Fuse keeps blowing

I need some help figuring this one out - the F109 fuse (4 amps, 250 volts) keeps blowing on my TOTAN CPU. Mostly, it melts right away during boot up, but last night I was able to play for a full half hour before it blew. When it does blow in the middle of a game, here's what happens:

1. The flippers stop working
2. The ball eject keeps firing, trying to kick out all the balls into the shooter lane
3. A few seconds later, the DMD goes blank

Everything else works fine - sound, lights, etc. Fuse F109 appears to get power directly from the transformer. The manual specifies T-series fuses, but I've also tried GMD's. Switch tests are all normal and There doesn't seem to be a particular feature that sets it off.

Any ideas about what I should be checking? Thanks!

#2 9 years ago

TOX

ChrisHibler

F109 fuses the 50V coil power between the transformer secondary and the gang of diodes D19-D22. The prime suspects are those diodes. You won't be able to reliably test those 6A2 diodes without lifting one leg as there is a filter cap in circuit.
--
Chris Hibler - CARGPB #31
http://www.Team-EM.com
http://webpages.charter.net/chibler/Pinball/index.htm
http://www.PinWiki.com - The new place for pinball repair info

#3 9 years ago

DUG

TopMoose

Pinside member

Thanks, Chris

I'm not great with circuit boards, so I hope you can help me further. I'm not sure what you mean about lifting a leg, but I found and tested those diodes. With the power off and the multimeter set to 20m amps, D19 and D22 don't register, while D20 and D21 get readings of 10.9 to 11.2. Other diodes in the same bank give similarly disperate results. Am I doing it correctly?

#4 9 years ago

TOX

ChrisHibler

To test diodes, your meter should be set to diode test. The symbol looks like an arrow with a vertical line through the tip.

Testing with a probe on each end of the diode, with power OFF, will yield null, or open as the diode blocks current flow in that direction. Testing with the probes reversed will yield .5 to .7 which is the typical voltage drop across a diode of this type. Your meter type may say something like 500 - 700.
--
Chris Hibler - CARGPB #31
http://www.Team-EM.com
http://webpages.charter.net/chibler/Pinball/index.htm
http://www.PinWiki.com - The new place for pinball repair info

#5 9 years ago

ZAZ

zaza

Pinside+ Frequent

10y 92,650 3,269

12Volt-u D3-D6

WPC95-PDB-12Vu.jpg

#6 9 years ago

TOX

ChrisHibler

Whoops. Sorry. I was reading a really blurry copy of the schematics. 1000 pardons.
F109 doesn't fuse coil power.
F109 fuses the unregulated 12VDC.
D3-D6 are the suspect diodes.

This makes more sense given the symptoms you describe.
When I say lift a leg, I mean desolder one leg from the PCB.

Now, we can isolate the issue somewhat, and it might not be one of those diodes. Unregulated 12VDC goes out to devices via connectors J138, J139, J140, and J141. You may be able to remove those connectors individually to identify the particular device that is causing the fuse to blow.
--
Chris Hibler - CARGPB #31
http://www.Team-EM.com
http://webpages.charter.net/chibler/Pinball/index.htm
http://www.PinWiki.com - The Place to go for Pinball Repair Info

#7 9 years ago

TOX

ChrisHibler

...and I see that zaza discovered my error too...
--
Chris Hibler - CARGPB #31
http://www.Team-EM.com
http://webpages.charter.net/chibler/Pnball/index.htm
htp://www.PinWiki.com - The Place to go for Pinball Repair Info

#8 9 years ago

ZAZ

zaza

Pinside+ Frequent

10y 92,650 3,269

sorry to interfere but wanted to help steering into the right direction.

#9 9 years ago

TOX

ChrisHibler

Quoted from zaza:
sorry to interfere but wanted to help steering into the right direction.

No reason to be sorry. Good catch!
--
Chris Hibler - CARGPB #31
http://www.Team-EM.com
http://webpages.charter.net/chibler/Pinball/index.htm
http://www.PinWiki.com - The new place for pinball repair info

#10 9 years ago

DUG

TopMoose

Pinside member

Thanks, guys

I unplugged J138, J139 & J141 (there's no plug in J140) and, as expected, the fuse didn't blow. Next, I plugged in J141 and got the same result. Then I plugged in just J138 (the color DMD) and got the error message "check fuses F101 & F109, J127 & opto 12V supply." Finally, I plugged in only J139 and that's when the fuse blew.

