Common G07-CBO (and related) Issues

Peale

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We've got topics for other monitors, but not this one.

I'll start by saying: if your monitor is all original, when you're replacing the capacitors, REPLACE THE FLYBACK AT THE SAME TIME. Without question. After 30 years, they have a high failure rate.
 
If the monitor is dead (or you suspect a flyback issue of any sort), discharge not only the tube at the anode, but also the larger cap(s) on the board to prevent a nasty surprise.

If the fuse is blown, you need to replace the flyback and HOT, absolutely no questions about it. You might want to get the kit that Bob Roberts sells. Look for the following in the Flyback section of his Parts page:
GO7 Flyback Repair Kit
G07 Super Repair Kit
G07 Deluxe Repair Kit

Almost every G07 I see has a bad (or failing, miserably cracked and rickety, or just plain stuck) width coil, so the Super Repair kit is really nice to have. Even if you don't use the width coil on the current monitor, then you have one on-hand for next time.

Also, the potentiometers for B+ on the G07 are a real oddball size and are generally unavailable. It seems that without fail, the one pot I continually find that's bad is this B+ adjustment pot (of course). Bob Roberts has a great site with suggestions for replacements (I can NEVER find this link when I want it): http://arcadecontrols.com/BBBB/g07pot.html

These G07 monitors are excellent, and are well worth repairing.
 
Standard practice on a GO7 is to reflow the input headers, meter FR901 & 908, check FR401 for rotted legs. Also check R303, 306, 314, 317 and verify they are 390Ω because some had wrong value from the factory.
 
Not an issue, but: how to read the B+ on a G07.

Set your meter to DC voltage. If it doesn't autorange, set it to 200VDC.

Take your black lead, use one of the holes in the frame to keep your probe in place. Or use your hand. But the black lead goes to the frame.

While you're facing the back of the monitor, the red lead goes to the ceramic resistor on the left, the one that's bolted to the frame. Meter from the leg of the resistor that is closest to the tube.
 
I got some great information from a tech related to G07 repair. I'm pasting them, below.


"pin 11 of IC501 is 12v for IC. pin 10 is horizontal drive output from IC.

X501 is horizontal driver and should have 50 - 70 vdc at collector.

if it is up near 140 vdc, you are probably not getting drive from IC501.

replace IC501 in that case. They have been known to fail.

make sure T501 is not damaged, open on one side, or bad connection to base of HO transistor."

Some stuff that I knew, some stuff that I did not, but all good information that should be shared.
 
Partial collapse, simply put:
When x401 fails, there will be no right side of the screen.....
When x4202 fails, there will be no left side of the screen......
Set B+ to 120vDC like this
 

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Here's an issue, I have now seen twice. No picture, no raster, I can hear high voltage, B+ is correct. Everything checks out fine, except one thing......the anode voltage is approximately half what it is supposed to be (9000 volts, give or take).

Solution: someone had replaced the HOT, and reversed the two wires that get soldered to it's legs (basically, installed it backwards).

Edward
 
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