G07 B+ voltage low (around 85V)

RobotWorkshop

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I've searched the forums for G07 low voltage but most seem to talk about not being able to adjust to 120V and the definition of low is a few volts lower than that. In the last couple weeks I've rebuilt 7 other G07 chassis with good results. A couple were a pain but got past all of them. Now I am stuck with this last problem chassis. I got it mixed in with a batch of boards and no history on it. I replaced the broken width coil, did a full cap kit, replaced the large B+ capacitor, the B+ pot, and gone over the chassis for cracked solder joints or cracked PCB. All look ok. Both of the fuses are ok. When powered I get about 160V on one side of the large resistor but on the other get around 85V and adjusting the B+ pot doesn't make a difference. I've started going through the 900 section. Pulled both transistors and those checked ok out of circuit in a transistor checker. To rule out the voltage regulator I pulled one of a parts chassis and swapped in another original. No change.

Have any of you run into a chassis with low voltage like this? If so what did you find?

I haven't tried swapping the IC or replace the flyback but could try that next if needed.

Hope to wrap this up soon then I can put away all the spare G07 parts and monitor test gear as this is the last one I'll need to do for a while.
 
After looking at your fb post, it looks like this started after you changed the filter cap? Show us pics of the top and bottom of the chassis when you get a moment.
 
I've seen low b+ issues when D905 was bad, and X901. I'm wondering if you didn't solder in
The new filter cap thoroughly enough.
 
The soldering looked ok but I pulled out the filter cap to test in case the new one was bad. It checked out OK with the Sencore LC103. Reinstalled it, replaced D905 from the parts chassis, and reflowed other joints in the area. Thought I saw a hint of a Crack and even though it seemed to have continuity scrapped off the soldering mask and soldered over that too.

With all that the B+ is up and adjusted to 120V. The new filter cap did adjust the geometry issue. So this chassis is working well. Going to let it run on the bench for a while. This is just an extra to keep on the shelf in case one goes out since I have a few running the G07.

At this point all my chassis are working. Just have one stripped chassis with broken neck board and one other that could be built up but will probably be a donor chassis.

Appreciate the help and suggestions.
 
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