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.

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 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

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.

I give it about a 70% chance it is the flyback.

It ain't the frequency, it is the waveshape that tells you.

Just to give it from the top once, you put the scope in 200Mv, 10uS
auto triggered. you put the probe near the fly, and you should see a
pulse, about 12-13 uS for a nonHDTV. If you do, you scope the vertical
windings of the yoke, put yout finger on the scope probe, take it into
freerun mode and use the vernier to sync it with the powerline pickup
from your body. Then you go to the yellow and green wires to the yoke
at 20V/div.

You should see a similar pulse but with a ramp on the end. It will be
moving, but you can still see it. If you do, you go to the main B+ and
set it to 50V/div and watch it rise, if you see it go over three divs,
suspect caps on the primary side of the SMPS or a bad opto or
something that drives it.

If the set is regulating properly, don't forget the audio IC, scope
the Vcc to it and see if it drops like a rock, if so, remove the audio
IC and try it again.

And never forget, if you get a ****ed up waveform out of the fly,
check ALL diodes connected to the fly, especially the big ones.

If all this fails, well it may be junk. Needing proprietary parts is
not an option. Aftermarket flys are out there, ome of better quality
than others, but when you get deep deep into the circuitry, it is not
usually worth the time unless the unit was expensive and hs as good
chance of having a good CRT. CRTs do not last like they used to, and
the old ones are old.

Off to bed.

JURB

On Jun 5, 11:25 pm, wrote:
I give it about a 70% chance it is the flyback.

It ain't the frequency, it is the waveshape that tells you.

Just to give it from the top once, you put the scope in 200Mv, 10uS
auto triggered. you put the probe near the fly, and you should see a
pulse, about 12-13 uS for a nonHDTV. If you do, you scope the vertical
windings of the yoke, put yout finger on the scope probe, take it into
freerun mode and use the vernier to sync it with the powerline pickup
from your body. Then you go to the yellow and green wires to the yoke
at 20V/div.

You should see a similar pulse but with a ramp on the end. It will be
moving, but you can still see it. If you do, you go to the main B+ and
set it to 50V/div and watch it rise, if you see it go over three divs,
suspect caps on the primary side of the SMPS or a bad opto or
something that drives it.

If the set is regulating properly, don't forget the audio IC, scope
the Vcc to it and see if it drops like a rock, if so, remove the audio
IC and try it again.

And never forget, if you get a ****ed up waveform out of the fly,
check ALL diodes connected to the fly, especially the big ones.

If all this fails, well it may be junk. Needing proprietary parts is
not an option. Aftermarket flys are out there, ome of better quality
than others, but when you get deep deep into the circuitry, it is not
usually worth the time unless the unit was expensive and hs as good
chance of having a good CRT. CRTs do not last like they used to, and
the old ones are old.

Off to bed.

JURB

Sorry I haven't updated in a few days - Iv'e had my head stuck in the
back of this ******* TV going on 4 days straight. Here is the latest -
I managed to narrow down the problem to the 14V or 15V supply off the
SMPS. If I disconnect the 14V from the main board, the power supply
stays up. I disconnected each individual 14V source (feeds a couple
regulators, PIP module ,etc) in hopes of finding the bad actor. Funny
thing is, if anything is connected to the 14V source, the voltage
swings wildly putting the set in shut down. Now it seems the problem
is the source voltage. Steady 14V with no load. Goes ape **** with any
load. I connected a flashlight to the 14V source (disconnected from
main board). The voltage was steady, but dropped to about 9.5V. I did
the same thing on the 15V source (steady with no load), and whamo, the
flashlight started clicking on and off as was this voltage swinging
big time (kinda looks like some AC in this voltage too). I checked
every component off the SMPS secondary and found nothing bad yet. I am
wondering if the switching transformer is gimped. The 35V supply is
reading 45 - 50V, but is steady. The other voltages are steady - 140V,
-15V. Sooo, I don't have experience with faulty SMPS transformers, but
if it can't supply the load demand without dropping the voltage,
doesn't it have to be this? Thanks again guys for all replies and
suggestions.