Interesting experience with Citizen 19" chassis.
Customer complaint: no vertical. Fine the usual fix repair vertical
circuit for small estimate and got that OK'ed. Got vertical fixed as usual, huh? B+ is jammed at 200V not 115V (this is SMPS), replaced the NPN small signal transistor in cold side feedback regulation circuit (measured OPEN on all 3 legs). Got 115V back and ran it on test wondering why I have good voltages except I haven't checked HV, that pic is bit dimmer and bit "blown up" as in oversized picture in small bezel. Then cinched the puzzlement: finally flyback failed, YOWCH! flyback core HOT! That HOT transistor didn't bat an eye, was running good temperatures. Now I know why! The high B+ happened to kill vertical circuit first with too high voltage but also damages flyback transformer enough in the process. This explains why I see number of HV blocks (205064) failures because of high B+ while in standby. And exiting standby to run voltage was zapping block eventually HV block failed. Gonna watch out for high B+ especially if customer left TVs running quite awhile with high B+! Many Citizen chassis didn't shut down on high B+ which is bothering me as most TVs even cheapest ones does cut out in seconds up to a minute. Cheers, Wizard |
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