My Issue 2 continuing problems and Issue 6s fixed

redgatemodels
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Joined: Tue Sep 05, 2023 11:56 am

Re: My Series 2 Died (but now resurrected)

Post by redgatemodels »

This is what I get on the big TV
DSC_0439.JPG
So pretty much the same, without the glitching. Looks like the old caravan TV has a problem with it's RF input ...
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1024MAK
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Location: Looking forward to summer in Somerset, UK...

Re: My Series 2 Died (but now resurrected)

Post by 1024MAK »

Well, it’s at least six colours :lol:

I may have asked this before, so forgive me, what test gear do you have? Do you have, or have access to a ‘scope?

What voltage do you get on ULA pins 15 and 16 with a white screen (border and text area white)?

What voltage do you get on pins 2 and 4 of IC14 (LM1889)?
Also confirm the DC voltages on pins 14, 15, 16, 12 and 3.

I presume IC14 is soldered in place rather than in a socket?

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.
redgatemodels
Posts: 172
Joined: Tue Sep 05, 2023 11:56 am

Re: My Series 2 Died (but now resurrected)

Post by redgatemodels »

Best I can get with this Comp mod pcb
DSC_0440.JPG
is this
DSC_0441.JPG
turning the vr1 trimmer goes from yellow tinge (PAL) to blue (SECAM)

Can't get white
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1024MAK
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Re: My Series 2 Died (but now resurrected)

Post by 1024MAK »

VR1 and VR2 kinda interact with one another.

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.
redgatemodels
Posts: 172
Joined: Tue Sep 05, 2023 11:56 am

Re: My Series 2 Died (but now resurrected)

Post by redgatemodels »

I don't have a scope but can get the voltages, LM1889 is soldered
redgatemodels
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Joined: Tue Sep 05, 2023 11:56 am

Re: My Series 2 Died (but now resurrected)

Post by redgatemodels »

1024MAK wrote: Thu Sep 14, 2023 2:35 pm

What voltage do you get on ULA pins 15 and 16 with a white screen (border and text area white)? 1.8v, 1.68v

What voltage do you get on pins 2 and 4 of IC14 (LM1889)? 5v, 4v
Also confirm the DC voltages on pins 14, 15, 16, 12 and 3. 11v, 11v, 11v, 11v, 4.4v


Mark
redgatemodels
Posts: 172
Joined: Tue Sep 05, 2023 11:56 am

Re: My Series 2 Died (but now resurrected)

Post by redgatemodels »

would it be worth swapping out c65?
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1024MAK
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Re: My Series 2 Died (but now resurrected)

Post by 1024MAK »

It’s unlikely that it would have degraded so badly that it would cause this. But yes, you could try.

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.
redgatemodels
Posts: 172
Joined: Tue Sep 05, 2023 11:56 am

Re: My Series 2 Died (but now resurrected)

Post by redgatemodels »

are the voltages OK?
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1024MAK
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Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...

Re: My Series 2 Died (but now resurrected)

Post by 1024MAK »

I’ll be busy until this evening, sorry.
But at a glance, no.

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.
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