Are TS1000 <-> ZX81 parts interchangeable?

[Dukes909]

Are the chips in a TS1000 interchangeable with a ZX81? Asking if I had a working TS1000, could I swap chips out into my non-working ZX-81 to figure out what is wrong with it? My Z is an issue one board (red).

Dukester

[David G]

if I had a working TS1000, could I swap chips out into my non-working ZX-81

Some are, some aren't

The TS1000 board is identical to the later ZX81 (red revision 3)

CHIPS
* Z80A CPU
* RAM (2 small chips or 1 large chip)
* ROM
* ULA

CPU is either NEC or Zilog, both interchangeable

For RAM the ZX81 boards can take either 2K or 1K, but is not socketed. My USA ZX81 came with 1K. TS1000 came with 2K

ROMs are all interchangeable marked -550 (original with several bugs) or -622 (improved with one bug) or -649 (improved). Some had an EPROM (with viewable window). And some users modded the board to take a newer chip that requires some rewiring

ULA differs early vs late but is interchangeable. Early 2C184E produces inferior video signal, while 2C210E is improved

[Dukes909]

Thank you for this. Ok so I have an issue one board, it doesn’t sound like it will work in the way I hoped it would for swapping out each chip until I hit on what isn’t working.

[David G]

Forgot to say the early ULA works with most CRT TV (but doesn't work with some CRT), and fails to work with many LCD TV (but works OK with some LCD TV)

[Moggy]

There is an even earlier ULA 2C158 and also SGS-Thomson manufactureds Z80's

The two early ULA's lack the back porch signal hence fairly unusable with colour CRT and LCD TV's but perfectly usable on B/W CRT TV's

[David G]

I have an issue one board, it doesn’t sound like it will work in the way I hoped it would for swapping out each chip until I hit on what isn’t working.

I think that will work fine

The boards are different, but the chips are interchangeable

for example, some Issue One boards came with 1-chip RAM, some with 2-chip RAM. Some ISS 3 board came with either type. But the chips can be used with any board

[1024MAK]

For a normal production ZX81 that uses a mask ROM, apart from the RAM chips, the remaining chips are interchangeable/swappable between issue one ZX81s, issue three ZX81s and TS1000 machines.

The RAM can also be interchanged/swapped but as it is normally soldered in, it’s quicker and easier to just use an external RAM pack (preferably a know working one) as that disables the internal RAM (although if the RAM chip has short circuits between pins, it will still cause problems).

If you do have RAM chips that are in sockets, and the same physical size chips are in both machines, then they can be swapped. A 2k byte SRAM will however only work as a 1k byte device in a ZX81 unless wire link L1 is removed and wire link L2 is fitted. If a 1k byte SRAM chip is used in a TS1000, L2 needs to be removed and L1 fitted.

Mark

[Dukes909]

Cool! So I was going to ask how the ROM would know about how much addressable space there is if I put in a 2k chip in place of a 1k but, duh, it must figure it out somehow whenever a ram pack is attached on the back...

[1024MAK]

There is an even earlier ULA 2C158 and also SGS-Thomson manufactureds Z80's

The two early ULA's lack the back porch signal hence fairly unusable with colour CRT and LCD TV's but perfectly usable on B/W CRT TV's

Alas, predicting if either of the early ULAs (that don’t produce the ‘back porch’ part of the video signal) will work on a colour CRT or a LCD TV is a bit like trying to predict which slot the ball is going to settle in on a roulette table while playing with a blindfold and ear defenders on... Some work fine, but most object and give you a very, very dark image.

Mark

[Dukes909]

Ok well I don’t have one yet but the TS1000 seem to go for less than the ZX81’s. I may buy one now knowing I can do this (unless there is another source for replacement components???)

For a normal production ZX81 that uses a mask ROM, apart from the RAM chips, the remaining chips are interchangeable/swappable between issue one ZX81s, issue three ZX81s and TS1000 machines.

The RAM can also be interchanged/swapped but as it is normally soldered in, it’s quicker and easier to just use an external RAM pack (preferably a know working one) as that disables the internal RAM (although if the RAM chip has short circuits between pins, it will still cause problems).

If you do have RAM chips that are in sockets, and the same physical size chips are in both machines, then they can be swapped. A 2k byte SRAM will however only work as a 1k byte device in a ZX81 unless wire link L1 is removed and wire link L2 is fitted. If a 1k byte SRAM chip is used in a TS1000, L2 needs to be removed and L1 fitted.

Mark