Strange TS1000 mod, anyone has seen it before?

[kokkiklhs]

As the title says, I recently acquired a nice TS1000, which came to me with two modifications, visible from the outside...
The one with the button is obviously a reset switch (very nice idea), but the other one? Please have a look at the following pictures, there is a female jack plug which connects inside to a little IC ( TIL 111 ) and has a little wiring all over the mobo...
Tried to get some more detailed pics of the wiring, but my crappy camera didn't help.
Apart from these, I don't see any other modifications inside, the PCB seems to be totally intact, except of the solderings of the fine blue pieces of cable, coming from the TIL 111 and female jack assembly...

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[kokkiklhs]

...and 2 more pics, where the wirings (kind of) can be seen...

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N.B. that all the ICs on the board are the normal ones (not any special EPROMs or so) and I haven't noticed anything special, other than expected, during the computer's operation...
Please give any ideas, I'm very curious about it!!!
Cheers!!!

[stefano]

Perhaps it is an audio output.
Try connecting it to an amplifier.. if you hear the video raster noise then we're on the right guess, but you need to look for the proper software (z88dk supports this kind of sound).

[kokkiklhs]

Hmmm, I see, but wouldn't it be super-silly to drive the sound output on another jack, since usually MIC is used for this purpose?
I'll try your idea, though, at least it seems harmless!! I thought that it might be for feeding the machine with a second source of DC for some reason, but I would never try to do it!!
Thanks for sharing it!!

[RetroTechie]

Looks like those wires pick up signals near the keyboard connectors? Maybe it's just something rigged up to connect an external 'fire button' or something.

Another option is that it's a 1-bit I/O port. That is: 1 bit out, or 1 bit in, or both (should be straightforward to determine by following where signals/wires go). Perhaps for on/off control of an external device, monitoring a "yes/no" status from external hardware. Or again, both.

Or... a serial interface. For example to talk to temperature sensors & such that use a 1-wire serial connection. Plain RS232 but with different voltage levels, MIDI, who knows.

The TIL111 is a simple optocoupler, which will have served to provide galvanic isolation in the signal's path. To protect against static discharge, overvoltage etc. Note that MIDI connections use optocouplers that way, but in this case I think that's just coincidence.

So it should be easy to determine what it does - which tells you nothing, really. But for what purpose it served, you'd need some clues from a previous owner.

Personally I'd just rip it out (that TIL111 circuit, that is), and if any circuit tracks were cut / modified for it, restore those. Not reset button, of course - that's a useful add-on.

[1024MAK]

The interesting thing, is, that most opto-couplers (sometimes called opto-isolators) come in 6 pin DIL (Duel In-Line) packages (also known as DIP).

But in the picture posted above, it looks like a 8 pin chip
Also, it is hard to see, but at first glance, are any of the right hand chip legs connected?

If I had to guess, I would say that it is for allowing an external device to "press a key" on the Zeddy keyboard. The opto-coupler being needed because the Zeddy keyboard is a grid matrix.

Mark

[stefano]

<blush>.. you are right, it makes very little sense to open the zeddy to add a second audio plug !

I'm wondering.. how was the BASICODE "bascoder" implemented on the zx81 ?
I know the Philips P2000 used an hardware mod to interface to the regular cassette players (rather than its embedded microcassette one).

Also, if it is connected to the keyboard, it could be a "one-bit" software driven input like this one:
http://www.qsl.net/kp4md/petascii.htm <- this one works on the audio input, but I/O address can be changed.

[sirmorris]

Connect a switch and see

[RetroTechie]

Or draw up how wires / IC / jack plug are connected. Hand drawn sketch will do, IC as a square box with pin numbers, resistor(s?) marked by its color code.

Then the 'boffins' on here can check the datasheet, figure out what the circuit does, effect & how to use. Or as said: just rip it out - it's not something special or valuable.

[1024MAK]

I've just had a thought

Maybe it was adapted to control a nuclear power station

Mark