Sony KV-35S45 Power Supply
 

I acquired this set with a blown HOT and power supply, and
presumably a bad flyback as well. I replaced the flyback, HOT, and a
number of power supply components including the MX0841 IC. Wouldn't
you know it, I had missed a shorted zener in the power supply, and of
course blew the brand new switching IC. Since I didn't have another IC
in stock, and it appears to be nothing more than two switching
transistors in one package, I tried replacing them with a pair of
normal switching transistors, similar to those used in other Sony
power supplies. This was of course after removing the shorted zener
diode from the secondary side. The power supply now starts but the
voltages are very low. There are three supplies on the secondary side
of this switching transformer (a separate xfrmr & circuit is used for
the 5V standby); the B+, which measures at just 50V, a 12V supply
which measures at 3V, and a 9V supply which is at zero. Removing the
12 and 9 volt rectifiers brought the B+ up to about 100V, but the
power supply makes a noticeable squeal and sounds like it's either
straining itself or not running hard enough (the switching transistors
don't seem to be getting warm though).
I've gone through the power supply and can't find any bad resistors
or diodes, which leaves me with just one question: is the problem
related to my subbing the MX0841 IC, or is there something else wrong
with this power supply? This is a difficult circuit to troubleshoot
and I'm just afraid there might be something more serious at fault.
Thanks for any help.

Sony KV-35S45 Power Supply
 

On Wed, 2 Apr 2008 10:38:16 -0700 (PDT), packrat79
put finger to keyboard and composed:

I acquired this set with a blown HOT and power supply, and
presumably a bad flyback as well. I replaced the flyback, HOT, and a
number of power supply components including the MX0841 IC. Wouldn't
you know it, I had missed a shorted zener in the power supply, and of
course blew the brand new switching IC. Since I didn't have another IC
in stock, and it appears to be nothing more than two switching
transistors in one package, I tried replacing them with a pair of
normal switching transistors, similar to those used in other Sony
power supplies. This was of course after removing the shorted zener
diode from the secondary side. The power supply now starts but the
voltages are very low. There are three supplies on the secondary side
of this switching transformer (a separate xfrmr & circuit is used for
the 5V standby); the B+, which measures at just 50V, a 12V supply
which measures at 3V, and a 9V supply which is at zero. Removing the
12 and 9 volt rectifiers brought the B+ up to about 100V, but the
power supply makes a noticeable squeal and sounds like it's either
straining itself or not running hard enough (the switching transistors
don't seem to be getting warm though).
I've gone through the power supply and can't find any bad resistors
or diodes, which leaves me with just one question: is the problem
related to my subbing the MX0841 IC, or is there something else wrong
with this power supply? This is a difficult circuit to troubleshoot
and I'm just afraid there might be something more serious at fault.
Thanks for any help.

I don't recognise your Sony model, but I've seen Sony sets where a
dried out B+ capacitor produced the same symptom.

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

Sony KV-35S45 Power Supply
 

On Apr 2, 5:45 pm, Franc Zabkar wrote:
On Wed, 2 Apr 2008 10:38:16 -0700 (PDT), packrat79
put finger to keyboard and composed:



I acquired this set with a blown HOT and power supply, and
presumably a bad flyback as well. I replaced the flyback, HOT, and a
number of power supply components including the MX0841 IC. Wouldn't
you know it, I had missed a shorted zener in the power supply, and of
course blew the brand new switching IC. Since I didn't have another IC
in stock, and it appears to be nothing more than two switching
transistors in one package, I tried replacing them with a pair of
normal switching transistors, similar to those used in other Sony
power supplies. This was of course after removing the shorted zener
diode from the secondary side. The power supply now starts but the
voltages are very low. There are three supplies on the secondary side
of this switching transformer (a separate xfrmr & circuit is used for
the 5V standby); the B+, which measures at just 50V, a 12V supply
which measures at 3V, and a 9V supply which is at zero. Removing the
12 and 9 volt rectifiers brought the B+ up to about 100V, but the
power supply makes a noticeable squeal and sounds like it's either
straining itself or not running hard enough (the switching transistors
don't seem to be getting warm though).
I've gone through the power supply and can't find any bad resistors
or diodes, which leaves me with just one question: is the problem
related to my subbing the MX0841 IC, or is there something else wrong
with this power supply? This is a difficult circuit to troubleshoot
and I'm just afraid there might be something more serious at fault.
Thanks for any help.

I don't recognise your Sony model, but I've seen Sony sets where a
dried out B+ capacitor produced the same symptom.

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

Nope, the caps are fine. I guess the next thing is to get an original
MX0841 IC, in case I'm just wasting my time looking for other problems.

Sony KV-35S45 Power Supply
 

I strongly suggest to use an original part. Sometimes the specs in the
service manual show a device like a simple transistor type, and it may
be using Darlington pairs or something like that.

--

JANA
_____


"packrat79" wrote in message
...
I acquired this set with a blown HOT and power supply, and
presumably a bad flyback as well. I replaced the flyback, HOT, and a
number of power supply components including the MX0841 IC. Wouldn't
you know it, I had missed a shorted zener in the power supply, and of
course blew the brand new switching IC. Since I didn't have another IC
in stock, and it appears to be nothing more than two switching
transistors in one package, I tried replacing them with a pair of
normal switching transistors, similar to those used in other Sony
power supplies. This was of course after removing the shorted zener
diode from the secondary side. The power supply now starts but the
voltages are very low. There are three supplies on the secondary side
of this switching transformer (a separate xfrmr & circuit is used for
the 5V standby); the B+, which measures at just 50V, a 12V supply
which measures at 3V, and a 9V supply which is at zero. Removing the
12 and 9 volt rectifiers brought the B+ up to about 100V, but the
power supply makes a noticeable squeal and sounds like it's either
straining itself or not running hard enough (the switching transistors
don't seem to be getting warm though).
I've gone through the power supply and can't find any bad resistors
or diodes, which leaves me with just one question: is the problem
related to my subbing the MX0841 IC, or is there something else wrong
with this power supply? This is a difficult circuit to troubleshoot
and I'm just afraid there might be something more serious at fault.
Thanks for any help.