K4700 High B+

zed7

Twinkle Star Sprite
My K4700 (13" K4600) is having high B+ Im running into an issue. I replaced the caps, including the filter. First time he turned it on, he said there was a loud hum then an arc, followed by the fuse blowing. Turned out to be a bad filter (bought from a local shop). Now when turning it on, B+ is at 170V, no neck glow.

Heres everything that was tested / substituted with working one:
- VR
- Tested all semiconductors on power pcb
- HOT
- Diodes near HOT
- X601 Diode
- Reflowed all headers + cards
- X/Y Board from another working monitor does not work in this monitor
- X/Y Board from this monitor works in another working monitor

Following the flowchart, since HOT case is 0V, it should be cracked traces, but I didnt see any looking over it lightly, will look more in depth whenever I get a chance.
Any advice on how to proceed would be appreciated...

I believe it would be a resistor, as there are very components on that monitor. Which resistors are involved with B+?

Thank you
 

ShootTheCore

Baseball Star Hitter
Just to make this easier for anyone else that comes in to help, here's the documentation I was able to find on that chassis:

Schematics

Troubleshooting Flowchart

I agree with your conclusion from the flowchart given that your B+ is over 160V, you've confirmed that the horizontal deflection functions with another chassis and your HOT is dead.

Here's a few ideas:

  • When you checked the diodes near the HOT, did you test them out of circuit? You have to desolder at least one diode leg from the chassis to assess the diode accurately.
  • I know you reflowed them, but double-check the solder joints around the connectors for the upright boards and P607 with your multimeter. Set it to Continuity test and check each connector pin against its destination point(s) as listed on the schematic.
  • Also look for cold solder joints around caps and some of the large resistors that sit up off the board - some of those big resistors get so hot that they practically desolder themselves.
  • Take another look at the big B+ filter cap - try desoldering and testing it out of circuit to make sure it isn't shorted open or closed.

As far as resistor numbers go, you'll want to look at all the resistors in the V OUT and PROTECTOR section of the schematic, including:
R325
R324
R323
R322
R321
R320
R319
R318
R317
R316
R315
R314
R313
R312
R311
R307
R306
Check and make sure that they aren't shorted closed (zero resistance) or shorted open (infinite resistance)
 

zed7

Twinkle Star Sprite
Thank you for some guidance. I'll go through them when I can. Thank you! Will come back with results
 
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