Blown TV power transistor (diagram)

[ac]

I have a goodmans 3375 TV that has just gon pop. It was blowing the internal
2a fuse as soon as it was powered. I found that 2 of the rectifier diodes
had shorted, and 1 main transistor in the PSU area was also dead.

After removing the transistor and replacing the diodes, the fuse no longer
blows. I will have to order the transistor. Meantime, attached is a circuit
diagram. The big transistor that blew is TR15, (S2000AF). I have checked the
2 diodes, D35 & D36 near to it - these are ok. Would there be anything else
to look for or would TR15 have blown 1st and taken out the rectifier diodes.

Should I still get voltages out of IC14 without the TR15 in the circuit or
could that be blown as well ?

Diagram : http://www.photo-it.com/3375.jpg

Cheers

Adam

 

[Orange]

"ac" <blueleds@btinternet.com> wrote in message
news:bnmpr6$dc$1@sparta.btinternet.com...

I have a goodmans 3375 TV that has just gon pop. It was blowing the
internal
2a fuse as soon as it was powered. I found that 2 of the rectifier diodes
had shorted, and 1 main transistor in the PSU area was also dead.

After removing the transistor and replacing the diodes, the fuse no longer
blows. I will have to order the transistor. Meantime, attached is a
circuit
diagram. The big transistor that blew is TR15, (S2000AF). I have checked
the
2 diodes, D35 & D36 near to it - these are ok. Would there be anything
else
to look for or would TR15 have blown 1st and taken out the rectifier
diodes.

Should I still get voltages out of IC14 without the TR15 in the circuit or
could that be blown as well ?

Diagram : http://www.photo-it.com/3375.jpg

Cheers

Adam

 

[Orange]

"ac" <blueleds@btinternet.com> wrote in message
news:bnmpr6$dc$1@sparta.btinternet.com...

I have a goodmans 3375 TV that has just gon pop. It was blowing the
internal
2a fuse as soon as it was powered. I found that 2 of the rectifier diodes
had shorted, and 1 main transistor in the PSU area was also dead.

After removing the transistor and replacing the diodes, the fuse no longer
blows. I will have to order the transistor. Meantime, attached is a
circuit
diagram. The big transistor that blew is TR15, (S2000AF). I have checked
the
2 diodes, D35 & D36 near to it - these are ok. Would there be anything
else
to look for or would TR15 have blown 1st and taken out the rectifier
diodes.

Should I still get voltages out of IC14 without the TR15 in the circuit or
could that be blown as well ?

Diagram : http://www.photo-it.com/3375.jpg

The TDA 4601 IMO is one of the best power supplies ever, looking at that
particular circuit I believe that it's a pretty bog-standard Thomson [F1?]
chassis.

A coincidence but I repaired one today, it wouldn't run [had horrendous
squealing noises coming from the power supply] replacing 'all' of the small
electrolytic capacitors cured the problem.

Also it's quite common for those stupid little underrated INxxx type diodes
in the bridge rectifier circuit to go short circuit for no apparent reason,
I would suggest uprating them for something a little more substantive, or
replacing them with a decent bridge rectifier, hope this helps.

Cheers

Adam

 

[Orange]

"Orange" <cheap@chips.co.uk> wrote in message
news:bnmsms$13gigu$2@ID-60535.news.uni-berlin.de...

"ac" <blueleds@btinternet.com> wrote in message
news:bnmpr6$dc$1@sparta.btinternet.com...
I have a goodmans 3375 TV that has just gon pop. It was blowing the
internal
2a fuse as soon as it was powered. I found that 2 of the rectifier
diodes
had shorted, and 1 main transistor in the PSU area was also dead.

After removing the transistor and replacing the diodes, the fuse no
longer
blows. I will have to order the transistor. Meantime, attached is a
circuit
diagram. The big transistor that blew is TR15, (S2000AF). I have checked
the
2 diodes, D35 & D36 near to it - these are ok. Would there be anything
else
to look for or would TR15 have blown 1st and taken out the rectifier
diodes.

Should I still get voltages out of IC14 without the TR15 in the circuit
or
could that be blown as well ?

Diagram : http://www.photo-it.com/3375.jpg


The TDA 4601 IMO is one of the best power supplies ever, looking at that
particular circuit I believe that it's a pretty bog-standard Thomson [F1?]
chassis.

A coincidence but I repaired one today, it wouldn't run [had horrendous
squealing noises coming from the power supply] replacing 'all' of the
small
electrolytic capacitors cured the problem.

Also it's quite common for those stupid little underrated INxxx type
diodes
in the bridge rectifier circuit to go short circuit for no apparent
reason,
I would suggest uprating them for something a little more substantive, or
replacing them with a decent bridge rectifier, hope this helps.

