Entertainment Center: TVs, Stereos, VCRs and DVDs - Hitachi Ct7872b 26'' Tv Dead !

On initial turn-on power relay engages on, and hi-v tries to come on for a second, but nothing happens, No screen or sound ! only power relay clicks on/off with power button on-off
+5 and +9V are present at power supply, fuse and hi-v components checked ok, I suspect power regulator IC 901 :
UPC 1394C ? Any thoughts or suggestions how to troublesoot will be appreciated.. Thank You.

Check for open resistors at the flyback transformer before changing the voltage regultor.

Hi Craftsman, Thank You for replying, I've checked the resistors arround the Flyback, they all check ok, except
R742 which is discolored due to overheating, it checks
like 150k+ Ohms, I can not find the schematics, can some
one possibly tell me the value of R742 ? Meanwhile I will
replace it with higher wattage 150k flameproof resistor and
replace the IC901 as well, and see what happens..

R742 is 150K. Check R721 to make sure its .5 ohm . That feeds the vertical and will cause the set to shut down. If its ok then changing the regulator would be the next step.

*Replaced R742 with 150K/1W, Disconnected one end of R721 and checked ok. Replaced IC901( UPC1349C) from other set.
Tested with series 100W Bulb. On initial turn-on relay engaged
and bulb lit very bright, turned on/off few times bulb dimmed
connected direct to mains, now I hear high pitch oscilattion
(before died immediately) which makes me think high voltage
is or trying to come on, but still no screen, back of the tube heaters are not glow, I have no diagram showing pin outs and connections of IC901, measures about -60Volts all around the pins? No 0V (GND) or +V reading.. Also TH901 across the degauss coil is very hot( is this normal?) regardless coil is connected or not.Wires marked: PX3 (Brn/Org) from PSU measures +64V Could it be bad Flyback ? I don't know what to do next.awaiting more suggestions..

High pitch squeal sounds like a shorted horizontal output trany or a short on the output side of the ac transformer that the regulator runs.

Desoldered and checked Hor.O/P Transistor and Transformer, both checked ok. Could it be bad (partially shorted) Flyback ?
IC901 voltages checks arround -60 V ! according to found diagram pin 8 is Vcc + should be 6.6V and pin 9 is ground which should be 0V. respect to chassis ground, does it tells
something like open ground..?

Lets start from the begining.
There should be 306 volts on the emmiter and 127 volts on the collector of Q901.Thats the main power trany.
Light bulb?
Let me know what it reads on trany.

Craftsman, Thanks for helping me, But :
Found diagram shows exactly opposite,Q901 Collector = +305V
Emitter= +130V ( instead of Emitter= +305V collector= +130V)
please follow the below link to verify :
http://www.steveselectronics.com/files/power%20supply.pdf
*
What I found is IC901 pin 9 doesn't measures 0V Gnd.
( measures-60V!) traced goes to Q901 Heatsink, I am using Tuner Chassis (case) as a ref. Gnd. and it measures open with
IC901 pin9 ! However when I use jumper from Q901 Heatsink to
Tuner chassis, -60v dies and all voltages arroun IC 901 checks
within limits. also Q901 Voltages checks correct using shorting
jumper lead. Obviously, I have a open ground to IC901 but I can not find any burnt trace or open component. Further checking I found CRT Heater connections at connector marked: T are shorted and traced the short at Flyback Transformer, reason heaters never glow at the neck of the CRT
Therefore now I am thinking the FBT is gone bad and may be the reason for the missing ground ? The part# of FBT is unreadible..and I was unable to find, I will apreciate if you can help me with this. Let me explain the Lamp Test since you've raised a question mark. This is what I learned from other techs.
and it saves replaced questionable components being shorted,
Lets say you have a short on a tv set, and you are replacing a suspected component(s), You connect the tv with series of
at least 100W light bulb to mains, bulb acts there as a load,
if bulb lights bright then short is stil present, so part you replaced did not solve the problem but did not damaged the repleced part either,if you connected direct to wall, sice the short is present you could have damaged to replaced part!
if bulb starts lighting bright but gradually dimmes to very low,
that means replaced part did the job, now you can remove the bulb and connect straight to wall without any doubt. You can experiment this Bulb Test with any working set, simply connect 100W light bulb (higher Wattage for sets draws more current) with series to mains. <---------0------------>
Regards.. TV Bulb AC
<---------------------->

* lines jumped.. diagram sould be :

<--------(-)--------->
TV Bulb AC
<-------------------->

I need the Part Number for the : FLYBACK Transformer for :
HITACHI CT 7872B 27''TV. Any help will be apreciated..

Sorry my diagram I'm looking at is barely readable.The other ones you found are correct.If you follow the instructions in it , should be no problem finding the problem.
Never had heard of that light bulb trick.I have the proper Isolated variable voltage transformer to use.
Your part # is T702 2435376
Good luck!

* Thank You Craftsman, I already verified that Heater connection is shorted to ground internaly in FBT.
Trying to find it at a resonable price (Quoted over $100) when I replace it will let you know the result.. thanks for your help again.. Teknofix.

Try suburban-elect.com $18.00

* actually, I found cheaper ( $14.00) + 8.80 S/H = $ 22.80
and ordered from : http://www.electronix.com/catalog/
will let you know the result, when I receive and install..
Regards.. Teknofix.

* actually, I found cheaper ( $14.00) + 8.80 S/H = $ 22.80
and ordered from : http://www.electronix.com/catalog/
will let you know the result, when I receive and install..
Regards.. Teknofix.


* installed newFTB but, did Not fix the problem.!

Well this start from scratch.First thing to check is the voltage on the horizontal output transistor collector.Plug the set in ,use the tuner shield as ground for the meter and check the voltage reading before and after hitting the power button.Post back and let me know what you observe.

Craftsman, Thank You for replying, I think I found the problem:
C716 is Shorted ! looks like a clear polyster cap. marked 334K
I don't have it, need to find..another thing I like to ask is components CP901 and CP903, they look like brown ceramic caps.wrapped with clear pvc, they are in power supply in between different ground sections, since they marked as CP.(Circuit Protect) I thought they are just like Fuse, but both checks open, and thats why I don't have Ground continuity on different sections and thats why I read negative and erratic voltages..unless they close as voltage applied I am puzzled.? do you know anything about these CP901 and CP903 if you have the schamatics..the letterings on tham are: ME C131 R2.5-4M 125VAC 96 and both of them identical.meanwhile I am
trying to find the shorted cap. (C716) I hope it will solve the problem, but I am puzzled with these CP's any info. will be appreciated.. Thanks again.. ~ Teknofix ~

:thumbup: Those are fuses.You can use Pico fuses to replace them.The .4m is 4 milliamps,I usually just replace them with a .5 amp fuse.Easier to find.

Craftsman, Replacing C716 solved the problem.. tv works fine now :-) Thanks for your concern and help.. ~ Teknofix ~