Submitted for the first time into the show as one of ten machines. Following in the footsteps of its brother it ran for less than a day before the game started resetting. The next day I brought in a spare board only to have the monitor fail an hour later with a mostly white screen :( Disappointing but not unexpected.
The brightness pot had no affect at all but screen and contrast were still working so the first place to start was the brightness pot and the two transistors, TR25 and TR36, that make up the brightness control circuit. The brightness pot metered out OK so I popped out the two transistors to test in the meter - one BC237 was bad (Hfe = 0). Replacing it fixed the brightness.
The game PCB drew the scores and then reset, being kicked by the watchdog. Disabling
the watchdog just caused it to freeze after the score display. Thankfully the four
2114 RAMs are all socketed so I swapped them all out with new and tried it again - the game
booted and ran fine. Going through the RAM yielded one bad NEC 2114 and three still good
ones. Easy fix for a change.
Whilst set up for this PCB I went through the rest of the spare Jackrabbit (JR) & Money Money (MM) boards. Out of three sets, one JR and one MM appeared to work fine and one MM was dead. Switching the CPU board confirmed that the CPU board was dead and that the remaining boards in the dead set all worked fine. Scoping around yielded nothing out of the Z80 - all outputs dead. Swapping out the Z80 with another yielded signs of life on the scope but no sign of real booting still. A little more poking around on the scope suggested a bus fault on D1 and D3 on the Z80 side of the data bus buffers. No change swapping out the RAM and the ROM PCB was already confirmed working so it was time to pop out other contenders directly connected to this bus. Popping out the 8255 yielded a boot to the DIP help screen. A new 8255 brought the game to life again.
During the burn in test the picture started flashing the green and eventually ended up with green somewhat low. At first I thought this was a simple dirty pot that needed to be cleaned but on closer inspection of the picture it looked like some entire graphic elements were missing - most notebly that the money had no dollar sign on it. Swapping the board for a spare had no effect and the board on the bench looked fine. Back suspecting the monitor.
Suspecting more small signal transistor issues I popped out the whole middle column of the green pre-amplifier transistors to test in the meter. Sure enough the BC237 at TR37 tested bad (Hfe = infinite). Replacing it brought the green back.
More burn in testing yielded no further issues :)
Whilst it was in the back of the van for transport I replaced the feet with castors. This time trialing rubber wheeled ones rather than the hard wheeled ones use previously. Moves quieter and with less vibration than the hard wheeled ones but we'll see if they flat-spot over time...