I forgot to mention 'definitely' replace C103 [100mfd] and because of the
blow up it might be a good idea to also check its associated components
including IC14, [although surprisingly I find these rarely suffer] also
check R160 [100K]

Cheers

Adam

 

[ac]

All the caps around the PSU area are visually ok.

I have just ordered a couple of the S2000AF's, just in case something else
did cause it to blow. The rectifier diodes are 1N4007's. These were the 1st
thing I replaced, but they blew again straight away. Then I removed the
S2000AF which was found to be shorted and changed the diodes
again....fingers crossed...

Cheers

Adam
"Orange" <cheap@chips.co.uk> wrote in message
news:bnmsms$13gigu$2@ID-60535.news.uni-berlin.de...

"ac" <blueleds@btinternet.com> wrote in message
news:bnmpr6$dc$1@sparta.btinternet.com...
I have a goodmans 3375 TV that has just gon pop. It was blowing the
internal
2a fuse as soon as it was powered. I found that 2 of the rectifier
diodes
had shorted, and 1 main transistor in the PSU area was also dead.

After removing the transistor and replacing the diodes, the fuse no
longer
blows. I will have to order the transistor. Meantime, attached is a
circuit
diagram. The big transistor that blew is TR15, (S2000AF). I have checked
the
2 diodes, D35 & D36 near to it - these are ok. Would there be anything
else
to look for or would TR15 have blown 1st and taken out the rectifier
diodes.

Should I still get voltages out of IC14 without the TR15 in the circuit
or
could that be blown as well ?

Diagram : http://www.photo-it.com/3375.jpg


The TDA 4601 IMO is one of the best power supplies ever, looking at that
particular circuit I believe that it's a pretty bog-standard Thomson [F1?]
chassis.

A coincidence but I repaired one today, it wouldn't run [had horrendous
squealing noises coming from the power supply] replacing 'all' of the
small
electrolytic capacitors cured the problem.

Also it's quite common for those stupid little underrated INxxx type
diodes
in the bridge rectifier circuit to go short circuit for no apparent
reason,
I would suggest uprating them for something a little more substantive, or
replacing them with a decent bridge rectifier, hope this helps.




Cheers

Adam

 

[ac]

Thanks, will order the IC14, R160 & C103.
Can you tell me the wattage of the R160, 100k ?

Cheers

Adam

 

[Orange]

"ac" <blueleds@btinternet.com> wrote in message
news:bnmuad$9v0$1@sparta.btinternet.com...

All the caps around the PSU area are visually ok.

I have just ordered a couple of the S2000AF's, just in case something else
did cause it to blow. The rectifier diodes are 1N4007's. These were the
1st
thing I replaced, but they blew again straight away. Then I removed the
S2000AF which was found to be shorted and changed the diodes
again....fingers crossed...

Cheers

Adam

I wouldn't rely on how the capacitors look physically, especially as they're
only a few pence each so I would recommend replacing all of them.

I don't know the actual wattage of R160 but it should be in the parts list,
however I would imagine the usual quarter watt type.

As you don't show the complete circuit it's difficult to see where the [pin
nine] start-up voltage derives from, presumably from an arm of the bridge
rectifier via a resistor/s, or a small positor which can all cause problems.

I don't have a circuit diagram to hand, but could probably dig one out
tomorrow, however it would be on the left-hand side of the diagram if you
trace back from pin nine of the 4601.

 

[ac]

OK, I have uploaded a bit more of the diagram to the same address, I have
the complete diagram, it came with the TV.
http://www.photo-it.com/3375.jpg

You are right, from pin 9 it goes through a small posistor PTC2 then through
2 resistors and into the bridge rectifier. I have ordered a couple of
S2000AF's, and the TDA4601 and will also replace the caps.

I will test the 2 resistors, can I check that PTC2 is working ok ? do you
just check that it is not shorted ? What is it for any how ?

Some one else also told me to remove PTC1 that the degauss is connected to.

Thanks again ,

Adam

As you don't show the complete circuit it's difficult to see where the
[pin
nine] start-up voltage derives from, presumably from an arm of the bridge
rectifier via a resistor/s, or a small positor which can all cause
problems.

I don't have a circuit diagram to hand, but could probably dig one out
tomorrow, however it would be on the left-hand side of the diagram if you
trace back from pin nine of the 4601.

 

[ac]

oops, just realised from the symbols on the diagram that the 2 resistors it
goes through R153/R154 are FUS, I guess that is fuse ? and that R160 100k
is a MELF ??? what ever that is ?

There are also 38 small pics coniciding with test points on the diagram that
look like waves on an oscillascope. Someone gave me an oscillascope but I am
not 100% sure what I doing with it, actually I haven't got a clue....



