Recently purchased a 1991 Bally (Williams) Party Zone with WPC system. Replaced a bunch of bulbs and found only 2 faults:

One (1)  flasher bulb stays on always, so I will remove bulb to prevent burning (no big deal, many more flashers present).

The second issue is that when testing thru diagnostics function, all the lampss do not light on the "lower half backbox" string. On the upper half light string they all light and go through 1-10 brightness intensity with no problems. I have never dealt with this stuff before so was going to check the manual and locate the appropriate transistor.  It this correct? What do I need to look for with DMM?  Is it easy to get and replace with new transistor if that is the issue (I can solder, and have reasonable intelligence>

Hope it doesnt go back to the MPU.

I think Silvain is the guru here...

Quoted from wbradley

Recently purchased a 1991 Bally (Williams) Party Zone with WPC system. Replaced a bunch of bulbs and found only 2 faults:

One (1)  flasher bulb stays on always, so I will remove bulb to prevent burning (no big deal, many more flashers present).

The second issue is that when testing thru diagnostics function, all the lampss do not light on the "lower half backbox" string. On the upper half light string they all light and go through 1-10 brightness intensity with no problems. I have never dealt with this stuff before so was going to check the manual and locate the appropriate transistor.  It this correct? What do I need to look for with DMM?  Is it easy to get and replace with new transistor if that is the issue (I can solder, and have reasonable intelligence>

Hope it doesnt go back to the MPU.

I think Silvain is the guru here...

Check for any broken wires or solder joints. If all the lights in the backbox are supposed to work together, there might be a broken wire that feeds all these lights, or a broken daisy chain.

Check the schematics for a common point between all these lights and use a multimeter to see if voltage is getting to the lights.

The locked-on flasher is probably a dead transistor on the driver board. You can test it with the diode function of a DMM.

http://www.pinrepair.com/wpc/index2.htm#trans

The dead GI string is most likely a bad connector but there are several other possibilities.

http://www.pinrepair.com/wpc/index3.htm#gi

As others have already indicated:

1) you have a shorted drive transistor for that stuck-on flasher.
Use the manual/schematics to identify the transistor, and confirm with your DMM (with machine power off)
either with diode or continuity setting.  tinyrodent provided a link for such check.

2) broken common wire, bad/burned connector/pin on power/distribution board, cold solder joint, or fuse.


...Common issues with pinball machines, and easy fixes if you know enough about electronics and soldering.


Good luck!
- Sylvain.

Thanks guys...sounds like y'all got lotsa experience. Will work on it. Finding time is  the problem these days. I will post my result when I have a fix.

Cheers,

Warren

Update-

Fixed light string in lower half of backbox. Traced wire back to plug on to circuit board. Noticed that plug is hot to the touch, but anyway just unplugged and the plugged back in and the lights are working. The plug is dark looking as if there is heat stress but it seems ok for now.

Gotta go back and test the transistor that controls 2 flashers (one in playfield and other in back box) which are both locked on. Wasnt quite sure of DMM testing procedure but will know what to do by tomorrow. Hope the TTL chip is OK.

Quoted from wbradley

Fixed light string in lower half of backbox. Traced wire back to plug on to circuit board. Noticed that plug is hot to the touch, but anyway just runplugged and the plugged back in and the lights are working. The plug is dark looking as if there is heat stress but it seems ok for now.

Excellent, you located the problem, and temporarily got the lights to work, congrats !

... But the actual problem is not really fixed yet  

You will need to replace that pin with a stronger trifurcon 0.156 pin
(and perhaps the header pins too on the board).


Cheers,
- Sylvain.

Quoted Text

You will need to replace that pin with a stronger trifurcon 0.156 pin
(and perhaps the header pins too on the board).

Couldn't find the trufurcon pins at the local electrical supply, bought Molex header and female. The actual socket on the board is 9 pin but I could only get 10 pin. That said, hope I can make it work. Transistors were cheap, bought a few in case the one I am testing tonight is shorted on as it appears.

If the Molex doesnt fit to the board I will probably hardwire the molex header and hotglue in place. Not too comfortable with removing the circuit board  to rerun solder on back...concerned that by opening all the plugs can bring on more issues. Will cross fingers.

Quoted from wbradley

The actual socket on the board is 9 pin but I could only get 10 pin. That said, hope I can make it work.

It may be possible to cut off the 10th pin.

Quoted from wbradley

Transistors were cheap, bought a few in case the one I am testing tonight is shorted on as it appears.

There are actually two transistors of different type per solenoid/flasher circuit - a driver and a pre-driver. This is fully described on pinrepair.

Quoted from wbradley

If the Molex doesnt fit to the board I will probably hardwire the molex header and hotglue in place. Not too comfortable with removing the circuit board  to rerun solder on back...concerned that by opening all the plugs can bring on more issues. Will cross fingers.

In my opinion it is not possible to do a proper job of any soldering on the board without removing it from the backbox. If this exposes more connector problems so be it - they need fixing too. Hardwiring makes a huge mess that is difficult to remove & repair later.

Quoted from wbradley

Couldn't find the trufurcon pins at the local electrical supply, bought Molex header and female. The actual socket on the board is 9 pin but I could only get 10 pin. That said, hope I can make it work. Transistors were cheap, bought a few in case the one I am testing tonight is shorted on as it appears.

If the Molex doesnt fit to the board I will probably hardwire the molex header and hotglue in place. Not too comfortable with removing the circuit board  to rerun solder on back...concerned that by opening all the plugs can bring on more issues. Will cross fingers.

http://www.greatplainselectronics.com/

Best source for specific molex/connector parts.  I started ordering a few years back and don't even bother with my local stores (like Sayal) for these parts anymore.

Incidently, bought at Sayal

10 pin can be ground down with a Dremel tool or bench grinder. Trying to cut it probably isn't going to yield the type of outcome your looking for.

Checking transistors you should check the driver and pre-driver for problems as they may both have issues.

If they are fine you could be looking at the TTL behind it, but normally you test from the load back up the circuit.

Replaced the Socket (female) and all is well. Turns out is was a 10 pin plug but only 4 pins used. Left the header as is for now, dont want to take out the circuit board and remove all the plugs in case something breaks. Hopefully the resistance is reduced and the new socket wont burn. Otherwise will have to remove board and reflow on back.

Weird, checked the big transistor,and  the pre driver transister as well and it reads same on the DMM using OHM setting as all the others of the same type when powered off. Must be the TTL or the maybe the MPU? Might leave well enough alone and accept that on an 18 year old machine 2 flashers stuck on is a simple fix...remove the bulbs.

Again, thanks for the advice guys.

On the page I linked above, search for "Transistor Testing procedures using a DMM." It uses the diode setting of the DMM (not ohms), and the procedure is slightly different depending on the type of transistor. The 74LS374 chip can also be tested in a similar way, as described.