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Apple ][+ Up And Running

brassicGamer

brassicGamer

Experienced Member
Joined
Aug 18, 2015
Messages
52
Location
UK
Hi all. I'm very excited. I discovered a dusty Apple ][+ in a server room at my workplace. I checked the PSU and it was in, frankly, amazing condition for a PC of this age. I guess quality components were used. Initially, when I powered it on, all I got was a garbled screen so I reseated the ROM chips (thanks to Mike Willegal) and it worked! Incredible. However, slightly odd issue. Sometimes immediately, sometimes after a few minutes, random characters start appearing on the screen. Does anyone recognise this as a known issue? Thanks.

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Reseat the ram in the sockets, failing that reseat all the chips. 99% likely a bad socket connection. If the video doesn't waver and is steady then its not likely to be a power supply problem.
 
If it's not sockets and reseating doesn't help, try running with the cover off. You may have an intermittent RAM that doesn't like the heat.
 
Thanks, guys - I'll give these things a go and see what happens. Interestingly I tried reseating the character ROM and that made it worse. Might try running it with the top case removed completely. Hopefully I won't have to get the 'scope out.
 
If the video isn't wavering or flicking and you don't hear any high pitched noises from the power supply its not going to be the power supply.
I've never had a supply with failing capacitors cause ram faults without also giving unstable video and or audible noise.

The most likely culprits will be the CPU,74LS367's or 74ls153's so try reseating them first. There are some others in the address decode logic but I'd have to pull out a schematic to tell you which ones to focus on.
Given the pattern of bad characters its not likely to be faulty ram, its not a bit flip pattern typical of RAM errors. I'd say the problem is more likely noise on the address bus or decode logic causing writes to the wrong memory locations. The noise of that type is generally caused by a bad connection between chip and socket.
 
Many thanks, David. I concur with your thoughts about the PSU but I won't rule it out just yet. I'll try the reseating and see what effect that has.
 
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