Timex Sinclair 1000 repair

[JKnightandKARR]

Ok, the VCF forums said it should be low. Probly replace all caps n go from there...

The VCF forums said the /RESET line should be LOW normally? That is incorrect. It should only be LOW for like a millisecond at power-up. After that it should remain HIGH. And it must be, since you already confirmed that the /M1 line was changing states, which indicates the Z80 is executing instructions. It couldn't do that if /RESET was LOW.

Ok, then that's normal then. Rechecked n I missread the info..

[JKnightandKARR]

https://jknightandkarr.altervista.org/Computers/20260128_112338.jpg

Well, Hooked up my Rigol DS1194Z's Logic Analyzer up to D0-D3, saw no need to try all 8 data lines. Anyhow, the Z80 is clearly doing something, so thinking of picking up one of the more modern replacements, such as this: https://www.tindie.com/products/charlieingley/vla81-zx81-ula-replacement/ since from my searching, the originals are prone to failure, so that's what I have so far.

[Chris Savage]

So it appears that the issue is either in the video output, or the video input of your display.

[granz]

Before you spend $33, plus S/H, have you tried swapping the ULA from the other TS1000? That may help (unless the other one is also dead - although it shouldn't cost you more than a bit of time to try it.)

[JKnightandKARR]

So it appears that the issue is either in the video output, or the video input of your display.

My TV is fine, I been using the inputs for my Wii.  I'll hook up my scope to pin 16 of the ULA n see what I get now that I have it figured out, shouldn't be my composite mod, iI replaced my transistor with one I tested with my LCR meter.

Before you spend $33, plus S/H, have you tried swapping the ULA from the other TS1000? That may help (unless the other one is also dead - although it shouldn't cost you more than a bit of time to try it.)

Can't hurt, however it didn't work either when I hooked up to. CRT tv. As I said above, probly hook up my scope to the ULA to see what I get.

[granz]

Can't hurt, however it didn't work either when I hooked up to. CRT tv.

Yeah, I was meaning that you could swap the ULAs and then try both computers; it is possible that one ULA, and the other TS-1000 may work. That would be a quick, easy way to test that.

[JKnightandKARR]

Can't hurt, however it didn't work either when I hooked up to. CRT tv.

Yeah, I was meaning that you could swap the ULAs and then try both computers; it is possible that one ULA, and the other TS-1000 may work. That would be a quick, easy way to test that.

Yup.

[JKnightandKARR]

https://jknightandkarr.altervista.org/Computers/Ch2_ULA_Pin16.jpg
Not much here.


https://jknightandkarr.altervista.org/Computers/Ch3_ULA_Pin16.jpg
WE HAVE A SIGNAL!!


https://jknightandkarr.altervista.org/Computers/After_Trans.jpg
This is the signal after the transistor.


https://jknightandkarr.altervista.org/Computers/RCA_Out.jpg
Output on the jack. Pretty much the same.

If I am guessing, which I am, I'd say my issue is the composite mod... I followed the directions, so either my NPN is fried, even though my cheap LCR meter says "We're Good" or something wrong with the design and it fried when turned it on... IDK... Guess buy a composite mod kit n go from there.

[JKnightandKARR]

https://web.archive.org/web/20250123231729/https://www.bytedelight.com/?page_id=3560
This is the circuit I used for the composite mod btw.

Well...... Pretty sure I figured out my problem, on one of the ZX-81s anyhow... Circuit above is the one I used. Now...... PROVIDING..... I could pay attention to what I was doing, I'd wire it as in the link.....
E-Output
B- Signal
C- 5V+
it MIGHT work..... Me:
E-Signal
B- 5v
C- Output

Need to pay more attention and not work on stuff when tired..... new transistor and will try again..... I think Bill Engval said it best...... HERE'S YOUR SIGN........

[Chris Savage]

Well, it seems you may have figured it out. Let us know how it goes.

[JKnightandKARR]

Well, it seems you may have figured it out. Let us know how it goes.

Just guessing, but if the transistor was wired right, probly would have worked...

[JKnightandKARR]

https://jknightandkarr.altervista.org/Computers/screen.jpeg
It's a start!!

[granz]

Congrats, Joe! Hopefully you will get the rest worked out quickly.

[Chris Savage]

Looks like, "POKE" and then some scribble. But, as @granz said, it's a start. At least you know now that it's alive.

[JKnightandKARR]

Congrats, Joe! Hopefully you will get the rest worked out quickly.

Thanks.  I'll probly replace that mod with one that'll work better.

Looks like, "POKE" and then some scribble. But, as @granz said, it's a start. At least you know now that it's alive.

Yeah.  The mod 1) didn't have power, and the 33 ohm resistor was killing the signal, so maybe it's not strong enough??