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kortek ki-2-vo brand chassis repair help - only high voltage
perjmolsen:
--- Quote from: grantspain on January 11, 2020, 06:32:35 am ---i would suggest checking any tantalum caps, there is one next to the sync processor
--- End quote ---
Will do, a tantalum cap, it is the blue ones, right?
I have pulled blue tantalum cap next to HA11235, the reading on the cap is 2.2 35 I guess that means 2.2nf 35V
It reads 2130nf, so that is good right?
I have also pulled out and tested all the polyester caps around flyback,to me they all look OK
c711 - 434J (0.43uf) TESTS: 417nf
c709 - 332J 1600V (3.3nf / 3300pf) TESTS: 3147 pf
c712 - 104K 200V (100nf) TESTS: 99.90pf
c706 - 152J 1600V (1.5nf / 1500pf) TESTS: 1496pf
c705 - 392J 1.6KV (3.9 nf) TESTS: 3925pf
c704 - 533K 200V TESTS: 57.05nf
grantspain:
that is ok
princess prin prin:
What's the voltage at the cathode of D541 with anode lifted? What diode is it? If the voltage is higher than the zener breakdown voltage the diode becomes conductive and the voltage arrives at the HA11235 which shuts down.
perjmolsen:
Hi
Is is 41,6V with the annode lifted.
The diode is 1N5 242. I have also tested the diode with a leg lifted, it tests OK
princess prin prin:
That's a 12V zener so no wonder it's conductive when 41V is applied to it. The monitor uses a flyback derived secondary voltage for x-ray protection. The circuit is designed so that an anode voltage potentially dangerous (well above 25KV for a 20" tube) generates a secondary voltage high enough to make D541 conductive so that the voltage can go to the HA11235 which detects it as too high and stops outputting the signal that drives the HOT and hence the flyback. You have not measured the anode voltage so we don't know if the protection circuit is working as it should or if it's faulty/incorrectly adjusted. The protection circuit is very simple so you can easily check if all parts are good. If they are and if the adjustment pot that forms a voltage divider with R542/R541 is set to maximum resistance and the protection still kicks in, that would point to the anode voltage being actually too high. On the other hand the b+ seems correct and the caps that could make the anode voltage too high (C705 etc.) seems good too. I don't see a damper diode so it must be in the HOT. Check that too.