Wg k7201

telmnstr

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Hello everybody,

Finally had all my games up and running good, then Ms Pac Man had a case or two where the monitor cut out. It quit for good recently, and now I'm on a mission to repair it.

A prior owner had obviously had the monitor in the Ms Pac Man replaced. The monitor is dated 1997, and of course is a later model.

Fuse is good, and line voltage is entering the board.

I have a question about the bridge rectifier diode. I can measure 123 vac coming into the bridge. The output side in DC appears to be 85vdc (pin 1 +, 3-). Does this sound correct?

I'm testing it with the degaus wire loop disconnected, as it's hard to test the board with the short cable length.

I do not see high voltage DC on the neck board transistors or input cable, and there is no neck glow.

WG has troubleshooting dox and lots of info online given that it's a "modern" model. Diode D16 is supposed to have 127.1vdc on it according to the typical voltages (I have no input signal though), and reads .27vdc on mine.

Any thoughts?

There is no static sound or whine or anything. Dead. I'm just not sure if the bridge should be 1:1 on voltage.
 
Grr the big cap is reading 170v, which matches the block diagram. All is good up to there.

Bridge is fine. So much for easy fixes.
 
Was looking at that thread last night. Will work through it.

Oddly enough, I see no voltage on the other side of the isolation transformer. I see the 173vdc going in, but nothing on the other side. I unsoldered the two pins on the isolated side, and see continuity there, so the coil should be good.

Going to have to look at the schematic more, maybe fire it up with the transformer unattached on the isolated side to see if anything shows up.

I'm going to check your fix, the R005 as well.

I haven't recapped the monitor. 1997, you'd think the caps would be okay. Then again, arcade monitors seem to have a high number of issues.
 
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Was looking at that thread last night. Will work through it.

Oddly enough, I see no voltage on the other side of the isolation transformer. I see the 173vdc going in, but nothing on the other side. I unsoldered the two pins on the isolated side, and see continuity there, so the coil should be good.

Going to have to look at the schematic more, maybe fire it up with the transformer unattached on the isolated side to see if anything shows up.

Don't do that. Your problem seems to be the same as mine. Voltage on one side (high) and nothing on the other. Did the lightbulb trick in that thread to verify the problem was definitely in the power section (between the power connector and that transformer).

I haven't recapped the monitor. 1997, you'd think the caps would be okay. Then again, arcade monitors seem to have a high number of issues.

13 years is plenty long enough to be a problem. I've seen monitors have cap problems after a few years....

http://www.badcaps.net/pages.php?vid=4
 
Resistor 005 checks out (out of circuit)

Cap 011 (22uf) replaced

Don't have a replacement for 015, but it looks like it's been replaced before and the value is different from the schematic. Schematic says 160v, the one in there is a 35vdc. I don't have a replacement of that value, but tried a 33uf 50v and a 10uf 50v and it didn't come up.

It's odd.
 
Had my numbers wrong.

C015 was replaced the other day, no change

C011 had a 35v in it, when schematic calls for 160v. Replaced that a few minutes ago, no change.

Just replaced IC001, no change

Doesn't appear to be high voltage on the other side of transformer T3, which is an isolation transformer. But I do get ~170vdc on the input side, on two of the 4 input pins.

T3 isolation transformer:
Pin 1 to pin 6 = 170vdc

Pin 12 to pin 10 = 0vdc

I don't have a ring tester, but the coil checks out?
 
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You shouldn't read any voltage directly on the output of T3, but you should have a voltage reading on the output of D101 (side not connected to T3).

If not, check ZD001, R005, Q001, and Q002...
 
Update:

Still no worky.

I've since replaced Q002, Q001, IC001, the parts in this thread, and Capacitor 36 (Pulled a close value from another monitor just to test.)

Removed and checked Q11 (HOT).

I replaced the isolation transformer completely.

Still not seeing any real voltage on the other side of the isolation transformer, but not sure if it's because of the feedback loop (some sort of inductive pickup) that is connected to the "line side" of the monitor power supply.

Next I plan to check Q10 which feeds Q11.

The bridge diode BD001 is fine.

D101 checks out, but I'm going to take a look at it again.

The rough part is the flowchart from WG has the flyback listed as a possible dead thing. Not sure how to really test that.
 
You can do the light bulb test to see if the power supply section is good. If the bulb lights, then your problem is after the transformer. If it doesn't, then it is before the transformer...
 
7201 or 7203?

If you search around here, I posted the yoke readings of each in the same thread. They aren't the same. Also, I think the 7200's are 10-pin, right? And most 19" 7000's are 8-pin....
 
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