(Topic ID: 156664)

TECH: WPC blowing F115

By ArcadeUpkeep

5 years ago


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  • 13 posts
  • 7 Pinsiders participating
  • Latest reply 5 years ago by zaza
  • Topic is favorited by 2 Pinsiders

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#1 5 years ago

Working on TAF and could use a little help. It started out as the normal "check fuses 114/115" error and I've been tracking from there. What I've found is that fuse F114 is fine, F115 is blowing out. When I meter it there's a pull of about 1.7 amps on the fuse, obviously blowing the 3/4 amp fuse. If I disconnect J210, the power going to the WPC CPU board, the amperage draw drops to nearly nothing. I'd normally think it's a shorted switch somewhere but I've disconnected everything from the CPU board, all ribbon cables and switch connectors and just plug in J210 and the amperage jumps back up to 1.7 amps, blowing F115. So there must be a problem on the CPU board, any thoughts on what commonly goes on them to cause this symptom? Or better yet, tell me I'm wrong and I missed something stupid!

Thanks Pinside!
Brandon

#2 5 years ago

From the wiki:

Short on the MPU causing F115 to blow
There is one more way for the 12VDC power to be lost and for F115 to blow. A shorted IC on the MPU that uses 12VDC can cause F115 to blow. To help isolate the problem to the MPU, replace F115, disconnect power going to the MPU at J210, and turn power to the game on. If the fuse does not blow, the problem is almost definitely on the MPU board. Any of the LM339s (theoretically) or the ULN2803 (definitely) can fail and short 12V to ground, causing F115 to blow.

#3 5 years ago
Quoted from snakesnsparklers:

To help isolate the problem to the MPU, replace F115, disconnect power going to the MPU at J210, and turn power to the game on. If the fuse does not blow, the problem is almost definitely on the MPU board.

That's exactly what I did. So your saying the 2803s are more likely to fail?

#4 5 years ago
Quoted from ArcadeUpkeep:

So your saying the 2803s are more likely to fail?

Both fail quite often, hard to isolate to one chip making troubleshooting a pain.

#5 5 years ago
Quoted from ArcadeUpkeep:

When I meter it there's a pull of about 1.7 amps on the fuse, obviously blowing the 3/4 amp fuse.

When using the multimeter to measure 'current' , it effectively creates a new path in the circuit -overruling fuse F115- and generates a maximum pull from the 7812 regulator and give huge stress to the already blown 2803.
I would advice NEVER to use this method to locate a problem in the circuit.
With DMM set to 'resistance' and machine 'OFF' it is just as easy to find the problem.

RHAAaaaahh_(resized).JPG

#6 5 years ago
Quoted from zaza:

When using the multimeter to measure 'current' , it effectively creates a new path in the circuit

I definitely agree that measuring current as you described is a problem. Additionally, it wouldn't work if the fuse was intact.

To measure current, you should lift one end of the fuse, and put the multimeter between the fuse and the fuse clip. That leaves the fuse in the circuit.

#7 5 years ago
Quoted from mot:

I definitely agree that measuring current as you described is a problem. Additionally, it wouldn't work if the fuse was intact.
To measure current, you should lift one end of the fuse, and put the multimeter between the fuse and the fuse clip. That leaves the fuse in the circuit.

I think you missed his point. You should not measure current ever by bypassing the fuse as you no longer have overcurrent protection and a short can easily blow more components. It's the same problem whether you measure across an installed blown fuse or if you pull one end of a good fuse out of the holder.

#8 5 years ago

The 2803 is such a common failure that WMS started socketing it from the factory on later boards. I socket it on CPU repairs if I get a board in that wasn't socketed from the factory.

If you aren't comfortable with troubleshooting the CPU problem, I repair these - but yours could already be socketed - it's worth checking!

#9 5 years ago

I suppose I should have explained my setup before posting this. I have an in-line fuse on my meter lead. I put the fuse in, set the meter to grab peak amperage and measure across the fuse holder. The circuit was still protected, in this case there was a max 1.7amp draw before the fuse blew. But yeah zaza, in your case there would be no protection.

And thanks John, 2803 was the issue and it's now socketed. I didn't realize they went bad that often!

#10 5 years ago

Nice fix.

Just to get back on your fuse thingy and the fact that the circuit 'is still protected while measuring with a multimeter'. It's not. Well not with the correct fuse anyway. There's a reason there's a 0,75 amp fuse there. There should never go anymore than that amount of amps in the circuit. With your fused multimeter, you might be getting an accurate measurement of just 'how much' extra juice goes into the circuit, but the fuse in that meter is probably a 10A. Theoretically, the short circuit could have been 10 amps then, and it could have made the damages even more.

#11 5 years ago

It's an in line fuse, I put the correct fuse in it for the application. In this case a 0.75 amp fuse. The circuit is protected as it should be. There is no increased chance of damage to the circuit.

#12 5 years ago

Oh shoot, missed that you put in the correct fuse. Good thinking that way.

#13 5 years ago
Quoted from ArcadeUpkeep:

It's an in line fuse, I put the correct fuse in it for the application. In this case a 0.75 amp fuse. The circuit is protected as it should be. There is no increased chance of damage to the circuit.

picture update with 3/4A fuse inline.
075_inlinefuse1.jpg

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