(Topic ID: 284998)

F-14 Tomcat: Blowing F5 backbox fuse

By hanasu

5 months ago


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  • 34 posts
  • 4 Pinsiders participating
  • Latest reply 3 days ago by hanasu
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#1 5 months ago

For reference: I had a previous issue (https://pinside.com/pinball/forum/topic/f-14-tomcat-no-slings-or-pops-transistors-shorted) that involved replacing Q69/Q71/Q75, the associated pre-drivers, and a 7402. I am familiar with arcade/monitor repair, but this is my first pinball machine.

After making this fix, I started the game back up. After maybe 20-30 seconds, F5 blows. One thing to note: immediately after it blows the backbox 'siren' lights also turn on.

So, it seems I still have a solenoid issue, but at least the playfield fuse is no longer blowing. Where should I be looking next? Thank you.

#2 5 months ago

Which F5 fuse?
There are 2 F5 fuses.
One on the power supply and one in the back box.
http://www.pinballrebel.com/pinball/cards/Tech_Charts/Williams_F-14_Tomcat_Tech_Chart.pdf

#3 5 months ago

The backbox fuse.

#4 5 months ago

Post a pic of your power supply. Measure the 5 volts on the power supply.

#5 5 months ago

Is it this 2.5A fuse (in the center of the picture)?

F-14_Tomcat_F5_fuse (resized).jpg

#6 5 months ago

If yes, then you have 7 options.

The following 7 coils are listed for this fuse.

1) Ball shooter lane feeder (through).
2) Right eject
3) Center left eject
4) Center right eject
5) Ball popper (up-kicker)
6) Line of Death kickback (Jargov Kicker)
7) Rescue kickback (left outlane)

I once had the Jargov Kicker going bad.
The outlane kickback is also a big possibility.

#7 5 months ago

I've attached some pictures of the power supply.

Yes, that is the correct fuse I'm referring to.

My 5v measured at TP2 on the CPU board is 4.88.
My 12v measured at TP3/4 on the PSU is +14/-16.

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#8 5 months ago

I would assume that your game had reset due to low 5 volt. This may have caused one or more coils to lock on, burning the F-5 fuse. Someone has replaced the caps on the power supply in the past. They did not use the correct one for C-10, it should had been 18000 uf instead of 15000 uf. Can you test the voltage on IC1 pin 10.

4 months later
#9 27 days ago
Quoted from Inkochnito:

If yes, then you have 7 options.
The following 7 coils are listed for this fuse.
1) Ball shooter lane feeder (through).
2) Right eject
3) Center left eject
4) Center right eject
5) Ball popper (up-kicker)
6) Line of Death kickback (Jargov Kicker)
7) Rescue kickback (left outlane)
I once had the Jargov Kicker going bad.
The outlane kickback is also a big possibility.

So when checking the resistance of all the coils on the playfield, they're all around either 4 Ohms or 14 Ohms. I believe that 0 would indicate a short, correct? So therefore the coils are not locked and it could be a transistor problem?

Quoted from GRUMPY:

I would assume that your game had reset due to low 5 volt. This may have caused one or more coils to lock on, burning the F-5 fuse. Someone has replaced the caps on the power supply in the past. They did not use the correct one for C-10, it should had been 18000 uf instead of 15000 uf. Can you test the voltage on IC1 pin 10.

Thank you for noticing that! I will fix it. Is that related to this problem?

Dumb question, what/where is IC1?

#10 27 days ago
Quoted from hanasu:

Dumb question, what/where is IC1?

Check pin 10, should be about 6.45 volts DC.

ddd (resized).jpg
#11 25 days ago

Will do. What connections should I remove in order to test this voltage without sending 6V to the MPU?

#12 24 days ago

You could remove the large connector above the IC1 chip, but it's not necessary.

1 week later
#13 17 days ago

These are with the connector above IC1 disconnected.

IC1 pin 10 - 5.81v
PSU TP1 - 4.77v
TP3 - 14.19v
TP4 - -14.54v

I checked the two bridge rectifiers while I was in there. The top one measures 34.1v and the bottom 18.5v. Is it normal for there to be a difference?

