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Timex Sinclair 1000 repair help needed.

I got a vLA81 and an adjustable composite mod with Inverse screen option from Ebay. Since I know my orig ULA is good(ish), I'll use that one in my 2nd ZX-81 & see if I can get it working, didn't when I swapped em, so probly start with the caps on that one, and if I can get that one working, I have a small LCD screen, so maybe I'll make it into a small laptop.
 

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You should probably first test the stuff you bought with the machine that's known to work.

That way you know the replacement ULA works properly, because even brand new stuff can sometimes be non-working on arrival.
 
channelmaniac said:
Start with the CPU. Caps won't cause that to stop working.
Click to expand...
I tested voltage rails and cpu for function on one, but not the other, that one, I'll start with voltages to see whats got what n go from there.
Istarian said:
You should probably first test the stuff you bought with the machine that's known to work.

That way you know the replacement ULA works properly, because even brand new stuff can sometimes be non-working on arrival.
Click to expand...
That's what I am going todo. I'm going to fix the first unit, and save the original ULA, and my composite mod, to use in the 2nd unit , which sadly the ULA in that one seems bad, I did swaps and nada from the one that I got a bad picture on, and still nada from the 2nd, but that could be only part of the problem on that unit. I was hoping the 2nd unit ULA was good, it has the backporch signal, the working one does not. Later I'll upgrade the 2nd unit with new parts as well once I figure out why it's not functioning. For now, work on the first unit, just gotta figure out the memory settings for the memory on the new ULA, instructions little confusing to me, but guessing that it sets it to support specific ranges of memeory and not set it to have the range selected like I added more memory.
 
I forget, do you have two or three of these systems? Could have sworn you had at least one that was working okay.

As far as memory configurations, reading up on historical upgrades may be helpful. The original ZX81 initally shipped with 1K ram and I believe most of the U.S. TS-1000 models have 2K of ram in the stock confguration.

It is important to know the memory organization though, as memory chips have over time come in many variant organizations ( 1-bit, 4-bit, 8-bit, 16-bit, 32-bit, ... )

The "size" of the chip itself is usually measured in n-bit words or total bits rather than bytes, at least by the manufacturer

E.g.

A 32Kx8 memory IC is 32K bytes or 32,768 8-bit words. Sometimes they may be described as a 256K-bit memory (262,144 bits).

A 32Kx4 bit memory IC is 32K nybbles or 32,768 4-bit words. And as above may be described in terms of the total number of bits.

The latter is technically equivalent to 16Kx8 in bit count, but must be used with a second 32Kx4 to be used in the same circuit design as a single 32Kx8. Otherwise you'd need a more complex computer design with slower memory access to account for two 4-bit reads before presenting an 8-bit processor with a full 8-bit word.

this stuff only gets more complicated as move you go from the late 1970s to the modern day
 
Istarian said:
I forget, do you have two or three of these systems? Could have sworn you had at least one that was working okay.

As far as memory configurations, reading up on historical upgrades may be helpful. The original ZX81 initally shipped with 1K ram and I believe most of the U.S. TS-1000 models have 2K of ram in the stock confguration.

It is important to know the memory organization though, as memory chips have over time come in many variant organizations ( 1-bit, 4-bit, 8-bit, 16-bit, 32-bit, ... )

The "size" of the chip itself is usually measured in n-bit words or total bits rather than bytes, at least by the manufacturer

E.g.

A 32Kx8 memory IC is 32K bytes or 32,768 8-bit words. Sometimes they may be described as a 256K-bit memory (262,144 bits).

A 32Kx4 bit memory IC is 32K nybbles or 32,768 4-bit words. And as above may be described in terms of the total number of bits.

The latter is technically equivalent to 16Kx8 in bit count, but must be used with a second 32Kx4 to be used in the same circuit design as a single 32Kx8. Otherwise you'd need a more complex computer design with slower memory access to account for two 4-bit reads before presenting an 8-bit processor with a full 8-bit word.

this stuff only gets more complicated as move you go from the late 1970s to the modern day
Click to expand...
I only have 2 of them. 1st with the ULA2C184E (workingish), and the 2nd with ULA2C210E (dead, including the ULA, failed to produce any image on the workingish unit.) Here is a link to the new ULA manual. https://vdrivezx.com/wp-content/uploads/2019/12/vla81_user_manual_v1.3-1.pdf I know I outta set SW1/SW2 to On/Off for the ULA2C210E for the backporch signal, but not sure what to set the SW3/SW4 should be set to. Right now, it has the 2KB RAM and I have what I think is a 16KB expansion module. Since this kinda thing is new to me, I have no clue what to set these to. I kinda had an idea that is what is meant by a 32Kx8. Maybe I'll add more internal RAM, but for now, staying as is, with the exception of the memory module.
 
