I have a Kenwood VR-407 which keeps going into protection. The ±12VDC
supplies are unbalanced. The schematic for the circuit is posted in
a.b.s. It's just a basic circuit, it uses a center tapped transformer
feeding into a full-wave bridge, with the center tap grounded, with a
positive and negative three terminal 12 volt regulator. No rocket
science here. However, the supplies are unbalanced, pretty severely.
The input to the bridge is 14.24 & 14.15 VAC. The output of the
bridge is -25.28 & 10.23VDC with .685 & .240VAC ripple, respectively.
I pulled the board from the unit and powered up each regulator
individually . With -18VDC in across the negative, there was .1A draw
& -11.90VDC out. With +18V in across the positive regulator, there
was .1A draw & 11.83VDC out, so the reguators are fine and neither has
excessive current draw down the line. When I put an external supply
across both bridge capacitors I saw the same unbalance. With 35VDC
across the caps, there was 25.94 across the negative cap and 8.99V
across the postitive cap. I connected a capacitor in parallel across
both caps individually, but it didn't create any significant change.
Is it probable that one of the caps is bad causing the unbalance?

Thanks, and I'll provide any more information if necessary.

On Sun, 28 Sep 2008 15:11:30 -0500, Steve put finger to
keyboard and composed:

I have a Kenwood VR-407 which keeps going into protection. The ±12VDC
supplies are unbalanced. The schematic for the circuit is posted in
a.b.s. It's just a basic circuit, it uses a center tapped transformer
feeding into a full-wave bridge, with the center tap grounded, with a
positive and negative three terminal 12 volt regulator. No rocket
science here. However, the supplies are unbalanced, pretty severely.
The input to the bridge is 14.24 & 14.15 VAC. The output of the
bridge is -25.28 & 10.23VDC with .685 & .240VAC ripple, respectively.
I pulled the board from the unit and powered up each regulator
individually . With -18VDC in across the negative, there was .1A draw
& -11.90VDC out. With +18V in across the positive regulator, there
was .1A draw & 11.83VDC out, so the reguators are fine and neither has
excessive current draw down the line. When I put an external supply
across both bridge capacitors I saw the same unbalance. With 35VDC
across the caps, there was 25.94 across the negative cap and 8.99V
across the postitive cap. I connected a capacitor in parallel across
both caps individually, but it didn't create any significant change.
Is it probable that one of the caps is bad causing the unbalance?

Thanks, and I'll provide any more information if necessary.

You can interchange the capacitors to see if the unbalance goes with
the cap. However, it looks to me like you may have an open centre tap,
or the trace between the centre tap and the junction of the caps may
be open.

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

Steve wrote:

I have a Kenwood VR-407 which keeps going into protection. The ±12VDC
supplies are unbalanced. The schematic for the circuit is posted in
a.b.s. It's just a basic circuit, it uses a center tapped transformer
feeding into a full-wave bridge, with the center tap grounded, with a
positive and negative three terminal 12 volt regulator. No rocket
science here. However, the supplies are unbalanced, pretty severely.
The input to the bridge is 14.24 & 14.15 VAC. The output of the
bridge is -25.28 & 10.23VDC with .685 & .240VAC ripple, respectively.
I pulled the board from the unit and powered up each regulator
individually . With -18VDC in across the negative, there was .1A draw
& -11.90VDC out. With +18V in across the positive regulator, there
was .1A draw & 11.83VDC out, so the reguators are fine and neither has
excessive current draw down the line. When I put an external supply
across both bridge capacitors I saw the same unbalance. With 35VDC
across the caps, there was 25.94 across the negative cap and 8.99V
across the postitive cap. I connected a capacitor in parallel across
both caps individually, but it didn't create any significant change.
Is it probable that one of the caps is bad causing the unbalance?

Thanks, and I'll provide any more information if necessary.

Have you tested the bridge rectifier?

