Ok the front panel was dead, had 2 fuses blown, and the MN2488 and MP1620
was shorted in the right channel. the rest was fine.

Well, i replaced both fuses, replaced both outputs and the 2 10ohm base
resistors. I checked every other resistors and found things to be normal. i
replaced a high ESR 47uf cap also.

there was a small PNP transistor near the 2 outputs that was shorted also,
replaced that.


The set now turns on and works, except as soon as I hook a speaker up to the
right channel output, it goes into protector. i checked and double checked
the resistors in the output circuit. If i leave the speaker unhooked, its
fine. there is NO DC offset according to me meter on the right channel. if i
set the meter on AC, I can see the AC signal on the meter, and on my scope
just normal. if i hook the speaker up to the right channel, it fires
protector mode. the other channels work fine.

any ideas?

I removed the protector current detector from the right channel, and if i
scope it, the top half the wave is clipped off. meaning no drive to NPN?


and all resistor paths to the NPN is fine, so im suspecting the STK3102
driver is fuxified.


"Mike" wrote in message
...
Ok the front panel was dead, had 2 fuses blown, and the MN2488 and MP1620
was shorted in the right channel. the rest was fine.

Well, i replaced both fuses, replaced both outputs and the 2 10ohm base
resistors. I checked every other resistors and found things to be normal.
i replaced a high ESR 47uf cap also.

there was a small PNP transistor near the 2 outputs that was shorted also,
replaced that.


The set now turns on and works, except as soon as I hook a speaker up to
the right channel output, it goes into protector. i checked and double
checked the resistors in the output circuit. If i leave the speaker
unhooked, its fine. there is NO DC offset according to me meter on the
right channel. if i set the meter on AC, I can see the AC signal on the
meter, and on my scope just normal. if i hook the speaker up to the right
channel, it fires protector mode. the other channels work fine.

any ideas?

as soon as i unhook the speaker, the wave is fine. any ideas???



"Mike" wrote in message
...
Ok the front panel was dead, had 2 fuses blown, and the MN2488 and MP1620
was shorted in the right channel. the rest was fine.

Well, i replaced both fuses, replaced both outputs and the 2 10ohm base
resistors. I checked every other resistors and found things to be normal.
i replaced a high ESR 47uf cap also.

there was a small PNP transistor near the 2 outputs that was shorted also,
replaced that.


The set now turns on and works, except as soon as I hook a speaker up to
the right channel output, it goes into protector. i checked and double
checked the resistors in the output circuit. If i leave the speaker
unhooked, its fine. there is NO DC offset according to me meter on the
right channel. if i set the meter on AC, I can see the AC signal on the
meter, and on my scope just normal. if i hook the speaker up to the right
channel, it fires protector mode. the other channels work fine.

any ideas?

well, the output of that channel is normal with no load, HOWEVER the base
drive signal to both transistors is clipped on the bottom half. results in a
top half clip with a load.


"Mike" wrote in message
...
Ok the front panel was dead, had 2 fuses blown, and the MN2488 and MP1620
was shorted in the right channel. the rest was fine.

Well, i replaced both fuses, replaced both outputs and the 2 10ohm base
resistors. I checked every other resistors and found things to be normal.
i replaced a high ESR 47uf cap also.

there was a small PNP transistor near the 2 outputs that was shorted also,
replaced that.


The set now turns on and works, except as soon as I hook a speaker up to
the right channel output, it goes into protector. i checked and double
checked the resistors in the output circuit. If i leave the speaker
unhooked, its fine. there is NO DC offset according to me meter on the
right channel. if i set the meter on AC, I can see the AC signal on the
meter, and on my scope just normal. if i hook the speaker up to the right
channel, it fires protector mode. the other channels work fine.

any ideas?

"Mike" wrote in message
...
well, the output of that channel is normal with no load, HOWEVER the base
drive signal to both transistors is clipped on the bottom half. results in
a top half clip with a load.

With no load on the output stage, the output transistors will not be
required to pass any current, other than the few mA idle current. This in
turn, means that the output transistor bases are demanding no current from
the driver stage, again other than the very small current required to drive
the idle current through them. However, once there is a load, and signal,
the outputs will demand current from the drivers, and if they are unable to
supply this in a symmetrical fashion, as your scope checks would suggest,
then the output stage will shift its midpoint towards one side, resulting in
effectively, a DC offset that the protection circuit will detect as such,
causing the shutdown that you are experiencing.

The driver stages within the STK will likely be very similar in topology to
the discrete output stages, employing an NPN / PNP transistor pair. If you
are seeing one side of your drive waveform clipped, then it is likely that
either the NPN or the PNP transistor is failing to supply the current being
demanded by the output transistor that it's driving. This will be because
either the transistor has failed in some way, or some internal resistor has
failed, either of which has likely been caused by the original output
transistor failure. I would suspect the STK first, closely followed by any
external bias resistors.

Arfa

it has to be the STK.

because the output looks normal on no-load condition, however, the base
drive to both transistors is clipped on the bottom of the waveform.

load and no load. its clipped. the other channel is fine signal.

So, the chip most likely. because all the resistors and capacitors test
fine. same with the 2 current limiting/bias transistors. it also tests fine.

STK is last.

"Mike" wrote in message
...
Ok the front panel was dead, had 2 fuses blown, and the MN2488 and MP1620
was shorted in the right channel. the rest was fine.

Well, i replaced both fuses, replaced both outputs and the 2 10ohm base
resistors. I checked every other resistors and found things to be normal.
i replaced a high ESR 47uf cap also.

there was a small PNP transistor near the 2 outputs that was shorted also,
replaced that.


