Bally SS Gold Ball - All Phase 0A Backbox Feature Lamps Out

[astyy]

This is a head scratcher...switched on Gold Ball after its winter hibernation and a bunch of backbox feature lamps went out. Nothing obvious in continuity, bulbs, holders etc so checking in schematic it turns out to be all 5 feature lamps on phase 0A aren't lighting, the 5 on phase 0B are working fine.

The obvious common to me is the phase 0A blue "hot" wire, but this measures at approx 10 VAC to ground, similar to the phase 0B grey "hot" wire, with 20VAC between them, I understand this to be correct across the centre tapped transformer to feature lamps. So power seems to be arriving at the lamps.

I think the connectivity to the driving SCRs must be ok too, as each is daisy chained to its pair of lamps (and the paired 0B lamp works on each chain). Also if I ground he SCR anode only the 0B lamp lights when it should be both. On normal Bally SS this would indicate the problem downstream to the lamp.

Everything on the playfield is ok, so phase 0A is working in general (fuse, transformer, rectifier).

As a reminder, Gold Ball is one of the rare machines that runs AC feature lamps on two phases, similar to the later 6803 platform machines - memory jogger added below!

I'd appreciate any t/shooting tips, ideas or advice, something blindingly obvious may be facing me here

 

[AlanJ]

is the combo board grounded properly?

 

[astyy]

AlanJ thank you for the idea which prompted me to spend more time ground and voltage testing. The 10 VAC on the common blue wire wasn't as stable as I'd previously thought. Following some careful jumpering before the GI flasher cards full lighting was restored. I just need to tidy up the area to fix it properly

 

[AlanJ]

Excellent

ps got a new backglass for mine on order.

just need to sort my cab artwork. gonna have to get the frisket out as no stencils available

 

[AlanJ]

The gold ball I sold a couple of months ago has developed a very similar problem - there are 3 lamps at the top left of the playfield - P lane . L Lane and the Extra ball - all are served by a common Grey 0B wire. Trying to help new owner sort it - so sent them a croc clip and they connected this grey to another grey 0B feeding the "1" and "2" targets top right of pf (as these are working ok) Still no joy. Im at a loss as what to try next. The SCR's are all fine as the 0A lamps all work. Bulbs are ok as they have swapped them round with workers and all work in other sockets. I even sent diodes in case the lamp socket diodes were knackered, they tied these around the old ones as no soldering iron - looked all ok though in the pics they sent me. Its got to be something silly but cant quite see it.