FIXED Spectrum +2 grey RAM fault but RAM is good
Re: Spectrum +2 grey RAM fault but RAM is good
No corruption on the screen, only if I remove IC31 do start to see corruption.
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Re: Spectrum +2 grey RAM fault but RAM is good
So the Z80 is likely able to write to this RAM and the ULA can read from it okay.
It could be that something is causing the signal to be marginal at the Z80, or it could be that there is a strange control fault.
Strange RAM faults in models that use the custom multiplexer chip (IC10, PCF1306P / ZX8401 / 40058) may be caused by a partial failure of it. But new spares are not available.
This fault may be rather hard to diagnose.
Mark
It could be that something is causing the signal to be marginal at the Z80, or it could be that there is a strange control fault.
Strange RAM faults in models that use the custom multiplexer chip (IC10, PCF1306P / ZX8401 / 40058) may be caused by a partial failure of it. But new spares are not available.
This fault may be rather hard to diagnose.
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor 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 being good this year.
ZX81 Chip Pin-outs
ZX81 Video Transistor 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 being good this year.
Re: Spectrum +2 grey RAM fault but RAM is good
Indeed, hard to pinpoint.
But the stuck key warning may be a clue.
This sometimes clears and I am presented with the main diag menu and the keyboard works.
I have had AY-3-8912 ICs fail before now and their IO ports are known to be susceptible on the Amstrad CPC.
See how some keys are stuck on and this happens without keyboard also.
Or is this just a symptom of a stuck D1 line?
But the stuck key warning may be a clue.
This sometimes clears and I am presented with the main diag menu and the keyboard works.
I have had AY-3-8912 ICs fail before now and their IO ports are known to be susceptible on the Amstrad CPC.
See how some keys are stuck on and this happens without keyboard also.
Or is this just a symptom of a stuck D1 line?
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- 1024MAK
- Posts: 5165
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: Spectrum +2 grey RAM fault but RAM is good
Yeah, there are replacement modules, but these are not exactly cheap. Especially if it's more of a guess as to what's wrong...
Mark
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor 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 being good this year.
ZX81 Chip Pin-outs
ZX81 Video Transistor 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 being good this year.
Re: Spectrum +2 grey RAM fault but RAM is good
I have a spare Sinclair ZX8401, I bought for a later 48k plus and did not need.
Can I use that?
Can I use that?
Re: Spectrum +2 grey RAM fault but RAM is good
Thanks, have put a watch on.
Re: Spectrum +2 grey RAM fault but RAM is good
Well it's not the multiplexer
ZX8401 fitted and still the problem persists.
Next
ZX8401 fitted and still the problem persists.
Next
Re: Spectrum +2 grey RAM fault but RAM is good
Right need to have a think about this one.
- 1024MAK
- Posts: 5165
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: Spectrum +2 grey RAM fault but RAM is good
Yes, this is a tricky fault. You said earlier that you had changed the Z80. Did you try the removed chip in another Spectrum?
Mark
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor 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 being good this year.
ZX81 Chip Pin-outs
ZX81 Video Transistor 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 being good this year.