I bought a Playmatic “Big Town” recently.
Never had so much work on a pin. (owning 8 )
Due to a former “nitwit- fixing” the machine the MPU got 14V in stead of the max 10 volt .
So ROM, RAM (2x) and CPU were fried, most (but 2) CMOS chips were ok. Soundboard and decoderboard were not functioning too.
The reason : The transistor in the power part was mounted wrong / shortcut between collector and emitter, so the direct rectified voltage of 14V was put on the whole MPU board.
A problem was that diagrams were not (directly) available. I took parts of the other 5 machines with the same MPU (IPDB.org), and brought together my own good diagram set.
Took me about 3 weeks to sort all out, and reverse engineer what part of what diagram to use.
Since the original CPU, as well as the ROM and RAM’s were suitable for 10 volt, but these chips were unobtainable, I converted the MPU to a 5 V system, with 5 V CPU. (original 1802D version is never to be found again)
Used a 2716 in one ROM socket and a wide 6116 RAM in the other.
Adapted the PCB (cut traces and rewire) so all logic was OK again.
Adapted the decoder board so the 5V MPU signals were brought back to 10 V, took the example from the “change” pin.
Fixed some chips on this.
Also fixed display error.
Much effort was put in getting the used connectors OK again. Never seen worse connectors.
Not replaceable, no alternative, just clean and adjust one by one.
What do I like about this playmatic:
The playfield. Absolutely as new after 43 yrs. Backglass is in fine shape.
The used technique in controlling the lights with SCR’s.
Cleverly done, 2 bulbs on a single SCR, driven by phase-synchronized interrupt on the CPU.
What is “not so good”: As written before, all rivets fall apart (switches, fuse holders, etc) , bulb fittings fall apart, the flipper assemblies are crap, connector are bad-bad-bad. Wood quality of most parts of the cabinet is not so good… ( chipboard.... no plywood) .