Hi.  My friends' machine sometimes resets (kind of randomly).
TP2 only shows 4.82 volts or so.  Since it is not within the 4.9-5.1 range, I feel that this might be the problem.  I changed the bridge but voltage still measures 4.82.  Could the problem be the 15000uf 35v CAP that works with this Bridge also?  Should I replace that cap?  Or should I also replace the LM723 chip which I believe controls this portion of the Power Board also?  

Any other thing to look for?

Thanks.

which bridge did you change ?

I changed both of the ones under the Heatsink which I know BR2 regulates the +5v and I changed the other one since I was there so to speak....
Nothing changed....
I guess C5 is next....

Note: this post is for people who are versed sufficiently in electronics and repairs.
All the usual warnings about safety, proper procedures, etc. apply.
While many of us here on this board are knowledgeable experts, I have seen
too many hacked boards and fire-hazard pinball machines in the last few years!.

You may need to change that big capacitor, but that machine is not very old...
With a DVM, set it to AC volts and measure the AC ripple on that cap.
If larger than 0.3-0.5 VAC, it will probably need to be replaced.

To try if it is the problem, clip a good cap in parallel with it if you can
(ensure it has same or higher operating voltage and that the polarity
of your connections are correct!).
Re-measure the DC voltage and see if it is closer to +5 volts.
The AC ripple should be lower also.

TP2 at 4.82 volt for is sure too low, and is most probably the lead cause
to the sporadic resets when flippers or coils draw current.

For those Williams self-resetting, the problem is not always easy to find.
I spent quite a few hours last year to troubleshoot and fix Steph's self-resetting
Pinbot. The bridge and cap were already replaced on his machine.

Check the following to start:
- check that your digital voltmeter is properly calibrated (or compare to another
   +5V source)
- do not use a low-quality AC extension wire to plug your machine in;
- measure the AC voltage at your plug; should be 115-120 VAC;
- ensure the AC plug itself (if a replacement) is not corroded and wires tight;
- ensure the +5V fuse is of the correct type and amp, and that the fuse
   holder is clean and tight against the fuse;
- check that the soldering on the bridge rectifier are well done;
- check all coils in the machine to verify that a diode is well connected across lugs
- and that none of those coils previously overheated;
- check transformer voltage tap settings (should be set for 115V)
- was the machine purchased or operated in Ontario ? then an additional isolation
   transformer may be present inside - if too low its rating, it will cause the AC line
  viewed by the machine as too low when high current drawn, and will cause reset
- check under the metal box inside the cabinet for the AC line filter, to ensure all
   connections well soldered
- verify all boards tight inside, and that ground connections are secure and tight

If still no help and bridge/cap already replaced:
- identify if reset always when same coil or motor operating;
   replace diode across that coil
- verify that there are no cold solder joints under the power supply board;
   carefully reflow if necessary.

If all else fails, this is what I had to do on the above Pinbot, as its +5V was +4.88:
- check that all components on the +5V circuit (esp. resistors and caps) on the
   power supply board are within specs;
- identify on the power supply schematics the resistor used to get the +5V reference
  voltage to the LM723 regulator (on Pinbot's power supply board it is R7 of value
  2.15K, connected between pins 5-6 of the LM723 voltage regulator); its value can
  be slightly reduced by installing a resistor 10 times its value in parallel on top of
  the board, to bring up slightly the reference voltage to the +5V regulator (ONLY if
+5V too low and if everything else was already checked/replaced).
  With the added resistor installed, re-measure the +5V voltage; it now should be
  closer to its proper expected value; you may need to experiment with another
  resistor value to get closer to +5 volts.
- on the Pinbot, I also had to install a 75volt spike-snubbing component across
  the visor motor, as Pinbot did not have motor spike control on motor turn on/off.


Hope this helps,
Bonne chance / Good luck !
- Sylvain

I had a problem with a Williams game resetting and found it to be the power circuit line voltage was low.  This only happened when the dehumidifier was running.  It was pulling too much power and drop the line voltage.

Measure the socket voltage with the usual stuff turned on and see if it is below 115V.

Good Luck

Brian

Thanks.  The machine was at my place before and it also had reset 2-3 times in like 3 years that I owned it so I don't think it has to do with the line voltage (plus my friends' house is brand new and high quality construction).  

Funny thing is that I have a White Water (I had sold my first one to my friend) and today, I measured TP2 in mine, and sure enough, I get 4.81 volts on mine!  Yet mine has never reset on me.  The way I am measuring is that I put the negative(black) prong on the screw which touches PCB ground.  I assume this is ok.  Well, the +12 volt test point measures fine and so this (and my Multi Meter) must be ok.

Now I am unsure about going ahead to try to change the C5 on my friends' machine (and I cannot get to the darn thing to test it while on unless I try to slide something underneath it front top side of PCB).

I will continue reading Sylvain's great points (and marvin3m site also) and at least test the Thermistor (and ok, the line voltage also) and check that nothing strange is going on there.  Then, I may as well save myself some effort and just swap Power Supply /Driver PCB with my friends' machine and see if mine starts reseting or if his doesn't reset anymore then.

This is going to be really hard, I just feel it.  Well, then again, I am not only into this hobby just to play games....