Disconnect the Regs from the output of the bridge. that remove all doubt
with circuit load. Do some more testing.

http://webpages.charter.net/jamie_5"

On Mon, 29 Sep 2008 06:51:58 +1000, Franc Zabkar
wrote:

On Sun, 28 Sep 2008 15:11:30 -0500, Steve put finger to
keyboard and composed:

I have a Kenwood VR-407 which keeps going into protection. The ±12VDC
supplies are unbalanced. The schematic for the circuit is posted in
a.b.s. It's just a basic circuit, it uses a center tapped transformer
feeding into a full-wave bridge, with the center tap grounded, with a
positive and negative three terminal 12 volt regulator. No rocket
science here. However, the supplies are unbalanced, pretty severely.
The input to the bridge is 14.24 & 14.15 VAC. The output of the
bridge is -25.28 & 10.23VDC with .685 & .240VAC ripple, respectively.
I pulled the board from the unit and powered up each regulator
individually . With -18VDC in across the negative, there was .1A draw
& -11.90VDC out. With +18V in across the positive regulator, there
was .1A draw & 11.83VDC out, so the reguators are fine and neither has
excessive current draw down the line. When I put an external supply
across both bridge capacitors I saw the same unbalance. With 35VDC
across the caps, there was 25.94 across the negative cap and 8.99V
across the postitive cap. I connected a capacitor in parallel across
both caps individually, but it didn't create any significant change.
Is it probable that one of the caps is bad causing the unbalance?

Thanks, and I'll provide any more information if necessary.

You can interchange the capacitors to see if the unbalance goes with
the cap. However, it looks to me like you may have an open centre tap,
or the trace between the centre tap and the junction of the caps may
be open.

- Franc Zabkar

The center tap checks good, as well as the trace between center tap to
the capacitor center point. Also, the bridge checks out ok. I guess
I need to pull the regs & put voltage across the caps & see if I have
unbalance then. Also, the caps are different sizes, it looks like
they may have designed the circuit to have higher current out of the
12v reg, which makes perfect sense, I guess the caps could have aged
at different rates then being dramatically different sizes. I'll do
some more testing, thanks for the replies.
Steve

On Sun, 28 Sep 2008 16:27:43 -0500, Steve put finger to
keyboard and composed:

On Mon, 29 Sep 2008 06:51:58 +1000, Franc Zabkar
wrote:

On Sun, 28 Sep 2008 15:11:30 -0500, Steve put finger to
keyboard and composed:

I have a Kenwood VR-407 which keeps going into protection. The ±12VDC
supplies are unbalanced. The schematic for the circuit is posted in
a.b.s. It's just a basic circuit, it uses a center tapped transformer
feeding into a full-wave bridge, with the center tap grounded, with a
positive and negative three terminal 12 volt regulator. No rocket
science here. However, the supplies are unbalanced, pretty severely.
The input to the bridge is 14.24 & 14.15 VAC. The output of the
bridge is -25.28 & 10.23VDC with .685 & .240VAC ripple, respectively.
I pulled the board from the unit and powered up each regulator
individually . With -18VDC in across the negative, there was .1A draw
& -11.90VDC out. With +18V in across the positive regulator, there
was .1A draw & 11.83VDC out, so the reguators are fine and neither has
excessive current draw down the line. When I put an external supply
across both bridge capacitors I saw the same unbalance. With 35VDC
across the caps, there was 25.94 across the negative cap and 8.99V
across the postitive cap. I connected a capacitor in parallel across
both caps individually, but it didn't create any significant change.
Is it probable that one of the caps is bad causing the unbalance?

Thanks, and I'll provide any more information if necessary.

You can interchange the capacitors to see if the unbalance goes with
the cap. However, it looks to me like you may have an open centre tap,
or the trace between the centre tap and the junction of the caps may
be open.

- Franc Zabkar

The center tap checks good, as well as the trace between center tap to
the capacitor center point. Also, the bridge checks out ok. I guess
I need to pull the regs & put voltage across the caps & see if I have
unbalance then. Also, the caps are different sizes, it looks like
they may have designed the circuit to have higher current out of the
12v reg, which makes perfect sense, I guess the caps could have aged
at different rates then being dramatically different sizes. I'll do
some more testing, thanks for the replies.
Steve

How can you get 25VDC across a cap when the AC supply is only 14Vrms?
The maximum voltage should be only ...

14 x 1.414 = 19.8 - Vf(diode) = 19V

Try desoldering each bridge diode one at a time. That way you'll be
able to test each half of the bridge on its own.

