Why does my HOT blow every 2-3 months??

[tem00]

I have a Toshiba 65H80 that I replaced the normal HOT section stuff
including the flyback, some caps, cap block (splitter) and of course
the HOT, etc. etc.

It works good about 3 months and blows again. I replace the HOT,
works for another 3 months.

B+ seems right.

Is there anything else that is a common failure point for HOTs that
I'm overlooking?

Thanks

tem00

 

[Jamie]

I have a Toshiba 65H80 that I replaced the normal HOT section stuff
including the flyback, some caps, cap block (splitter) and of course
the HOT, etc. etc.

It works good about 3 months and blows again. I replace the HOT,
works for another 3 months.

B+ seems right.

Is there anything else that is a common failure point for HOTs that
I'm overlooking?

Thanks

tem00

Hmm, maybe you're using incorrect rated HOTranny ?

are you putting on heat sink compound?.

are you getting the exact replacement ?

is it possible it was replaced before by some one else
that may have used a different number ? something they had
lying around..

also, You may want to test for the load current in the B+
line, it could be exceeding and the regulator could be driving
the HOT harder to keep it stable. I've seen C+ taps from the HOT
have leaky caps for lower voltage supplied derived from the HOTxformer.
etc.. This would cause the flyback to work harder.
Also, improper adjustments to the screen controls could cause the
flyback to run hotter along etc...
theirs a lot of variables here.

You may also want to test the input to the HOTransistor with a
scope to see if you're getting full on/off input drive and don't
have some constant DC there driving the base.

 

[b]

tem00 ha escrito:

I have a Toshiba 65H80 that I replaced the normal HOT section stuff
including the flyback, some caps, cap block (splitter) and of course
the HOT, etc. etc.

It works good about 3 months and blows again. I replace the HOT,
works for another 3 months.

B+ seems right.

Is there anything else that is a common failure point for HOTs that
I'm overlooking?

Thanks

tem00

check the capacitors in the line drive circuit. these are often rated
quite low, something like 10-47uF. In one vestel set recently which
ran hot i changed the cap from 10uF to 22uf and it now runs cooler.

also check the cap across the c-e of the HOT.

faulty line o/p transformers can cause these problems too.
good luck.
-B

 

[Mark D. Zacharias]

I have a Toshiba 65H80 that I replaced the normal HOT section stuff
including the flyback, some caps, cap block (splitter) and of course
the HOT, etc. etc.

It works good about 3 months and blows again. I replace the HOT,
works for another 3 months.

B+ seems right.

Is there anything else that is a common failure point for HOTs that
I'm overlooking?

Thanks

tem00

Resolder the horizontal drive transformer and associated parts (driver
transistor, resistors...) ?

Mark Z.

 

[Eeyore]

I have a Toshiba 65H80 that I replaced the normal HOT section stuff
including the flyback, some caps, cap block (splitter) and of course
the HOT, etc. etc.

It works good about 3 months and blows again. I replace the HOT,

Just the HOT ? Do you have to replace all the other above-mentioned too ?

Graham

 

[Simoc]

I'd recommend to check all the electrolytics in the set with an ESR
meter. I do so always when I have to repair a many years old device
and the cap test has not been done within years. There are often found
some "stray bad caps", and they sometimes cause mystic semiconductor
failures etc. It might take a half an hour or so to test all the
electrolytics, but it gives a far lower chance of failure in near
future.

 

[Heinz Schmitz]

You may also want to test the input to the HOTransistor with a
scope to see if you're getting full on/off input drive and don't
have some constant DC there driving the base.

This is the thing I would check first. I had that once: A small copper
wire coil to the base of the HOT had a faulty solder joint on one
side. If the HOT is not properly switched (i.e. too long rise and
fall time of the pulse) it will be thermally overstressed and fail
prematurely.

Regards,
H.

 

[Meat Plow]

Just the HOT ? Do you have to replace all the other above-mentioned too ?

Graham

Seems the op says he just replaces the HOT, not HOT section stuff.

 

[tem00]

Seems the op says he just replaces the HOT, not HOT section stuff.

Thanks for the input everyone.

Yes, it was only the HOT that failed, but the 2nd time it blew I
replaced a lot of related parts as well in an attempt find a marginal
part. They were all parts spec'd from Vance Baldwin for my unit and
seemed to be the same numbers. I used proper mounting and heatsink
grease. I can test the load current, but it is not specified in the
service manual so I don't know what to look for.

I'll use all the suggestions here from the drive waveform to checking
the copper coil legs and post if I find something.

Thanks again
tem00

 

[R!]

I have a Toshiba 65H80 that I replaced the normal HOT section stuff
including the flyback, some caps, cap block (splitter) and of course
the HOT, etc. etc.

<snip>


I had a set that would do something similar, turned out to be a bad CRT.

It sometimes arced internally at turn on before the heaters were
completely heated blowing the H.O.T .

R!

 

[tem00]

<snip>

I had a set that would do something similar, turned out to be a bad CRT.

It sometimes arced internally at turn on before the heaters were
completely heated blowing the H.O.T .

R!

Not what I wanted to hear, but thank you, I'll keep an eye on it

 

[Meat Plow]

Not what I wanted to hear, but thank you, I'll keep an eye on it

This sucks but I recall reading some other HOT failures because of a
shorted CRT.

 

[Heinz Schmitz]

This sucks but I recall reading some other HOT failures because of a
shorted CRT.

There's a lot to die before the HOT, if the CRT is bad.

Regards.
H.

 

[R!]

Not what I wanted to hear, but thank you, I'll keep an eye on it

Just thinking does the H.O.T. run unusally warm ?

If not, I read that there was some problems with the sealing of the
anode connector on some projection sets that would arc, but this should
be a very audible snap!

If it is a bad tube it would not be much of a snap.

R!