Big Guns: Upper Center flashers over volting and constantly on

[Smithers]

Big Guns: Upper Center flashers over volting and constantly on

Greetings,
I recently picked up a BG and have been having a great bit of fun refurbishing it. I've done all the usual maintenance and set about replacing all the blown 89 bulbs last night. When I replaced the pair of top/center flash bulbs (behind the clear globe on the trans) they blew instantly. I measured their voltage and instead of the expected 12-13V it is measuring 31.5V. I thought that maybe the sockets had been mislabeled somehow so I tossing in some 1251 bulbs and boy did they light up! Turns out the sockets are constantly hot (see attached pic). I referenced the manual to determine what is inline between these lights and the incoming power but without a schematic I'm a bit lost. I did determine that D13 on the Aux power board is bad but it doesn't appear to be in circuit with the bulbs in question. All the resistors on the lower resistor board appear okay visually but I need to ohm them out.
My question is: Which components are inline with these particular bulbs? What type of failure would result in a higher/constant voltage? What checks do I need to run? Am I crazy and these are in fact 1251's that are constantly lit?

Thanks so much!
Smithers

 

[Kilgore]

I'm a little busy to explain the whole System 11 multiplexing coils and flashers, A/C select relay thing right now. But I have a feeling if you search the forum for either you should find your answer. You have a shorted coil driver.

Rodger Kilgore

 

[Smithers]

Thanks! So perform a test of the transistors on the AUX board?

 

[WindDrake]

Should be BB Top Mid FL - 05 16 in solenoid tests. 8P3 Pin 16 PF/Cab, 1P12 Pin 9 @ CPU Board.

Couple things to check.

Failure @ Q6 (TIP122) on the CPU board.
Failure @ Q2 (2N4401) on the CPU board.
Failure @ U17 (7408) on the CPU board. Your output pin is pin 6.

Should be an easy fix.

Edit: These flashers are directly CPU board controlled, and are not in the A/C multiplexer arrangement. Don't bother with the aux boards.

 

[Kilgore]

Looks like WindDrake did your home work for you. Follow his instructions and you should get it working.

Rodger Kilgore

 

[Smithers]

Thanks so much guys! I'll get to testing those tonight. I am going to pull the aux board as I found some diodes that are bad. I'll replace those tonight.

 

[Smithers]

Q6 was bad. Thanks so much for the help! I wouldn't have known to look there. I'll be replacing components real soon. Greatly appreciated!

Edit: Windrake, I meant to ask. Where did you find that schematic. I didn't see it in the manual.

 

[WindDrake]

I checked my manual also - no schematics. Must be omitted on the Sys11 games.

Got mine from here.

http://arcarc.xmission.com/Pinball/PDF Pinball Misc/

It's kind of a mess, though. Pages out of order, etc.

http://www.filedropper.com/sys11areorganized

That's my resorted copy.

 

[Smithers]

So I replaced Q6 and no dice. The transistor acts fine when I take it out of circuit but then the same behavior when it's connected. Same for the associated diodes on the Aux board. I guess I need to look elsewhere and compare against a good circuit of similar design.

 

[Kilgore]

You should have replaced the predriver for Q6 as well, Q2 and if you still have a problem then U17

Rodger Kilgore