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

Franc Zabkar wrote:

On Sun, 28 Sep 2008 16:27:43 -0500, Steve put finger to
keyboard and composed:


On Mon, 29 Sep 2008 06:51:58 +1000, Franc Zabkar
wrote:


On Sun, 28 Sep 2008 15:11:30 -0500, Steve put finger to
keyboard and composed:


I have a Kenwood VR-407 which keeps going into protection. The ±12VDC
supplies are unbalanced. The schematic for the circuit is posted in
a.b.s. It's just a basic circuit, it uses a center tapped transformer
feeding into a full-wave bridge, with the center tap grounded, with a
positive and negative three terminal 12 volt regulator. No rocket
science here. However, the supplies are unbalanced, pretty severely.
The input to the bridge is 14.24 & 14.15 VAC. The output of the
bridge is -25.28 & 10.23VDC with .685 & .240VAC ripple, respectively.
I pulled the board from the unit and powered up each regulator
individually . With -18VDC in across the negative, there was .1A draw
& -11.90VDC out. With +18V in across the positive regulator, there
was .1A draw & 11.83VDC out, so the reguators are fine and neither has
excessive current draw down the line. When I put an external supply
across both bridge capacitors I saw the same unbalance. With 35VDC
across the caps, there was 25.94 across the negative cap and 8.99V
across the postitive cap. I connected a capacitor in parallel across
both caps individually, but it didn't create any significant change.
Is it probable that one of the caps is bad causing the unbalance?

Thanks, and I'll provide any more information if necessary.

You can interchange the capacitors to see if the unbalance goes with
the cap. However, it looks to me like you may have an open centre tap,
or the trace between the centre tap and the junction of the caps may
be open.

- Franc Zabkar

The center tap checks good, as well as the trace between center tap to
the capacitor center point. Also, the bridge checks out ok. I guess
I need to pull the regs & put voltage across the caps & see if I have
unbalance then. Also, the caps are different sizes, it looks like
they may have designed the circuit to have higher current out of the
12v reg, which makes perfect sense, I guess the caps could have aged
at different rates then being dramatically different sizes. I'll do
some more testing, thanks for the replies.
Steve


How can you get 25VDC across a cap when the AC supply is only 14Vrms?
The maximum voltage should be only ...

14 x 1.414 = 19.8 - Vf(diode) = 19V

True how ever, if he does not have a True RMS meter and the wave form is
abnormal, then I guess it would stand the reason he'd be under reading
the AC voltage?
Which is why, the old fashion analog meter was good out side a true
RMS meter that used thermo technology.

Try desoldering each bridge diode one at a time. That way you'll be
able to test each half of the bridge on its own.

- Franc Zabkar



http://webpages.charter.net/jamie_5"

On Mon, 29 Sep 2008 08:02:01 +1000, Franc Zabkar
wrote:

On Sun, 28 Sep 2008 16:27:43 -0500, Steve put finger to
keyboard and composed:

On Mon, 29 Sep 2008 06:51:58 +1000, Franc Zabkar
wrote:

On Sun, 28 Sep 2008 15:11:30 -0500, Steve put finger to
keyboard and composed:

I have a Kenwood VR-407 which keeps going into protection. The ±12VDC
supplies are unbalanced. The schematic for the circuit is posted in
a.b.s. It's just a basic circuit, it uses a center tapped transformer
feeding into a full-wave bridge, with the center tap grounded, with a
positive and negative three terminal 12 volt regulator. No rocket
science here. However, the supplies are unbalanced, pretty severely.
The input to the bridge is 14.24 & 14.15 VAC. The output of the
bridge is -25.28 & 10.23VDC with .685 & .240VAC ripple, respectively.
I pulled the board from the unit and powered up each regulator
individually . With -18VDC in across the negative, there was .1A draw
& -11.90VDC out. With +18V in across the positive regulator, there
was .1A draw & 11.83VDC out, so the reguators are fine and neither has
excessive current draw down the line. When I put an external supply
across both bridge capacitors I saw the same unbalance. With 35VDC
across the caps, there was 25.94 across the negative cap and 8.99V
across the postitive cap. I connected a capacitor in parallel across
both caps individually, but it didn't create any significant change.
Is it probable that one of the caps is bad causing the unbalance?

Thanks, and I'll provide any more information if necessary.

You can interchange the capacitors to see if the unbalance goes with
the cap. However, it looks to me like you may have an open centre tap,
or the trace between the centre tap and the junction of the caps may
be open.

- Franc Zabkar

The center tap checks good, as well as the trace between center tap to
the capacitor center point. Also, the bridge checks out ok. I guess
I need to pull the regs & put voltage across the caps & see if I have
unbalance then. Also, the caps are different sizes, it looks like
they may have designed the circuit to have higher current out of the
12v reg, which makes perfect sense, I guess the caps could have aged
at different rates then being dramatically different sizes. I'll do
some more testing, thanks for the replies.
Steve

How can you get 25VDC across a cap when the AC supply is only 14Vrms?
The maximum voltage should be only ...