The set now turns on and works, except as soon as I hook a speaker up to
the right channel output, it goes into protector. i checked and double
checked the resistors in the output circuit. If i leave the speaker
unhooked, its fine. there is NO DC offset according to me meter on the
right channel. if i set the meter on AC, I can see the AC signal on the
meter, and on my scope just normal. if i hook the speaker up to the right
channel, it fires protector mode. the other channels work fine.

any ideas?

Mike wrote:
it has to be the STK.

because the output looks normal on no-load condition, however, the base
drive to both transistors is clipped on the bottom of the waveform.

load and no load. its clipped. the other channel is fine signal.

So, the chip most likely. because all the resistors and capacitors test
fine. same with the 2 current limiting/bias transistors. it also tests fine.

STK is last.

One per channel? Swap to verify....

jak


"Mike" wrote in message
...
Ok the front panel was dead, had 2 fuses blown, and the MN2488 and MP1620
was shorted in the right channel. the rest was fine.

Well, i replaced both fuses, replaced both outputs and the 2 10ohm base
resistors. I checked every other resistors and found things to be normal.
i replaced a high ESR 47uf cap also.

there was a small PNP transistor near the 2 outputs that was shorted also,
replaced that.


The set now turns on and works, except as soon as I hook a speaker up to
the right channel output, it goes into protector. i checked and double
checked the resistors in the output circuit. If i leave the speaker
unhooked, its fine. there is NO DC offset according to me meter on the
right channel. if i set the meter on AC, I can see the AC signal on the
meter, and on my scope just normal. if i hook the speaker up to the right
channel, it fires protector mode. the other channels work fine.

any ideas?

Mike wrote:
it has to be the STK.

because the output looks normal on no-load condition, however, the
base drive to both transistors is clipped on the bottom of the
waveform.
load and no load. its clipped. the other channel is fine signal.

So, the chip most likely. because all the resistors and capacitors
test fine. same with the 2 current limiting/bias transistors. it also
tests fine.
STK is last.

"Mike" wrote in message
...
Ok the front panel was dead, had 2 fuses blown, and the MN2488 and
MP1620 was shorted in the right channel. the rest was fine.

Well, i replaced both fuses, replaced both outputs and the 2 10ohm
base resistors. I checked every other resistors and found things to
be normal. i replaced a high ESR 47uf cap also.

there was a small PNP transistor near the 2 outputs that was shorted
also, replaced that.


The set now turns on and works, except as soon as I hook a speaker
up to the right channel output, it goes into protector. i checked
and double checked the resistors in the output circuit. If i leave
the speaker unhooked, its fine. there is NO DC offset according to
me meter on the right channel. if i set the meter on AC, I can see
the AC signal on the meter, and on my scope just normal. if i hook
the speaker up to the right channel, it fires protector mode. the
other channels work fine. any ideas?

I suspect you've missed a bad resistor...

Mark Z.

well according to how its wired, the right front, and center, is run by the
STK3102.

the left channel which works fine is run by an STK350-230.

Well I decided to test the center channel, and is also distorted, and that
channel wasnt touched. so the STK has to be the problem.




"Mark D. Zacharias" wrote in message
t...
Mike wrote:
it has to be the STK.

because the output looks normal on no-load condition, however, the
base drive to both transistors is clipped on the bottom of the
waveform.
load and no load. its clipped. the other channel is fine signal.

So, the chip most likely. because all the resistors and capacitors
test fine. same with the 2 current limiting/bias transistors. it also
tests fine.
STK is last.

"Mike" wrote in message
...
Ok the front panel was dead, had 2 fuses blown, and the MN2488 and
MP1620 was shorted in the right channel. the rest was fine.

Well, i replaced both fuses, replaced both outputs and the 2 10ohm
base resistors. I checked every other resistors and found things to
be normal. i replaced a high ESR 47uf cap also.

there was a small PNP transistor near the 2 outputs that was shorted
also, replaced that.


The set now turns on and works, except as soon as I hook a speaker
up to the right channel output, it goes into protector. i checked
and double checked the resistors in the output circuit. If i leave
the speaker unhooked, its fine. there is NO DC offset according to
me meter on the right channel. if i set the meter on AC, I can see
the AC signal on the meter, and on my scope just normal. if i hook
the speaker up to the right channel, it fires protector mode. the
other channels work fine. any ideas?

I suspect you've missed a bad resistor...

Mark Z.

replacing the STK fixed the issue.



"Mike" wrote in message
...
Ok the front panel was dead, had 2 fuses blown, and the MN2488 and MP1620
was shorted in the right channel. the rest was fine.

Well, i replaced both fuses, replaced both outputs and the 2 10ohm base
resistors. I checked every other resistors and found things to be normal.
i replaced a high ESR 47uf cap also.

there was a small PNP transistor near the 2 outputs that was shorted also,
replaced that.


The set now turns on and works, except as soon as I hook a speaker up to
the right channel output, it goes into protector. i checked and double
checked the resistors in the output circuit. If i leave the speaker
unhooked, its fine. there is NO DC offset according to me meter on the
right channel. if i set the meter on AC, I can see the AC signal on the
meter, and on my scope just normal. if i hook the speaker up to the right
channel, it fires protector mode. the other channels work fine.

any ideas?

"Mike" wrote in message
...
replacing the STK fixed the issue.


Glad to hear it. Thanks for posting your end result. It's always nice when
someone actually bothers, and helps to make the time spent by everyone
venturing help and advice, seem worthwhile.

Arfa