View Single Post
  #1   Report Post  
Jason D.
 
Posts: n/a
Default 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