Kenwood KAC 848

[mike49504]

Yes directly across each channel And all 4 channels pulse dc i thought at first it was only 2 but all 4 of them do it..


I also placed black meter probe on amps ground terminal and red probe on speakers positive for each channel and i get the pulsing that way also

 

[Perry Babin]

If you saw a pulsing DC on ALL of the positives with the black probe on the amp's ground terminal, you have an open ground somewhere because 2 of the 4 positive terminals (right channel positives) connect directly to the amp's ground terminal.

 

[mike49504]

OK now that i touched up some solder connections this is what i get now..


With the black probe on amps ground terminal..

Red probe on the left channels positive speaker terminal:0.40 volts

Red probe on right positive speaker terminal:0.00 volts

Red probe on right channels negative speaker terminal:0.40 volts


Back Channels

Red probe on left channel speaker terminal:0.40 volts
Red probe on right speaker terminal 0 volts

Red probe on right channels negative terminal:6.09 volts

 

[mike49504]

Ok i do not get this amp..

I put the outputs back in the right rear channel and the amp play clean output from that channel..

So i decided to put outputs back in one channel at a time..

As soon as i did that the right rear channel quit playing ..

On the left and right rear channels i get 0 volts of DC measured directly across the speaker terminals...


On the Front channels i get pulsing DC still measured directly across the speaker terminals ...

I also get pulsing DC on the Front left channels positive terminal with the black probe on amps ground terminal..

If i place the black probe on amps ground terminal and red probe on the right fronts negative speaker terminal i get the pulsing DC also..

All protection transistors are removed

Any ideas ? Im lost

 

[mike49504]

Any ideas on what to look for next on this amp ??

The back 2 channels work perfecly if i leave the front channls outputs out of the amp..


As soon as i stick any outputs in the front channels it pulses DC on the speaker terminals and the back 2 channels quit working

 

[Mote]

I have not worked on any Kenwood amps (yet, I have one waiting for me to start work on it) but I have seen something similar in other amps.

One amp had broken RCA shield to GND trace, two sets of RCAs for 4 channels, one set OK, other with broken trace, you get where I am going with this.

Other amp had Power LEDs leg giving 12V to trace going from opamp output to channel input. That amp also had two channels working perfectly when the bad channels had their outputs out.

Although your problem might be entirely different.

 

[Perry Babin]

Do the pulses on pins 9 and 10 of the 494 pulse on and off at the same rate as the pulses of DC on the outputs?

Are the protection circuit transistors out of the circuit?

If you plug a grounded signal source into the RCA jacks (on in a front channel, one in a rear channel), does that make a difference?

 

[mike49504]

Do the pulses on pins 9 and 10 of the 494 pulse on and off at the same rate as the pulses of DC on the outputs?

If i use the amps ground terminal pins 9 and 10 do not pulse. If i use the negative speaker terminal as ground pins 9 and 10 pulse the same rate as the DC on the speaker terminals..

Are the protection circuit transistors out of the circuit?

The Protection circuit transistors are out of circuit

If you plug a grounded signal source into the RCA jacks (on in a front channel, one in a rear channel), does that make a difference?

Makes no difference at all
__________________

 

[Perry Babin]

If you look at the square wave on pin 9/10 with your scope, does the square wave remain at all times during the pulsing of the output section.