ZX81 rebuild

Discussions about Sinclair ZX80 and ZX81 Hardware
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Paul
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Re: ZX81 rebuild

Post by Paul »

Lardo Boffin wrote: Wed Dec 06, 2017 5:16 pm Well, so long as they are polite! :D
I hope I wasn't unpolite.
In theory, there is no difference between theory and practice. But, in practice, there is.
Lardo Boffin
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Re: ZX81 rebuild

Post by Lardo Boffin »

Paul wrote: Wed Dec 06, 2017 5:53 pm
Lardo Boffin wrote: Wed Dec 06, 2017 5:16 pm Well, so long as they are polite! :D
I hope I wasn't unpolite.
No - you were very polite!
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
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Paul
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Location: Germanys west end

Re: ZX81 rebuild

Post by Paul »

Lardo Boffin wrote: Wed Dec 06, 2017 5:54 pm No - you were very polite!
Thanks for the feedback, it's always hard to tell for me because I don't usually communicate in english :oops:
In theory, there is no difference between theory and practice. But, in practice, there is.
Lardo Boffin
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Re: ZX81 rebuild

Post by Lardo Boffin »

Arrggghhhh!

The ZTX313s arrived today so I put them in (the right way round 8-) ), got a pulse and switched on.
I get a white screen and no K. Did I say argh? :evil:

The board was working - when I temporarily put the original TR2 back in earlier in the week I got a K. So I guess the question is - what have I broken while I was messing around? The ICs are Ok I think - I put them in another board and got a K.

Helllpppp!

:D
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
sirmorris
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Re: ZX81 rebuild

Post by sirmorris »

Did you change resistor values?
Lardo Boffin
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Re: ZX81 rebuild

Post by Lardo Boffin »

sirmorris wrote: Thu Dec 07, 2017 3:22 pm Did you change resistor values?
No - I left the original resistor in and removed the test ones.

The only thing I can think of is that I shorted something while soldering but cannot see anything.

I’m getting the same pulse on pin 6 of the Z80 on this board as another working one so it looks like that side of it is ok.

Edit - almost the same. The working board is pulsing and showing Lo at the same time. The non-working board is just pulsing. Not sure if that is significant.

Really wish I had left that ZTX313 in there... :cry:
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
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1024MAK
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Location: Looking forward to summer in Somerset, UK...

Re: ZX81 rebuild

Post by 1024MAK »

Don't Panic!
Just start your fault finding investigation from the start...
  • Test the +5V power rails
  • Check for solder splashes using your eye (and maybe a magnifying glass)
  • Test the Z80 CPU pins, A14, A15 plus /RESET, /MREQ etc...
You'll get there in the end ;)

Mark
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.
Lardo Boffin
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Joined: Sat Nov 26, 2016 2:42 am

Re: ZX81 rebuild

Post by Lardo Boffin »

1024MAK wrote: Fri Dec 08, 2017 2:53 am Don't Panic!
Just start your fault finding investigation from the start...
  • Test the +5V power rails
  • Check for solder splashes using your eye (and maybe a magnifying glass)
  • Test the Z80 CPU pins, A14, A15 plus /RESET, /MREQ etc...
You'll get there in the end ;)

Mark
Its more stress than panic. This was supposed to be fun but has rapidly developed into a ‘mare.

I have checked for solder with my eyes and a times 3 magnifiying glass (need a better one) and can’t see any. But that is not 100% proof.

Test results:-

Results
Results
B72597C0-24F8-4BDB-8C69-5DD0C8867E40.jpeg (71.46 KiB) Viewed 3574 times
There is always time for Excel! May extend that for all pins...

I do randomly sometimes get a pulse on A14 but not always. I never get a fast pulse on A15.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
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gammaray
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Location: Texas

Re: ZX81 rebuild

Post by gammaray »

Its more stress than panic. This was supposed to be fun but has rapidly developed into a ‘mare.
That is why everything is called "work"!

"I have to work on something."
"i have to finish working on something."
"Something is not working, I have to work it."
"I am going to work."
"I wish that guy would work."
"I am tired of working on someone else's responsibilities."
"I am tired of repairing this, I wish it would work."
5-TS1000,UK ZX81<-Sheelagh, US ZX81, 2-TS1500/KDLX , 3-TS2040 printer, 2-TS2020 cassette decks, ZXPAND+AY, ZeddyNET, ZXBlast, UDG, ZX8CCB, AERCO, BUILDS/REPAIRS ZX Spectrum, ZX80 Minstrel, ZXMAX48 v1 v2, 2-TS-2068, ROM, 16kRAM
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1024MAK
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Location: Looking forward to summer in Somerset, UK...

Re: ZX81 rebuild

Post by 1024MAK »

Don't Panic is a phrase on the cover of The Hitchhiker's Guide to the Galaxy...
Hence is the standard response to any situation... :lol:

Mark
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.
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