Could it be a problem with the ball troth optos?

Zaza may remember when my old nemesis the F101 blew, but it's not giving the same symptoms.

I tried testing diodes D3-6 with the diode test but couldn't get a steady reading. Maybe they're getting fueled by the C8 capacitor?

#11 9 years ago

TOX

ChrisHibler

Good test so far.
Now, start over, with all those connectors off.
Install a new fuse.
Connect J139 only.
Power on.
The fuse should blow.
If it does, we will track down what is connected to J139. Something that is consuming 12V is causing the short.

Power off.
Put a new fuse in.
Disconnect the trough opto boards, the 7 opto board, and the flipper opto boards. Disconnect anything else that uses 12VDC on the PF.
Connect J138-J141 again.
Power on.
The fuse should not blow if you've successfully disconnected every 12VDC user on the PF, and J139 does, in fact, supply power to the PF.
One at a time, reconnect everything that's been disconnected. Wait a bit between connections, checking to see if the fuse blows.

Report back.
Carry on soldier...
--
Chris Hibler - CARGPB #31
http://www.Team-EM.com
http://webpages.charter.net/chibler/Pinball/index.htm
http://www.PinWiki.com - The Place to go for Pinball Repair Info

#12 9 years ago

DUG

TopMoose

Pinside member

We're thinking alike now! With everything plugged back in, I traced the J139 to the opto board, unplugged the opto J1 (power in) and the fuse blew upon boot-up.

Next, I traced the J139 to its other destination, the coin door board, where it enters the J2 connector. I unplugged the coin board J2 and everything works perfectly! I played for about 40 minutes, waiting for the fuse to blow, but it never did. I got to the Genie Battle twice, so I know every switch was hit and every coil fired.

Does this make any sense?

#13 9 years ago

TOX

ChrisHibler

If your game has a coin counter in it (which is a 12V coil) or
a European Coin Door or a dollar bill acceptor, that might make sense.

Reconnect the coin door interface board.
Disconnect J4 and J6. Those are the only two 12V consumers from the coin door other than the coin counter (if installed). This will further divide and isolate the problem.

Nice work so far!
--
Chris Hibler - CARGPB #31
http://www.Team-EM.com
http://webpages.charter.net/chibler/Pinball/index.htm
http://www.PinWiki.com - The Place to go for Pinball Repair Info

#14 9 years ago

KLB

kbliznick

Firebird Pinball

Phoenix, AZ

11y 63,900 2,438 5 4

Looks like you guys are on the right track.
The 12V on the coin door board is a popular spot to pull power for light up mods. Does the game have any light up flipper buttons or any other mods connected to the coin door board?

#15 9 years ago

TOX

ChrisHibler

Quoted from kbliznick:
Looks like you guys are on the right track.
The 12V on the coin door board is a popular spot to pull power for light up mods. Does the game have any light up flipper buttons or any other mods connected to the coin door board?

Good thought Kris.
The coin door interface board is also a favorite place for loose junk to accumulate. Check the board for goofy things that might have landed on it.
--
Chris Hibler - CARGPB #31
http://www.Team-EM.com
http://webpages.charter.net/chibler/Pinball/index.htm
http://www.PinWiki.com - The Place to go for Pinball Repair Info

#16 9 years ago

DUG

TopMoose

Pinside member

Guys, I think we cracked it.

Coin Board J6 is where I had my flipper button lights plugged in. I re-attached the J2, disengaged the flipper lights and everything is working fine. Is there a better place to plug those in?

#17 9 years ago

TOX

ChrisHibler

It's hard to imagine two flipper button LEDs increasing the load enough to blow the fuse. Are those lamps shorted to something?
--
Chris Hibler - CARGPB #31
http://www.Team-EM.com
http://webpages.charter.net/chibler/Pinball/index.htm
http://www.PinWiki.com - The new place for pinball repair info

#18 9 years ago

DUG

TopMoose

Pinside member