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(Topic ID: 282051)

TOM - Is it a bad transformer?


By LilRocky

9 days ago



Topic Stats

  • 10 posts
  • 8 Pinsiders participating
  • Latest reply 6 days ago by Pin_Guy
  • No one calls this topic a favorite

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#1 9 days ago

I'm working on a Theater of Magic that had numerous issues and has probably been sitting in a warehouse for quite sometime. I'd gotten most issues resolved, including PCB work replacing BR2 due to no 5v, yet during a playthrough, all the backbox flashers locked on, where upon checking inside the backbox, I found C11 ruptured. I replaced C11 and also did BR4 just for good measure and everything began working again for a day. The next day, upon booting up a game, I noticed that the flashers were not working once again. I removed and checked the fuse in F11 and have continuity, but then I checked for voltage on F11 and have none. Checking J102, pins 1-4 and there's no AC here. I check the white/red line output from the transformer and no AC here. Does this sound like a transformer issue or is there somewhere else I should troubleshoot before doing a transformer swap?

#2 8 days ago

Check ac voltage one probe on pin 1 and other on pin 4 and have none? Transformer could be bad, but would be extremely rare. Most likely wiring problem or bad coin door switch.

#3 8 days ago

Try reseating the output connector(s) at the back of the transformer.

#4 8 days ago

It’s nearly never the transformer.

#5 8 days ago
Quoted from LilRocky:

all the backbox flashers locked on

Make sure you have these plugged in.
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J123 and J131 should be empty (these are keyed the same as J106)

#6 7 days ago

Agreed it’s rare, as I’ve been doing pin repairs for a good 10+ years and never dealt with a bad transformer, but at this point I’m out of ideas on any other possibilities.

All wiring is correct, game plays fine except for no flashers, reseated everything.

#7 7 days ago

Unlikely, but a break in the transformer secondary winding would cause the issue you're seeing. With the power off, check for continuity on the white/ red wires at the transformer output connector. While you have the connector apart, look for pushed or worn pins on both sides of the connector.

#8 7 days ago

Regarding the ruptured C11, see here: https://pinwiki.com/wiki/index.php?title=Williams_WPC#Exploding_or_Damaged_15.2C000uf_Capacitor_at_C11_.28C10_on_WPC-95.29

and also this from Clay's repair guide:

Exploding +20 volt Capacitor.
There are cases when the +20 volt capacitor (Driver board C11 on WPC-S and prior, C10 on WPC-95) can just explode. This happens when a shorted flipper coil diode or shorted transistor on the Fliptronics board causes the 70 volt coil power to feedback into the 20 volt flashlamp circuitry. Because of reverse voltage, this blows the 20 volt capacitor. Also installing one of the ribbon cable connectors in the backbox on the header pins (top row of header pins to bottom row of housing) can do the same thing. And lastly, if connector J124 is mistakenly plugged into the driver board connector J128 (they are keyed alike!), this can cause capacitor C11 to explode.

First check the ribbon cable header pins to make sure they are attached correctly. Then check the flippers. If when the flippers are activated, one of the flashlamps dimly lights, there may be a bad flipper transistor on the Fliptronics board.

There is a preventive measure which can be taken for this. Install a blocking diode on the driver board ceramic 10 watt resistor R224 (or R9 on WPC-95). To do this, first remove the lower leg of resistor resistor R224 (the leg just above TP7). Connect the anode (non-banded end) of a 1N4004 (or 1N4007) diode to the resistor's leg. Then solder the cathode (banded side) of the diode back into the driver board (where one leg of R224 was removed). This will prevent the problem.

#9 7 days ago
Quoted from Tuukka:

There is a preventive measure which can be taken for this. Install a blocking diode on the driver board ceramic 10 watt resistor R224 (or R9 on WPC-95). To do this, first remove the lower leg of resistor resistor R224 (the leg just above TP7). Connect the anode (non-banded end) of a 1N4004 (or 1N4007) diode to the resistor's leg. Then solder the cathode (banded side) of the diode back into the driver board (where one leg of R224 was removed). This will prevent the problem.

Excellent advice!

This safety measure is implemented in my reproduction WPC-89 power board. One reason that new reproduction circuitry can be better than new re-manufacturing of the original Williams circuitry.

blocking_diode_20v_flasher_power.jpg
#10 6 days ago

Seems obvious, but since no one mentioned it, don't forget to check the interlock switch as the AC voltage for the flashers from the transformer goes through the coin door interlock switch. You can always back probe the connector across the two WHT-RED wires on the connector coming from transformer to see if you have voltage there.
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You can also completely bypass the interlock switch and its wiring by connecting the PDB directly to the transformer secondary's by making the connection shown below:
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