(Topic ID: 284690)

Gulfstream went full Exorcist & blew 110v fuse

By Mikala

9 months ago


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  • 23 posts
  • 6 Pinsiders participating
  • Latest reply 9 months ago by Tuukka
  • Topic is favorited by 1 Pinsider

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3E66447F-1321-4FF5-B049-82D025E70109 (resized).png
Rectifier simulation (resized).jpg
Gulfstream rectifier short (resized).jpg
21482DC4-40D3-479C-A19C-FF3E63118431 (resized).jpeg
25E999BA-0674-4E69-89AA-E1CA10108081 (resized).jpeg

#1 9 months ago

I did a full restoration on this Gulfstream five years ago. Has played perfectly ever since. In the middle of a game the other night, the playfield and backbox lights all started flashing, and not necessarily in sync. Loud buzzing from all over the machine. I quickly flipped the power off and gave it a rest. Flipped it back on, hit the left flipper button, GI came on, no problems. I hit the start button, game reset then all heck broke loose again, then the 110 fuse blew. I have given the machine a full go over twice, once sober. Have not yet found any loose wires or broken parts anywhere yet. I am going to get into this today. If anyone has any suggestions, I would appreciate it.

I’m going to start with isolating the playfield and backbox first and see what happens.

#2 9 months ago
Quoted from Mikala:

I have given the machine a full go over twice, once sober.

That, and the subject line, are quite probably the funniest things I've ever read here. Not to make light of the sitch, by any means ...

I'm thinking short ... somewhere.

#3 9 months ago

I have narrowed it down to this 18 pin Jones plug from the playfield. If I leave it out, game reset fine. Once I plug it in, the 110v fuse blows. Now I just have to figure out what these all go to.

25E999BA-0674-4E69-89AA-E1CA10108081 (resized).jpeg
#4 9 months ago

Do you think Im looking in the right direction? I’m going to check these three relays and two reset banks.

21482DC4-40D3-479C-A19C-FF3E63118431 (resized).jpeg

#5 9 months ago

Take the 1.6 amp slo blo fuse out and see what happens

#6 9 months ago

With the slo-blow removed, it does the same thing. Ball count stepper starts to count balls up to 3, loud unusual buzzing on and off as it steps. I kill the power before it goes to end. If I let it go to end, it will blow 110 fuse.

So is it safe to rule out the two reset banks?

#7 9 months ago

Seems like it! You could also try to remove the 10 amp bridge rectifier fuse in case the bumpers or flippers are involved.

#8 9 months ago

Look for a coil that stays energized but drops out when you cut the power.

#9 9 months ago
Quoted from dr_nybble:

Seems like it! You could also try to remove the 10 amp bridge rectifier fuse in case the bumpers or flippers are involved.

Tested, no different.

Also triple checked three suspected relays. 3-in line, special, & coin. All look fine.

#10 9 months ago
Quoted from dr_nybble:

Look for a coil that stays energized but drops out when you cut the power.

This is a little difficult for this reason.
With PF up, I hit the start button, machine resets and then goes black/off, like a slam tilt was activated. Left flipper brings it back to life.
PF up, I hold the ball trough switch closed, emulating a ball in there, I hit the start button, ball count unit starts to count up, loud buzzing between the count up, if I let it finish, it will blow fuse. Happens so fast, hard to see what’s going on with relays. I’ll switch to 5 ball and see if that gives me more time.

#11 9 months ago

You can put the score motor into service position and turn it by hand.

You can also try slo-mo video recording on your phone.

#12 9 months ago
Quoted from dr_nybble:

You can put the score motor into service position and turn it by hand.
You can also try slo-mo video recording on your phone.

Unfortunately, this machine is before service switches were installed.

#13 9 months ago

There is a jack you can move so the score motor is in service position.

Page 7 of the instruction manual.

#14 9 months ago
Quoted from dr_nybble:

There is a jack you can move so the score motor is in service position.

Just found it, it was not in normal place.

#15 9 months ago

I would look at score motor switches 1b and 2b. When you removed the 1.6 amp slow-blow fuse it should have removed everything from the 110 side. Since it is still blowing, maybe one of the other switches at score motor #1 or #2 are contacting the 110 volt wiring. Sending raw 110 volts into one or more your 25v coils.

#16 9 months ago

A shorted DC bumper rectifier might be the problem. Its fuse is on the DC side, and will not help if rectifier is internally shorted. Try removing one of the AC leads going to rectifier.

Since probably only one of the 4 diodes inside the rectifier is shorted, it will short only one half of the AC sinewave input, causing DC current to flow through transformer 24VAC secondary, saturating the transformer core. That is why the 110V primary fuse blows before the 24V secondary fuse.

