T
Tom Rolfe
Guest
Hi Guys,
Anyone out there familiar with the Philips G112 Chassis?
I've recently been doing battle with one, and would appreciate any
advice on the following fault....
Basically the set arrived with a shorted Line Output transistor.
Someone before me substituted a BU508, which has a lower power
dissipation, so I replace with the original spec 2SD1577, but after
about 5 minutes running it failed shorted again. The transistor shorts
entirely, i.e. base, emitter and collector are all linked. The
heatsink runs reasonably cool for the 5 minutes, which probably means
its not excessive dissipation causing the failure.
I've checked all damper diodes and capacitors around the transistor
and the base drive resistors. With the set running (before it blows up
again), I've checked the 140v main rail which was in spec for both dc
voltage and ac ripple.
I've also checked the line transistor base drive waveforms, and they
correlate exactly with the waveforms given in the service manual.
I'm running out of ideas here, and am starting to suspect the line
output transformer. The weird thing is the picture comes up ok for the
5 minutes the set runs before failing again.
Anyone out there have any prior history with the G112. Do they tend to
have line output tranformer failures which behave like this?
Would appreciate advice from any techs who have done battle with a
G112 and won!!!!!
Regards,
Tom Rolfe.
Anyone out there familiar with the Philips G112 Chassis?
I've recently been doing battle with one, and would appreciate any
advice on the following fault....
Basically the set arrived with a shorted Line Output transistor.
Someone before me substituted a BU508, which has a lower power
dissipation, so I replace with the original spec 2SD1577, but after
about 5 minutes running it failed shorted again. The transistor shorts
entirely, i.e. base, emitter and collector are all linked. The
heatsink runs reasonably cool for the 5 minutes, which probably means
its not excessive dissipation causing the failure.
I've checked all damper diodes and capacitors around the transistor
and the base drive resistors. With the set running (before it blows up
again), I've checked the 140v main rail which was in spec for both dc
voltage and ac ripple.
I've also checked the line transistor base drive waveforms, and they
correlate exactly with the waveforms given in the service manual.
I'm running out of ideas here, and am starting to suspect the line
output transformer. The weird thing is the picture comes up ok for the
5 minutes the set runs before failing again.
Anyone out there have any prior history with the G112. Do they tend to
have line output tranformer failures which behave like this?
Would appreciate advice from any techs who have done battle with a
G112 and won!!!!!
Regards,
Tom Rolfe.