White screen and no cursor at all

Discussions about Sinclair ZX80 and ZX81 Hardware
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mrtinb
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Re: White screen and no cursor at all

Post by mrtinb » Sun Jun 02, 2019 3:13 pm

Martin
ZX81, Lambda 8300, Commodore 64, Mac G4 Cube

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Papalapa
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Re: White screen and no cursor at all

Post by Papalapa » Sun Jun 02, 2019 4:51 pm

mrtinb wrote:
Sun Jun 02, 2019 3:13 pm
Here’s one on eBay: https://www.ebay.com/itm/Sinclair-ZX81- ... 672?_ul=DK
Thanks Martin, I have not seen this, but it is the american model I guess, probably from an Timex-Sinclar. I'm not sure if this ULA will be compatible with my Zeddy....

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mrtinb
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Re: White screen and no cursor at all

Post by mrtinb » Sun Jun 02, 2019 5:43 pm

The only difference in a UK ZX81 and an US TS1000 is the modulator.

The ULA does not care. All is handled in software. The ULAs are equal. One connection on the PCB is open or shorted depending on whether it is sold in UK or US.
Martin
ZX81, Lambda 8300, Commodore 64, Mac G4 Cube

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Papalapa
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Re: White screen and no cursor at all

Post by Papalapa » Sun Jun 02, 2019 6:51 pm

mrtinb wrote:
Sun Jun 02, 2019 5:43 pm
The only difference in a UK ZX81 and an US TS1000 is the modulator.

The ULA does not care. All is handled in software. The ULAs are equal. One connection on the PCB is open or shorted depending on whether it is sold in UK or US.
Thank you for the clarification, anyway I'll try to find an ULA here in Europe to reduce costs because shipping from the USA is almost double the price of the chip. Recently I bought a working ZX81 from Lardo Boffin and was only 37 pounds. Also maybe @Andy decides to issue a new batch of his ULAs, we will see.

As I'll take the ULA from the ZX81 that Lardo sent, my ZX81 will be ready to work and Lardo's one will be in standby until I cand found a solution but it will not be an urgent matter.

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Papalapa
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Re: White screen and no cursor at all

Post by Papalapa » Sat Jun 08, 2019 8:13 pm

Well, finally I have located and ordered an ULA and while it arrives I made a "lifting" to ZX81 bought to @Lardo Boffin.

I found a small breakage on the flat cable that goes to the keyboard that has affected 8 keys but fortunatelly a cut with the scissors has been enough to go back to the normallity and now all the keys are working.

Later I recaped the board (very easy, only two capacitors), replaced the 7805 regulator by a more efficiente TracoPower and installed the Pokemon's video output PCB. Now it looks like this:

Image

It took me a bit to adjust the video, I guess that the problem was the video - VGA converter so I connected the ZX81 to a DVD-VHS combo and although it rescaled the output signal to 1080p it has been much easier to adjust. When connected again to the PC monitor the signal was really good and stable to be a ZX81, I was surprised:

Image

Although it only has 1K of RAM I have connected the 16K Memotech module that came with the first ZX81 and it worked like a charm. As the first ZX81 already have had the Wilco mod it has 32K inside then, the Memotech module will be used with this ZX81.

That's all concerning this ZX81, now once the ULA arrives I'll try to fix his brother.

.

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RetroTechie
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Re: White screen and no cursor at all

Post by RetroTechie » Sat Jun 08, 2019 8:38 pm

Isn't that mini-pcb supposed to go into the modulator can? :? (after you rip its contents out). That would very much tidy up the wiring since all signals / power supply you need is right there.

Lardo Boffin
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Re: White screen and no cursor at all

Post by Lardo Boffin » Sat Jun 08, 2019 8:58 pm

Once you adjust the ZX8-CCB you should get a really good picture.

For later ULAs I start with this position and then fine tune:-

35DC1118-6135-4F8E-B637-8CCB59040850.jpeg

Yellow lines added for clarity. ;)

Before adjusting I always take a photo of the current position. Very useful when it gets worse. :o
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Various Spectrum 48ks plus a DIVMMC future and SPECTRA

Lardo Boffin
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Re: White screen and no cursor at all

Post by Lardo Boffin » Sat Jun 08, 2019 9:24 pm

RetroTechie wrote:
Sat Jun 08, 2019 8:38 pm
Isn't that mini-pcb supposed to go into the modulator can? :? (after you rip its contents out). That would very much tidy up the wiring since all signals / power supply you need is right there.
:oops:

I always do it like this:-

8E420FA4-54FA-4B78-8AB2-7F9080AE92B7.jpeg

The brown wire goes into the RF modulator in a Spectrum style composite mod.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Various Spectrum 48ks plus a DIVMMC future and SPECTRA

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Papalapa
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Re: White screen and no cursor at all

Post by Papalapa » Sun Jun 09, 2019 11:37 am

RetroTechie wrote:
Sat Jun 08, 2019 8:38 pm
Isn't that mini-pcb supposed to go into the modulator can? :? (after you rip its contents out). That would very much tidy up the wiring since all signals / power supply you need is right there.
Yeah that's right but if someday you want to go back and to get the RF signal it's easy and if do you rip the modulator circuit is impossible.

That's why I installed the circuit in this way...

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Papalapa
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Re: White screen and no cursor at all

Post by Papalapa » Sun Jun 09, 2019 11:39 am

Lardo Boffin wrote:
Sat Jun 08, 2019 8:58 pm
Once you adjust the ZX8-CCB you should get a really good picture.

For later ULAs I start with this position and then fine tune:-


35DC1118-6135-4F8E-B637-8CCB59040850.jpeg


Yellow lines added for clarity. ;)

Before adjusting I always take a photo of the current position. Very useful when it gets worse. :o
R1 is totally turned to the right then?

This is the recommended position when do you start the adjust but later it seems that should be turned to the left. Anyway, if do you have a good video signal it doesn't matter..

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