#17 9 months ago

Thank you, I’ll be looking into both of these suggestions tomorrow.

#18 9 months ago
Quoted from Tuukka:

A shorted DC bumper rectifier might be the problem. Its fuse is on the DC side, and will not help if rectifier is internally shorted. Try removing one of the AC leads going to rectifier.
Since probably only one of the 4 diodes inside the rectifier is shorted, it will short only one half of the AC sinewave input, causing DC current to flow through transformer 24VAC secondary, saturating the transformer core. That is why the 110V primary fuse blows before the 24V secondary fuse.

G.. I love you guys and Pinside. It was the bridge rectifier. I replaced it and I am up and playing like new. Thank you Tuukka!!!

#19 9 months ago
Quoted from Tuukka:

Since probably only one of the 4 diodes inside the rectifier is shorted, it will short only one half of the AC sinewave input, causing DC current to flow through transformer 24VAC secondary, saturating the transformer core. That is why the 110V primary fuse blows before the 24V secondary fuse.

Very cool Tuukka . I'd like to understand this a little better so I grabbed the schematic:
Gulfstream rectifier short (resized).jpg
If I understand correctly one of the rectifier diodes has shorted so that it conducts presumably in both directions rather than the single direction it is intended to. If the red diode for example were shorted then the rectified DC output voltage on the -J- or jumper wire would short to the AC input voltage on the -RED- wire and eventually find its way back into the 24 volt secondary transformer winding. The extra DC current apparently isn't enough to blow the 15 amp fuse on the 24 volt circuit.

The steady DC current flowing through the 24 volt secondary winding would create a constant magnetic field in the transformer core that would combine with the normal alternating magnetic field created by the 110 volt AC input current in the core. The combined magnetic fields saturate the transformer core at some point. A saturated core essentially means that the core cannot support any more magnetic field. Once the core is saturated any current applied to the core doesn't go towards increasing the magnetic field but instead gets wasted as heat.

Once the core saturates the input 110 volt current isn't doing the work of creating more magnetic field. Does that make the saturated transformer core look to the 110 volt supply like a lower resistance (or actually lower impedance) load which draws more current which in turn blows the 110 volt 10 amp fuse?

/Mark

#20 9 months ago

Yes Mark, you got it absolutely right!

Normally the transformer core has large inductance, reducing the power it draws from primary input, even though its resistance is low. Inductance causes the primary current and voltage to be in different phase regarding to each other, and thus the apparent power is low. That's why a transformer without load stays cool.

Now, if one diode gets shorted, that means one half of AC input gets shorted via the other diode in series with the shorted one, while the other AC half is still blocked by the other diodes. Because current then flows only during one half, that effectively means that current only flows one way through the transformer secondary. Each half-wave magnetizes the core a little more, and after a while it can't be magnetized any further - it is saturated. Then its inductance drops to much smaller value, allowing primary current to flow almost in phase with the primary voltage, making the power consumed in primary much larger - and blowing the primary fuse.

This is also why a half-wave rectified power supply needs to have a much larger transformer than what would be expected from the load current - it needs to withstand the DC current without getting into saturation.

#21 9 months ago

There is a great online circuit simulator that can demonstrate this better than I can explain it but here are two screen shots:
Rectifier simulation (resized).jpg
On the left is a simplified version of the rectifier circuit with a 60 Hz voltage source representing the transformer and a 100 ohm resistor representing the various coils (e.g. pop bumpers) using the DC supply. Along the bottom you can see that the current through the voltage source is less than an amp and the voltage across the load is fully rectified. (Ignore the 1 ohm resistor on the bottom which was added to avoid a dead short in the simulation.)

On the right side the lower right diode of the rectifier is replaced by a wire to represent the short. In this case the circuit looks like the original circuit half of the time. But the other half of the time all of the current flows through the upper right diode of the rectifier, then down through the short on the lower right and back out to the voltage source. No voltage is generated on the output so the DC is only half rectified. The current through the voltage source is measured in amps, not in milliamps.

To see these animations and experiment with the circuit try these links:

Normal rectifier: https://tinyurl.com/y84jb78b
Damaged rectifier: https://tinyurl.com/y7kbqljs

Then click on the Run/Stop button in the upper right to start or stop the animation.

BTW, I wonder if the topic title could be revised to make the shorted rectifier discussion easier to find in the future.

#22 9 months ago

@ Tuukka- I used a rectifier from my parts box, but I would like to grab a couple extra for future. Which of these are the correct replacement? The 100v or the 400v?

3E66447F-1321-4FF5-B049-82D025E70109 (resized).png
#23 9 months ago

Both are fine, since the voltage is only 24V, but get the 400V one, so it could be used in higher voltage circuits also if needed.

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