WPC reset when both flipper, TP2 at 4.8V

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I'm getting the usual WPC reset when both flippers are hit. I've gone through the usual diagnostic steps, and all the connections look good. The + terminal on the bridge rectifier showed 8.8V DC and about 120 mV AC.

However, the 5V test point TP2 shows only 4.8V. This seems like a problem. Is this a symptom of a bad regulator, or something else?

Another thing to note is this machine is on a very low voltage AC circuit. I get a reading of 107V. I've adjusted the butterfly molex connector to put it on 103.5V though, so I don't think that's a problem.
 
I've shorted the thermistor, and that helped a bit. It no longer reset on the first both-flipper-flip, but after about 10 very fast ones it resets.
 
First, the low AC voltage will most definitely cause this. Before you do any repairs use an AC source that is 117 or above. If no resets then, you've found the problem. If it still resets when on good AC the follow these steps,

Like I said I adjusted it to run on 103.5V.

I replaced the voltage regulator and it works now. 4.8V is within the spec, but the new runs at 5V.
 
I'm having the same exact issue. I get 4.8v on my TP2. My wall outlet is testing at 118v output. The game access plug is also 118 when the game is off. I am going to check the bridge rectifiers next.
 
I am working on a board right now that does that too. Or I should Say I have a board that does that but I haven't looked at it yet. LOL
 
Worked on a high speed 2 that had 4.87 and would reset. Installed a new voltage regulator and it brought it up to 5.0V and no more resets.
 
I've had the same issue with my TZ and RS.. On the TZ I followed all the info out there and replaced a few parts.. Actually didn't fix the problem.. What has fixed it was reseating the "Z" connector.. It's the one funky connect near the left side. Also reseated a few other connects and its been running well for a few years..
 
I just had the same thing on my Stargate.. I have an external sunfire subwoofer hooked up and on good bass notes the game would freeze lol. Found out the +5 was at 4.65!! Turned it up to 5 and the freezes went byebye so far.
 
Sounds like a lot of you had this problem.

In my case, I made sure the bridge rectifier was good (measured about 8.8V at the + terminal), and the capacitor was good (measured about .3mV on AC).

4.8V is in the spec for the voltage regulator, but a new one brought it back up to 5V. No more resets.
 
Hereis my odd one.

Mine is measuring 5.5Vat the TP2 and the positive to the C4 Its not dropping voltage when it resets with the flippers being activated. And my LED4 is not lit... but my LED 3 is lit and flashes

I replaced the br2 and the C5...

Can the Q1 cause high voltage read and can high voltage cause reset?
 
I've got a new problem now.

I got a new thermistor from Marco, and soldered it in. I'm back to getting resets with both the flippers. I checked the 18V rail (TP8), and it's only at 13V. The 12V after the regulator is only at 11V. I'm thinking these are part of my problem, so tomorrow I'm going to replace BR2. I also noticed two of the big caps are getting a little bit puffy, so I think I'll replace the 4 big ones too.
 
This would be a good day to sign up for Pinball Ninja if any one is having this problem. The ninja has instructions and a video about how to make sure the voltage will never drop that far again. The website is at pinaballninja.com but you'll need to sign up at pinrepair.com (donation required).
 
Two pages in and no one has even mentioned the filter cap for the +5V? If the original cap is in there, replace it and your problem will most likely go away. Very common cause of resets on WPC machines.

I would also check the flipper coil diodes. A bad flipper coil diode can also cause resets when both flippers are flipped. The thermistor should have no effect and checking for AC ripple with a multimeter is not really going to tell you anything beneficial.
 
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