G07 issue...

[modessitt]

G07 issue...FIXED!

EDIT*** See last post for resolution ***

I have an unknown history G07 19" chassis. Has new-style flyback. I've put in new caps, and checked the HOT and VR but they seemed okay. Touched up cold solder joints but it was still dead. B+ is running about 160vdc.

Did some more solder work and stuff, and had a B+ of 135vdc.

Swapped out the VR and had a B+ of about 124vdc. HV is present. Cool. I hook up the chassis and find I have no vertical deflection. Okay, that should be easy to fix.

I find FR401 is open. I replace it, and upon power up it heats up and goes open again. I replace it with a 5W version this time, and it now stays good, but now R420 burns up.

I replaced both vertical deflection transistors and R420, and burned up R420 again. I replaced R420 with a 1W version so I'd have more time to troubleshoot before it burned up. Eventually I determined that D401 was open. Got a false reading in circuit, but no readings out of circuit. Replaced D401 and no more burning parts.

BUT - my B+ is back to 160vdc again. If I take D401 out, it goes down to 124vdc. WTF?

If I pull X701, it works, but b+ is still way up at 153vdc. I've gone over the entire power and vertical sections, replaced all the caps again, and measured every single resistor, diode, and transistor - and I'm not finding much of anything. I did find R905 to be an 8.2k-ohm resistor, when the schematic calls for an 18k-ohm resistor, but changing it to 18k didn't make any difference.

Anybody for any bright ideas?

 

[salmart]

Did you check R908?

 

[modessitt]

Yes.

I mentioned in another post (and should mention here) that I've swapped every single 900 part with one from a known working chassis, with no change...

 

[KenLayton]

Isolate the power supply section's output and connect a 60 watt incandescent light bulb to the output.

Now see what the B+ reading is. If normal then the power supply section is good and you can concentrate on other sections of the monitor. If still wrong voltages, then trouble is in power supply.

 

[modessitt]

Ken,

I know I've seen the instructions for doing this somewhere, but I can't find them now. Got a link?

 

[KenLayton]

Looking at the schematic, You'd cut the foil trace after resistor R908 before it connects to FR401.

The output of the power supply is at R908 before it goes to the rest of the monitor. Connect a 60 watt light bulb from there to ground.

 

[modessitt]

Well, while I was waiting I did some more checking and found that at some point when dealing with the burning parts in the vertical section, I lost the VR. Replaced it and now have a picture, but it's not perfect. B+ is stuck at 131 and will not adjust. The picture shakes on the left side of the screen (bottom horizontally), and it gets worse and expands to more of the picture if the brightness is turned up.

Now what?

 

[KenLayton]

When the B+ reg went out, maybe X901, X902 or D905 (zener) went with it.

I recently had trouble with a G07 that the B+ was too low. Stuck at 100 volts and would not adjust. Turns out that transistor X901 was open. You might have X901 shorted or leaky.

 

[modessitt]

Leaky is a possibility.

I now have a B+ of 121vdc. Still have the squiggles. It gets MUCH worse when the brightness is turned up, and you can start to hear a bit of a squeal when it get turned up too far (but not from the flyback).

I'm thinking I have some AC bleedthrough. Measuring between the frame and the case of the HOT, I'm reading about 500vac. I don't think I should be, although I've never measured AC there before. I swapped out the filter cap a couple times during the repair process. I guess I should go check to see if something around there is letting AC through...

 

[KenLayton]

Never meter or measure the horizontal output transistor when it's working! Very dangerous.

Is the B+ adjusting? Won't it go lower than 121?

 

[modessitt]

Yes, it's adjusting now, but I get the squiggling even with it down to 105.

Just swapped out X901, X902, and the filter cap, and still have it. I also am not reading any AC above 0.5 volts coming out of the rectifying diodes or the filter cap.

Here's a pic of the issue. RF shield is on, and ground wire is connected. It does it regardless of whether a video signal is applied:

 

[KenLayton]

Were the two non polar electrolytics replaced?

Have any other electrolytics been replaced? If so did they get damaged by the bad regulator?

 

[modessitt]

Were the two non polar electrolytics replaced?

Have any other electrolytics been replaced? If so did they get damaged by the bad regulator?

See, this is why monitors can suck!

It's fixed, but let me walk through what fixed it.

1) I hadn't replaced the non-polarized caps, so I did that - no change.
2) Went ahead and replaced all other caps (again) - no change.
3) Replaced IC501 - no change.
4) Replaced X301 and X305 (just in case it was in the hor. sync) - no change.
5) Replace the HOT (again) - no change.

So - I'm sitting there thinking about what could be the problem. With it on, I gently tug on various wires to see if it clears up. I've done this before and didn't have any change. However, this time I moved the anode wire side ways while tugging a cable and the problem went away. After making sure the wire I tugged wasn't the culprit, I found that moving the anode wire farther away from the yoke made everything perfect. Shut the monitor off, rotated the anode cup so that the anode wire stayed away from the tube, fired it up, and have a perfect picture!

All this shit because of something stupid like that. Oh well, at least it's fixed now.

Thanks for the ideas, Ken...

 

[YellowDog]

Sorry, I wish I had seen this thread earlier. The squiggles are arcing inside the anode cup on the tube. There must have been something that got into the anode cup. In my case, it was a sliver of glass that the clip got caught on. I always give the anode clip an extra twist before I let the rubber cap down on the tube. Just in case.

ken