Nightmare Samsung PTV

[Chris F.]

This Samsung HCN4767W projection set is really making a nuisance of
itself. It had a blown convergence IC when I acquired it, so I replaced them
both. It ran for a few days in the shop (about 6-8 hours a day), then blew
one of the same IC's again. I replaced them again, and also replaced the
convergence processor board. Again, it seemed to work fine for a few days,
but now the bloody IC's have blown again. The supply voltage to the IC's is
a solid 25V (pos. and neg.), well within the 50V max. supply voltage the
IC's are rated for. Both IC's are properly heatsinked, though they seem to
run quite hot - I assumed this was just normal. I've also gone through the
convergence board and power supply looking for caps up in ESR, but found
none.
The replacement IC's were supposed to be OEM, but I have to wonder just
how compatible they really are. It's the only explanation I can think of.
I'm tired of wasting time and money on this piece of junk. Unless I can be
certain any further replacement parts will work, I'm going to scrap it and
take my losses, which would be close to $300 as of right now. I will also
vow to never gamble on a Samsung again - they're nothing but trouble.
Any advice would be appreciated

 

[David]

"Chris F." wrote in message

This Samsung HCN4767W projection set is really making a nuisance
of itself. It had a blown convergence IC when I acquired it, so
I replaced them both. It ran for a few days in the shop (about
6-8 hours a day), then blew one of the same IC's again. I
replaced them again, and also replaced the convergence processor
board. Again, it seemed to work fine for a few days, but now the
bloody IC's have blown again. The supply voltage to the IC's is
a solid 25V (pos. and neg.), well within the 50V max. supply
voltage the IC's are rated for. Both IC's are properly
heatsinked, though they seem to run quite hot - I assumed this
was just normal. I've also gone through the convergence board
and power supply looking for caps up in ESR, but found none.
The replacement IC's were supposed to be OEM, but I have to
wonder just how compatible they really are. It's the only
explanation I can think of.
I'm tired of wasting time and money on this piece of junk.
Unless I can be certain any further replacement parts will
work, I'm going to scrap it and take my losses, which would be
close to $300 as of right now. I will also vow to never gamble
on a Samsung again - they're nothing but trouble.
Any advice would be appreciated

Usually these problems are due to the static centering rings on
one or more of the CRTs being misadjusted and the convergence IC
has to put out a steady DC component to correct it. If you scope
the outputs from the convergence IC and see both positive and
negative current swings into the convergence magnets, everything
is OK. If not, you need to adjust the centering magnet(s) on the
appropriate tube(s) and then re-converge the set.

David

 

[Meat Plow]

Usually these problems are due to the static centering rings on one or
more of the CRTs being misadjusted and the convergence IC has to put out
a steady DC component to correct it. If you scope the outputs from the
convergence IC and see both positive and negative current swings into
the convergence magnets, everything is OK. If not, you need to adjust
the centering magnet(s) on the appropriate tube(s) and then re-converge
the set.

David

Certain Samsung models were pretty popular for this. I take it by your
knowledge that you've worked on a few.

 

[David]

Usually these problems are due to the static centering rings on

one or
more of the CRTs being misadjusted and the convergence IC has
to put out
a steady DC component to correct it. If you scope the outputs
from the
convergence IC and see both positive and negative current
swings into
the convergence magnets, everything is OK. If not, you need to
adjust
the centering magnet(s) on the appropriate tube(s) and then
re-converge
the set.

David

Certain Samsung models were pretty popular for this. I take it
by your
knowledge that you've worked on a few.

Yes, but those were not the only sets with this problem. There
were quite a few Sony sets as well. If the convergence ICs are
running hot, the scope comes out and 9 times out of 10, fixing
the static centering and re-convergence clears the overheating.

David

 

[Meat Plow]

Yes, but those were not the only sets with this problem. There were
quite a few Sony sets as well. If the convergence ICs are running hot,
the scope comes out and 9 times out of 10, fixing the static centering
and re-convergence clears the overheating.

David

Makes sense. I'd have to assume these were factory defects that resulted
in the sets affected to work for a couple years. Or do the static
adjustments somehow move on their own due to heat/cool cycles? I know on
my Panasonic 51" PTV the screws holding the convergence ICs were
laughably loose when I replaced them in 2006. The set worked fine from
1999. And has worked fine since the repair. I used a little compound on
the screw thread and a dab of glue on the heads after I torqued them down
so they wouldn't walk back loose which is what I theorized happened. No
way would the amps have lasted 6+ years as loosely set to the heat sink
as they were.

 

[Bruce Esquibel]

but now the bloody IC's have blown again. The supply voltage to the IC's is
a solid 25V (pos. and neg.), well within the 50V max. supply voltage the
IC's are rated for. Both IC's are properly heatsinked, though they seem to

Hate to sound like Joe Obvious, but where did you get the 50V max from and
is that max for each input voltage or a potential across them?

The one thing that jumps out with the above is, +25 and -25 gives a working
voltage of 50V, if you see what I mean.

Just saying, even if each leg was only a volt high (instead of +24/-24),
given the amount of current those things draw, probably adds up to a few
watts of less heat it has to get rid of.

Just throwing a thought out.

-bruce
[email protected]

 

[Chris F.]

Hate to sound like Joe Obvious, but where did you get the 50V max from and

is that max for each input voltage or a potential across them?

The one thing that jumps out with the above is, +25 and -25 gives a
working
voltage of 50V, if you see what I mean.

Never thought of that. It actually specifies +/- 20V on the board itself,
however I was measuring this with the convergence board disconnected - not
sure what the actual voltage is while under load, and now I'd have to
replace the IC's again to find out.
Not sure if I want to gamble another $50 on this thing or not.

 

[Chris F.]

I think I have this straightened out... I hope. After installing the two new
convergence IC's, I was surprised to see the exact same symptom. I pulled
the convergence processor board, which I had newly replaced, and saw a
burned zener diode. I replaced it with one from the old module, and
everything seemed back to normal. But to be certain, I reset the convergence
to factory default and started over. I also attached ammeters to the +25
and -25 supplies going to the convergence output board, to monitor the
current as I made the adjustments. Once the convergence adjustments were
done, the current draw was about 600mA on each supply, at 23V. The IC's were
still quite hot, and I realized that this was due to poor design: both were
bolted to a single, thin heatsink which mounts to the steel frame. Very
little heat was getting transferred to the steel frame, even though
everything was mounted properly. So what I did was remove the module from
the steel frame, and bolted a much larger heatsink to the existing one, and
mounted everything to the side of the cabinet. The IC's run much cooler now,
and hopefully this will prevent them from failing again.
I've learned a few things from this, the most important being to never
gamble money on a Samsung. Once this TV is sold I hope I never see it again.