48K Issue 2 strange lower ram fault

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Spectrum65535
Posts: 11
Joined: Tue Feb 16, 2021 8:19 pm
Location: Warrington

48K Issue 2 strange lower ram fault

Post by Spectrum65535 »

Hi all
Sorry to be a pain with this board but it’s driving me insane.
When I got this board it was in a pretty sorry state, I got a good ULA and I have a Diagnostic rom installed, all the voltages are in tolerance, but when it’s switched on, the diagnostic Rom does a lower ram test, the first time it said it was ok, but each time you turn it on it says random ICs are faulty first it was IC 7, then 10, then 13, if you leave it off for a while it sometimes says it’s ok, then it will say random IC numbers again. All the lower ram 4116s are brand new and all the same batch number. Anyone any ideas? Just to mention, the spider transistor is missing, could that cause it? The ULA is a 5C112E.
Simon
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1024MAK
Posts: 3629
Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...

Re: 48K Issue 2 strange lower ram fault

Post by 1024MAK »

Spectrum65535 wrote: Wed Mar 17, 2021 7:36 pm the spider transistor is missing, could that cause it?
No. The spider transistor deals with I/O contention issues, not memory.

What is the access time (speed rating) of the replacement DRAM chips?

Mark
Spectrum65535
Posts: 11
Joined: Tue Feb 16, 2021 8:19 pm
Location: Warrington

Re: 48K Issue 2 strange lower ram fault

Post by Spectrum65535 »

Hi Mark
The 4116s are STC 4116 2N type so 200ns if I recall, identical to the ones in my other working issue 2.
Simon
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