SOLVED: L/R Relay / Coil issues Data East Rocky & Bullwinkle and Friends

[Andy B]

Working on a DE Rocky & Bullwinkle and Friends for...a friend

The L/R relay for the coil multiplexing was not working so I replaced the Q29 transistor. Still not working so I replaced the relay.

Now it does not appear to be switching during gameplay or diagnostics though it will click on and off when I ground the Q29 transistor.

This manifests itself in the Left side coils working fine but the left side coils also firing when the right side flasher is supposed to be firing instead. E.g. during game play when #1R PLFD x 3, Insert x 1 flasher is supposed to fire the out-hole (#1L) fires instead (the out-hole works fine). Same in diagnostics - Out-hole (#1L) fires fine but when I move on to PLFD x 3, Insert x 1(#1R) the out-hole fires instead. This is only for the multiplexed coils all other non-multiplexed ones are fine.

As I said, relay is clicking off and on when I ground Q29.

So I am guessing it is something upstream of Q29?

I'm not so hot on "upstream" testing and repair guides doesn't appear to cover it. Anyone got any ideas where I need to start please?

Thanks

Andy

 

[AlanJ]

Q29 looks like driven by Q21 in turn driven by 7406 IC (pin 11) which controlled by Pin 12, which is controlled by PIA IC.
Logic probe the signal from the PIA forward - something is locked on: Q21, or the 7406 most likely, but could possibly be PIA too.

 

[Andy B]

Q29 looks like driven by Q21 in turn driven by 7406 IC (pin 11) which controlled by Pin 12, which is controlled by PIA IC.
Logic probe the signal from the PIA forward - something is locked on: Q21, or the 7406 most likely, but could possibly be PIA too.

Thanks Alan.

I took the board out to test Q21. It looked a bit bent over and I wasn't 100% sure but it looked like maybe two of the legs were touching each other - though with my eye sight they might have been 50 yards apart from each other!

Anyways it tested fine so I reinstalled the board to try and do the logic probe tests you suggested.

Switched it on and the thing played fine and the multiplexed coils all worked fine and tested correct in diagnostics.

So I moved on to the next job - replacing a VUK plunger.

Did that. Put playfield down. Started a game. Coil issue was back.

Went in backbox. Moved Q21 a little. Problem sorted!

Gonna do some other jobs that need doing and then whip the CPU board out (again!) and re-solder that transistor.

Thanks for the suggestion to check the pre-driver which I should have known to do myself of course but I'm tired and hungry

 

[AlanJ]

Nice one.

 

[Jay Walker]

The Stern game 'Ali' was one where a tech could introduce a problem by raising the playfield. It has a horse-shoe 'U' lane at the rear left, with a spinner at its centre, just about edge-on to the player. Unfortunately, the spinner bracket is exactly placed to touch the lower rail of the backbox when the playfield's raised to vertical. This can squash down the bracket, immobilising the spinner (and damaging the woodwork of the back box).

I'd be inclined to change that pre-driver, if it's so touchy.