I got a problem with the STK465.

The device I tried to replace was marked STK465 with a B on. ( that one is
defective. )

The new one is not marked with the B, just STK465. When I measure the
voltage at pin 4 and pin 13 with respect to ground, I got between +3.5 to +4
volts.

On the STK465 B I got -1.4 volts, what I did expected to measure
according to the internal schematics.

I have tryed with 2 STK IC's, and they both get about the same readings.

Output (pin 7 or 11) from the amp. is very distorted. It clips at the
negative half wave at low levels. At full power it looks like crossover
distortion on the oscilloscope.

Is there any difference between the "old" STK465 B and the new STK465 that I
get from the shop today ?


Anyone have some suggestions?

"Svein Helge" bravely wrote to "All" (10 Nov 05 18:36:56)
--- on the heady topic of "Problem with the STK465 ( B or A ... ? )"

SH From: "Svein Helge"
SH Xref: core-easynews sci.electronics.repair:348087

SH I got a problem with the STK465.

SH The device I tried to replace was marked STK465 with a B on. ( that
SH one is defective. )

SH The new one is not marked with the B, just STK465. When I measure the
SH voltage at pin 4 and pin 13 with respect to ground, I got between +3.5
SH to +4 volts.

SH On the STK465 B I got -1.4 volts, what I did expected to measure
SH according to the internal schematics.

SH I have tryed with 2 STK IC's, and they both get about the same
SH readings.
SH Output (pin 7 or 11) from the amp. is very distorted. It clips at the
SH negative half wave at low levels. At full power it looks like
SH crossover distortion on the oscilloscope.

SH Is there any difference between the "old" STK465 B and the new STK465
SH that I get from the shop today ?


SH Anyone have some suggestions?


I think the A or B part are similar enough not be totally
incompatible. (Often the main difference is more a performance issue.)
The only other thing that is common between both channels in the IC,
besides supplies and ground, is the ripple filter Pin 8. Perhaps a
leaky electro in this external circuit is holding down the bias in the
IC which results in the negative clipping even at low levels. There
isn't much else except for a low -Vcc that could cause a negative
clipping.

A*s*i*m*o*v

.... A couple of volts below threshold.

As I wrote in my previously posting, I did put back the "partly" defective
STK465 B.
Then I measured the "bias" at pin 4 and pin 13 with respect to ground and
the reading was -1.4 volt.

"Asimov" skrev i melding
...
"Svein Helge" bravely wrote to "All" (10 Nov 05 18:36:56)
--- on the heady topic of "Problem with the STK465 ( B or A ... ? )"

SH From: "Svein Helge"
SH Xref: core-easynews sci.electronics.repair:348087

SH I got a problem with the STK465.

SH The device I tried to replace was marked STK465 with a B on. ( that
SH one is defective. )

SH The new one is not marked with the B, just STK465. When I measure the
SH voltage at pin 4 and pin 13 with respect to ground, I got between +3.5
SH to +4 volts.

SH On the STK465 B I got -1.4 volts, what I did expected to measure
SH according to the internal schematics.

SH I have tryed with 2 STK IC's, and they both get about the same
SH readings.
SH Output (pin 7 or 11) from the amp. is very distorted. It clips at the
SH negative half wave at low levels. At full power it looks like
SH crossover distortion on the oscilloscope.

SH Is there any difference between the "old" STK465 B and the new STK465
SH that I get from the shop today ?


SH Anyone have some suggestions?


I think the A or B part are similar enough not be totally
incompatible. (Often the main difference is more a performance issue.)
The only other thing that is common between both channels in the IC,
besides supplies and ground, is the ripple filter Pin 8. Perhaps a
leaky electro in this external circuit is holding down the bias in the
IC which results in the negative clipping even at low levels. There
isn't much else except for a low -Vcc that could cause a negative
clipping.

A*s*i*m*o*v

... A couple of volts below threshold.

"Svein Helge" bravely wrote to "All" (11 Nov 05 09:55:35)
--- on the heady topic of " Problem with the STK465 ( B or A ... ? )"

SH From: "Svein Helge"
SH Xref: core-easynews sci.electronics.repair:348178

SH As I wrote in my previously posting, I did put back the "partly"
SH defective STK465 B.
SH Then I measured the "bias" at pin 4 and pin 13 with respect to ground
SH and the reading was -1.4 volt.

That normal looking -1.4 volt might still be indicating the negative
leg output transistor(s) is open. The +4 volts in the replacement IC
may be indicating that the negative transistor is being turned off
hard. I think you have a bias unbalance problem affecting both
channels. How much voltage is present on the output terminals? Is it
more than about +/- 10mV?

A*s*i*m*o*v

.... Back when I was a boy, we carved our own ICs out of wood.

I get about 200 mV.... on then output terminals.