14 x 1.414 = 19.8 - Vf(diode) = 19V

Try desoldering each bridge diode one at a time. That way you'll be
able to test each half of the bridge on its own.

- Franc Zabkar

I'll have to remove the bridge as a whole, it's a four terminal
package. I was using a Fluke 87 III for the measurements. What you
said about the center tap makes sense, that would explain everything,
but it measures fine, .9 ohms between either winding & center, 1.8
total. I'll yank the bridge & caps tomorrow, it can't be too hard to
find, this is a simple circuit for heaven's sake.

Thanks for the posts,
Steve

On Sun, 28 Sep 2008 19:03:28 -0400, Jamie
t put finger to
keyboard and composed:

Franc Zabkar wrote:

How can you get 25VDC across a cap when the AC supply is only 14Vrms?
The maximum voltage should be only ...

14 x 1.414 = 19.8 - Vf(diode) = 19V

True how ever, if he does not have a True RMS meter and the wave form is
abnormal, then I guess it would stand the reason he'd be under reading
the AC voltage?
Which is why, the old fashion analog meter was good out side a true
RMS meter that used thermo technology.

AIUI, a standard multimeter assumes you are measuring a sinusoid and
estimates the RMS voltage based on the peak value. I can't imagine
that the OP's waveform would be greatly distorted at a load current of
0.1A. In any case, how can you distort the waveform so as to increase
its amplitude?

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

On Sun, 28 Sep 2008 19:40:35 -0500, Steve put finger to
keyboard and composed:

What you
said about the center tap makes sense, that would explain everything,
but it measures fine, .9 ohms between either winding & center, 1.8
total.

Could it be that the transformer's centre tap pin has a dry solder
joint that closes up when you probe it? I always reflow the solder at
coils and transformers for this reason.

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

"Steve" wrote in message
...
On Mon, 29 Sep 2008 08:02:01 +1000, Franc Zabkar
wrote:

On Sun, 28 Sep 2008 16:27:43 -0500, Steve put finger to
keyboard and composed:

On Mon, 29 Sep 2008 06:51:58 +1000, Franc Zabkar
wrote:

On Sun, 28 Sep 2008 15:11:30 -0500, Steve put finger to
keyboard and composed:

I have a Kenwood VR-407 which keeps going into protection. The ±12VDC
supplies are unbalanced. The schematic for the circuit is posted in
a.b.s. It's just a basic circuit, it uses a center tapped transformer
feeding into a full-wave bridge, with the center tap grounded, with a
positive and negative three terminal 12 volt regulator. No rocket
science here. However, the supplies are unbalanced, pretty severely.
The input to the bridge is 14.24 & 14.15 VAC. The output of the
bridge is -25.28 & 10.23VDC with .685 & .240VAC ripple, respectively.
I pulled the board from the unit and powered up each regulator
individually . With -18VDC in across the negative, there was .1A draw
& -11.90VDC out. With +18V in across the positive regulator, there
was .1A draw & 11.83VDC out, so the reguators are fine and neither has
excessive current draw down the line. When I put an external supply
across both bridge capacitors I saw the same unbalance. With 35VDC
across the caps, there was 25.94 across the negative cap and 8.99V
across the postitive cap. I connected a capacitor in parallel across
both caps individually, but it didn't create any significant change.
Is it probable that one of the caps is bad causing the unbalance?

Thanks, and I'll provide any more information if necessary.

You can interchange the capacitors to see if the unbalance goes with
the cap. However, it looks to me like you may have an open centre tap,
or the trace between the centre tap and the junction of the caps may
be open.

- Franc Zabkar

The center tap checks good, as well as the trace between center tap to
the capacitor center point. Also, the bridge checks out ok. I guess
I need to pull the regs & put voltage across the caps & see if I have
unbalance then. Also, the caps are different sizes, it looks like
they may have designed the circuit to have higher current out of the
12v reg, which makes perfect sense, I guess the caps could have aged
at different rates then being dramatically different sizes. I'll do
some more testing, thanks for the replies.
Steve

How can you get 25VDC across a cap when the AC supply is only 14Vrms?
The maximum voltage should be only ...

