Half a picture

R

Ray

Guest
I have a stubborn one on the bench. It's a Philips Model 27TS54C101
Chassis 27B800-7562 with a vertical problem. A somewhat distorted
picture only sweeps the upper half of the screen and R420 is
overheating. See the screen shot at
http://personalpages.tds.net/~rcarlsen/philips.jpg
The vertical IC TDA9302H has been replaced along with the boost
diode, and all the caps have been checked for leakage and ESR. I have no
schematic but the vertical circuit seems to have a split supply with 12V
positive and negative scan derived supplies. R420 comes off the flyback
pin 5 to feed the diode for the negative end. Both supplies are up but I
can't leave the set on for more than about 10 seconds or the resistor
and/or supply diode will fail. Has anyone been down this trail before?
Thanks in advance for any help! (I read the newsgroup frequently.)

Ray
--
My return address is obviously fake. To email me directly, use
rrcc at myuw dot net
 
I had this type of problem in another type of set. The fault ended up to be
a cap that became resistive instead of opened as they normally go. The ESR
meter was telling me that the cap was good, but it was resistive!

This is a lot of work, but you can try to remove all the caps one at a time,
and use an ohm meter to test them to make sure that there is no DC
resistance. If you have an analog ohm meter (like in the old days), this is
better for testing the DC resistance of caps. Many digital meters pulse
sample when measuring resistance, thus your readings may not be accurate.
If your digital ohm meter is using continuous DC sampling for the ohms
readings, then it should work out for this they of test.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
Instruments http://www.zoom-one.com/glgtech.htm
=========================================


"Ray" <bogus@non.com> wrote in message news:3F62D09C.119C7302@non.com...
I have a stubborn one on the bench. It's a Philips Model 27TS54C101
Chassis 27B800-7562 with a vertical problem. A somewhat distorted
picture only sweeps the upper half of the screen and R420 is
overheating. See the screen shot at
http://personalpages.tds.net/~rcarlsen/philips.jpg
The vertical IC TDA9302H has been replaced along with the boost
diode, and all the caps have been checked for leakage and ESR. I have no
schematic but the vertical circuit seems to have a split supply with 12V
positive and negative scan derived supplies. R420 comes off the flyback
pin 5 to feed the diode for the negative end. Both supplies are up but I
can't leave the set on for more than about 10 seconds or the resistor
and/or supply diode will fail. Has anyone been down this trail before?
Thanks in advance for any help! (I read the newsgroup frequently.)

Ray
--
My return address is obviously fake. To email me directly, use
rrcc at myuw dot net
 
Look for bad filter cap 470 or 1000 mfd close to flyback

kip


--
"Watch the return E-Mail addy its false"
"Ray" <bogus@non.com> wrote in message news:3F62D09C.119C7302@non.com...
I have a stubborn one on the bench. It's a Philips Model 27TS54C101
Chassis 27B800-7562 with a vertical problem. A somewhat distorted
picture only sweeps the upper half of the screen and R420 is
overheating. See the screen shot at
http://personalpages.tds.net/~rcarlsen/philips.jpg
The vertical IC TDA9302H has been replaced along with the boost
diode, and all the caps have been checked for leakage and ESR. I have no
schematic but the vertical circuit seems to have a split supply with 12V
positive and negative scan derived supplies. R420 comes off the flyback
pin 5 to feed the diode for the negative end. Both supplies are up but I
can't leave the set on for more than about 10 seconds or the resistor
and/or supply diode will fail. Has anyone been down this trail before?
Thanks in advance for any help! (I read the newsgroup frequently.)

Ray
--
My return address is obviously fake. To email me directly, use
rrcc at myuw dot net
Click to expand...
 
On Sat, 13 Sep 2003 01:09:00 -0700, Ray <bogus@non.com> wrote:

I have a stubborn one on the bench. It's a Philips Model 27TS54C101
Chassis 27B800-7562 with a vertical problem. A somewhat distorted
picture only sweeps the upper half of the screen and R420 is
overheating. See the screen shot at
Click to expand...
Yes, Philips is strange design and vertical IC MUST be isolated (using
isolation thermal pad) from heatsink due to dual voltage design. When
this solder connections on the vertical IC breaks up IC dies and takes
out any of those supply diodes for this also maybe a resistor.

That -12V is busted this is for bottom half portion. Get your scope
on that -12V and I expect to see BIG noise on it.

BTW, you can sub that vertical IC to TDA8172. This is uprated
vertical IC if you have any sets that use blown TDA9302.

I had panasonic with squeezed vertical sweep appox 3" tall in center,
it was the 26V filter cap dried up, scope showed loads of noise
instead of quiet tiny ripple.

Cheers,

Wizard
 
Follow the Philips service bulletin on upgrading/repairing that vertical
circuit and replace ALL the parts listed and it will be fixed and stay
fixed. Do not forget to FIRMLY attach the heatsink to the pcb as one common
problem after the proper fix is the heatsink moving and breaking the legs of
the vertical ic.

Both the + and - scan derived diodes need upgraded to the new number, the
fusible resistors need replaced, as well as the vertical output itself.

