G07-CBO Over Voltage Shutdown

HMOON

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I recently updated a few components on one of my G07-CB0 Chassis. I recapped the chassis, replaced the flyback, hot and regulator. The chassis worked great for a few minutes and then went into over voltage shutdown. I don't have the schematic in front of me, but I think it is x701 that is on.

Here is what I know:

All fuses are good, X04 is not shorted, B+ is at 153V. Hot Collector is at 160V, base is at 145V and emitter is at 153V. Isn't B+ derived from the HOT Base - Vbe (approx 120.6V -.6V)? What would cause the Emitter to be above the Base in this circuit?

Any help would be appreciated..
 
That B+ is high, it should be about 120V and there is an adjustment pot for it behind the other vertical pots. Have you tried to adjust the B+ yet? Where are you taking your B+ voltage reading from? Is it the same location that Bob Roberts points out on his page?

Luke
 
Luke,

Adjusting the B+ has no affect. I even measured the pot and verified it is the correct value and is changing value when adjusting. There is a fault in the chassis, there is no question about it. B+ was originally the correct voltage or it would never have come on. I'm just looking to find out if there is a specific component I should target, if this is a common component failure for this chassis when it goes into HV shutdown.
 
look for cold solder joints and reflow them. got my eye on the voltage regulator being bad. any burnt/smoked resistors?
 
X04 is the regulator that splattergatz is referring to, it controls the B+ rail. The only other semiconductors in the regulation circuit are X901 and X902 and D905, but I have never had to change them out. I have changed many of the X04 regulators and I know you have to make sure the plastic white insulators are installed and that the regulator isn't shorting a leg to the chassis somewhere.

Luke
 
Luke,

Thanks..I will have to take a look tomorrow and actually probe around a bit and. I'm sure it is something simple. I will post what I find.
 
Pull X701 and fire it up. If it works, then you definitely have a problem in the PS section (all the 900's). If it doesn't, then your problem could be elsewhere...
 
I probed around last night again and found it not to be the regulator X04. I will try pulling 701 verify the monitor comes back on. I will also try the filter cap.

Thanks for the help. I will respond with results shortly.
 
Update

I went home over lunch today to test and replace the main filter cap. It was a little low in value 450uF, and replaced it with another cap from another chassis (don't have a new one on hand) 580uF. The problem is still there. I then removed X701 and the monitor still will not come on.

After replacing the cap the voltage decreased from 172V to about 164V. So the cap was definately on its last leg.

I probed around in the power supply section and found the following:

X902E = 6.8V
X902B = 7.4V
X902C = 6.9V? Supposed to be 71V.

Transistor measures good out of circuit, replaced anyway and achieve the same results.

Pulled X901 and measured and it also looks good but did not have a replacement.

FR901 measures low but is not open?


I am going to order some parts to eliminate any suspect parts:

D901-904
New X04 Regulator
New 600uF 200V Filter Cap.


Any other suggestions?
 
I think that 71V is a misprint and shoud read 7.1, because I've seen perfectly working G07's measure the same as what you've got and still work fine.

On your B+ measurement, what is the reading on both sides of the big white resistor, and is it measuring 220-ohms?
 
Modessitt,

The resistor across the Vce of X04 measures 220 Ohms. The voltages on X04 are as follows:

B1-X04E 151V
B2-X04B 143C
B3-X04C 163V
 
So, you have 163 on the side of the resistor closest to you, and 143 on the opposite side?
 
Thought....What if there was no load on the rectifier circuit and the regulator is just flying up to a "peak" voltage provided by the 120Vac to DC circuit (bridge and filter cap). I haven't checked, but what if FR401 was open, wouldn't that look like a no load conditon?
 
Well it has been a while, but I finally had a chance to try and solve the problem. I probed around a bit and after changing IC501 the problem was still there. Took a closer look at T501 and it looked to be soldered pretty well but I reflowed it anyway. Then I measured T501 and found the primary winding open. AHHHHHHHHHH. Replaced T501 and we are back in business. Thanks for all your help. I appreciate it all..........
 
Having the exact same problem. Cap kit. Perfect picture. then flickering after a minute of me being happy, then indication of HV shutdown (170VDC at R1). removed X701, and have raster. now troubleshooting. will post results.
 
on the primary of T501 getting about 50 ohms and on the secondary getting less than 1. does that sound right? Am going to pull another g07 chassis tomorrow to check
 
If the monitor is working with X701 removed the problem lies within the power supply section. Start checking all of the components in the 900's and X04.
 
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