DIYbanter - RCA 32V550T tries to power on.

On 17 May 2004 19:10:09 -0700, (Tyrone Park)
wrote:

It's as if some cap is discharging or something, then stops. Its a
weird problem! Sometimes it doesn't startup when you press power on
the remote or panel, but this is very intermittent. You can also hear
the supply while in standby. You would suspect a cap, but I've
checked and cannot find a faulty one!

Tyrone

FYI: this ITC008 SMPS is full-time duty for both standby and run.

Okay what I would do is remove the power supply transformer (main
one). Bust out the meter and carefully measure all high value
resistors in primary side that is for start up. Once in awhile I find
open or resistance went up. If in doubt unsolder one end of resistor
and recheck resistance.

Reason for removing SMPS transformer was to remove "short circuits" to
make resistance checks *much* easier and accurate. This method
speeded up a no-start troubleshooting and finding bad part in one
monitor's SMPS few weeks ago, from hours down to one.

Seconded on that pincushion circuit three wire cable simple fix is cut
plugs off and solder wires directly in instead. Those thin pins is
NOT MEANT FOR that kind of POWER. :-( Very highly intermittent and
easy to MISS because once you wiggle those wires even act of removing
board and reinstalling will cause the problem to disappear and takes
days of waiting for fault to reappear. (Experience speaking!)

Pay attention to customer description, if says tv picture width is
twiching and this chassis is *ITC008* go straight to that three wire
cable assembly for PCC and cut off plugs and solder wires in. Pay
attention that cable has pin 1 and 3 swapped, keep that way, this is
very strange! Also, RCA is rather sloppy on mounting pincushion
transistor to heatsink. I almost find that every time, remember these
transistor run HOT.

Also these small blue electrolytic capacitors is a potiential problem.
Found one in a sagging B+ SMPS (unusual fault) of a RCA 13" new
chassis (difference is in watts, newer one is 55W, older ones based on
TX826 was higher.), with a ESR meter. I suggest you do have ESR meter
like bob parker's or Capacitor Wizard. Most SMPS tend to scream
higher if a cap dries out not LOWer especially those dumb SMPSes in
later chassis that RCA likes to use. :-O

Cheers,

Wizard

PS: I've seen my coworker struggle with SMPSes for hours especially
quirky faults. Didn't remove transformer and measure resistance on
everything, he thought that is too much effort. SMPS are not that
complex and not that "mysterious". I showed him that techique to save
his time.