Adam

 

[Orange]

"ac" <blueleds@btinternet.com> wrote in message
news:bnp1pc$pdo$1@sparta.btinternet.com...

OK, I have uploaded a bit more of the diagram to the same address, I have
the complete diagram, it came with the TV.
http://www.photo-it.com/3375.jpg

You are right, from pin 9 it goes through a small posistor PTC2 then
through
2 resistors and into the bridge rectifier. I have ordered a couple of
S2000AF's, and the TDA4601 and will also replace the caps.

I will test the 2 resistors, can I check that PTC2 is working ok ? do you
just check that it is not shorted ? What is it for any how ?

Some one else also told me to remove PTC1 that the degauss is connected
to.

Thanks again ,

Perhaps I should have pointed out that if you're not familiar with servicing
switch mode power supplies then it's advisable to take extreme care, even
when disconnected from the mains, as some of the larger capacitors can stay
charged up with circa 300v for a quite a lengthy period, and are therefore
capable of giving a serious electric-shock.

In this case C100 has a couple of bleed resistors across it, but I must
emphasise once again you should still be very careful. whilst I don't mind
offering advice, if you have any doubts concerning your ability or issues of
safety, then I would strongly recommend that you leave it to a qualified
technician to carry out the repair for you.

I shouldn't think that you would find any problems with R153/4 the fuseable
resistors, the little blue positor can cause intermittent start-up or
destruction of the control chip, but they don't often give problems [like
the earlier white ones] however they can/do often suffer from dry joints.

The MELF means that it's a metal film resistor which will probably be OK,
however high value resistors in power supplies are 'always' worth checking
as routine, as in some circumstances open circuit ones can cause the
immediate destruction of all those nice new components you to took all that
time and trouble to replace!

I think it's highly unlikely that PTC1will cause the the destruction of the
bridge rectifier and output transistor, normal symptoms are patches of
colour on the screen plus mains fuse blowing, if you're uncertain it won't
hurt to leave out during testing, usually when they're defective in the
majority of cases, shaking it will produce a rattling noise inside.

Adam

As you don't show the complete circuit it's difficult to see where the
[pin
nine] start-up voltage derives from, presumably from an arm of the
bridge
rectifier via a resistor/s, or a small positor which can all cause
problems.

I don't have a circuit diagram to hand, but could probably dig one out
tomorrow, however it would be on the left-hand side of the diagram if
you
trace back from pin nine of the 4601.

 

[ac]

OK, finally got the parts in the post.... fitted them and it's now dead but
does not blow the fuse any more. Every thing is plugged back in.
One thing I did notice was that the circuit diagram shows TR15 as S2000AF,
but the one I took out of the circuit was an S2000N. I ordered and fitted
the S2000AF...

I also replaced the TDA4601 and C103 like you said and repaired some dry
joints.

Any pointers on where to check next ?

Thanks again,

Adam

PS, I am a service engineer working on electrical equipment, copiers,
printers, computers etc, but not trained on TV's.

Perhaps I should have pointed out that if you're not familiar with
servicing
switch mode power supplies then it's advisable to take extreme care, even
when disconnected from the mains, as some of the larger capacitors can
stay
charged up with circa 300v for a quite a lengthy period, and are therefore
capable of giving a serious electric-shock.

In this case C100 has a couple of bleed resistors across it, but I must
emphasise once again you should still be very careful. whilst I don't mind
offering advice, if you have any doubts concerning your ability or issues
of
safety, then I would strongly recommend that you leave it to a qualified
technician to carry out the repair for you.

I shouldn't think that you would find any problems with R153/4 the
fuseable
resistors, the little blue positor can cause intermittent start-up or
destruction of the control chip, but they don't often give problems [like
the earlier white ones] however they can/do often suffer from dry joints.

The MELF means that it's a metal film resistor which will probably be OK,
however high value resistors in power supplies are 'always' worth checking
as routine, as in some circumstances open circuit ones can cause the
immediate destruction of all those nice new components you to took all
that
time and trouble to replace!

I think it's highly unlikely that PTC1will cause the the destruction of
the
bridge rectifier and output transistor, normal symptoms are patches of
colour on the screen plus mains fuse blowing, if you're uncertain it won't
hurt to leave out during testing, usually when they're defective in the
majority of cases, shaking it will produce a rattling noise inside.




Adam

As you don't show the complete circuit it's difficult to see where
the
[pin
nine] start-up voltage derives from, presumably from an arm of the
bridge
rectifier via a resistor/s, or a small positor which can all cause
problems.

I don't have a circuit diagram to hand, but could probably dig one out
tomorrow, however it would be on the left-hand side of the diagram if
you
trace back from pin nine of the 4601.