This one had a bad power supply, and the customer had been trying to fit more modern replacements. Re-soldering cold solder joints bought the base power supply back to life on the bench, and when fitted to the Emulator the root issue was shown to be a shorted tantalum capacitor on the input to the -15v regulator. The harness was in a sorry state where it connected to the power supply, and a new connector was fitted. This unit has a lot of corrosion, especially in the sockets (and there are many of them!). It had memory issues that were a mixture of bad sockets, and bad driver chips. This is a complicated set-up with 2 Z80 CPU’s and a “Micro-controller”. The micro-controller here is not what we are used to these days as in MicroChip PIC’s, or Atmel AVR’s, but instead is a prom based “state-machine”.
Once the unit was booting OK it was time to deal with its other issues, crackly voices and wrong sound bytes played randomly. The random playing of bad sound bytes was, surprise, surprise, a rusty socket pin on a micro-controller ROM that was generating the wrong memory fetch addresses. This left crackly and dead voices. A TL084 was replaced to get one voice back, and a CMOS chip for another. General crackle was resolved by replacing the 3 CD4051’s that interface with the digital board. After this extensive work the heads were cleaned on the floppy drives, and switches/pots cleaned. Its alive and plays well, but the amount of time and parts to achieve this was high. As a note I made good use of a Z80 ICE debugging tool from Bob Grieb.