The Elusive STRF6456 Home | Search | Products | Tips |
Newsletter | For Sale | Wanted Click here to return to the
Miscellaneous Tips index page
All repair tips and service information on these pages are
supplied as per our site terms &conditions PLEASE READ
Author: Ismail Msheikh
Have you searched the Internet for the elusive STRF6456 ? read
this
I was recently called to repair a brand new Zec TV ZT296ST in
Nairobi, Kenya, which was perpetuallystuck on standby. My first
suspicion fell on the power supply. I had no service diagram but
voltage checkson the outputs of the chopper transformer showed the
HT was at 135v which looked within range for a 29"chassis. The
others auxiliary output measured fine. Things remained unchanged
with a dummy load. Thefrequency of the line oscillator was present
but the screen remained blanked. I advanced the screen pot andwas
greeted by retrace lines with a severe pincursion distortion. The
OSD was present. There was no remotecontrol function and the preset
control function were not working.
Suspicion now fell on the the processor which was being fed a
good 5v by a fixed regulator. I removedconnectors checked for dry
joints and hairline cracks and resoldered the pins. The set came to
life albeitwith an increased height. I switched off the set and on
again but the set could not come out of standby. Ithen went on a
blanket replacement exercise, distrusting all ESR meters, I
replaced and upgraded to 105degree all capacitors standing near the
processor and the EEPROM. The set remained on standby. I now
didwhat cured the fault - resoldered the chroma chip. I was greeted
by a beautiful raster and clear picture butthe pictures on the
screen were minus their heads, there was an EW fault too. No-one
could tell what thepreacher on the TV was holding! was it the
Bible? my headache had just began!I tried reducing the B+ but the
power supply had no pot. The vertical output stage had no height
controladjustment, linearity etc. There was no horizontal hold or
centering pots. I tried things with the verticalsection, adding
resistive loads to get a clue of the source of the fault and
checked all passive components,but the fault was not in the
vertical section and no remedial action could set back things. I
examined threebulky ceramic capacitors all connected in parallel
each of 2.2nf 2kV. They read fine on the ESR meter. Idecided to
remove one and the picture size was reduced considerably. I was
about to say repaired! and thepower supply fuse was shattered,
STRF6456 shorted, all caused by the reduce capacitance in the line
tuningsection which killed the line transistor. It was one of the
many repair-generated failures.
The following morning I discovered to my chagrin, that no
distributor on the globe had the SMPS chip. Ivisited the chip
manufacturers web site, Sanken.the company described it as
quasi-resonant chip forsecondary isolated SMPS, no further details.
I visited the web site of Allegromicro which also deals withSanken
products. The chip was not listed anywhere, or anywhere else on the
Internet, at least in English.Allegromicro (www.allegromicro.com)
were however helpful.They have a pdf file of the
superabundantlyavailable STRF66XX series with good information on
its configuration and specs. I chose STRF6656 andcompared it with
the layout of my power supply, they looked the same. To allow the
chip to operate on AC85-265 volts I reduced the startup resitor
connected to terminal 4 of the chip to 68K 2watts. The powersupply
worked well and it still works.
The cause of the height and EW error was TA8859CP chip described
by Toshiba as a "deflection distortioncorrection chip" for the
"flat" screen. Long live information sharing!
Copyright 2000 - 2003 - E.C.S (Technical Publishing)Site Design
& Layout 2000
All Rights reserved
All Information is supplied as per our Site Terms.Use of this
site deems your acceptance of these terms.Click links to view our
Site Terms and Privacy Policy
.
The Elusive STRF6456
http://www.e-repair.co.uk/tipsgeneral100.htm
1 of 2 01.04.2013 19:20