David

Ray <bogus@non.com> wrote in message news:3F62D09C.119C7302@non.com...
I have a stubborn one on the bench. It's a Philips Model 27TS54C101
Chassis 27B800-7562 with a vertical problem. A somewhat distorted
picture only sweeps the upper half of the screen and R420 is
overheating. See the screen shot at
http://personalpages.tds.net/~rcarlsen/philips.jpg
The vertical IC TDA9302H has been replaced along with the boost
diode, and all the caps have been checked for leakage and ESR. I have no
schematic but the vertical circuit seems to have a split supply with 12V
positive and negative scan derived supplies. R420 comes off the flyback
pin 5 to feed the diode for the negative end. Both supplies are up but I
can't leave the set on for more than about 10 seconds or the resistor
and/or supply diode will fail. Has anyone been down this trail before?
Thanks in advance for any help! (I read the newsgroup frequently.)

Ray
--
My return address is obviously fake. To email me directly, use
rrcc at myuw dot net
Click to expand...
 
Not based on experience with this particular set, but I'm betting
shorted yoke.
Click to expand...
Tom,
I was starting to think so too, so I desoldered it and checked both
halves. They matched resistance wise. With a partial schematic from Eric
(many thanks to him and to all who responded), I replaced both supply
diodes with beefier ones, and the fuse-resistors and caps as David
suggested. The final problem was the IC (itself a replacement). The set
works fine now and the new IC runs cool. This chassis uses a large
wraparound sink that also holds the HOT, not the individual one David
mentioned. Last note: the original problem was likely only bad solder on
the IC legs. When I was resoldering it, I noticed a tiny spark as I
accidently shorted two pins with the iron (set off and unplugged, of
course). One cap was obviously still charged up and that area is hard to
see under the plastic sub-chassis. Thanks again for all the suggestions
and help.

Ray
--
My return address is obviously fake. To email me, use
rrcc at myuw dot net
 
FYI it is the large wrap around heatsink that was causing the problems, the
info indicated placing a solid spot of hv silicone on the heatsink to each
side of the vertical ic to hold it tight to the pcb.
The B8 chassis also needs the upgraded b+ diodes for the vertical and the
fusible resistors need to be 1/3W metal film flameproof 1 ohm jobs.


Ray <bogus@non.com> wrote in message news:3F63A1FA.BC1B8D8A@non.com...
Not based on experience with this particular set, but I'm betting
shorted yoke.

Tom,
I was starting to think so too, so I desoldered it and checked both
halves. They matched resistance wise. With a partial schematic from Eric
(many thanks to him and to all who responded), I replaced both supply
diodes with beefier ones, and the fuse-resistors and caps as David
suggested. The final problem was the IC (itself a replacement). The set
works fine now and the new IC runs cool. This chassis uses a large
wraparound sink that also holds the HOT, not the individual one David
mentioned. Last note: the original problem was likely only bad solder on
the IC legs. When I was resoldering it, I noticed a tiny spark as I
accidently shorted two pins with the iron (set off and unplugged, of
course). One cap was obviously still charged up and that area is hard to
see under the plastic sub-chassis. Thanks again for all the suggestions
and help.

Ray
--
My return address is obviously fake. To email me, use
rrcc at myuw dot net
Click to expand...
 
On Sat, 13 Sep 2003 16:02:18 -0700, Ray <bogus@non.com> wrote:

Not based on experience with this particular set, but I'm betting
shorted yoke.

Tom,
I was starting to think so too, so I desoldered it and checked both
halves. They matched resistance wise. With a partial schematic from Eric
(many thanks to him and to all who responded), I replaced both supply
diodes with beefier ones, and the fuse-resistors and caps as David
suggested. The final problem was the IC (itself a replacement). The set
works fine now and the new IC runs cool. This chassis uses a large
wraparound sink that also holds the HOT, not the individual one David
mentioned. Last note: the original problem was likely only bad solder on
the IC legs. When I was resoldering it, I noticed a tiny spark as I
accidently shorted two pins with the iron (set off and unplugged, of
course). One cap was obviously still charged up and that area is hard to
see under the plastic sub-chassis. Thanks again for all the suggestions
and help.

Ray
Click to expand...
Always nice to hear good news, even when my WAG is wrong as wrong can
be. :)

Tom
 
On Sat, 13 Sep 2003 21:47:53 -0500, "David" <dkuhajda@locl.net.spam>
wrote:

FYI it is the large wrap around heatsink that was causing the problems, the
info indicated placing a solid spot of hv silicone on the heatsink to each
side of the vertical ic to hold it tight to the pcb.
The B8 chassis also needs the upgraded b+ diodes for the vertical and the
fusible resistors need to be 1/3W metal film flameproof 1 ohm jobs.
Click to expand...
There was a Magnasonic chassis that had a windowblind effect for the
same reason a number of years ago. I guess the heatsink vibrated at a
harmonic of the vertical frequency, creating the windowblind effect?

Tom

Ray <bogus@non.com> wrote in message news:3F63A1FA.BC1B8D8A@non.com...
Not based on experience with this particular set, but I'm betting
shorted yoke.

Tom,
I was starting to think so too, so I desoldered it and checked both
halves. They matched resistance wise. With a partial schematic from Eric
(many thanks to him and to all who responded), I replaced both supply
diodes with beefier ones, and the fuse-resistors and caps as David
suggested. The final problem was the IC (itself a replacement). The set
works fine now and the new IC runs cool. This chassis uses a large
wraparound sink that also holds the HOT, not the individual one David
mentioned. Last note: the original problem was likely only bad solder on
the IC legs. When I was resoldering it, I noticed a tiny spark as I
accidently shorted two pins with the iron (set off and unplugged, of
course). One cap was obviously still charged up and that area is hard to
see under the plastic sub-chassis. Thanks again for all the suggestions
and help.

Ray
--
My return address is obviously fake. To email me, use
rrcc at myuw dot net
Click to expand...
 
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