I got the new ULA installed as well as the composite mod, and well, no signals, no image. Verified voltage at the module n I have 5V to it. Tried Gnd on module .to 5V out from the voltage reg. and got reading, since the module has 8 PTH connected to the functions, I can use them as test points. Found the pin for the input signal, and I've got a wave form similar to the manual, so the new ULA is clearly working, I've got the output pin and not getting any kinda waveform, other then what looks like noise. So probably start with adjusting the pots. Outta hook it up to my vcr, maybe the tv is the issue as well, so vcr outta help, since I already got a video from it, so far that's what I got.
 
You mean on the previously working system?

-----

If you haven't done so already, I would suggest testing the Z80 CPU and maybe the ROM chip from the non-working system on the one that seems to work.

That way you'll know if there's any reason to bother sorting out why the ULA replacement didn't do the trick.

RAM is important too, but whether it works or not is moot if any of the other key components is dead or malfunctioning.

-----

If that seems like too much work, start with the CPU from the non-working board and a simple test circuit that just feeds the Z80 a constant NOP.

Thomas Scherrer Z80-Family HomePage

Z80, Z180, Z280, Z380, Programming, Hardware, Software, Utilities, FAQ, Support, CPU, assembler
www.z80.info
 
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Istarian said:
You mean on the previously working system?

-----

If you haven't done so already, I would suggest testing the Z80 CPU and maybe the ROM chip from the non-working system on the one that seems to work.

That way you'll know if there's any reason to bother sorting out why the ULA replacement didn't do the trick.

RAM is important too, but whether it works or not is moot if any of the other key components is dead or malfunctioning.

-----

If that seems like too much work, start with the CPU from the non-working board and a simple test circuit that just feeds the Z80 a constant NOP.

Thomas Scherrer Z80-Family HomePage

Z80, Z180, Z280, Z380, Programming, Hardware, Software, Utilities, FAQ, Support, CPU, assembler
www.z80.info
Click to expand...
I know the system is actually ok other then the image https://forum.vcfed.org/index.php?t...-1000-repair-help-needed.1255940/post-1489027 this is a photo I took of the system, hard to see but you can see POKE and random letters,
 
Maybe you should double check the schematic and wiring of the composite mod?
 
Fixed.jpg

https://jknightandkarr.altervista.org/Computers/Fixed.jpg
I GOT IT! Just took alittle bit o tweaking with the signal input n output wires to get it up. THANKS all for the help!

Edit: Appears keyboard is needing replaced or signal cable needs pushed in.... least it's easier then the other. lol
 
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You can always build your own keyboard replacement, it just probably won't look the same or fit nicely. And of course you still have to deal with the slightly awkward way of entering BASIC keywords.

P.S.

It's not super cheap at $20+ (after incl shipping), but if you are in the US you can get a replacement membrane from ebay (and possibly other sources). Presumably with similar limitations to the original.

E.g.
 
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Istarian said:
You can always build your own keyboard replacement, it just probably won't look the same or fit nicely. And of course you still have to deal with the slightly awkward way of entering BASIC keywords.

P.S.

It's not super cheap at $20+ (after incl shipping), but if you are in the US you can get a replacement membrane from ebay (and possibly other sources). Presumably with similar limitations to the original.

E.g.
Click to expand...
May just use membrane one for now n design my own later. Use the broken one for easy lables
 
As expected, the connectors on my keyboard are damaged, I managed to swap the other top on and the system "should" be at 100% now. Getting ready to test the system. I am keeping the old keyboard, and will be using it to create a PCB to repair it using SMD buttons in the original layout using the top as an overlay, just for giggles. Keyboard swap tested and 100% FUNCTIONAL!! Thanks all for the help.
 
My father started with a ZX-81 (a TS-1000 with just half memory). He later went to buy a Spectrum. And he always thought Sinclair was better than Amstrad... until we started collecting, then he found the crude reality and he now understands why the keyboard or the ULA break so easily...

Congratulations for your repair, just be cautious, these computers are really fragile.
 
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