there's a problem with the RAM above 512KB, Exec will think there's just 512KB fitted and work away like that. Maybe there's an issue with the 74F244 chips that drive the address bus and RAS & CAS signals, faults on any of those lines could cause entire regions of memory to go missing.

02 February 2018, 10:51

Quote:

Originally Posted by Daedalus

The memory is discovered during boot by probing the chip RAM at increasing addresses until an error occurs, which indicates that no RAM is fitted there. Once it finds this point, it stops looking for chip RAM, so it won't find any in the expansion region (1-2MB). If there's a problem with the RAM above 512KB, Exec will think there's just 512KB fitted and work away like that. Maybe there's an issue with the 74F244 chips that drive the address bus and RAS & CAS signals, faults on any of those lines could cause entire regions of memory to go missing.

Thank you so much for answering and giving me some hope back!
So you think I should replace U35?
Could it be one of the RAM blocks? I am thinking about soldering them all out and adding one at the time?
What order are the RAM tested?

02 February 2018, 14:11

I have now moved all RAM to sockets and shuffled them around. Twice I have seen the full amount of RAM. But when I turn off and on again they are gone.

02 February 2018, 22:09

Just a quick update, I think I solved it. It was U16 the was faulty. Changed it and it is on 1mb now. Thank you Daedalus!

02 February 2018, 10:14	#1
Tezting Posts: n/a	Amiga 500+ only sees 512kb Ram Hi, I have a acid damged 500+ that I have cleaned and is now booting and working. (replaced U10, U12 and U13) Only thing that is not working is the RAM. It only sees 512kb, also if I add extra memory in the expansion port. It makes no different. I have tested traces U10-U13, U5 and other places. But what can curse this? I find it very strange.. As it "works". Any help is very much appreciated :-)

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02 February 2018, 10:35	#2
Daedalus Registered User Join Date: Jun 2009 Location: Dublin, then Glasgow Posts: 6,348	The memory is discovered during boot by probing the chip RAM at increasing addresses until an error occurs, which indicates that no RAM is fitted there. Once it finds this point, it stops looking for chip RAM, so it won't find any in the expansion region (1-2MB). If there's a problem with the RAM above 512KB, Exec will think there's just 512KB fitted and work away like that. Maybe there's an issue with the 74F244 chips that drive the address bus and RAS & CAS signals, faults on any of those lines could cause entire regions of memory to go missing.

02 February 2018, 14:11	#4
Tezting Posts: n/a	I have now moved all RAM to sockets and shuffled them around. Twice I have seen the full amount of RAM. But when I turn off and on again they are gone.

02 February 2018, 22:09	#5
Tezting Posts: n/a	Just a quick update, I think I solved it. It was U16 the was faulty. Changed it and it is on 1mb now. Thank you Daedalus!

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