WPC-S flipper diode question (Fixed the matrix issue!)

[Ran]

Hey guys
Finishing up (finally!) the TOM I picked up a few months ago and I just noticed while rebuilding the flippers that the previous owner (or tech that helped maintain the game) cut the diode that connects the red wire lug to the center lug on both flipper coils.
Anyone know why someone would do this?
And should I solder on new diodes or leave them cut?

Thanks in advance guys.
-Ran

[tullster]

Great to hear it's coming together Ran!

I've seen diode leads break, but no idea why someone would cut one. Either way, they need to be on there to stop the voltage spike that occurs when the magnetic field collapses on the coil.

Let us know when she's up & running so we can stop over & test it!!

[Ran]

Thanks for the insight Tully!
Gonna solder a new diode on each coil. So weird that the previous person(s) snipped those diodes.
Fired her up tonight and realized I still have a bit of work to do. No credit dots but LOTS of switch issues and two dead eddy sensor boards (one the pot does nothing when trying to adjust and the other one for the trunk eddy is super flaky).
First time dealing with switch matrix issues. Confused but starting to narrow down the culprits I think.
One column's switches are either totally dead or trigger 3 other switches when activated.
Plus a few other row issues.
Good times learning the electronic side of these games.

[KingPin Games]

As far as the switch matrix goes, check the diodes on the switches in that row. If one is broken (or shorted) it will cause issues with the rest.

[Ran]

As far as the switch matrix goes, check the diodes on the switches in that row. If one is broken (or shorted) it will cause issues with the rest.

Thanks Chris
I went through what pinwiki suggested for determining its not a CPU issue (using test jumpers to test the pins in J207 and J209) so now I'll follow your lead and check the diodes in that column that's acting up.
More to come...

[Ran]

One more question about the switch matrix.
What causes multiple switches to activate all at once in Switch Edge Test when I press a single switch?
Getting a few of those as well.
Sometimes it's 3 switches all at once in a single column.
Sometimes it's only 2 switches in a single row.

And if I have a spare U20 should I try replacing that first or would that be a waste of time at this stage?

Thanks guys!
-Ran

[tullster]

Make sure you've got clean 12 volts coming from your driver board. Hook up your meter to the 12 V output in the lower left hand corner of the board ( J 116,17 or 18 pins 2 &3 ) Then switch the meter over to AC. If there's any AC voltage, that'll screw up your optos. I've seen more than once someone has changed the bridge (BR 5) & cap (C 30) and ripped the traces on the topside of the board! If you're good, then I'd doublecheck the wiring, then maybe worry about U 20 as a last resort.

[Ran]

Make sure you've got clean 12 volts coming from your driver board. Hook up your meter to the 12 V output in the lower left hand corner of the board ( J 116,17 or 18 pins 2 &3 ) Then switch the meter over to AC. If there's any AC voltage, that'll screw up your optos. I've seen more than once someone has changed the bridge (BR 5) & cap (C 30) and ripped the traces on the topside of the board! If you're good, then I'd doublecheck the wiring, then maybe worry about U 20 as a last resort.

Thanks again Tully!
I'll do that tonight after I clean all the sap and squirrel crap off me from putting up the Christmas tree

Check the DC on the power supplies. (All the test points showed accurate power but I know they are more high level indicators.)
Then will switch to AC and see if there's and AC coming through those same areas.
Then will follow the wiring to see if there are any loose connections or connections accidentally grounded.
Then start checking diodes in the column that's acting up.
Then deal with U20 if necessary. (The good thing with U20 in the game is that it's socketed so I can pop it out and drop a new one it.)
Thanks again!
-Ran

[Ran]

Make sure you've got clean 12 volts coming from your driver board. Hook up your meter to the 12 V output in the lower left hand corner of the board ( J 116,17 or 18 pins 2 &3 ) Then switch the meter over to AC. If there's any AC voltage, that'll screw up your optos. I've seen more than once someone has changed the bridge (BR 5) & cap (C 30) and ripped the traces on the topside of the board! If you're good, then I'd doublecheck the wiring, then maybe worry about U 20 as a last resort.

No significant AC current in any of those areas
Only one that registered a bit (00.1) was J117 pin 2 (the gray-yellow wire) that sends +12VDC to J606 pins 6-7.
Gonna start investigating the wiring in the playfield.
Thanks again for your help!
-Ran

[Ran]

So I figured out the problem.
Gonna chalk this one up to my own stupidity.
After going through Tullys recommendations with checking the board for AC I started following the wires and diodes like Chris recommended.
Upon following one of the main culprit wires I came to a molex connection under the playfield that looked off because the wires on one side didn't match the wires on the other. Found the other molex connection under the field that corresponded (which also had mix matched wires) reconnected them and boom- the game is working 100%!
Just need to do a few more minor things but all in all she's all set and playing really well.

Thanks agin guys for your support and advice!
I learned a ton about the matrix and following the circuits.

-Ran