I have a general question regarding horizontal frequency in a TV. I
have this set that tries to power up but shuts back down. Anyhow, I am
going to scope the H drive pulse and such, but if the frequency isn't
what it should be (suppose to be around 15.7Khz?), would this likely
be part of a protection circuit shut down in some models? Would the
same be true for Vertical as well? The screen and heater voltage is
swinging also. I am trying to repair this with as little help as
possible. This is why I'm not going into details on model #, make, and
such. Thankyou group.

On Mon, 04 Jun 2007 15:25:02 -0700, Golf wrote:

I am trying to repair this with as little help as
possible. This is why I'm not going into details on model #, make, and
such. Thankyou group.

OK, we'll be all too glad to give you as little help as possible.

The answer to your question is maybe.

Without the make, model, and chassis number of the set this is the kind of
answer you will receive. Post relevant data and symptoms so we can at least
attempt an educated and relevant guess.
"PeterD" wrote in message
...
On Mon, 04 Jun 2007 15:25:02 -0700, Golf wrote:

I am trying to repair this with as little help as
possible. This is why I'm not going into details on model #, make, and
such. Thankyou group.

OK, we'll be all too glad to give you as little help as possible.

The answer to your question is maybe.

OK Art, here it goes - Sanyo model #HT32744, chassis #32744-00. Hit
power button, Relays click, high voltage starts, then relay clicks
again and set shuts down (approx 2 seconds time). Can repeat this once
before having to unplug the set to repeat this sequence. I have
checked the power supply including the SMPS which is operating
normally. I have 140vdc at the collector of the HOT (steady). There is
a power failure circuit that I am trying to understand by looking at
the schematic. I disabled this (set stays on) to keep the set running
long enough to check a few more voltages. Even though the set stays
on, there is a faint raster in the middle of the screen about 2"
square that pulses (seems to be in sync with the slight ticking noise
of the flyback). The screen and heater voltage is swinging all over. I
have never checked these voltages on a working set, so I'm not sure
what's normal.
I work on TV's as a hobby, and have about 2 years experience.
I have a good basic understanding of electronics and electricity, and
am self taught with the exception of help from this group. This is why
I may ask some seemingly retarded questions. I hope this is enough
info. Thanks for replying.

On Jun 4, 5:16 pm, "Art" wrote:
Without the make, model, and chassis number of the set this is the kind of
answer you will receive. Post relevant data and symptoms so we can at least
attempt an educated and relevant guess."PeterD" wrote in message

Art, I thought my questions (yes/no/possibly) were pretty straight
forward, but obviously I was wrong. "if the frequency isn't what it
should be (suppose to be around 15.7Khz?), would this likely
be part of a protection circuit shut down in some models? Would the
same be true for Vertical as well? "
Peter gave a better answer (maybe) anyway. Thanks

Golf wrote:
I have a general question regarding horizontal frequency in a TV. I
have this set that tries to power up but shuts back down. Anyhow, I am
going to scope the H drive pulse and such, but if the frequency isn't
what it should be (suppose to be around 15.7Khz?), would this likely
be part of a protection circuit shut down in some models? Would the
same be true for Vertical as well? The screen and heater voltage is
swinging also. I am trying to repair this with as little help as
possible. This is why I'm not going into details on model #, make, and
such. Thankyou group.


As others have said, information is key. However there are a couple of
things you might try to zero in on the problem:

From your comments, I assume that the HOT is not shorted. Jumper the
base to the emitter of it to force it to stay turned off and see if the
power will stay up. Of course you will not see a raster due to the HOT
being shorted out, but if the power stays on your problem is located on
one of the output terminals of the flyback transformer. If this is the
case look for a shorted diode off of one of those secondary windings.

It could be other things, but that is often the reason based upon the
symptoms you described.

On Jun 4, 7:23 pm, Ken wrote:
Golf wrote:
I have a general question regarding horizontal frequency in a TV. I
have this set that tries to power up but shuts back down. Anyhow, I am
going to scope the H drive pulse and such, but if the frequency isn't
what it should be (suppose to be around 15.7Khz?), would this likely
be part of a protection circuit shut down in some models? Would the
same be true for Vertical as well? The screen and heater voltage is
swinging also. I am trying to repair this with as little help as
possible. This is why I'm not going into details on model #, make, and
such. Thankyou group.

As others have said, information is key. However there are a couple of
things you might try to zero in on the problem:

From your comments, I assume that the HOT is not shorted. Jumper the
base to the emitter of it to force it to stay turned off and see if the
power will stay up. Of course you will not see a raster due to the HOT
being shorted out, but if the power stays on your problem is located on
one of the output terminals of the flyback transformer. If this is the
case look for a shorted diode off of one of those secondary windings.

It could be other things, but that is often the reason based upon the
symptoms you described.

Thanks for the reply Ken. For the sake of me explaining everything
I've done in the past 2 hours, I think I found a problem on a 6.5V
supply. It goes to the P in P module, an RGB drive IC, and somewhere
in the video deflection circuit I think. Long story short - removing
power from this 6.5 regulator keeps all voltages stable off the SMPS.
I was going to disconnect the output of this regulator first though to
see if it was OK.

On Mon, 04 Jun 2007 15:25:02 -0700, Golf put finger
to keyboard and composed:

I have a general question regarding horizontal frequency in a TV. I
have this set that tries to power up but shuts back down. Anyhow, I am
going to scope the H drive pulse and such, but if the frequency isn't
what it should be (suppose to be around 15.7Khz?), would this likely
be part of a protection circuit shut down in some models?

I have seen a fault of this kind in an old IBM monitor. A ceramic cap
drifted in value, causing the horizontal frequency to increase (or was
it the duty cycle?), which in turn caused the pulse amplitude on the
collector of the HOT to increase. This was reflected in a secondary
winding of the FBT which then triggered the HV protection and shut
down the unit.

Would the
same be true for Vertical as well? The screen and heater voltage is
swinging also. I am trying to repair this with as little help as
possible. This is why I'm not going into details on model #, make, and
such. Thankyou group.

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