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falter
February 12th, 2014, 03:56 PM
I have a couple of small issues with my SuperPET, which was my original collector computer, taken directly out of service at a school and into my possession.

I never noticed before, but today I was firing it up to test my 8032 keyboard and was surprised to see only 15k RAM reporting. I have *tons* of RAM chips now thanks to a bunch of acquisitions, so there is no problem replacing them.. my question is, how best to nail down which is our problem? Remembering too that this is a SuperPET and I'm not sure how the other boards fit into things.

And then the other problem is the transformer buzzes loudly. Is there anything I can do about this or do I need to look for another transformer? The machine seems to operate fine, apart from the RAM issue.. but yeah, that buzzing is loud and annoying and even a bit unnerving. Makes you think it's going to blow up.

barythrin
February 12th, 2014, 04:17 PM
Piggyback a memory chip and test it out, hopefully you'll isolate one. There's also a memory check program out there in basic but I don't think it'd work if it doesn't already detect the correct amount. I'm also not sure if it'd be as easy as knowing the size of the memory chips onboard and finding the one that would be at 15000 (IBMs you could pretty reliably know that).

KC9UDX
February 12th, 2014, 05:19 PM
If any chips are noticably hotter than others, replace them. They're shorted, and putting another chip in parallel won't gain anything.

MikeS
February 12th, 2014, 05:40 PM
And then the other problem is the transformer buzzes loudly. Is there anything I can do about this or do I need to look for another transformer? The machine seems to operate fine, apart from the RAM issue.. but yeah, that buzzing is loud and annoying and even a bit unnerving. Makes you think it's going to blow up.Does the transformer buzz even when it's disconnected from the motherboard? Does it get warm?

Since it's working, it should be easy to isolate any bad RAM chips; start by
A=17000
POKE A,0: ? PEEK(A)
POKE A,255: ? PEEK(A)
POKE A,170: ? PEEK(A)
POKE A,85: ? PEEK(A)

You should see whatever you POKEd; if you don't, then the value will tell which chip is bad.
If you do, then write a little loop to test locations 16384 to 32767 the same way.