Sinclair ZX80 / ZX81 / Z88 Forums

Ok, Replaced all the caps in the power circuit and the transistor, all voltages same as originally reported. No -5, no +12. What would be next on the list? Could a ram chip problem pull mess up the voltages?

Spinnetti,

Take an inductor(L4) off the board and test the inductor with continuity range on your multimeter. It should be continuity on 2 legs of the inductor's sides. And also test the inductor with a piece of equipment that tests yokes and flyback transformers.

Try to test diodes and resistors with one leg in the air. Let us know the result.

You might have to take all 8 DRAMs off the board to read the voltages of -5 and +12.

DesSony

Thanks. My best friend since childhood when we had TS1000's and programmed together (Don) was down this weekend from Mi (I'm in TX), and we did the caps and transistors. I sent it back with him as he's got a ram tester and the patience to pull all the rom chips lol. I appreciate all the guidance, and will pester him on how its going - I imagine he'll reply here with the voltages after pulling the ram chips. I think he ordered new diodes too

PS, He also brought me a TS1000 with composite mod for the collection! On that one, works great, but the black level is low - any way to boost that?

Please take a picture of a ULA itself and post the picture here. If the ULA is lower than 2C210E then, ask 1024MAK for his help. He is a great gentleman who knows about the ZX81 / TS1000's ULAs history and its quirks!

I also am the owner of two running TS1500s. I live in the state of IN.

DesSony

Thanks... here's the board/ula

Thanks, however, I meant the picture of the TS1000's ULA's, not TS1500.

I plan to take one TS1500's ULA off its board anytime. I created a file of the TS1500 ULA's pinout somewhere around this forum.

As for your TS1500's no video issue.
1. Try to lift a Zvid "small board" of the motherboard a little bit.
2. Find a Zvid's input wire.
3. Solder the Zvid's input wire to a diode's (D19) anode side.

I created a little cute board with 1024MAK's transistor video buffer circuit design.
viewtopic.php?p=35493#p35493

Cheers,
DesSony

Spinnetti wrote: ↑Tue Mar 09, 2021 3:12 amHe also brought me a TS1000 with composite mod for the collection! On that one, works great, but the black level is low - any way to boost that?

By ‘black level is low’ do you mean that the screen is grey even after adjusting the brightness and contrast controls?

If yes, can you tell us the part/type number of the ULA in the TS1000, or take a photo of the ULA.

There only known to be three versions of the ULA chips used in TS1000 and ZX81 computers. The first two ULA versions don’t generate the part of the video signal known as the ‘back porch’. Unfortunately a lot of colour TVs use this part of the video signal to automatically calibrate their ‘black level’, and as as a result, get the setting wrong when used with a TS1000 or ZX81 computer.

There is a fix for this, but I will await your reply first, before going into details.

Mark

As far as I know TS1000 ULA all are the newer kind with backporch. They were released on 1982.. but I may miss something...

TS1000 mainy left factory with 2C210E ULA onboard. This variant was good with "back porch" in the video signal.

TS1500 were build around Timex TS 1500A chip and this SLCD generated to the correct video signal with back porch. I took some measurements last weekend and they are are as follows:

* white level: +3.98V
* black level: +3.11V
* sync level: +0.35V

Thanks for the inputs... I probably shouldn't have dove into the TS1000 in this thread; I appreciate the inputs on that.

"McKlaud", where would I pick up the white, black and sync levels? Is that off the ULA pins?

"DesSony", thanks for the tips. Voltages are off, so will try other things once I can get the 12v and -5 to show up.