IC25/26 being faulty will certainly cause you issues with upper RAM..
I would socket them both and replace them. Probably find that will sort the issue.
KbJ
ZX Fail
Re: ZX Fail
Folks are like binary, one or the other..
- 1024MAK
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Re: ZX Fail
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.