#14 17 days ago

FYI - the coil resistance is only a "guide", never assume it is definitive.

Also, the resistance measured isn't connected to the phrase "coils locked".

"Coils locked on" means something is causing the coil to remain energized all the time such as a shorted driver transistor etc.

Also be aware that there is a diode across each coil and this can affect your reading.

You are correct thinking that 4~8 ohms is about right for a coil that is OK but again, that is only a guide.

The difference between 18000uf and 15000uf isn't going to be causing this issue. Electro caps are often 10% tolerance, sometimes worse - that could make the original 18000 cap actually be 15000 anyway.

I would ignore that cap for the moment, it won't be your problem.

#15 17 days ago
Quoted from hanasu:

IC1 pin 10 - 5.81v

This is low. This voltage goes to the base of Q-5. Q-5 regulates the 5 volt line. So this is why you have 4.77 volts instead of 5.00. Anything under 4.85 volts will cause the cpu to stop running, when this happens coils lock on burning fuses.

Either Q-5 or IC1 could be bad, but before you replace anything do one more test. Test the voltage on IC1 pin 12, should be 26.7 volts. If this voltage tests is good I would replace IC1. If this voltage is low then I would replace D-1, D-5, D-6, C-7 and C-8.

#16 16 days ago

IC1 pin 12 is 26.7v on the dot. Thanks

#17 12 days ago

Replaced IC1. Pin 10 is now about 6.05v which seems low still. Is the next step to replace D-1, D-5, D-6, C-7 and C-8 then? Or Q-5?

#18 11 days ago
Quoted from hanasu:

Replaced IC1. Pin 10 is now about 6.05v which seems low still. Is the next step to replace D-1, D-5, D-6, C-7 and C-8 then? Or Q-5?

What does the 5 volt read now?

#19 11 days ago

I don't know why I didn't check that as well, good question. TP1 is right at 4.99v. Is the pin 10 low voltage worrying at all?

#20 11 days ago
Quoted from hanasu:

TP1 is right at 4.99v.

4.99 volts is a lot better then 4.77 volts. Try playing some games, see what happens.

#21 10 days ago

The good news is we still have 5v right on at the MPU test point. Bad news is F5 still blows immediately.

#22 10 days ago
Quoted from hanasu:

The good news is we still have 5v right on at the MPU test point. Bad news is F5 still blows immediately.

Is this at power up or at start of game?

#23 10 days ago

Power up, about two seconds in.

#24 10 days ago

So you have one of the transistors turning on or shorted out for the high voltage coils that are controlled by snubber relays. In the pic below I have high lighted the transistors for all of the snubber relays. If you leave the fuse out at F5 fuse holder and turn on the game, one or more of the snubber relays will turn on and stay on. This is not correct and why the fuse is burning. An easy way to find out which snubber relay is on is to do a voltmeter test. If you set your meter to DC volts and place the black lead under the ground braid, then use the red lead to test the transistors I highlighted. Touch the red lead to the metal tab of the TIP 122 transistors and you should get a voltage reading of @ 32 volts. The metal tab is the same as the collector lead of the transistor. If you find a transistor that reads zero volts, this will be your problem. Let me know what you find.

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#25 8 days ago

I have about 33-34 volts at all of those. The backbox siren lights and one of the relays were coming on intermittently while I was testing if that's a clue. All other fuses still check good.

#26 6 days ago

New info: displays read "U10 PI Failure". Not sure if that's related but I can swap it with U9 to test, correct? Looks like it was socketed by previous owner so not sure if that means I should look elsewhere on the board for a hacky fix of some sort.

It looks like this might be related to PSU caps, which seems likely given we've been working on it earlier.

https://pinside.com/pinball/forum/topic/u10-pia-failure-where-to-find-and-replacement-repair-advice

I'll recap the PSU as preventative maintenance anyways. Anything else I should look at while I wait for caps to arrive?

#27 6 days ago
Quoted from hanasu:

I have about 33-34 volts at all of those. The backbox siren lights and one of the relays were coming on intermittently while I was testing if that's a clue. All other fuses still check good.

