Sears TV Vertical Collapse

C

Craig McLean

Guest
Hello I have a Sears TV which currently has vertical collapse (the white
line across the middle of the screen). The TV is a rebadged JVC of unkown
model number. The Sears model is 509.14359.

No schematic is available, however I did some tracing and found the vertical
section. I poked around and didn't notice any damaged passive components so
I took a chance and replaced the vertical output amplifier chip (PN:
LA7832). After I replaced the chip the problem changed, now when I turn the
TV on it turns itself off after about 4 or 5 seconds. I do get audio, but I
can't tell if there is any video because the tube doesn't warm up enough for
me to see. Can anybody give me any hints on what I might have done. I seem
to have changed the problem.

Some things I have already tried. I took out the new LA7832 and put the old
one back in, same problem, TV turns itself off after about 4 seconds. I
also took a close look to make sure I hadn't messed up the soldering I did,
but I don't see anything.

Anybody have any ideas?
 
Check the electrolytic caps in both the power supply and in the vertical
deflection circuit. Also open resistors and damaged traces.
"Craig McLean" <craigmclean@shaw.ca> wrote in message
news:E13fc.111118$Ig.80027@pd7tw2no...
Hello I have a Sears TV which currently has vertical collapse (the white
line across the middle of the screen). The TV is a rebadged JVC of unkown
model number. The Sears model is 509.14359.

No schematic is available, however I did some tracing and found the
vertical
section. I poked around and didn't notice any damaged passive components
so
I took a chance and replaced the vertical output amplifier chip (PN:
LA7832). After I replaced the chip the problem changed, now when I turn
the
TV on it turns itself off after about 4 or 5 seconds. I do get audio, but
I
can't tell if there is any video because the tube doesn't warm up enough
for
me to see. Can anybody give me any hints on what I might have done. I
seem
to have changed the problem.

Some things I have already tried. I took out the new LA7832 and put the
old
one back in, same problem, TV turns itself off after about 4 seconds. I
also took a close look to make sure I hadn't messed up the soldering I
did,
but I don't see anything.

Anybody have any ideas?
Click to expand...
 
Look for a D422 or D442 in that circuit.....should be a 75V Zener. Change
it.

Also look for a D542 Shorted Rgp10j = Ecg552 Equiv.

Also..........check the input/output voltages of any of the 78xx and 79xx
series regulators.


--
==========================
Jeff Stielau
Shoreline Electronics Repair
344 East Main Street
Clinton,CT 06413
860-399-1861
860-664-3535 (fax)
jstielau@snet.net
========================
"If you push something hard enough it will fall over."
Fudd's First Law of Opposition - Sir Sidney Fudd


"Craig McLean" <craigmclean@shaw.ca> wrote in message
news:E13fc.111118$Ig.80027@pd7tw2no...
Hello I have a Sears TV which currently has vertical collapse (the white
line across the middle of the screen). The TV is a rebadged JVC of unkown
model number. The Sears model is 509.14359.

No schematic is available, however I did some tracing and found the
vertical
section. I poked around and didn't notice any damaged passive components
so
I took a chance and replaced the vertical output amplifier chip (PN:
LA7832). After I replaced the chip the problem changed, now when I turn
the
TV on it turns itself off after about 4 or 5 seconds. I do get audio, but
I
can't tell if there is any video because the tube doesn't warm up enough
for
me to see. Can anybody give me any hints on what I might have done. I
seem
to have changed the problem.

Some things I have already tried. I took out the new LA7832 and put the
old
one back in, same problem, TV turns itself off after about 4 seconds. I
also took a close look to make sure I hadn't messed up the soldering I
did,
but I don't see anything.

Anybody have any ideas?
Click to expand...
 
First of all, thank you all for your advice. Both the people who emailed me
and the people who replied here. I found a burned out resistor. Replacing
that fixed the problem where the TV would shut itself off 5 seconds after
turning it on.

Unfortunately after I did that the la7632 chip started smoking and burned
itself out. Does anybody have any ideas on that? I don't think it is a
defective component because I tested almost every component in the vicinity
of the la7832 and they were all fine (with the exception of the resistor I
mentioned above). The only thing I can think of is I didn't screw the
la7832 back onto its heat sink before starting the TV up, is it actually
possible for that thing to get hot enough that fast to start smoking? The
only thing I can think of is trace damage.
"Shoreline Electronics" <jstielau@snet.net> wrote in message
news:YR9fc.300$0y4.213@newssvr32.news.prodigy.com...
Look for a D422 or D442 in that circuit.....should be a 75V Zener. Change
it.

