Zenith Z27A11S won't turn on.

[monitorGUY]

i have this Z27A11S zenith tv. It will not turn on. i opened it and changed
a few caps that appeared good to me.
put the board back in and it turned on. great! ah, no. once i put the board
in and buttoned up the back of the set it would not turn on again.
hmmm
put the thing away for a while.
back to it today. opened it up and changed a couple more caps. and voila, it
turned on. I turned it off. and turned it back on a few times. looks good.
put the back back on the set and it would not turn on again!. what gives?
pulled it appart and soldered a bunch of connections thinking its a cracked
trace perhaps. now i cannot get it to turn on at all.

where is the turn on signal? this is perplexing. it is so close to working i
am reluctant to give up and chuck it.
Can anybody offer some help or advice?
thanks
MG

 

[monitorGUY]

this thing is driving me nuts. can't get it to turn on at all any more.
anybody have that "turn on" section of the scehmatic they could mail me?

 

[JANA]

There is probably a cold solder connection, and when the board is sitting in
the cabinet, it is being stressed in the fashion to have the cold connection
not making contact. Pull the board out, and jig run it. Then you can put
pressure on and off the board in various areas to aggravate the fault.

--

JANA
_____


i have this Z27A11S zenith tv. It will not turn on. i opened it and changed
a few caps that appeared good to me.
put the board back in and it turned on. great! ah, no. once i put the board
in and buttoned up the back of the set it would not turn on again.
hmmm
put the thing away for a while.
back to it today. opened it up and changed a couple more caps. and voila, it
turned on. I turned it off. and turned it back on a few times. looks good.
put the back back on the set and it would not turn on again!. what gives?
pulled it appart and soldered a bunch of connections thinking its a cracked
trace perhaps. now i cannot get it to turn on at all.

where is the turn on signal? this is perplexing. it is so close to working i
am reluctant to give up and chuck it.
Can anybody offer some help or advice?
thanks
MG

 

[monitorGUY]

thanks Jana
Tried that.
i actually just redid all the solder joints in the area and anywhere near
the area. tried flexing the board. the thing is that this unit failed while
in an entertainement center and never moved.....
Probing it hot now... carefully....
i notice that there is no voltage on either side of the power on softswtich.
that would make it dificult for it to have any affect i'm thinking.
There is a smlal transistor on the hotside of the switching transformer. I'm
wondering if that is what must be turned on?. without a schematic i'm just
stabbing in the dark. can i hot wire the turn on ckt?

 

[Scott Lane]

i have this Z27A11S zenith tv. It will not turn on. i opened it and changed
a few caps that appeared good to me.
put the board back in and it turned on. great! ah, no. once i put the
board in and buttoned up the back of the set it would not turn on again.
hmmm
put the thing away for a while.
back to it today. opened it up and changed a couple more caps. and voila,
it turned on. I turned it off. and turned it back on a few times. looks
good.
put the back back on the set and it would not turn on again!. what gives?
pulled it appart and soldered a bunch of connections thinking its a
cracked trace perhaps. now i cannot get it to turn on at all.

where is the turn on signal? this is perplexing. it is so close to working
i am reluctant to give up and chuck it.
Can anybody offer some help or advice?
thanks
MG

Google the model number. I found this thread . .
..http://www.diybanter.com/showthread.php?t=64368

Good luck. Scott

 

[Golf]

I had a Magnavox that did the same thing. What I did notice is it
wasn't when I put the back on, rather once I unplugged it, it would not
power back on unless I removed the back, fooled with the chassis and
tried it again. Are you having to unplug the set to put the back on? If
so, I found a bad resistor in the standby voltage supply. If I happened
to touch the circuit (set unplugged), this somehow would reset or drain
a transistor that was keeping the set shut down. Replaced the resistor
and no more problems. Good luck.

 

[monitorGUY]

Yes, thats it!
I also found a bad resistor in that section near the STR53041 Regulator. it
was rx3404 180k. it measured very high. i put in a couple resistors in
parallel to make a higher wattage resistor (equiv of ~177k) but it still
will not work at all. I was sure that was it when i found that resistor.no
joy
I pulled teh transistor and it seems to be ok. especially since it works
intermittently. now is a new problem. the top of the board is screened with
the opposite BCE pin configurations as the bottom of the board. Now i'm not
sure which way the transistor goes back in :/
I'm VERY close now.
Thanks for the reply Golf. right on the money.
i actually found a ref pasted below that helped me track down the resistor
it is originally for a different TV but obviously uses the same chassis.

####################################
Using STR53041 Regulator Always replace: CX3413 = 22mf 63V, CX3416 =
100mf, 25V, RX3404 180k (use 1/2W). Also check: RX3407 = 47 ohm,1W,
Rx3408 22 ohm, 1/2W QX3401 121-1348 (use ECG184 or one of many other
transistors with similar spec's listed in the ECG guide under TO-220 and
TO-220J case styles 4 only (A 1Amp rating is required). If that doesn't do
it replace ICX3431 - STR53041.
####################################

I'll keep plugging away but anymore help will be greatly appreciated.
thanks
MG

 

[monitorGUY]

yeah that was me....same set. it got shoved asside till i descided to clean
up and tackled it again.
nothing in that thread took me any further.

 

[Golf]

If the transistor is an NPN, the emitter junction should go to ground
(looking at top of board). If PNP, the Collector should go to ground.
You should be able to determine the transistor type using a DMM. Good
luck again.