Repeat same test but check Q-77 and Q-79 this time. These 2 are for the divertor ramp. Some games have these coils wired for 50 volts instead of 25 volts so if they are on 50 volts they will be on the same F5 fuse.

#28 6 days ago

Those are the ones! Both read shorted.

#29 6 days ago

Houston we have a problem!

Ok go under the play field and cut off the purple/yellow wires from the two coils and cap with a wire nut. Replace the fuse F5 with a 2.5 amp slow blow fuse. Power on the machine and start a game. Everything but those two coils should be working now. Let me know what happens.

#30 4 days ago

So when removing the 'doubled' wire from the coil that controls the top diverter, the wire that was supposed to connect to the rest of the chain basically just fell off. It looks like it was squeezed between something and broke. So now the only thing that purple/yellow wire is connected to is the coil that fires the left eject near the pop bumper. With nothing on the other end of the diverters. I have no 'second wire' to wire nut it together with. I'm trying to trace it but it's not really apparent where this goes. I'll keep looking around.

#31 4 days ago

I also just noticed that there is a group that contains four wires. Two of them appear to be the grounds (?) for both diverter coils, which are connected properly. However the other two are jumped together? With a quick look it doesn't seem like there's a component that is obviously missing them. They are both red/white. Hopefully the pictures are sufficient.

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#32 4 days ago

So for the following that are all listed above for this fuse, here are the wire colors that are currently attached to the coils:

1) Ball shooter lane feeder (trough) - two solid purple (not purple/yellow??), one purple/red
2) Right eject - two purple/yellow, one gray/green
3) Center left eject - two purple/yellow, one green/blue
4) Center right eject - two purple/yellow, one solid yellow
5) Ball popper (up-kicker) - two purple/yellow, one solid grey
6) Line of Death kickback (Yagov Kicker) - seems like I need to take the wireforms off so I'll wait until it's necessary to check
7) Rescue kickback (left outlane) - two purple/yellow, one brown/white

Diverters after removing purple/yellow wires:
1) Top - one blue/green
2) Bottom - one blue/black

#33 4 days ago
Quoted from GRUMPY:

Some games have these coils wired for 50 volts instead of 25 volts so if they are on 50 volts they will be on the same F5 fuse.

So like I said earlier some games are 50 volt (purple/yellow) and some games are 25 volts (red/white). I have always suggested to people to use the red/white wires to reduce the stress on the transistors. But in saying this you need to keep the purple/yellow chain connected and insulated so the coils down the line still have power. You can remove the purple/yellow wire that is connected to both divertor coils and use it to splice the broken purple/yellow wire.
For the low voltage to work, the divertors need to work smoothly, the pivot points need to be clean and oiled, clean coil sleeves and polished plungers. There is a service bulletin you should look over too.

https://www.ipdb.org/files/804/Williams_1987_F_14_Tomcat_Service_Bulletin_no_number_undated_to_resolve_binding_diverter_gate_assembly.pdf

Also you still have issues on the CPU board that need to be fixed. After you get the purple /yellow wire fixed, then run a coil test to ensure every coil works but the 2 divertor coils.

#34 3 days ago

Not sure I'm understanding well enough, or maybe not explaining the situation the right way. Are you saying that there should be two yellow/purple wires to connect together with the wire nut?

If so, there's no way to keep the chain connected. The only purple/yellow wire I have that's not wired to anything comes off the left center eject coil. That's it. There's no other end to connect to. Nothing comes off of the diverter coils. Are you saying to just cap that? If I do F5 still blows immediately.

I'm not sure what's supposed to be down the line either before or after this component. It looks like the coil before the left center eject is the outlane kickback if I've traced it correctly. I don't know where it's supposed to go after that.

I can't seem to get into the coil test because of the PIA error message. I have no blanking light on the MPU which I assume is related to that.

I'll take all the playfield apart since the only thing I can't see is the Yagov kicker and try to go from there. EDIT: Yagov looks fine.

Thanks again so much for all the help this far! I would like to be able to find these sort of things out myself, but I don't really know where to look. Is there a coil ordering list or something like there is for the switch matrix?

Hey there! Got a moment?

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