[TechAssist] Re: Sony CTV KV27EXR20 (Chassis ANU-2) H. O. T. Shortsafter 20 Minutes.

I have had Panasonic flybacks do the same thing.  The flyback rings
good, but yet after 5-20 minutes the HOT shorts.  Replacing the flyback
fixed the problem.  

Kevin Wilks
Kevin's TV & Video Repair
Penticton BC Canada
kevintv@xxxxxxx 
 

-----Original Message-----
From: techassist-bounce@xxxxxxxxxxxxx
[mailto:techassist-bounce@xxxxxxxxxxxxx] On Behalf Of
HarrisTV50010@xxxxxxx
Sent: Saturday, May 31, 2003 2:44 PM
To: techassist@xxxxxxxxxxxxx
Subject: [TechAssist] Sony CTV KV27EXR20 (Chassis ANU-2) H. O. T. Shorts
after 20 Minutes.

I have a Sony Model KV27EXR20 Chassis ANU-2. The first time this set was
in 
the shop it had a bad STRS6301 Regulator IC but the H. O. T. Was Ok. I
checked 
and resoldered any questionable connections. The customer had the unit
home 
about 2-weeks and it died again.
This time the 2SD1886 H. O. T. had shorted. I checked the horizontal
circuit 
using our Sencore TVA62 and everything checked ok. I replaced the H. O.
T. and 
it ran for 20 minutes and shorted again. 

This time I thoroughly rechecked the regulator circuit using a resistor
load 
and everything checked perfectly. I thoroughly went over the chassis for
any 
questionable connections. I resoldered everything is the base drive &
collector 
circuits of the H. O. T. I replaced the 2SD1886 again. I monitored the
base 
drive and the collector waveform using our X100 scope probe. Everything
looked 
textbook perfect. The Collector pulse width was 14us, which is normal. I
did 
start monitoring the temperature of the H. O. T. Using an Infrared
Thermometer. 
The temperature started rising and the transistor shorted at about 165 
degrees. 

Does anyone have any ideas what might be causing problems? I am using
RCA SK 
2SD1886 which I haven't had any problems in the past. I checked
RepairWorld 
and someone had used a 2SC4729 as a replacement. Do I need to try an
exact Sony 
replacement? Any thought would be greatly appreciated.

TIA,
Dale

Dale A. Lubow... HarrisTV50010@xxxxxxx ..515-232-1109..(Fax)515-232-3356
Harris TV & Appliance..........335 Lincoln 
Way.....Ames.....Iowa.....50010-3384


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