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storhemulen
28th March 2012, 21:20
I just got my hands on a SupraDrive 500XP (sold with "unknown functionality") and the disk part of the expansion seems to be working OK. I can boot from the drive anyway.

The RAM part however is faulty in some way. When starting up I get a red screen:

System Expansion Board Check

Status Manufacturer Product
BAD 1056 9
OK 1056 13

If I disable the RAM via dip switch #5, this board check does not show up.
If I set the RAM to 0 by setting J1-J3 to OFF, it does not show up.
Also, I removed all 256x4 chips (8 of them) and put in 4 new ones that I had, and set the RAM to 512k at J1-J3. I get the same BAD status however, so mem chips is probably not the issue.

There also was an IC missing when I got the expansion (IC19) which should be a 74F32PC if you look at the picture here (http://amiga.resource.cx/photos/photo2.pl?id=supra500xp&pg=1&res=hi&lang=en). I had a SN74F32N available, which should be equivalent. Someone installed a socket and there are also two wires on the back of the PCB which seem to be jumpering damaged tracks, so an attemt to fix it has obviously been made. I tested for continuity and repair seems OK to me. The damaged tracks are located at IC19, so damage probably occured when IC19 was de-soldered and replaced with the socket.

My own pictures are here:
http://www.flickr.com/photos/storhemulen/sets/72157629687819927/

Any clever ideas welcome. For instance, does anyone know which ICs are used by the RAM part of the expansion? I could follow the tracks I suppose...

storhemulen
30th March 2012, 14:34
None?

How about this then: is piggy-backing the logic ICs closest to the mem chips a good idea for finding faulty ones or is it just a stab in the dark? Or even harmful?

roy_bates
30th March 2012, 14:38
None?

How about this then: is piggy-backing the logic ICs closest to the mem chips a good idea for finding faulty ones or is it just a stab in the dark? Or even harmful?




i dont think its a good idea to piggyback logic ic's,you could damage them and any logic connected to it.:)

storhemulen
30th March 2012, 14:44
OK, thanks! Well I guess the only way to find out is to start de-soldering ICs one at a time, then solder a socket and install a new IC.

roy_bates
30th March 2012, 14:47
OK, thanks! Well I guess the only way to find out is to start de-soldering ICs one at a time, then solder a socket and install a new IC.


good call,when you install a new one also try the one before and after this ic as well.:)if you can get them

rkauer
30th March 2012, 18:13
A good trick is power the board on and touch your fingers on the logic chips to check if they are stone-cold (dead) or too hot to touch (short-circuited).

Without a logic analyser that's the only method besides the swap-one-by-one.

storhemulen
31st March 2012, 12:29
Thanks for the tip rkauer. This implies that an infrared camera could be a useful tool to discover chips that are either colder or hotter than the rest.

As for piggybacking, is that mainly used for troubleshooting memory chips (RAM/ROM)?

roy_bates
31st March 2012, 14:59
Thanks for the tip rkauer. This implies that an infrared camera could be a useful tool to discover chips that are either colder or hotter than the rest.

As for piggybacking, is that mainly used for troubleshooting memory chips (RAM/ROM)?


yes this used to be common place with old 8 bit computers years ago,but i wouldent advise it myself.

the best solution for bad ram/rom is to just replace them and to check the 5 volt rail. memory isent very reliable over 5.25 volts and under 4.85 volts.
good luck:)