K7300 Blowing Q801

[Vectordreams]

Helping out a friend with a K7300 that had a blown fuse and flyback was cracked. Replaced flyback and did a cap kit. Tested Q801 was bad so replaced it. Powered up and Q801 and R812 popped and tested D805 as a dead short. Replaced both Q801, R812, D805 and Q801 blew apart and D805 is shorted out again.

What else should I be looking for?

 

[PinFixin]

Excerpt from Ken Layton's repair guide:

Common problems: Power applied, Monitor dead, No neck glow. Cause: Resistor R812, Transistor Q801, and Capacitor C807 are all bad and should be all replaced. Solution: Replace R812 (68 ohms, 1/2 watt), Q801 (2SC2073 or 2SD478 or NTE 375), and C807 (100 uf @ 16 volts). Check zener diode (7.5 volt) D805 for a shorted condition.

Did you replace C807?

-Pat

 

[Vectordreams]

I read that guide as well and C807 is part of the cap kit so it is brand new. The kit replaced C807 as 100uf at 50 volts.

 

[DarrenF]

What else should I be looking for?

I don't have experience with this particular model monitor, but based on what you describe, I'd probably be checking parts nearby in the same part of the circuitry. A snip of K7301 schematic is below. Maybe I'd check R813, R814, D303, and C806, then move outward if they're OK...

 

[Vectordreams]

Thanks I will look at that tonight.

 

[DarrenF]

Thanks I will look at that tonight.

...unless someone with more experience with this model (which is a pretty low bar) chimes in first with better advice.

 

[Vectordreams]

Finally had a chance to look at the board again and everything in the circuit tested good. I started looking in the next area of the I802 and D807 was shorted. Pulled D807 and it was not shorted but pins 2 and 3 of the STR-S6707. I have one on order now and will report back.

 

[Vectordreams]

I replaced the STR-26707 voltage regulator and now it is not blowing up the Q801. I heard HV start when turning it on and now I have a ticking sound and no picture. I am guessing this is the HV section problem now.

 

[Vectordreams]

Got my HV probe out and no HV at the tube. I was hearing the degaussing coil. From looking at the Vision Pro manual it talks about a pulse needed on pin13 of I301 chip for the shutdown circuit. I checked that pin and no voltage at all. I guess this is my next section to figure out.