Hot horz. output transistor
 

I have a GE 35GT695 35" TV (chassis # CTC187) with a horizontal output
transistor that runs hot, and hotter. The original one, a BUH517, failed,
and I replaced it with another one. Most of the time it runs at ~135 deg F,
but every 4 - 8 hrs, it spikes up to 200. It has run for about 48 hrs. The
picture and sound are fine.

I rang the flyback and yoke and used a DMM on the diode setting to check the
diodes in the horizontal output stage (in-circuit) and they look OK. The B+
is 140v, and the 190v supply is at 200v. Both measurments were made using a
DMM.

Any suggestions? I have the SAMS Photofact, a scope and an isolation xfrmr.

Thanks
Bill

Hot horz. output transistor
 

Many years ago I saw a problem like this, Horz O/P xistors not lasting
very long. There was a capicator from the collector to emitter of the xistor
that had become open. It's purpose there was to prevent ringing. Might be
something to check.

"Bill" wrote in message
news:zLSTb.168220$Rc4.1291914@attbi_s54...
I have a GE 35GT695 35" TV (chassis # CTC187) with a horizontal output
transistor that runs hot, and hotter. The original one, a BUH517, failed,
and I replaced it with another one. Most of the time it runs at ~135 deg
F,
but every 4 - 8 hrs, it spikes up to 200. It has run for about 48 hrs.
The
picture and sound are fine.

I rang the flyback and yoke and used a DMM on the diode setting to check
the
diodes in the horizontal output stage (in-circuit) and they look OK. The
B+
is 140v, and the 190v supply is at 200v. Both measurments were made using
a
DMM.

Any suggestions? I have the SAMS Photofact, a scope and an isolation
xfrmr.

Thanks
Bill

Hot horz. output transistor
 

Bill:
Since you have a scope and the SAMS Photofact you are way ahead of the game
........
Check the horizontal driver and other waveforms around that area.... the
Photofact will have a pictorial of the way the waveforms should look as well
as the approximate P-P amplitude..... if there is ringing or out of spec
rise-times, etc..... you may have located the problem.... could be a cap,
coil, ? ? ?
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -


"Bill" wrote in message
news:zLSTb.168220$Rc4.1291914@attbi_s54...
I have a GE 35GT695 35" TV (chassis # CTC187) with a horizontal output
transistor that runs hot, and hotter. The original one, a BUH517, failed,
and I replaced it with another one. Most of the time it runs at ~135 deg
F,
but every 4 - 8 hrs, it spikes up to 200. It has run for about 48 hrs.
The
picture and sound are fine.

I rang the flyback and yoke and used a DMM on the diode setting to check
the
diodes in the horizontal output stage (in-circuit) and they look OK. The
B+
is 140v, and the 190v supply is at 200v. Both measurments were made using
a
DMM.

Any suggestions? I have the SAMS Photofact, a scope and an isolation
xfrmr.

Thanks
Bill

Hot horz. output transistor
 

On Tue, 03 Feb 2004 19:37:04 GMT, "Bill" wrote:

I have a GE 35GT695 35" TV (chassis # CTC187) with a horizontal output
transistor that runs hot, and hotter. The original one, a BUH517, failed,
and I replaced it with another one. Most of the time it runs at ~135 deg F,
but every 4 - 8 hrs, it spikes up to 200. It has run for about 48 hrs. The
picture and sound are fine.

I rang the flyback and yoke and used a DMM on the diode setting to check the
diodes in the horizontal output stage (in-circuit) and they look OK. The B+
is 140v, and the 190v supply is at 200v. Both measurments were made using a
DMM.

Any suggestions? I have the SAMS Photofact, a scope and an isolation xfrmr.

Thanks
Bill

Check the SMD 2.4K resistor off emitter of the hot driver circuit.
Usually this is bad. Also remove and scrape thorughly & carefully on
horizontal transformer driver.

Caps & dampers, pincushion circuit checks is also good idea.

BTW, use original RCA parts especially for this horizontal circuit.

Cheers,

Wizard

Hot horz. output transistor
 

The power devices, and many critical components used in these sets are
usually select on test. This is why we use origional manufacture
parts, especialy for power devices, such as switching drivers, and
output devices ( as like HOT's ).

The normal operating temperature for an HOT or vertical output
transistor can be about 50 to 70 deg Cels. Above 75 deg Cels, the
device is running very close to the maximum temp for most of these
devices to have reliability. After 90 deg Cels, it will be on the edge
of its max temperature endurance, and can easily fail.

It is normal for this device to run fairly hot, around 70 deg Cels.
It can overheat, if some of the coupler or decoupler caps in the
associated circuits are starting to go high in ESR. Failing support
components, or improper biasing, or improper drives to devices can
cause overheating. It is possible for caps or other support components
to go unstable before they fail. This can cause unpredicable effects,
on other associated components as well.

If the set is running properly, you are sure that there are no
defective components, and you want to make a heatsinked device run a
bit cooler, it is possible to add an extended aluminum plate on the
back of the heatsink if there is space. The plate has to be properly
thermo coupled, and mounted to help dissipate the heat. But, it is
important to know that there are no defective components, causing some
over heating in the first place.

Jerry Greenberg
http://www.zoom-one.com

==


"Bill" wrote in message news:zLSTb.168220$Rc4.1291914@attbi_s54...
I have a GE 35GT695 35" TV (chassis # CTC187) with a horizontal output
transistor that runs hot, and hotter. The original one, a BUH517, failed,
and I replaced it with another one. Most of the time it runs at ~135 deg F,
but every 4 - 8 hrs, it spikes up to 200. It has run for about 48 hrs. The
picture and sound are fine.

I rang the flyback and yoke and used a DMM on the diode setting to check the
diodes in the horizontal output stage (in-circuit) and they look OK. The B+
is 140v, and the 190v supply is at 200v. Both measurments were made using a
DMM.

Any suggestions? I have the SAMS Photofact, a scope and an isolation xfrmr.

Thanks
Bill