SoundTech 6150 Powred Mixer

[cbass]

Has DC on the speakers.None of the transistors are shorted.Its not drawing much current according to my lightbulb limiter.Diodes are ok but a couple of zeeners check both ways.No open resistors.No blown fuses.Whatelse should I be looking for?By the way this is an awesome forum! I recognize a couple of guys from the Weber forum.

[Jazz P Bass]

Can you please quantify "has dc on speaker"
Measure it & post the results.
Volts DC.

[cbass]

I don't remeber exactly way to much around 34vdc

[km6xz]

Are both rails correct in voltage, as measured on the collector of the power output transistors. Be sure to keep the load off the amp, no speaker or dummy load until it is repaired and stable. Without a load it would be reasonable to not be pulling high current.
What voltage do you read on pin 4 and 8 of IC101? If they are 15volts, one being positive and the other negative, what is the voltage on pin 7?
How did you measure the power transistors to determine none were shorted?

[cbass]

Thank you km6xz I'll check voltages on IC 101 and report back.I just tested for shorts between C,B,E on all the transistors.I actually pulled a couple of the power transistors out and diode tested thm and they checked good.

[cbass]

Pin 4 was +18dc Pin 8 almost no voltage at all.

[km6xz]

OK, that is a good bit of information for tracking the problem down. I assume you measured the 43volt rails at the power transistors. If not be sure to fuse F101, the positive rail for the power amp. I am also assuming the 18 volts you measured is closer to 15 than 18volts because it is Zener regulated.
If there is +43 or about the same voltage (but opposite polarity) on the power transistors Q14,15,16 the problem is in the zener regulated +15 supply for the opamp IC101 feeding the positive supply pin 8. While in-circuit measure the resistance(power off) of pin 8 to ground. If it is higher than a few thousand ohms check the divider resistor R107. Is there 43 or whatever volts are also on the power transistors on one side of the resistor and close to "0" on the other?
The posiitive supply for the IC is a simple circuit that drops, and regulates the main 43 volt rail down to 15volts needed on pin 8.
The resistor R107 could be open, F101 main rail fuse might be open if you are not getting a positive 43 volts on the collectors of Q111, 112, 113.
Please report what voltage you are seeing on those collectors.

[cbass]

Fuse checks good.Pin 8 to ground was 28Mohms.I have +38vdc on the collectors on Q111,112,112 and -38vdc Q114,115,116.I am also getting +38vdc on all the bases and emitters .It looks like someone has replaced Q104 perhaps they got the pins wrong?

[km6xz]

We would expect a DC offset all over the amp if the Diff amp, IC101 is working on only one rail. With pin 8 high resistance, that eliminates all the low voltage regulator(Zener, caps, IC) and brings us back to R107. The symptoms seen in the Diff amp, and current amp with offset can all be explained if R107 is open. I don't know the value but it is the same as the dropping resistor in the negative side low voltage regulator, that is connected to pin 4 and the Zener....my print is poor...it might be R146.
If Q104 was in backwards the result would not be impacting the low voltage regulator feeding pin 8.

[cbass]

I replaced r107 even though it tested good at 2.2k no difference.

[cbass]

Also I have +38VDC on one side of R107 and around 2volts on the other side

[km6xz]

The low side of R107 is directly connected to pin 8 of IC101. You measured very high resistance to ground at pin 8. So what is dropping 30++ voltage when so little current is being drawn? I would carefully inspect the traces, around the resistor, because there are no components in the circuit that could be dropping that much and still see a high resistance to ground at pin 8.
Do you have a schematic of it? The value of 2.2k with 30volts dropped across it would mean the resistor R107 is dissipating almost 1/2 watt so it should be getting warm. Is it possible pin 8 is not really pin 8, but counted the wrong direction? Is R107 getting warm?
Try measuring resistance from pin 8 to the cold side of R107. It should be a direct connected to that resistor at less than 1/2 an ohm resistance through that path.

[Jazz P Bass]

Also I have +38VDC on one side of R107 and around 2volts on the other side

In a previous post you stated that you found "some" zener diodes that where suspect.
Which ones.
That "2 volts on the other side of R107" is not good.
Are D101 (15V) & D102 (12V) zeners o/k?

[cbass]

Sorry I screwed up the readings on IC101.I got +18VDC on PIN5.PIN4 has almost 0volts. PIN8 has about +3vdc.R145 has -39VDC One one said and nearly 0 on the otherside.R145 checks good at 2.2k. Pulled one end of D101,102 and checked good.

[cbass]

Pin 4 and Pin8 on IC101 are both shorted to ground.BAd capacitors maybe?