Kenwood kac-5201

[michaeleanor]

Hello Everyone,

I would appreciate if some one helps me in fixing my car amplifier KAC-5201.
While playing it on high volume the amp hot burned, i have changed the power supply fets and the resistor (R91-94), i have attached the schematic .
on powering on it, it still remains in protection mode, i have checked the voltages on IC1,2,3,4 all the readings are correct as per the schematic except in IC 4 at pin 7 I am getting 5volts when the voltage is suppose to be 1.2 volt, can some one advice me which parts should i check to identify the problem.

 

[michaeleanor]

I can pm the schematic

 

[Perry Babin]

IC4 pin 7 is ground and should read 0v.

 

[michaeleanor]

Hi Perry my mistake I meant ic 3 pin 7 should have 0.1 volt but its giving me 5volts

 

[Perry Babin]

Post the DC voltage on all pins of that IC. Copy and paste the following list.


Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:

 

[michaeleanor]

with the ic in

Pin 1: -20.20
Pin 2: 0.08
Pin 3: 0
Pin 4: -21.56
Pin 5: 0
Pin 6: 0
Pin 7: -20.30
Pin 8: 21.74

 

[michaeleanor]

voltage on circuit board after removing the ic

Pin 1: 1.40
Pin 2: -0.80
Pin 3: 0
Pin 4: -22.09
Pin 5: 0
Pin 6: 0
Pin 7: -6.40
Pin 8: 22.14

 

[Perry Babin]

What is the DC voltage measured directly across the left channel speaker terminals?

 

[michaeleanor]

All the above readings that I have given is after removing the output transistor from the circuit, will check and post the dc voltage across the left channel speaker terminals.

Thanks Perry for your assistance

 

[michaeleanor]

Hi Perry the voltage is 0 both right and left channel

 

[Perry Babin]

The output transistors have to be in the circuit for the voltages on IC3 to be near what's shown in the service manual.

 

[michaeleanor]

Noted will check and advice

 

[michaeleanor]

Sorry for the late reply, due to time difference i work in kuwait.
The DC voltage on IC 3 with the output transistors in the circuit is as follows:
Pin 1: 0.19
Pin 2: 0
Pin 3: 0
Pin 4: -21.33
Pin 5: 0
Pin 6: 0
Pin 7: 0.20
Pin 8: 21.40

The above reading is with power supply of 12Volts

 

[michaeleanor]

The ressistance of the output transistors outside the circuit is as follows:

q13
E -C :2.35
E-B:2.371

Q15
B-E:3.198
C-E:3.016

Q16
B-E:3.020
C-E:2.834

Q14
E-C:1.940
E-B:2.272

THE READINGS ARE IN MEGA oHMS

I PRESUME THE TRANSISTORS ARE FINE AND CAN BE USED, KINDLY ADVICE....

 

[Perry Babin]

All of that looks OK. The voltage on pins 1 and 7 will likely change slightly if you adjust the bias (if necessary) but 0.2v is close enough.

 

[michaeleanor]

Thanks Perry i will try that out but why is it not coming out of protect, the led light is still red, isn't IT suppose to be green if all is fine. All the testing i have done is with out giving any input signal and without connecting the speaker.

I haven't yet fasten the output to the heat sink, i guess its fine for testing purpose as long they dont get very hot, kindly advice....

 

[Perry Babin]

There is only one LED and it's red. As far as I know, there is no protection indicator. If the amp is in protect, the LED is unlit.

 

[michaeleanor]

Thanks Perry I dont know for some reason i thought the led light should be green if its working. Anyways I will connect everything and will power it up and see if its working. Will keep you posted on it after some time....

 

[michaeleanor]

Hi Perry, Thanks the amp is back to life, it was possoible only because of your help and support. Just need to clean the board nicely and apply fresh heat sink compound and thats it. Thanks once again