You are looking for the 12 VDC at TP3. Set meter to VDC, in the red area is the scale. Set that to "20" (you are looking for 12 volts so that scale measures up to a maximum of 20 volts) Attached is a diagram from another thread.

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Hi!

Nice meter!

In order to read a voltage, you have to have voltage present, so voltage readings are done with the power to the game on.

When you read in your manual or on the pinwiki:

https://pinwiki.com/wiki/index.php/Williams_WPC#LEDs_and_test_points_on_WPC-089_Power.2FDriver_Boards

You'll normally be given a hint about what you are measuring.

In this case, TP3 should have 12VDC on it. So we are looking at the DC Voltage, so switch to the VDC section.

Then turn the dial to the lowest number that is above the voltage you are trying to read. If you want to read 12 volts, set the meter on 20.

If you wanted to read 70VDC, you would turn the dial to 200, because that's the next lowest number that is above the voltage you are trying to read.

The next thing to do is to connect your black meter wire to ground.

Ground in pinballs can be the little peg in the middle of the driver board marked GND, or because lots of things are connected to ground, you can put your black meter probe on one of the screws that hold the boards, or you can find a piece of 'ground strap' that looks like a braided ribbon of silver wire. Some of that is in the backbox, on the bottom of the box area.

So you connect your black probe to ground, and then you touch your red probe to the Test Point. In this case TP3.

This is supposed to be 12V, but it frequently measures 11.9V. That's OK.

Let us know what you find.

Hmm. I know what I want to say, but let me ask questions first. There is no 20K setting for DC voltage on that meter (that would be 20000 VDC). Could you take a picture of the meter when making the measurement?

I think 11.45VDC is fine in this case (If that is truly what you are measuring). Then check voltage at both ends of the fuse F115 to see if the 11.45VDC is "making it" from the test point and through the fuse.

Ideally, I would want to check AC ripple at TP3 as well, but didn't want to overload you with new information. Typically this error is not caused by subtle variations, but something terminal such as an open trace or component. Keep following the Pinwiki, take your time and ask the questions.

disregard, saw your 2nd pic.

For future reference, that 20k is in the Ohms section, completely different function.

• First image result should be disregarded. It's a measurement of resistance not potential difference (voltage).
• Second image shows +0.55V (as you've measured it). Next step is to check continuity across the fuse. It's probably blown. Set your DMM to 200 in the Ohms section (south as you look at the setting knob). Put your leads across the fuse (F115). Report the reading. You should strictly remove the fuse from the holder but for this circuit it is not necessary.

Fuse itself is good, as I said before you want to check for voltage at each end of the fuse holder. If you have a good fuse, think of it as a bridge on a road. The bridge is good, but if you have no voltage there it is pointless. Checking for voltage at each end of the fuse is more thorough, more helpful, and saves a step of having to test both ohms and voltage on this component.

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Do you have 12VDC on either side of the fuse?

Next thing I would check is to look for +18 VDC coming into the rectifier. This is an unregulated voltage so it might vary by as much as a couple of volts. If you have this voltage coming in to Q2, then the problem is isolated to the section containing Q2 and C2. If the +18 VDC is not present at these points, further investigation "upstream" will be needed.

If you have the +18VDC at these points, you could have a failed Q2 or a cracked (open) trace somewhere under Q2 or C2, as possible causes.

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That's quite an assortment of problems that may or not be related to each other. They don't sound like power problems, there's a possibility something else got damaged, but that is only speculation. I would start with investigation of the switch issue first. How to diagnose is below.

"Don't rule out a short on the playfield somewhere. Chips generally don't
just go bad, something must have taken it out if it is indeed a chip issue.

Rule out or confirm a problem exists with the CPU...

Remove the connectors from the CPU (J212, J206/207, J208/209). Put the game
into self test, switch edges (you can get into this test because you've left
J205 connected on the CPU). Grab a jumper wire and attach a diode to one
end. Attach the other end of the jumper wire to pin 1 of J208 being careful
not to touch pin 2 with the jumper at the same time. Now take the diode end
and touch the free end of the diode to pin 1 of J206, then pin 2 and so on
(if you get nothing on the DMD, turn the diode around on the jumper).

Do you get just one switch closure or something else when touching the diode
to the pin? If only one switch per touch for all the pins, then your CPU is
fine. If you get multiple switch closures with each touch, or the Ground
Short error, then you've got a CPU problem. U20 is a good place to start in
that case, but it could be further as well.

If everything is working as it should with the diode test you'll need to go
over the playfield to find what's shorting. Could be anywhere, a switch lug
shorting to a lamp socket, diode touching something it shouldn't, almost
anything really. If you've worked on the game before this happened,
concentrate there."
- Borygard