|
|
The game ran OK all through setup but began to have issues on show day 1. Both main and backup game PCBs had sound issues with loud audio hum. Game PCB #006 also developed an intermittent flashing picture. Suspecting game PCB, power supply and/or monitor chassis. issues the game was withdrawn to the dead zone :(
|
Initially the display appeared blank, but a closer look revealed a faint ghost of an image.
The game was running in the background but scrolling & sprites both looked like they had
issues. Starting with a video probe on IC 9D (LS175) found no video on either inputs or
outputs. Moving on to IC 9J (LS374) outputs found:
| Pin | Video Probe | Scope |
|---|---|---|
| 19 | snowy pixels | low with spikes |
| 18 | video | active |
| 17 | blank | idle low |
| 16 | blank | idle low |
| 15 | blank | idle low |
| 14 | blank | idle low |
| 13 | blank | idle low |
| 12 | snowy pixels | low with spikes |
| 11 | clock | clock |
The blocky sprite issue on this PCB observed before the show was also back. It disappeared again, on power cycle and the game was running OK. Nothing marginal was found on the scope on ICs 8C,8N (82S100) or ICs 7E,7D,7K,7L (2148) data bus. ICs 8C,8N,6J,6K were reseated and again, there were no issues flexing the PCB. The board was declared working until the next occurrence.
|
Suspecting a power supply issue causing the audio problems, the IGR power supply was removed and bench tested with a dummy load:
|
None of the three IGR power supply based cabinets included a cabinet base fan and I'd seen quite a few monitor and game PCB failures in a lot of shows. I decided to add a fan and selected a low power 12V version that could be run off the present but unused -12V supply output of the IGR power supply (Buck Rogers does use the -12V supply, but it has an extraction fan in the cockpit cabinet already).
|
Whilst there was an unused -12V power supply there wasn't a spare ground line to go with it and I didn't want to hack the cabinet wiring or insert a whole new plug assembly just to tap one. Instead, there were several empty unused pin sockets that could be used to add a third ground line. The IGR power supply PCB also already had some spare ground pin holes allowing a new ground wire and pin to be installed adjacent to the -12V pin very cleanly. I also updated the pinout chart label for the connector to annotate the presence of the new ground pin.
|
The fan was a retail Noctua NF-A9 1.2W 0.1A that the low power -12V 0.5A supply was more than capable of driving. It also came with an adaptor from PC fan to SATA power that I used to provide a separate inline connection to allow replacing the fan easily in future. The SATA power connector was removed, and pin sockets added ready to insert into the cabinet plug housing. The fan was tested on the bench and was working OK.
|
The fan was fitted to the cabinet splitting the air flow between the power supply and game PCB. The connecter pins were fitted into the cabinet connector and testing confirmed a breeze in the bottom of the cabinet over the power supply and game PCB OK.
|
The chassis had overall poor brightness and intermittent flashing. Freezer spray on various portions of the colour drive circuitry identified something in the pre-amp section on the IE2 PCB. Using drops of freezing liquid on various transistors narrowed the cause to TR24 (BC237) and replacing it fixed the brightness. TR24 also tested bad out of circuit.
|
Restesting the chassis back in the cabinet found no issues.
The game had missing elements from the music track. Checking the two AY-3-8910 with a scope found: