Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Default Panasonic TV model CT2784VY power supply problems

This set came in from a local school, dead. As with many others of
these I've repaired over the years I found cracked solder on almost
all of the terminals of the STK 730-020. In the past I've found that
many times simply soldering it up fixes the set. If that doesn't work
then usually replacing the STK does it. I tried soldering first and
the set would still not power up. It did click though when the power
cord was plugged in. This seemed strange. It does not click when the
power button is pressed though. I looked for obvious things first and
then removed the STK. I have no schematic of the set but I did have 3
new STK's. I compared resistance readings between several pins on the
removed chip with my new one and noted some significant differences.
This suggested that the STK was bad so I replaced it. The new STK did
the same thing so I removed it and compared it to a second new one. My
fist new one seems to now have a discrepancy when compared to a second
unused part, suggesting that it is now very likely damaged as well. I
don't want to chance burning up any more STk's, (if thats what I've
done), I only have one left. Does anyone have any tips on this set? A
schematic would also be really helpful too if someone has one. Thanks
very much. Lenny.
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Default Panasonic TV model CT2784VY power supply problems

On Mon, 10 Nov 2008 09:01:26 -0800 (PST),
" put
finger to keyboard and composed:

This set came in from a local school, dead. As with many others of
these I've repaired over the years I found cracked solder on almost
all of the terminals of the STK 730-020. In the past I've found that
many times simply soldering it up fixes the set. If that doesn't work
then usually replacing the STK does it. I tried soldering first and
the set would still not power up. It did click though when the power
cord was plugged in. This seemed strange. It does not click when the
power button is pressed though. I looked for obvious things first and
then removed the STK. I have no schematic of the set but I did have 3
new STK's. I compared resistance readings between several pins on the
removed chip with my new one and noted some significant differences.
This suggested that the STK was bad so I replaced it. The new STK did
the same thing so I removed it and compared it to a second new one. My
fist new one seems to now have a discrepancy when compared to a second
unused part, suggesting that it is now very likely damaged as well. I
don't want to chance burning up any more STk's, (if thats what I've
done), I only have one left. Does anyone have any tips on this set? A
schematic would also be really helpful too if someone has one. Thanks
very much. Lenny.


The datasheet for the STK730-020 ...

http://www.datasheetarchive.com/pdf-...DSA-577487.pdf

.... has a simple application circuit. Perhaps that will help.

IME with similar designs, common problems are the capacitor between
pins 1 and 3, the startup resistor at pin 4, and maybe the zener
diode. Also make sure the back-EMF diode for the internal MOSFET has
not gone O/C. It may help to know which pins are showing a
discrepancy.

Have you replaced the line stage with a dummy load?

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
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Default Panasonic TV model CT2784VY power supply problems

On Nov 10, 3:20*pm, Franc Zabkar wrote:
On Mon, 10 Nov 2008 09:01:26 -0800 (PST),
" put
finger to keyboard and composed:





This set came in from a local school, dead. As with many others of
these I've repaired over the years I found cracked solder on almost
all of the terminals of the STK 730-020. In the past I've found that
many times simply soldering it up fixes the set. If that doesn't work
then usually replacing the STK does it. I tried soldering first and
the set would still not power up. It did click though when the power
cord *was plugged in. This seemed strange. It does not click when the
power button is pressed though. I looked for obvious things first and
then removed the STK. I have no schematic of the set but I did have 3
new STK's. I compared resistance readings between several pins on the
removed chip with my new one and noted some significant differences.
This suggested that the STK was bad so I replaced it. The new STK did
the same thing so I removed it and compared it to a second new one. My
fist new one seems to now have a discrepancy when compared to a second
unused part, suggesting that it is now very likely damaged as well. I
don't want to chance burning up any more STk's, (if thats what I've
done), *I only have one left. Does anyone have any tips on this set? A
schematic would also be really helpful too if someone has one. Thanks
very much. Lenny.


The datasheet for the STK730-020 ...

http://www.datasheetarchive.com/pdf-...ts-29/DSA-5774...

... has a simple application circuit. Perhaps that will help.

IME with similar designs, common problems are the capacitor between
pins 1 and 3, the startup resistor at pin 4, and maybe the zener
diode. Also make sure the back-EMF diode for the internal MOSFET has
not gone O/C. It may help to know which pins are showing a
discrepancy.

Have you replaced the line stage with a dummy load?

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.- Hide quoted text -

- Show quoted text -


Thanks for the link Frank. I'll check those things. Lenny.
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