14 x 1.414 = 19.8 - Vf(diode) = 19V

Try desoldering each bridge diode one at a time. That way you'll be
able to test each half of the bridge on its own.

- Franc Zabkar

I'll have to remove the bridge as a whole, it's a four terminal
package. I was using a Fluke 87 III for the measurements. What you
said about the center tap makes sense, that would explain everything,
but it measures fine, .9 ohms between either winding & center, 1.8
total. I'll yank the bridge & caps tomorrow, it can't be too hard to
find, this is a simple circuit for heaven's sake.

Thanks for the posts,
Steve

Definitely a loss of ground reference. I've run into this several times
lately.


Mark Z.

On Mon, 29 Sep 2008 05:37:36 -0500, "Mark D. Zacharias"
wrote:


"Steve" wrote in message
.. .
On Mon, 29 Sep 2008 08:02:01 +1000, Franc Zabkar
wrote:

On Sun, 28 Sep 2008 16:27:43 -0500, Steve put finger to
keyboard and composed:

On Mon, 29 Sep 2008 06:51:58 +1000, Franc Zabkar
wrote:

On Sun, 28 Sep 2008 15:11:30 -0500, Steve put finger to
keyboard and composed:

I have a Kenwood VR-407 which keeps going into protection. The ±12VDC
supplies are unbalanced. The schematic for the circuit is posted in
a.b.s. It's just a basic circuit, it uses a center tapped transformer
feeding into a full-wave bridge, with the center tap grounded, with a
positive and negative three terminal 12 volt regulator. No rocket
science here. However, the supplies are unbalanced, pretty severely.
The input to the bridge is 14.24 & 14.15 VAC. The output of the
bridge is -25.28 & 10.23VDC with .685 & .240VAC ripple, respectively.
I pulled the board from the unit and powered up each regulator
individually . With -18VDC in across the negative, there was .1A draw
& -11.90VDC out. With +18V in across the positive regulator, there
was .1A draw & 11.83VDC out, so the reguators are fine and neither has
excessive current draw down the line. When I put an external supply
across both bridge capacitors I saw the same unbalance. With 35VDC
across the caps, there was 25.94 across the negative cap and 8.99V
across the postitive cap. I connected a capacitor in parallel across
both caps individually, but it didn't create any significant change.
Is it probable that one of the caps is bad causing the unbalance?

Thanks, and I'll provide any more information if necessary.

You can interchange the capacitors to see if the unbalance goes with
the cap. However, it looks to me like you may have an open centre tap,
or the trace between the centre tap and the junction of the caps may
be open.

- Franc Zabkar

The center tap checks good, as well as the trace between center tap to
the capacitor center point. Also, the bridge checks out ok. I guess
I need to pull the regs & put voltage across the caps & see if I have
unbalance then. Also, the caps are different sizes, it looks like
they may have designed the circuit to have higher current out of the
12v reg, which makes perfect sense, I guess the caps could have aged
at different rates then being dramatically different sizes. I'll do
some more testing, thanks for the replies.
Steve

How can you get 25VDC across a cap when the AC supply is only 14Vrms?
The maximum voltage should be only ...

14 x 1.414 = 19.8 - Vf(diode) = 19V

Try desoldering each bridge diode one at a time. That way you'll be
able to test each half of the bridge on its own.

- Franc Zabkar

I'll have to remove the bridge as a whole, it's a four terminal
package. I was using a Fluke 87 III for the measurements. What you
said about the center tap makes sense, that would explain everything,
but it measures fine, .9 ohms between either winding & center, 1.8
total. I'll yank the bridge & caps tomorrow, it can't be too hard to
find, this is a simple circuit for heaven's sake.

Thanks for the posts,
Steve

Definitely a loss of ground reference. I've run into this several times
lately.


Mark Z.

Sorry to dissappoint, but it appears it was bad caps. Actually,
probably just one bad cap, but I replaced both (I don't have a
capacatince meter at home). One is 470uF, the other 2200uF. The
470uF is nested in with a couple of 12ohm 1w resistors, so it was
probably running quite warm. Now oth supplies are balanced within a
volt or so on the input, and the output is regulating beautifully.
Unit powers up & doesn't go into protection. It's an interesting
protection circuit they use. They put equal dividers in all three
supply rails, the +-65V, +-35V, & +-12V. It looks like they are all
summed & fed to a current mirror, and if any drifts off zero the
mirror turns on the protection 2 circuit & shuts down the amp. Maybe
this is common for amplifiers, I just never dug this deep into the
protection circuits before. Usually I deal w/ blown output
transistors or amplifier packs.

