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During setup the monitor chassis developed a single HV arc from the LOPT body to ground and was then dead. With no spare MTC-900 chassis available to swap in, the game was withdrawn to the dead zone.
Testing on the bench confirmed the HV arc issue seen at the show.
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The LOPT was removed, and a light bulb fitted across pins 13 and 17. The bulb was dim and the scope showed switching that was fuzzy compared with the manual. Moving the light bulb to B+ found 113.2V at 40W and 113.9V at 60W. Taken together I concluded that the power regulation & switching were likely working OK. The manual stated the B+ should be 126VDC for this 900.03 chassis and I set the B+ to 120VDC, confirming again that either bulb power was properly regulated. With no indication the chassis had an issue, I concluded the LOPT was bad and replaced it with one reclaimed from another chassis.
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With the new LOPT the chassis powered up OK and displayed a good picture.
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For a local event, a friend requested Lady Bug in this cabinet rather than Mr. Do!. Most of the Universal games share the same game PCB pinout so many vertical Universal games could be run in this cabinet - Lady Bug, Mr. Do's Castle, Mr. Do's Wild Ride, Do Run Run etc. One difference between the original Mr. Do! and later games was that the audio amplifier is external to the Mr. Do! game PCB but later game PCBs had the audio amplifier built in and output amplified audio.
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Whilst the game PCB itself could be converted to unamplified, I had several other Universal games so instead I decided to convert the external audio amplifier in the cabinet to connectors and construct a small plug-in bypass adaptor to use with games that didn't need it.
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There were no sound issues running Mr. Do! with the external amplifier or Lady Bug with the amplifier bypassed.
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A friend asked about options for converting a game PCB to run the rare Universal game Snap Jack. According to MAME, Snap Jack appeared to use the same hardware as Lady Bug and could be a simple ROM swap. The Lady Bug PCB I had was slightly different than described in MAME, labeled 8106-II, and setup to support larger EPROMS. The Snap Jack EPROM images were composed and programmed; however I had no spare blank PROMS to program for the Snap Jack colour PROMS. With the EPROMS fitted into the Lady Bug game PCB, Snap Jack ran OK with incorrect colours but was still playable. Since Snap Jack is a horizontal game, it couldn't be run in my Mr. Do! cabinet so the Snap Jack EPROM set was set aside for later use.