Validity of Flyback Test?

[packrat79]

Some years ago, I built the flyback tester that was described in
Sams FAQs - the one with the simple two-transistor oscillator,
connected by winding your own 10 turns onto the flyback core. The
flyback is of course tested out-of-circuit. Over the years it has been
quite accurate, but the results with one recent flyback are rather
inconclusive, and I thought maybe you could give me some advice.
I don't have the model # of the set handy, but it's a 36" Sony made
in 1998. It came in with a blown HOT and switching regulator, so
naturally the flyback was the first thing I suspected.
Normally when a flyback is tested with this device, it will produce
a decent-looking arc of about 1/2". The flyback in question, however,
seems to produce a weak arc of less than 1/4", and it doesn't have the
"sizzle" and thickness I normally see with this test. Given the size
and high voltage requirements of the CRT, I expected a lot more from
this flyback (if it's good, that is). Would I be right to suspect it
as bad?
I really don't want to replace the other components and leave the
original flyback installed, because if it's bad, as you know, it will
just take out the other components again (nice design, Sony).
Any advice would be appreciated.

 

[James Sweet]

Some years ago, I built the flyback tester that was described in
Sams FAQs - the one with the simple two-transistor oscillator,
connected by winding your own 10 turns onto the flyback core. The
flyback is of course tested out-of-circuit. Over the years it has been
quite accurate, but the results with one recent flyback are rather
inconclusive, and I thought maybe you could give me some advice.
I don't have the model # of the set handy, but it's a 36" Sony made
in 1998. It came in with a blown HOT and switching regulator, so
naturally the flyback was the first thing I suspected.
Normally when a flyback is tested with this device, it will produce
a decent-looking arc of about 1/2". The flyback in question, however,
seems to produce a weak arc of less than 1/4", and it doesn't have the
"sizzle" and thickness I normally see with this test. Given the size
and high voltage requirements of the CRT, I expected a lot more from
this flyback (if it's good, that is). Would I be right to suspect it
as bad?
I really don't want to replace the other components and leave the
original flyback installed, because if it's bad, as you know, it will
just take out the other components again (nice design, Sony).
Any advice would be appreciated.

How much is a new flyback? A while back I replaced one on a 32" Sony which
was arcing internally, it was surprisingly inexpensive and fixed the
problem.

 

[Jim Yanik]

.

How much is a new flyback? A while back I replaced one on a 32" Sony
which was arcing internally, it was surprisingly inexpensive and fixed
the problem.

I recently put a new flyback in a 12" TV,it cost less than $20 from Acme
Enterprises. My old FB smoked.

 

[packrat79]

I recently put a new flyback in a 12" TV,it cost less than $20 from Acme
Enterprises. My old FB smoked.

--
Jim Yanik
jyanik
at
kua.net

So chances are it probably is bad huh? That's what I figured. However,
Sony has discontinued this part, so a generic replacement will have to
do (I could only find one supplier, with one left in stock). I didn't
think Sony discontinued parts so soon, but I guess that's the trend
these days.

 

[James Sweet]

So chances are it probably is bad huh? That's what I figured. However,
Sony has discontinued this part, so a generic replacement will have to
do (I could only find one supplier, with one left in stock). I didn't
think Sony discontinued parts so soon, but I guess that's the trend
these days.

Hard to say for sure, but if it isn't super expensive it might be worthwhile
to just replace it and see what happens. Flybacks can be difficult to test,
there's too many characteristics that are critical in some sets. I have a
flyback ring tester which works pretty well but even that isn't 100%.

 

[Sam Goldwasser]

Hard to say for sure, but if it isn't super expensive it might be worthwhile
to just replace it and see what happens. Flybacks can be difficult to test,
there's too many characteristics that are critical in some sets. I have a
flyback ring tester which works pretty well but even that isn't 100%.

I agree. If the self oscillating circuit works as well as it did, a
ring test probably won't be any more definitive without a side-by-side
compsrison. You may have to try a new one.

You might compare the DC current through the oscillator with the suspect
flyback, and with a known good one. If it's really significantly higher,
then that would be one more piece of evidence suggesting a bad flyback.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

 

[hr(bob) [email protected]]

I agree.  If the self oscillating circuit works as well as it did, a
ring test probably won't be any more definitive without a side-by-side
compsrison.  You may have to try a new one.

You might compare the DC current through the oscillator with the suspect
flyback, and with a known good one.  If it's really significantly higher,
then that would be one more piece of evidence suggesting a bad flyback.

--- sam | Sci.Electronics.Repair FAQ:http://www.repairfaq.org/
 Repair | Main Table of Contents:http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ:http://www.repairfaq.org/sam/lasersam.htm
        | Mirror Sites:http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line.  Or, you can contact me via the Feedback Form in the FAQs.

CAn you give a URL for the tester you mentioned. I didn't see one on
Sam Goldwasser's repair FAQ site.

H. R. (Bob) Hofmann

 

[James Sweet]

I agree. If the self oscillating circuit works as well as it did, a
ring test probably won't be any more definitive without a side-by-side
compsrison. You may have to try a new one.

You might compare the DC current through the oscillator with the suspect
flyback, and with a known good one. If it's really significantly higher,
then that would be one more piece of evidence suggesting a bad flyback.

--- sam | Sci.Electronics.Repair FAQ:http://www.repairfaq.org/
Repair | Main Table of Contents:http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ:http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites:http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above
is
ignored unless my full name AND either lasers or electronics is included
in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

CAn you give a URL for the tester you mentioned. I didn't see one on
Sam Goldwasser's repair FAQ site.

H. R. (Bob) Hofmann

This is the one I have:

http://members.ozemail.com.au/~bobpar/fbt.htm

 

[hr(bob) [email protected]]

This is the one I have:

http://members.ozemail.com.au/~bobpar/fbt.htm- Hide quoted text -

- Show quoted text -

Thanx!