"Asimov" skrev i melding
...
"Svein Helge" bravely wrote to "All" (11 Nov 05 09:55:35)
--- on the heady topic of " Problem with the STK465 ( B or A ... ? )"

SH From: "Svein Helge"
SH Xref: core-easynews sci.electronics.repair:348178

SH As I wrote in my previously posting, I did put back the "partly"
SH defective STK465 B.
SH Then I measured the "bias" at pin 4 and pin 13 with respect to ground
SH and the reading was -1.4 volt.

That normal looking -1.4 volt might still be indicating the negative
leg output transistor(s) is open. The +4 volts in the replacement IC
may be indicating that the negative transistor is being turned off
hard. I think you have a bias unbalance problem affecting both
channels. How much voltage is present on the output terminals? Is it
more than about +/- 10mV?

A*s*i*m*o*v

... Back when I was a boy, we carved our own ICs out of wood.

"Svein Helge" bravely wrote to "All" (12 Nov 05 10:43:35)
--- on the heady topic of " Problem with the STK465 ( B or A ... ? )"

SH From: "Svein Helge"
SH Xref: core-easynews sci.electronics.repair:348308

SH I get about 200 mV.... on then output terminals.

That is a lot offset but this explains why the negative leg Q's has
+4v at the input and shut off hard. Good news is this shows your new
STK might be just fine but you must now find the original problem.
Test input biasing resistors values and replace input coupling
electros for leakage. The problem is common to both channels so it
must be a single external cause.

A*s*i*m*o*v

.... A stereo system is the altar to the god of music.

I think you may be missed the important thing I did try to explain.

I think the new STK465 is not "BIAS" compatible with the old SFK465 B.
( May require different bias resistors, in my circuit they are 3k3 + 1k )
The reason for this is that when the SFK465B is put back in the same PCB as
the new one, I got the following readings:

a) pin 4 and pin 13: -1.4 volts, ( what I think it should be according to
the internal schematics.)
b) Outputs is less than 100 mV.

Another difference is that the heatsink is NOT connected to pin 14 on the
new STK465.
On the old one STK465B it is...
( substrate/pin14 is connected to heatsink. That is according to the
internal schematics I have.)

I can't find any information on what the difference between STK465B and
STK465 is. ( That is what I am looking for ).
( The new one is STK465 . I have two of these new IC's who i giving the same
readings when put in the PCB. )

I think may be the manufacturer has changed something inside the new IC ????
( and it is not marked with any letter, just STK465)

"Asimov"
...
"Svein Helge" bravely wrote to "All" (12 Nov 05 10:43:35)
--- on the heady topic of " Problem with the STK465 ( B or A ... ? )"

SH From: "Svein Helge"
SH Xref: core-easynews sci.electronics.repair:348308

SH I get about 200 mV.... on then output terminals.

That is a lot offset but this explains why the negative leg Q's has
+4v at the input and shut off hard. Good news is this shows your new
STK might be just fine but you must now find the original problem.
Test input biasing resistors values and replace input coupling
electros for leakage. The problem is common to both channels so it
must be a single external cause.

A*s*i*m*o*v

... A stereo system is the altar to the god of music.

"Svein Helge" bravely wrote to "All" (12 Nov 05 18:00:55)
--- on the heady topic of " Problem with the STK465 ( B or A ... ? )"

SH From: "Svein Helge"
SH Xref: core-easynews sci.electronics.repair:348345

SH I think you may be missed the important thing I did try to explain.

SH I think the new STK465 is not "BIAS" compatible with the old SFK465 B.
SH ( May require different bias resistors, in my circuit they are 3k3 +
SH 1k ) The reason for this is that when the SFK465B is put back in the
SH same PCB as the new one, I got the following readings:

SH a) pin 4 and pin 13: -1.4 volts, ( what I think it should be
SH according to the internal schematics.)
SH b) Outputs is less than 100 mV.

I don't think it needs different bias resistors at all. What exactly
is wrong with the original broken STK465B? It might give us a clue to
what kind of damage might have been done to the bias circuitry.


SH Another difference is that the heatsink is NOT connected to pin 14 on
SH the new STK465.
SH On the old one STK465B it is...
SH ( substrate/pin14 is connected to heatsink. That is according to
SH the internal schematics I have.)

The plain STK465 has the substrate connected to pin 14. So concerning
the substrate, both parts have the same internal pin 14 connection.


SH I can't find any information on what the difference between STK465B
SH and STK465 is. ( That is what I am looking for ).
SH ( The new one is STK465 . I have two of these new IC's who i giving
SH the same readings when put in the PCB. )

SH I think may be the manufacturer has changed something inside the new
SH IC ???? ( and it is not marked with any letter, just STK465)

You know, (hypothetically) the letter B might be simply a case
measurement that has been changed say from english inches to metric or
instead the thickness or shape and it doesn't even have to be
something electrical. Because both are rated at 30W +/-28V. I don't
think this letter difference has anything to do with the present
problem. As far as I can tell the new STK seems to be behaving
according to the improper external inputs. Try checking for continuity
to ground for both pin 3 and for pin 14. The only other thing I can
think of is if the -Vcc is too low, maybe open rectifier.

A*s*i*m*o*v

.... A couple of volts below threshold.