(Topic ID: 230031)

F-14 Coil locking on w/ mpu disconnected?


By megalo17

5 months ago



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  • 22 posts
  • 4 Pinsiders participating
  • Latest reply 4 months ago by megalo17
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#1 5 months ago

F-14 (system 11A): What could cause a coil to lock on with the mpu disconnected? Locks on immediately upon power up and will blow the fuse within 1.5 sec. It's the right center eject. Snubber board has been removed and inspected. Resistor is shot, like most, but relay seems to be ok (open b/w GND and COIL lugs). Coil diode was failed open, but this shouldn't lock it on, correct? Coil resistance is 4.2 ohms, which is proper (AE-23-800-11 coil). Scratching my head. I've got to be missing something on the snubber board? Nothing else in the circuit, right?

#2 5 months ago

Check the violet\green wire on the coil to see if it's grounded.

#3 5 months ago
Quoted from GRUMPY:

Check the violet\green wire on the coil to see if it's grounded.

I tried that. Not sure if the gnd wire in the front of the cab was good, but showed open, however, I didn't get continuity from that wire from snubber to mpu. I'll double check my results. And thank you for all the help you provide us! All the old posts I research have a few names that always pop up to offer assistance...

#4 4 months ago
Quoted from megalo17:

It's the right center eject. Snubber board has been removed and inspected. Resistor is shot, like most, but relay seems to be ok

Are you sure you have the correct snubber relay board? Post a pic of the snubber relay so I can see the wires.

#5 4 months ago

I believe so. I thought I read that C-11232, -1, or -2 could all be used. Trying to find that. C-11232 is what was there.

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#6 4 months ago

Nevermind. I misinterpreted the notes in the solenoid table.

#7 4 months ago

Manual shows this coil should be "A" part of A/C relay. Mine shows its the "C" side?

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#8 4 months ago

This is what I'm seeing for actual wiring...

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#9 4 months ago

Bounced it off another F-14 and the wiring looks correct. I get my brain wires crossed between the a/c relay and the snubber board.

#10 4 months ago

690 ohms between purple/green wire and ground.

#11 4 months ago
Quoted from megalo17:

I believe so. I thought I read that C-11232, -1, or -2 could all be used. Trying to find that. C-11232 is what was there.
[quoted image][quoted image][quoted image]

The picture shows your coil is mounted incorrectly. It looks like the diode leads and coil terminals are shorted to the coil bracket. The coil should be rotated to the right 90 degrees.

#12 4 months ago

Good eye

#13 4 months ago
Quoted from KenLayton:

The picture shows your coil is mounted incorrectly. It looks like the diode leads and coil terminals are shorted to the coil bracket. The coil should be rotated to the right 90 degrees.

Yeah, noticed that. Bought this at auction... It's mounted correctly now and still fires immediately at power up. Thanks tho!

#14 4 months ago
Quoted from megalo17:

690 ohms between purple/green wire and ground.

This is your problem, should be @ .600 meg of higher. Your diagram is correctly drawn, nicely done.
Test D-5 on the diode board, maybe its shorted.

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#15 4 months ago

If diode D-5 was to short then you would read low

Quoted from megalo17:690 ohms between purple/green wire and ground.
resistance to ground thru the flasher board resistors which connect to ground. Instead of the normal high resistance thru Q-31 and to ground.
This low resistance would be low enough to turn on the relay and energize the coil and burn the fuse just by turning the machine.

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1 week later
#16 4 months ago

Sorry, just getting back to this. A nice snowy day to work on pinball... D5 reads good. The 600 ohm reading I was getting was with the purple/green driver wire connected to the snubber board. After disconnecting (and starting to replace it), I realized it was measuring the resistance across the snubber relay coil to ground. I checked D5 and D13 (both sides of the a/c select relay) w/ wires disconnected (unnecessarily) and they read good. Grey/green wire from diode board to Q31 isn't shorted. +24V brown wire on snubber board is reading 150 ohms, same as on the other snubber boards. I don't really understand why a power wire would be grounded, although some of the snubber schematics show it tied in to the gnd pad. I'm gonna chase that, as it's all I've really got at this point. Hoping my logic isn't flawed...

#17 4 months ago

I would have thought if the brown wire was the problem that the relay would not energize. What do you read on the purple green wire with it disconnected?

#18 4 months ago

I would assume the same thing. Purple green reads open when it's disconnected.

#19 4 months ago
Quoted from megalo17:

Purple green reads open when it's disconnected.

Disconnected from the relay board but connected to the diode board, correct?

#20 4 months ago
Quoted from GRUMPY:

Disconnected from the relay board but connected to the diode board, correct?

Correct. I think I'll power it up with the snubber board disconnected, ensuring the fuse doesn't blow. Then methodically reattach one lead at a time (w/ power off obviously).

#21 4 months ago

Sounds like a good plan.

#22 4 months ago

Welp, not sure what I did, but it works... Cleaned off the diode board. Maybe that did it? Regardless, thanks for the help! I have a good understanding of the snubber boards and a/c relays now (at least for the next month). Pinsiders like Grumpy and Ken are great assets to the community.

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