Hi Scott,

Those should be 6.2V Zener Diodes.
You can "kind of" test them the same way you test a normal diode. Set your meter to diode test. You should see null one way, and about .5-.7V the other way.

Here's a picture of their location. They are there to protect the special solenoid switch inputs.
image.jpg

The 7402 in that circuit may have been damaged.
You can reliably test them:
http://www.pinwiki.com/wiki/index.php?title=General#Testing_an_integrated_circuit

Have a shot at it.
--
Chris Hibler - CARGPB #31
http:/www.Team-EM.com
http://webpages.charter.net/chibler/Pinball/index.htm
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No need to do that anymore.
Unless you lift one lead of the diode, you are measuring the voltage drop across the relay coil, which isn't much.
Remember that "electricity always takes the path of least resistance". It's a good thing too. This fact of nature/physics is what allows ALL of our electronics to work.

The path of least resistance when you measure that diode "in circuit" is through the relay's coil. That diode isn't going to fail anyway. Scratch it off the list.

The tool you need now is a logic probe. You would use it to probe the outputs of the ICs upstream of the transistors that you replaced. Do you have a logic probe? They are cheap...and easy to use. Here's an inexpensive one that I like. I have three of them around here.
http://www.amazon.com/Elenco-Electronics-LP-560-Logic-Probe/dp/B000Z9HAP4/ref=sr_1_1

--
Chris Hibler - CARGPB #31
http://www.Team-EM.com
http://webpages.charter.net/chibler/Pinball/ndex.htm
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Before you do anything else to the board check the RC network on the two switches and make sure they are not causing the bumpers to lock on.

viperrwk

resistor network is just a bunch of resistors in one package. You can make your own network with 8 or 9 of the same value resistor.

What did you learn from probing the 7402 outputs?
--
Chris Hibler - CARGPB #31
http://www.Team-EM.com
http://webpages.charter.net/chibler/Pinball/index.htm
http://www.PinWiki.com - The new place for pinball repair info

What Chris said.

Typically with special solenoid problems on system 11 and Data East games 90% of the time it's the TIP 102 and the 7402 chip that is bad. Since there are really only 3 chips involved, two 7402's and a 7407, I usually remove and socket all 3 of these TTL chips. (I rarely if ever have to replace the 3 PIA's for special solenoids) Saves time since I already have the board out and these circuits like to go bad quite often so it becomes an easier fix next time another special solenoid circuit pops.

Also this circuit can have you chasing your tail. If you replace the transistors but not the bad chip it doesn't take the game being on very long to reblow the transistors, also a fair amount of the time the diode is blown on the coil (or someone replaced it backwards and that is what blew it out) and the bad or backwards diode will immediately reblow the transistor and possibly the chips.

Also weirdly enough IIRC the blanking circuit uses some of the gates from one of these chips and damage from a bad transistor can lead to odd blanking problems, like the coils all firing when the game is turned on or display chips blowing up, so it's not a bad idea to put fresh ones in when they are suspect.

I believe the flipper relay goes through one of the 7402s. Are your solder joints good etc?

A solid disciplined process with testing to validate suspicions is always the way to go.
Great to hear it's fixed.
--
Chris Hibler - CARGPB #31
http://www.Team-EM.com
http://webpages.charter.net/chibler/Pinball/index.htm
http://www.PinWiki.com - The new place for pinball repair info

Someone here was wondering what the 6.2V zener diodes might be there for.
https://pinwiki.com/wiki/index.php?title=Williams_System_9_-_11#MPU_Driver_Boards
Here's a suggestion:
"Their purpose is to protect the special solenoid switch inputs. Either a ZPY6,2/ZD6,2/1N4735A (1 watt) or ZF5,2/1N5234B (1/2 watt) can be used. This mod is purely optional. In reality the diode doesn't help much if you short the switch input with the solenoid voltage. In this case the diode and the 7402 are usually damaged and need to be replaced."

And crazy enough, I was recently working on a System 11B board with two shorted Zener diodes.
As mentioned in some other thread (will link it when I find it), this will cause the 7402 output to read about 2,5V and lock on the corresponding coil as soon as a game is started or the test mode is entered.

//Enver

Yes, this makes perfect sense.

The use of a half watt zener is pretty wimpy if his function in life is to cut off excess voltage. I imagine his junction vaporizes rather quickly in the event of excess voltage. It is now recommended by manufacturers to use uni-directional transient voltage suppressor or "tranzorb" or "TVS" to do this function. They look like and behave just like zener diodes but can take more of a wallop. The standard part for protecting TTL logic is the P4KE6.8A.

But, like lots of other things Williams did, they only went half way - they only put in half of the required protection into the circuit. This zener clamps the voltage to a lower and more acceptable value. If the voltage remains for a long period of time then the zener (or TVS) will vaporize and the clamping function will be gone thereby exposing the 7402 to this high voltage. The amount of time to kill the zener diode is only a few milliseconds. Williams should have put current limiting between the zener and the connector pin. Probably a low value solid state resettable fuse or "Polyswitch" would have been the best method. Not sure what the board replacement guys are doing to protect the input logic but hopefully they didn't just blindly copy Williams with this one.