Diagnosing a B+ high on G07-CBO

JimD53

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I have a G07 with B+ stuck at 167V and does not vary with the position of R909. The light bulb is currently inline with B+ at W908. It stays dark and no fuses blow.

I found a very long thread on diagnosing a B+ power supply problem and want to restate what I think it says to do.

This is the thread
https://forums.arcade-museum.com/threads/g07-high-b-yes-another-one.471119/

Lay the circuit board on a non conductive surface without any external connections to the CRT.
Remove jumper W908 to isolate the B+ circuit from the rest of the chassis. (This came from the video near the bottom of the thread.)
Connect a 40, 60, 70 watt bulb at the B+ end of R01 (white wire) and the other end to chassis ground.
Connect 120VAC through an isolation transformer to the power connector.
Since W908 is missing there should be no high voltage but just in case put the anode connector in a glass jar.

Did I miss anything?
 
The weather moderated here and I was able to work on the G07. I found another video by Mike's Amateur Arcade Monitor Repair which showed using a 60 watt bulb as a load to allow checking the B+ circuit without the HV active. He disabled the HOT by removing wires. I accomplished the same by removing the W908 jumper as suggested by the video embedded in the thread above. I was able to prove the B+ regulator was good since I was able to adjust it to 120V. Embolden by my success I wired the bulb in series with the B+ circuit by soldering the lamp wires in place of the W908 jumper. That test wasn't successful unless triggering a HV shutdown counts. In that state B+ was 167V. More reading and measuring and probably another thread. I just wanted to update this with what worked for me.
 
You're not specifying what else has been done to troubleshoot. Have you capped it or has it been capped recently? Did you replace the flyback? Did you look for cracks in the chassis and lifted pads? Did you check the voltage regulator? Did you follow the basic troubleshooting steps on Fromm's flowchart?
 
You're not specifying what else has been done to troubleshoot. Have you capped it or has it been capped recently? Did you replace the flyback? Did you look for cracks in the chassis and lifted pads? Did you check the voltage regulator? Did you follow the basic troubleshooting steps on Fromm's flowchart?
Sorry, I forgot context.
All checking was done out of circuit
I put a cap kit on. Replaced the HOT, flyback, and horizontal coil.
I replaced the voltage regulator at X01.
I checked transistors in the x900, x500. x400 ranges. All were good
Checked b1 pot at r909.
Replaced the 4 pots on the back edge of the board
Replaced IC501..
Verified resistor values in the B1 circuit
Verified resistor values in the X-ray protection circuit
Replaced r908 which was way out of spec
Replaced r703 which was open. after this fix the x-ray protection circuit started working.
Replaced zener diodes d905 & d701

With bulb in series at w908 the monitor was in HV shutdown. B1 was 167v, x701 base was .773v, collector was 0.069v, emitter was 0v. the junction between d701 and r703 was 20.1v
I thought the collector of x701 should have been around 0.6v if the transistor was conducting so I pulled it and tested the transistor and it was good

Today I'm checking parts that touch the x501 transistor or any around the flyback. Without the bulb, the w908 jumper is open so i've been checking continuity with it and parts connected to it including the flyback. The resistance at the downstream side of w908 to ground is 9.6k.

With the bulb connected to b1 and ground it presents a load that allows me to adjust b1 to 120v. without the bulb b1 is 167v. Same reading when the bulb is in place of w908.

Where I think I stand now the B1 regulator works if it sees a load. The problem lies in the 500 series of parts.

Not sure if it matters but the circuit board in on my bench without any connection to the CRT. HV anode is in a glass jar just in case I fix the shutdown problem. Does the yoke need to be connected to the board to adjust B1 with just the flyback in circuit?
 
I have the B1 circuit fixed. I got 120V with the 60 watt bulb from B1 to ground and W908 removed. I put the bulb in series with b1 by soldering it in place of w908. I got 167v when the board had the yoke disconnected, however with the yoke connected the B1 was adjustable to 120V. The B1 circuit needs the load to keep regulated.

Done here. On to figuring out why I can't get the HV circuit to work which will be on a new thread.
 
Have you tested T501? With your meter in ohms, bottom of the chassis. 1 side has 2 pins the other has 3 pins. The side with 3 pins, use either lead in either spot on the 2 bottom of the 3 pins and it should read
50ish ohms.

Otherwise, It seems like you have a crack/bad trace somewhere and should be focusing on beeping out traces, vs testing components. (my opinion)


edit: I assume you got your parts from arcadepartsandrepair.com but if not, I've seen counterfeit HOTs measure good , in and out of circuit and cause HV shutdown.
 
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Have you tested T501? With your meter in ohms, bottom of the chassis. 1 side has 2 pins the other has 3 pins. The side with 3 pins, use either lead in either spot on the 2 bottom of the 3 pins and it should read
50ish ohms.

Otherwise, It seems like you have a crack/bad trace somewhere and should be focusing on beeping out traces, vs testing components. (my opinion)


edit: I assume you got your parts from arcadepartsandrepair.com but if not, I've seen counterfeit HOTs measure good , in and out of circuit and cause HV shutdown.
Thanks for the input. I just tested T501, it read 50 ohm on the three pin side. The HOT and flyback came from arcadepartsandrepair. I have the B1 circuit and X-Ray protection circuit working. IB1 reads 120V. According to voltage at the collector of X701 I'm not in HV shutdown. I've checked parts in the 500 range starting at X501 through to the flyback. I reflowed solder in those areas. I don't see solder bridges. I did check connectivity from each pin on the flyback to the components they are connected to. Nothing suspicious so far. I'm going to open a new thread related to the HV circuits. I replaced the HOT again being very careful to not put it in upside down and powered it up. I briefly got high voltage. Now nothing. I checked the CRT heater wires at K1 & K2. It read 0VAC. The light bulb initially glowed moderately and I heard HV before it burned brightly. Since the bulb is in series with the B1 circuit at the w908 jumper I'm assuming something upstream on the B1 circuit shorted out again.
 
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