#kludges

I'm slowly working on resurrecting an old terminal device I picked up at a thrift store a few years back, the IXO Telecomputing Device Model TC200. It's a decidedly weird beast, with a tiny keyboard and one-line screen, and was meant to hook into the phone lines and dial into a service IXO themselves ran. It went for about $500 in 1982.

The wires coming out from the battery compartment door are to provide the thing with electricity; it was supposed to run on either power over the phone line or a now-obsolete battery meant for Polaroid cameras.

Now, I haven't gotten it working yet; the thing has more wrong with it than just the power supply. But while I had it open to add those leads, I saw some startling bodges on the board.

The first image is the main board; at the bottom, it connects via ribbon cable to a second board that has all the key switches and the LCD. I don't know if there are bodges on that board, but there sure are on this one.

The second image shows one — the large chip (which some quick searches failed to turn up any data on) has a couple of its pins lifted from the board, and both connected to a point a fair distance away. Now, that's not unusual in itself; designing circuit boards is hard, and there are bound to be some errors. Particularly in that era, ordering a whole new lot of boards wouldn't have been trivial in either time or money, and you'll often see thin wires added to printed circuit boards even today. But I'm not sure I've ever seen _diodes_ instead of just wires. My best guess is that both pins need to feed the same thing, but need to not interfere with each other, so the two diodes are acting as an OR gate in what's sometimes jokingly referred to as Mickey-Mouse logic (MML, to compare with actually manufactured transistor-transistor logic, TTL, or older RTL or DTL, where one of the transistors is replaced with a resistor or a diode, respectively).

The third shows a chip where two of the pins have been bridged with both a resistor and a capacitor, in parallel. I'm not sure what's going on there; it looks to be a 45xx-series CMOS logic chip, so it may be some kind of input filtering. The fourth is similar, having resistors bridge pins on each side of an 8-pin chip; I think that's a dual op amp, and suspect that those are extra feedback resistance to stop self-oscillation.

The fifth image is a weird suspended circuit. Three devices are each hooked to the board by one pin each; the cap goes into the transistor and one side of the resistor, while the loose pin on the transistor bridges across the resistor. I'm really unclear on the purpose of this, and why the board didn't have the proper connections.

[percussion noises]