Timex Sinclair 1000 repair

[Chris Savage]

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

So, I looked around on the internet and there is a lot of varied schematics, and even in the ones like yours, much variance in the values.

Many people who have taken this task on have expressed issues that they've had finding the right values to get the signal they want. It seems there may also be a little bit of difference in the various displays and the signals they require.

As to your original question and schematic. I was concerned when I saw the 100Ω resistor, since at 5V (minus the transistor voltage drop), you're looking at nearly 200mW of power consumption, which is the max of the 2N3904. Normally you wouldn't choose a transistor that is at the max of your electrical specs.

[JKnightandKARR]

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

So, I looked around on the internet and there is a lot of varied schematics, and even in the ones like yours, much variance in the values.

Many people who have taken this task on have expressed issues that they've had finding the right values to get the signal they want. It seems there may also be a little bit of difference in the various displays and the signals they require.

As to your original question and schematic. I was concerned when I saw the 100Ω resistor, since at 5V (minus the transistor voltage drop), you're looking at nearly 200mW of power consumption, which is the max of the 2N3904. Normally you wouldn't choose a transistor that is at the max of your electrical specs.

That circuit, better you think? I see 1 issue with mine with that documentation, is the ULA 2C184E vs ULA 2C210E.  The ULA 2C210E has the back porch signal, the other doesn't, and mine is the 2C184E, so NO backporch signal.  This might be part of the problem, according to the documentation.

EDIT: I found this http://zx.zigg.net/misc-projects/ZX81_Video_Conditioning.pdf?ref=blog.codesurfer.dev This is what I need ain't it?

[granz]

Once you get your TS working, you will want some books for it. I had several books, but these are my favorites:

http://[url="https://dn720002.ca.archive.org/0/items/the-zx-81-companion/The%20ZX81%20Companion_text.pdf"
This has a disassembly of the ZX-81's ROM in the back. I don't really remember much else than that, but I used mine so much that it got pretty dog-eared.


https://www.amazon.com/Byteing-Deeper-into-Timex-Sinclair/dp/0471898880 $16.73 + $4.49 S/H (Could not find this as a PDF.)


https://www.historybit.it/wp-content/uploads/2018/09/ZX81_BasicProgramming.pdf
I was always captivated by the cover picture of the programming manual. It still grabs my attention.


https://www.scribd.com/document/323515982/zx80-81-refcard
This was another well-used document from my ZX-81 days.

I don't remember having this (although I probably did get it with my kit,) but it may help:
https://k1.spdns.de/Vintage/Sinclair/80/Sinclair%20ZX81/Service%20and%20Assembly%20Manual/ZX81%20Service%20and%20Assembly%20Manual%20%28scans%29.pdf

Hope these help.

[MicroNut]

@granz Those books are definitely great. The reference card was well used by me. In my moves I lost it though. A couple of years ago Bean (on the Parallax forums) was selling his ZX81 books and the reference card was one of them. So I bought it and some other books. Some of them are the ones you mentioned.

[granz]

@granz Those books are definitely great. The reference card was well used by me. In my moves I lost it though. A couple of years ago Bean (on the Parallax forums) was selling his ZX81 books and the reference card was one of them. So I bought it and some other books. Some of them are the ones you mentioned.

I had that reference card in my books, and carried it pretty much everywhere; that and The ZX81 Companion. I actually had many more books about the ZX81, but those listed above were my favorites.

[JKnightandKARR]

@granz Those books are definitely great. The reference card was well used by me. In my moves I lost it though. A couple of years ago Bean (on the Parallax forums) was selling his ZX81 books and the reference card was one of them. So I bought it and some other books. Some of them are the ones you mentioned.

I had that reference card in my books, and carried it pretty much everywhere; that and The ZX81 Companion. I actually had many more books about the ZX81, but those listed above were my favorites.

I'll check those out, thanks. IK do have the manual and one for games I got with it.  OK, I pulled the ULA from both of them, and did a swap. For ease I am calling the one I bought Mine/My, and the one Granz/His sent me as Granz. Anyhow, My ULA is the old ver so, no backporch signal, Granz has the newer ULA with the backporch signal.  After the swap, Mine no longer has a picture and the input looses and regains the signal, so maybe the newer ULA is bad, so Will do a swap back, and go from there.

[granz]

After the swap, Mine no longer has a picture and the input looses and regains the signal, so maybe the newer ULA is bad, so Will do a swap back, and go from there.

Yep, sounds like the ULA in the system that I sent is no good. Like I said, I have/had no idea of the status of that computer.

Good troubleshooting work, Joe.

[JKnightandKARR]

After the swap, Mine no longer has a picture and the input looses and regains the signal, so maybe the newer ULA is bad, so Will do a swap back, and go from there.

Yep, sounds like the ULA in the system that I sent is no good. Like I said, I have/had no idea of the status of that computer.

Good troubleshooting work, Joe.

Going to recheck the sockets and make sure it is seated correctly, also was GOING to try the one you sent since it has a working ULA on my other TV, though my VCR, but figures.... my VCR broke yesterday...