TS 1000 artifacts after warming up

Discussions about Sinclair ZX80 and ZX81 Hardware
embpic
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TS 1000 artifacts after warming up

Post by embpic » Sat May 04, 2019 12:57 pm

So I bought a TS 1000 and found the ULA was dead. I did the composite mod and the internal 16K memory upgrade. I bought Andy's ULA and everything worked! (for a little while). The first time I used it I had it on for about an hour and had it running a math problem. It worked great. Later though it started to show signs of a problem. After being off for several hours (nice and cool) I would plug it in and after about a minute it starts to get wavy artifacts. You can still the the 'K' at times. After a little more time the screen goes completely bonkers. Almost like the screen you see when loading or saving.

On the oscilloscope, the output shows a nice and steady signal with the back porch. When it starts having artifacts the signal is still there but it is jumping all over the place. (see video)

So any ideas why the signal starts jumping when it gets a little warm?
Last edited by embpic on Sat May 04, 2019 2:37 pm, edited 1 time in total.

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1024MAK
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Location: Looking forward to summer in Somerset, UK...

Re: TS 1000 artifacts after warming up

Post by 1024MAK » Sat May 04, 2019 1:35 pm

How much ripple is on the 9V PSU output and what voltage do you get?
Same question, but on the +5V rail.

Both can be tested on the pins of the 7805 voltage regulator, just be careful not to short anything out.

Mark

embpic
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Re: TS 1000 artifacts after warming up

Post by embpic » Sat May 04, 2019 1:50 pm

Here are the videos.
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embpic
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Re: TS 1000 artifacts after warming up

Post by embpic » Sat May 04, 2019 2:21 pm

1024MAK wrote:
Sat May 04, 2019 1:35 pm
How much ripple is on the 9V PSU output and what voltage do you get?
Same question, but on the +5V rail.

Both can be tested on the pins of the 7805 voltage regulator, just be careful not to short anything out.

Mark
PSU output is 11.3V

The 5V rail is right at 5V. Both Voltages have no ripples. Both are pretty clean.

embpic
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Re: TS 1000 artifacts after warming up

Post by embpic » Sat May 04, 2019 2:34 pm

Here is another picture. You can see the video signal spacing is random. On one scan line you can see where the 'K' is generated and then another scan line doesn't finish before it starts again.

At least that is what I (as a noob) see.

Sean
Attachments
IMG_8302.jpg

Lardo Boffin
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Re: TS 1000 artifacts after warming up

Post by Lardo Boffin » Sat May 04, 2019 2:49 pm

Do you have other chips from other zeddies you can try in it? It would probably be worth being certain the Z80 and ROM are ok.
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

embpic
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Re: TS 1000 artifacts after warming up

Post by embpic » Sat May 04, 2019 3:00 pm

Lardo Boffin wrote:
Sat May 04, 2019 2:49 pm
Do you have other chips from other zeddies you can try in it? It would probably be worth being certain the Z80 and ROM are ok.
Yup. I tried that already. Same result.

Something new however. I just left it on and and now I am getting long periods (20-40 seconds) of normal operation and then back to the artifacts.

It is definitely going crazy when the scan resets before it is completed.
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IMG_8302.jpg

zx-heinz
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Re: TS 1000 artifacts after warming up

Post by zx-heinz » Sat May 04, 2019 3:03 pm

Check, if the oscillator frequency (at Pin 6 CPU) is stable at 6.5MHz. Could you replace the ULA?

embpic
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Re: TS 1000 artifacts after warming up

Post by embpic » Sat May 04, 2019 3:08 pm

zx-heinz wrote:
Sat May 04, 2019 3:03 pm
Check, if the oscillator frequency (at Pin 6 CPU) is stable at 6.5MHz. Could you replace the ULA?
Its is nice and steady at 3.25mhz. Should it be as 6.5mhz?

Neither of my original ULAs work (210 and 184). I have Andy's ULA installed.
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IMG_8299.jpg

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1024MAK
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Re: TS 1000 artifacts after warming up

Post by 1024MAK » Sat May 04, 2019 3:38 pm

The Sinclair ULA uses a 6.5MHz ceramic resonator. Inside the ULA this frequency is divided by two to give the 3.25MHz CPU frequency. IIRC Andy’s replacement ULA module uses it’s own crystal and ignores the 6.5MHz ceramic resonator on the main board.

Have you tried another monitor / TV ?

The video output from a ZX81 is not compliant with broadcast video standards and it is possible that your monitor just does not like the video output from a ZX81.

Also, I assume this is a U.S.A. spec board. Is resistor R30 fitted?

Also, if you have a working keyboard membrane, try switching to FAST mode (the FAST keyword is in the ‘F’ key, so hold Shift then press ‘F’).

Mark

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