G08 popping fuses

SuperBee4406

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I have a G08 monitor that blows the fuses at locations F400 and F401. I found a burnt diode at location D407, replaced it and the fuses still pop. I did check the 2N6259 transistors, and no shorts there. Anybody have any suggestions on where to look next?
 
I have a G08 monitor that blows the fuses at locations F400 and F401. I found a burnt diode at location D407, replaced it and the fuses still pop. I did check the 2N6259 transistors, and no shorts there. Anybody have any suggestions on where to look next?

D407 was bad, but D406 was not? Both are part of a simpler doubler circuit. The only thing this output feeds is the 100V regulator on the HV board. You can see if this is shorted by removing the 10 pin connector on the HV cage. If one or both fuses still blow, you have another problem.

Actually, I think you do because a short in the 100V regulator should only cause F400 to blow.

If you're sure the 6259's are good, unplug their connectors from the paddle boards. There is no harm in running the monitor with them or the yoke unplugged for testing.
There are several driver transistors in each deflection channel with tall copper heat sinks. You've got +/-60VDC on these pairs. If they wind up touching, they will blow the fuses. If they have touched in the past, these transistors may be shot also.

Some of these chassis use the upper tab on these TO220 transistors as a signal path. One of the legs may be clipped and covered with silicon to prevent a short. Leaving only two legs to support them in addition to their tall size makes them prone to getting bent and shorting out somewhere.

If the power transistors have failed in the past, they may have blown some resistors on the little paddle boards. Just replacing the power transistors won't remove the problem.

Overall help:
There is a hack you can do to the main transformer that will lower the voltage supplied to the monitor that will let it run with less stress. It has worked nicely for me several times.
Look it up on the web- it simply involves moving the AC input lines from two inputs on the transformer to two different lugs. Quick disconnect spade connectors. No tools needed.


These monitors can be challenging to work on, but are straightforward in their operation. It is quite rewarding to get a zapped one going again.


Good luck-
Kerry
 
Thanks for the reply.

After reading what you said I went back and checked several things. I found a burnt resistor on one of the paddle boards(the smaller one, soldered to the trace). I checked the copper tabs to make sure they weren't touching. I then replaced the small reistor I found burnt, and tried to power the mointor, and pop, the larger resistor that is next to the smaller one I just replaced popped, but the main fuses are still intact. I checked the transistor that were hooked to that paddle board, and they are both shot(Dam, $5 a pop for those). I replaced the bad transistors, and did checks for shorts, and everything checks out. So now I need to find a replacement resistor and try again. But its looking better....
 
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The large resistor on the paddle board, does someone know the value of it, the paddle board closer to you, when looking in from the back of the monitor?

Are the large resistors on both paddle boards the same value, also the small
resistors?
 
Yes, both paddle boards are the same with the same valued components.

The big resistor 1W(?) is shown in the schematic as a .16 ohm resistor.
On a couple of boards I have laying around here, I have a .15, a .15, and a .20:

red, black, silver

brown, green, silver

and one just light blue marked .15

The smaller resistor is just a 100 ohm. Note the little pieces of teflon tubing that prevent the hacked-in resistors from shorting to traces on the paddle board.

Fun stuff.

K
 
Update:

Repaired paddle board. Rechecked for shorts on the 2N6259 transistors.

I then powered on the monitor and more zapping occured, but it was in the HV cage area. Removed the cage and examined the regulator board and found two of the transistors 2n6558,
what I would calls wings touching, and found that the TIP47 transistor has burn marks on it.

So now I need to find a TIP47.....
 
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The 'wings' are electrically connected to one of the transistor's terminals, in this case, the collectors.

Yeah- they kind of stand up there together, three in a row. Waiting to get bent and flexed and touching their brethren..

Even though the TIP47 has some marks, did you bend the three transistors back up and seperate them? I would have done that and tried it out :)

Sounds like you're getting closer.

When you replace that, you'll be able to hear if you're getting high voltage or not. If not, try pushing/pulling/flexing the 10 pin connector to the HV cage. Those solder joints are notorious for cracking.
 
Update:

Success!! I achieved deflection chatter!! Monitor is not smoking or blowing fuses anymore!!

Its scary to think about how easy it is for this monitor to have components touch and create a light show.

Game is still playing blind, and thats my next step.
 
Now that I turn on the monitor without blowing fuses, I can further toubleshoot the monitor.

I have deflection chatter, no picture. I checked the voltage at the HV cage, and
here is what I got.

Y pin: 1 to 4 volts dc
x pin: voltage jumps all over the place no definite reading
-9.1 pin: checks ok
+9.1 pin: 8.8 volts
Gnd: -
Gnd (heater): -
+6.3 (heater): no reading
126 volt pin: reading jumps all over the place

There is no neck glow.
 
The 126V pin is an input to the HV board. It comes from the main board, off the circuit where you first replaced a diode. I think the only other two components in that circuit are another diode and a capacitor.

The capacitor could stand to be replaced with a higher voltage rating.

You should be able to unplug the HV cage and measure the +126V line inside the connector. If it is still jumping, replace the components in that +126V circuit.

If it is steady, you need to check out the little 100V regulator board where those components were touching before. Something could be shot there, loading down the +126V.

The regulated 100V is needed for the HV transformer to work.

Keep at it.

Kerry
 
I am going over the monitor. The white wire that comes off the focus adjustment and goes to the neck board, it getting really short from be clipped and resoldered several times, I need to add length
to that, but its not regular wire. Its some kind of double insulated plastic wire, is there a way to add length to that wire? I need to add about 3 inches of length and splice it onto the white wire.
The cap in the 120v circuit you were talking about is rated at 1000uf 50v, it came in the Bob Roberts cap kit for this monitor.
 
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Quit clipping that wire.

Either unsolder it from the focus assembly where it is covered with the rubber boot, or better yet-

Cut it in the middle and put an insulated bullet connector on it.
 
The last person to work on this monitor, cut the majority of the length off the wire, I cut it once to repair it, when it broke off on its own.

I was reading that the spot killer will cut power to the HV cage if the board set is not sending proper signal, and I don't know if my board set is working properly. I am trying to find someone to look at the boards for me.
 
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I GOT THE MONITOR TO WORK!!!!

I found a bad trace on the regulator board. Repaired it. And bang, we got video.

Game still wont coin up or play any sounds. But I am still super pyched to get the
monitor working again.

For the wire problem I relocated the focus adjustment up a little so the wire reaches.
 

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I have been watching the attrach mode, since the game still wont coin up.
When you get action on the screen, like a shot being fired, I notice the picture
expands and then retracks. Is this a setting problem, or is this normal?
 
The additional vectors and/or brightness during these 'action' screens suck a little more current overall and may affect the HV regulation.

Turn down the brightness a little and possibly shrink the screen a little.

Since you've already gone through the monitor, I don't know what components could be replaced to help this. Maybe the giant caps, but they're kind of pricey.

Kerry
 
Brightness is now all the way down, now.

Found another bad trace. It was on the little board that goes in between the video cable from the game and the monitor. Fixed the trace and now all the colors are present.

I next need to adjustment the XY on the boards, to center the picture.
 
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