W
W.i.k.i.M.a.n
- Jan 1, 1970
- 0
Hi,
I had my tv repaired some time ago. All the functioning
was fine but the technician had replaced the main fuse with a
thick wire and I started using the tv without knowing about that.
Recently, it went bad again. I decided to check it myself. I opened
the casing and instantly spotted a broken/open resistor 3.3 ohm, 15W.
I replaced it and powered the set. It started but after about 5/6
seconds went down with explosion and lightning. The same resistor
broke open again. At this time I spotted the thick wire at the
main fuse holder.
I bought the tv's circuit diagram, read SER FAQs, and went on to
check for any bad power transistor in the supply section (since power
supply input read 50 ohms indicating that bridge or posistor is not
the problem IMO). HOT was good but another one, C4706, high voltage
switching transistor in the regulator section of SMPS, was bad, both
B-E and C-E were shorted.
I replaced the resistor, C4706 transistor, and fuse (T4.0A), and
powered the set. It ran for about 7/8 seconds, screen was brightened
white with a black horizontal line in the middle. And then it turned
off again with explosion and lightning. I rechecked, this time only
the fuse was blown.
Being an electrical engineer, I'm not considering an option to get it
repaired by someone else. For this, I need the following information:
- Is this start-up scenario typical with some common cause and
remedy?
- I think of first confirming if the SMPS is good, and for this I
should disconnect all other circuit (all load of SMPS) and check if
fuse still blows, and if it doesn't, are the output voltages correct
(according to the diagrams, SMPS should give 140v, 12v, and 5v DCs)?
- Any other ideas of how to proceed?
Thanks in advance,
W.i.k.i.m.a.n
I had my tv repaired some time ago. All the functioning
was fine but the technician had replaced the main fuse with a
thick wire and I started using the tv without knowing about that.
Recently, it went bad again. I decided to check it myself. I opened
the casing and instantly spotted a broken/open resistor 3.3 ohm, 15W.
I replaced it and powered the set. It started but after about 5/6
seconds went down with explosion and lightning. The same resistor
broke open again. At this time I spotted the thick wire at the
main fuse holder.
I bought the tv's circuit diagram, read SER FAQs, and went on to
check for any bad power transistor in the supply section (since power
supply input read 50 ohms indicating that bridge or posistor is not
the problem IMO). HOT was good but another one, C4706, high voltage
switching transistor in the regulator section of SMPS, was bad, both
B-E and C-E were shorted.
I replaced the resistor, C4706 transistor, and fuse (T4.0A), and
powered the set. It ran for about 7/8 seconds, screen was brightened
white with a black horizontal line in the middle. And then it turned
off again with explosion and lightning. I rechecked, this time only
the fuse was blown.
Being an electrical engineer, I'm not considering an option to get it
repaired by someone else. For this, I need the following information:
- Is this start-up scenario typical with some common cause and
remedy?
- I think of first confirming if the SMPS is good, and for this I
should disconnect all other circuit (all load of SMPS) and check if
fuse still blows, and if it doesn't, are the output voltages correct
(according to the diagrams, SMPS should give 140v, 12v, and 5v DCs)?
- Any other ideas of how to proceed?
Thanks in advance,
W.i.k.i.m.a.n