Kenwood KAC 848

[mike49504]

I powerd this amp up and checked for output.

Out of the B channels i get no sound

Out of the A channels i also get no sound so i checked to see if there was any DC on the outputs..


When i checked the speaker termianls for DC my meter was all over the place from 4 voltd of dc to 1 volt to 3 volts to 4 volts The DC on the output terminals just keeps pulsing all over the place .


Any ideas?

 

[Perry Babin]

Set all bias pots fully counter-clockwise. Measure the DC voltage across all of the emitter resistors. Do you find any with more than 0.000v DC on them?

 

[Perry Babin]

A lot of the kenwood amps have problems with broken solder connections on the bias transistors. Check those.

 

[mike49504]

Set the bias pots full counter clockwise and measured the voltage across the emitter resistors all of them have 0 volts across them..


I reflowed the solder on all of the bias transistors..


Amp still does the same thing

 

[Perry Babin]

0v isn't the same as 0.000v. Do you read 0.000v on every one of them?

 

[mike49504]

no 1 of them is pulsing voltages across it

 

[mike49504]

Ok replaced the emitter resistor that had pulsing voltage across it...


Now i get 0.000 V across everyone of them..


Amps speaker terminals still pulse DC voltage

 

[Perry Babin]

Was the resistor out of tolerance?

If not, the replacement should have the same voltage across it. Re-check.

If it was not out of tolerance, it may have told you which channel is causing the problem.

 

[mike49504]

Yes it was out of tolerance

 

[Perry Babin]

If no emitter resistor has any voltage across it, pull the rectifiers to see if the amp will power up.

 

[mike49504]

With the rectifiers removed amp will not power on at all..

 

[Perry Babin]

Post the DC voltage on the 494.

 

[mike49504]

With the rectifiers removed this is what i get on the 494

PIN 1:2.48
PIN 2:4.28
PIN 3:0.09
PIN 4:0.64
PIN 5:1.68
PIN 6:3.73
PIN 7:0
PIN 8:13.84
PIN 9:4.56
PIN 10:4.56
PIN 11:13.84
PIN 12:13.84
PIN 13:5.06
PIN 14:5.06
PIN 15:5.06
PIN 16:0

 

[Perry Babin]

The power supply is running. Why did you think it wasn't powered up?

 

[mike49504]

Ok put the rectifiers back in the amp and the rail voltage is also pulsing up and down..

Also the gate leg of the power supply fets is also pulsing dc voltages

Any ideas where to start?

 

[brandes.cm]

Pull the outputs if you haven't already.

Sent from my Punch 60.2

 

[Perry Babin]

The protection circuit transistor may be damaged. For the channel that had the bad resistor, remove the protection circuit transistor (Q21, 22, 121, 122). Watch for excessive current draw.

 

[mike49504]

I pulled Q21,22,121,122 Amp still pulses DC on the output termianls

 

[mike49504]

I also pulled all of the outputs along with Q21,22,121,122 amp still pulsing DC

 

[Perry Babin]

When you measured the voltage on the speaker terminals, did you measure the voltage with the probes directly across the speaker terminals for both channels?