ZX81 rebuild

Discussions about Sinclair ZX80 and ZX81 Hardware
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Paul
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Location: Germanys west end

Re: ZX81 rebuild

Post by Paul » Wed Dec 06, 2017 4:53 pm

Lardo Boffin wrote:
Wed Dec 06, 2017 4:16 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
Posts: 661
Joined: Sat Nov 26, 2016 1:42 am

Re: ZX81 rebuild

Post by Lardo Boffin » Wed Dec 06, 2017 4:54 pm

Paul wrote:
Wed Dec 06, 2017 4:53 pm
Lardo Boffin wrote:
Wed Dec 06, 2017 4:16 pm
Well, so long as they are polite! :D
I hope I wasn't unpolite.
No - you were very polite!
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

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Paul
Posts: 880
Joined: Thu May 27, 2010 7:15 am
Location: Germanys west end

Re: ZX81 rebuild

Post by Paul » Wed Dec 06, 2017 5:30 pm

Lardo Boffin wrote:
Wed Dec 06, 2017 4:54 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
Posts: 661
Joined: Sat Nov 26, 2016 1:42 am

Re: ZX81 rebuild

Post by Lardo Boffin » Thu Dec 07, 2017 1:18 pm

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
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

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sirmorris
Posts: 2699
Joined: Thu May 08, 2008 4:45 pm
Location: oxon, uk

Re: ZX81 rebuild

Post by sirmorris » Thu Dec 07, 2017 2:22 pm

Did you change resistor values?
--=== ZXpand+ ... A more moderner all-in-one upgrade solution for ZX81 ===--
* SD/MMC storage * 32K Hires-capable RAM * AY sound chip * Joystick port * Serial *
* BASIC enhancements - plug & play * Reset button * Auto-boot facility *

Lardo Boffin
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Joined: Sat Nov 26, 2016 1:42 am

Re: ZX81 rebuild

Post by Lardo Boffin » Thu Dec 07, 2017 2:40 pm

sirmorris wrote:
Thu Dec 07, 2017 2:22 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:
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

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1024MAK
Posts: 1803
Joined: Mon Sep 26, 2011 9:56 am
Location: Looking forward to summer in Somerset, UK...

Re: ZX81 rebuild

Post by 1024MAK » Fri Dec 08, 2017 1:53 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

Lardo Boffin
Posts: 661
Joined: Sat Nov 26, 2016 1:42 am

Re: ZX81 rebuild

Post by Lardo Boffin » Fri Dec 08, 2017 1:44 pm

1024MAK wrote:
Fri Dec 08, 2017 1:53 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:-

B72597C0-24F8-4BDB-8C69-5DD0C8867E40.jpeg
Results
B72597C0-24F8-4BDB-8C69-5DD0C8867E40.jpeg (71.46 KiB) Viewed 121 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.
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

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gammaray
Posts: 288
Joined: Sun Apr 17, 2016 1:44 am
Location: Texas

Re: ZX81 rebuild

Post by gammaray » Fri Dec 08, 2017 3:18 pm

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."
Finish what you start. Truth is over the mountaintop or six feet under.
4 x TS1000, 2 x TS1500 , 2 x timex 2040 printer, 1/2 x timex 2020 cassette deck, ZXPAND, ZeddyNET, ZXBlast..., unfinished Spectrum...Still no life!

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1024MAK
Posts: 1803
Joined: Mon Sep 26, 2011 9:56 am
Location: Looking forward to summer in Somerset, UK...

Re: ZX81 rebuild

Post by 1024MAK » Fri Dec 08, 2017 11:54 pm

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

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