Panasonic 27" TV w/ no vertical deflection
 

I have a TV with no vertical deflection, just the horizontal line
across the center.
It is a Panasonic PV-27D52, chassis KM-D2702, from 2002.

I checked the supply voltages to the vertical deflection chip
(LA7837).
Vcc (pin 1) was 23V (should be 12), and the pump-up supply voltage
(pin 8) was 28.4V (should be 24).
I removed the chip, and Vcc went to 11.8, and the pump-up V went to
29.4.

The pump-up V is derived from the flyback. The datasheet says it is a
nominal 24V, with 27V max. So I assume 29 is too high, and I
shouldn't just replace the chip without locating some other problem
first.

I have been checking all the diodes, caps, and resistors in the area
(with a DMM and with a simple ESR meter). I haven't found any that
read bad. I replaced a few borderline caps and one of the diodes.
Nothing I have done has any effect on the two voltages.

Any suggestions on where to look more specifically?

Thanks for any suggestions,
-Steve

That model number does not exist on the Panasonic site OR on a google
search.

In any case.........look at a typical pinout of this IC
http://www.alldatasheet.com/datashee...YO/LA7837.html

Do you an input pulse on Pin 2...etc

I would change the chip first before getting all involved.

--
==========================
Jeff Stielau
Shoreline Electronics Repair
344 East Main Street
Clinton,CT 06413
860-399-1861
860-664-3535 (fax)

========================

"Steve W. Neas" wrote in message
...
I have a TV with no vertical deflection, just the horizontal line
across the center.
It is a Panasonic PV-27D52, chassis KM-D2702, from 2002.

I checked the supply voltages to the vertical deflection chip
(LA7837).
Vcc (pin 1) was 23V (should be 12), and the pump-up supply voltage
(pin 8) was 28.4V (should be 24).
I removed the chip, and Vcc went to 11.8, and the pump-up V went to
29.4.

The pump-up V is derived from the flyback. The datasheet says it is a
nominal 24V, with 27V max. So I assume 29 is too high, and I
shouldn't just replace the chip without locating some other problem
first.

I have been checking all the diodes, caps, and resistors in the area
(with a DMM and with a simple ESR meter). I haven't found any that
read bad. I replaced a few borderline caps and one of the diodes.
Nothing I have done has any effect on the two voltages.

Any suggestions on where to look more specifically?

Thanks for any suggestions,
-Steve

On Thu, 17 Feb 2005 20:53:47 -0500, "Steve W. Neas" put
finger to keyboard and composed:

I have a TV with no vertical deflection, just the horizontal line
across the center.
It is a Panasonic PV-27D52, chassis KM-D2702, from 2002.

I checked the supply voltages to the vertical deflection chip
(LA7837).
Vcc (pin 1) was 23V (should be 12), and the pump-up supply voltage
(pin 8) was 28.4V (should be 24).
I removed the chip, and Vcc went to 11.8, and the pump-up V went to
29.4.

It seems to me that the IC is bad. AFAICS, there must be an internal
leak between the Vcc8 and Vcc1 supply pins. The 12V rail on Vcc1
probably supplies other ICs in the set. Hopefully Vcc1 is current
limited (by a 100 ohm series resistor?), otherwise those other ICs
would be damaged. After replacing the IC, I'd check to see that this
resistor, if it exists, has not been heat stressed.


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

"Franc Zabkar" bravely wrote to "All" (18 Feb 05 19:39:10)
--- on the heady topic of " Panasonic 27" TV w/ no vertical deflection"

FZ From: Franc Zabkar
FZ Xref: aeinews sci.electronics.repair:10853

FZ On Thu, 17 Feb 2005 20:53:47 -0500, "Steve W. Neas" put
FZ finger to keyboard and composed:

I have a TV with no vertical deflection, just the horizontal line
across the center.
It is a Panasonic PV-27D52, chassis KM-D2702, from 2002.

I checked the supply voltages to the vertical deflection chip
(LA7837).
Vcc (pin 1) was 23V (should be 12), and the pump-up supply voltage
(pin 8) was 28.4V (should be 24).
I removed the chip, and Vcc went to 11.8, and the pump-up V went to
29.4.

FZ It seems to me that the IC is bad. AFAICS, there must be an internal
FZ leak between the Vcc8 and Vcc1 supply pins. The 12V rail on Vcc1
FZ probably supplies other ICs in the set. Hopefully Vcc1 is current
FZ limited (by a 100 ohm series resistor?), otherwise those other ICs
FZ would be damaged. After replacing the IC, I'd check to see that this
FZ resistor, if it exists, has not been heat stressed.


If there is an external diode close to the LA7837 pins change it too.

A*s*i*m*o*v

.... The first rule of intelligent tinkering is to save all the parts.