Thanks for all the help, I really appreciate it.

Steve

"Steve" wrote in message
news
On Mon, 29 Sep 2008 05:37:36 -0500, "Mark D. Zacharias"
wrote:


"Steve" wrote in message
. ..
On Mon, 29 Sep 2008 08:02:01 +1000, Franc Zabkar
wrote:

On Sun, 28 Sep 2008 16:27:43 -0500, Steve put finger to
keyboard and composed:

On Mon, 29 Sep 2008 06:51:58 +1000, Franc Zabkar
wrote:

On Sun, 28 Sep 2008 15:11:30 -0500, Steve put finger to
keyboard and composed:

I have a Kenwood VR-407 which keeps going into protection. The
±12VDC
supplies are unbalanced. The schematic for the circuit is posted in
a.b.s. It's just a basic circuit, it uses a center tapped
transformer
feeding into a full-wave bridge, with the center tap grounded, with a
positive and negative three terminal 12 volt regulator. No rocket
science here. However, the supplies are unbalanced, pretty severely.
The input to the bridge is 14.24 & 14.15 VAC. The output of the
bridge is -25.28 & 10.23VDC with .685 & .240VAC ripple, respectively.
I pulled the board from the unit and powered up each regulator
individually . With -18VDC in across the negative, there was .1A
draw
& -11.90VDC out. With +18V in across the positive regulator, there
was .1A draw & 11.83VDC out, so the reguators are fine and neither
has
excessive current draw down the line. When I put an external supply
across both bridge capacitors I saw the same unbalance. With 35VDC
across the caps, there was 25.94 across the negative cap and 8.99V
across the postitive cap. I connected a capacitor in parallel across
both caps individually, but it didn't create any significant change.
Is it probable that one of the caps is bad causing the unbalance?

Thanks, and I'll provide any more information if necessary.

You can interchange the capacitors to see if the unbalance goes with
the cap. However, it looks to me like you may have an open centre tap,
or the trace between the centre tap and the junction of the caps may
be open.

- Franc Zabkar

The center tap checks good, as well as the trace between center tap to
the capacitor center point. Also, the bridge checks out ok. I guess
I need to pull the regs & put voltage across the caps & see if I have
unbalance then. Also, the caps are different sizes, it looks like
they may have designed the circuit to have higher current out of the
12v reg, which makes perfect sense, I guess the caps could have aged
at different rates then being dramatically different sizes. I'll do
some more testing, thanks for the replies.
Steve

How can you get 25VDC across a cap when the AC supply is only 14Vrms?
The maximum voltage should be only ...

14 x 1.414 = 19.8 - Vf(diode) = 19V

Try desoldering each bridge diode one at a time. That way you'll be
able to test each half of the bridge on its own.

- Franc Zabkar

I'll have to remove the bridge as a whole, it's a four terminal
package. I was using a Fluke 87 III for the measurements. What you
said about the center tap makes sense, that would explain everything,
but it measures fine, .9 ohms between either winding & center, 1.8
total. I'll yank the bridge & caps tomorrow, it can't be too hard to
find, this is a simple circuit for heaven's sake.

Thanks for the posts,
Steve

Definitely a loss of ground reference. I've run into this several times
lately.


Mark Z.

Sorry to dissappoint, but it appears it was bad caps. Actually,
probably just one bad cap, but I replaced both (I don't have a
capacatince meter at home). One is 470uF, the other 2200uF. The
470uF is nested in with a couple of 12ohm 1w resistors, so it was
probably running quite warm. Now oth supplies are balanced within a
volt or so on the input, and the output is regulating beautifully.
Unit powers up & doesn't go into protection. It's an interesting
protection circuit they use. They put equal dividers in all three
supply rails, the +-65V, +-35V, & +-12V. It looks like they are all
summed & fed to a current mirror, and if any drifts off zero the
mirror turns on the protection 2 circuit & shuts down the amp. Maybe
this is common for amplifiers, I just never dug this deep into the
protection circuits before. Usually I deal w/ blown output
transistors or amplifier packs.

Thanks for all the help, I really appreciate it.

Steve


I think you probably fixed the bad ground in the process. A bad cap on one
rail isn't going to make another rail double with respect to ground.

Mark Z.