Also look for a D542 Shorted Rgp10j = Ecg552 Equiv.

Also..........check the input/output voltages of any of the 78xx and 79xx
series regulators.


--
==========================
Jeff Stielau
Shoreline Electronics Repair
344 East Main Street
Clinton,CT 06413
860-399-1861
860-664-3535 (fax)
jstielau@snet.net
========================
"If you push something hard enough it will fall over."
Fudd's First Law of Opposition - Sir Sidney Fudd


"Craig McLean" <craigmclean@shaw.ca> wrote in message
news:E13fc.111118$Ig.80027@pd7tw2no...
Hello I have a Sears TV which currently has vertical collapse (the white
line across the middle of the screen). The TV is a rebadged JVC of
unkown
model number. The Sears model is 509.14359.

No schematic is available, however I did some tracing and found the
vertical
section. I poked around and didn't notice any damaged passive
components
so
I took a chance and replaced the vertical output amplifier chip (PN:
LA7832). After I replaced the chip the problem changed, now when I turn
the
TV on it turns itself off after about 4 or 5 seconds. I do get audio,
but
I
can't tell if there is any video because the tube doesn't warm up enough
for
me to see. Can anybody give me any hints on what I might have done. I
seem
to have changed the problem.

Some things I have already tried. I took out the new LA7832 and put the
old
one back in, same problem, TV turns itself off after about 4 seconds. I
also took a close look to make sure I hadn't messed up the soldering I
did,
but I don't see anything.

Anybody have any ideas?
Click to expand...
 
Craig McLean:
As you have just found out, without being properly attached to a heat sink,
most power semiconductors operating within normal specification will
overheat and become faulty almost immediately.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -


"Craig McLean" <craigmclean@shaw.ca> wrote in message
news:6A_fc.146378$oR5.116732@pd7tw3no...
First of all, thank you all for your advice. Both the people who emailed
me
and the people who replied here. I found a burned out resistor.
Replacing
that fixed the problem where the TV would shut itself off 5 seconds after
turning it on.

Unfortunately after I did that the la7632 chip started smoking and burned
itself out. Does anybody have any ideas on that? I don't think it is a
defective component because I tested almost every component in the
vicinity
of the la7832 and they were all fine (with the exception of the resistor I
mentioned above). The only thing I can think of is I didn't screw the
la7832 back onto its heat sink before starting the TV up, is it actually
possible for that thing to get hot enough that fast to start smoking? The
only thing I can think of is trace damage.
"Shoreline Electronics" <jstielau@snet.net> wrote in message
news:YR9fc.300$0y4.213@newssvr32.news.prodigy.com...
Look for a D422 or D442 in that circuit.....should be a 75V Zener.
Change
it.

Also look for a D542 Shorted Rgp10j = Ecg552 Equiv.

Also..........check the input/output voltages of any of the 78xx and
79xx
series regulators.


--
==========================
Jeff Stielau
Shoreline Electronics Repair
344 East Main Street
Clinton,CT 06413
860-399-1861
860-664-3535 (fax)
jstielau@snet.net
========================
"If you push something hard enough it will fall over."
Fudd's First Law of Opposition - Sir Sidney Fudd


"Craig McLean" <craigmclean@shaw.ca> wrote in message
news:E13fc.111118$Ig.80027@pd7tw2no...
Hello I have a Sears TV which currently has vertical collapse (the
white
line across the middle of the screen). The TV is a rebadged JVC of
unkown
model number. The Sears model is 509.14359.

No schematic is available, however I did some tracing and found the
vertical
section. I poked around and didn't notice any damaged passive
components
so
I took a chance and replaced the vertical output amplifier chip (PN:
LA7832). After I replaced the chip the problem changed, now when I
turn
the
TV on it turns itself off after about 4 or 5 seconds. I do get audio,
but
I
can't tell if there is any video because the tube doesn't warm up
enough
for
me to see. Can anybody give me any hints on what I might have done.
I
seem
to have changed the problem.

Some things I have already tried. I took out the new LA7832 and put
the
old
one back in, same problem, TV turns itself off after about 4 seconds.
I
also took a close look to make sure I hadn't messed up the soldering I
did,
but I don't see anything.

Anybody have any ideas?
Click to expand...
 
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