Testing, Testing. Is This Thing On?

So, after a bit of head scratching at the Cifer and the lack of IEEE488 bus, I opened my wallet (cue jokes about moths being released, we've been decimalised since the last time that was open etc etc) and bought a cheapo IC tester labelled as a TES200. It has the capability of testing many of the 74xx and 4xxx series of logic chips. It doesn't do them all but there's so much discrete logic on the boards there is a good chance I will be able to find some broken chips.

(But before it arrived I managed to check all of the Z80 processors, courtesy of my trusty ZX Spectrum, as well as the ceramic 68000 processor on the 68K board in a handy Amiga A500 motherboard.)

And then the tester arrived and it was good. Break out the chip removal apparatus!

TES200 on the right.

First up, the Display Processor. This is the first board in the system (or actually the last one when  disassembling it) and is the one with loads of EPROMs on it. There are several chips I can't test as they aren't supported by the tester (74LS244s, 74LS245s as well as the RS232 drivers 1488 and 1489s) but there's plenty to go at.

So many EPROMs...

And here's the list of broken chips the tester identified on this board (the 'ML' ref is just the component number on the board):

• 74LS163 at ML75
• 74LS01 at ML67
• 74LS166 at ML64
• 74LS166 at ML66

Next up, the Disc Processor board. This is the board that controls the floppy drive via the FDC chip and is the first on the IEE488 bus.

Disc processor board, for..er...processing discs..

Broken chips on this board:

• 74LS01 at ML40
• 74LS01 at ML45
• 74LS08 at ML51
• 74LS139 at ML83

Now for the Graphics board. This provides emulation of the Tektronix 4010 graphics standard (think about the computer line graphics used in the original TV series of Hitchhiker's Guide to the Galaxy - although that was actually a bit of a cheat as they were made with traditional drawn animation). The graphics mode has never worked so I was expecting some faulty chips. I wasn't disappointed..

64kb of RAM - not exactly an RTX 4080...

Broken chips on the Graphics board:

• 74LS166 at ML9
• 74LS163 at ML37
• 74LS163 at ML38
• 7425 at ML45

Finally, the 'big daddy' board. The 68000 user processor board. Now, I have tested the RAM on this board and some of it appears to be a bit flaky. So I should still be able to use half of it if I can work out where those 16 DRAM should go in the board. Also, there are two LEDs on the board that are permanently lit when the board is installed and I don't think they should be i.e. they're there to indicate a problem. And, lastly, there are two logic chips at the bottom of the CPU that get FREAKIN' HOT when the board is installed. So, what shall we find?

Gorgeous ceramic MC68000. Nice.

Broken chips on the MC68000 board:

• 74LS166 at ML5
• 74LS166 at ML10
• 74LS158 at ML17

Now, 74LS166s are shift registers and I suspect that with the two shift register chips being dead, this board is not going to do very much.

Anyway, following the release of more moths, replacement chips were ordered and are now 'on the way'. Once they arrive, the fun shall re-commence...