DTV-306 No horizontal sweep
 

This RCA DTV306 38" direct view wide screen HDTV powers up with HV,
CRT heaters lit and both fans running as soon as its plugged in. The
power button turns the power light on and off, but there's no other
noticeable effect. Turning up the G2 control reveals a sharp vertical
line about 4" long. There's zero horizontal sweep. It never goes
into shutdown. There's no sound, but without seeing a picture,
there's no way to tell if there should be any sound.

It appears to have had the standby power supply diode upgrade and I've
checked for obvious things like bad soldering, shorted HOT, swollen
caps, cracked PCB,... The standby power supply is working and there's
about 75v on the C of the HOT. There's no horizontal drive. Before I
do anything else, has anyone seen this problem before? I realize this
is a very complex chassis, but I would rather not buy a service manual
if I can avoid it.
Andy Cuffe

-- Use this address until 12/31/2005

-- Use this address after 12/31/2005

No sound could be the T.V. is switched on video input.
Check the two wire connectors in the pincushion correction
circuitry, & for a bad high voltage capacitor @ 400 volts, or
up to 1000 volts, depending on the unit. No horizontal drive
may be due to something bad further into the output stage, &
causing "shut down" of the drive signal from the "jungle IC".
Also check the horizontal drive coil. 75 volts is too low @ the
horizontal output, & MAY be the area to look for a "load" on
the output stage, could even be the flyback. Rono.

On Wed, 28 Sep 2005 17:51:08 -0230, "Rono" wrote:

No sound could be the T.V. is switched on video input.
Check the two wire connectors in the pincushion correction
circuitry, & for a bad high voltage capacitor @ 400 volts, or
up to 1000 volts, depending on the unit. No horizontal drive
may be due to something bad further into the output stage, &
causing "shut down" of the drive signal from the "jungle IC".
Also check the horizontal drive coil. 75 volts is too low @ the
horizontal output, & MAY be the area to look for a "load" on
the output stage, could even be the flyback. Rono.


This isn't a normal TV, it's far more complex than most TVs. From
what I've read the voltage on the HOT is actually running a little
high (probably because of no load). It has separate horizontal and HV
circuits.
Andy Cuffe

-- Use this address until 12/31/2005

-- Use this address after 12/31/2005

On Wed, 28 Sep 2005 11:49:59 -0400, Andy Cuffe
wrote:

This RCA DTV306 38" direct view wide screen HDTV powers up with HV,
CRT heaters lit and both fans running as soon as its plugged in. The
power button turns the power light on and off, but there's no other
noticeable effect. Turning up the G2 control reveals a sharp vertical
line about 4" long. There's zero horizontal sweep. It never goes
into shutdown. There's no sound, but without seeing a picture,
there's no way to tell if there should be any sound.

It appears to have had the standby power supply diode upgrade and I've
checked for obvious things like bad soldering, shorted HOT, swollen
caps, cracked PCB,... The standby power supply is working and there's
about 75v on the C of the HOT. There's no horizontal drive. Before I
do anything else, has anyone seen this problem before? I realize this
is a very complex chassis, but I would rather not buy a service manual
if I can avoid it.
Andy Cuffe

-- Use this address until 12/31/2005

-- Use this address after 12/31/2005

The -12v rectifier diode on the main board was shorted. It was
loading down the power supply causing the +5v supply on the main board
to be only 2v.
Andy Cuffe

-- Use this address until 12/31/2005

-- Use this address after 12/31/2005