K8021 not working

Kits Audio Hi Fi Projects
1

The kit was purchased on 16thApril 2009 and great care was taken in soldering the components.

Replacement of one of the Voltage regulator was made during the construction due to poor soldering.

On testing the unit was switched on without the IC’s included. The power LED lit so all was assumed well.

I proceeded with adding the IC’s ;’ switched the unit on and the control leds functioned correctly for each input.

However when I measured the voltage at J8 and J9 against ground there was no voltage.
I added the lid and tested the unit with a CD input and line output. There was only one channel working at low volume and highly distorted.

The IC2 OP amp was also running hot.

I have checked all the soldering and can’t find any problems. The GND is sepated via R52 470 ohm resistor . Is this correct: :imp:

Can you help?

Regards Mike Harvey.

2

Check if +5V, +15V and -15V are present at various locations.
Make sure to measure between GND, not chassis.
GND to chassis via 470 ohm is correct.

3

hI,
I have checked readings against GND (Potetiometer case) at various points:

At J16: +15V ok
At J17: -15V ok

At J13: +5V Ok
At pin 2 on SK7: +5V ok

At pin 7 IC2: +15V
At pin 7 IC3: +15V

At T7 emitter: +5v
At T8 emitter: +5v

IC2, IC3 (TLE2071)
At R25A: -15V
At R28A: -15V

Can measure DC offset voltage:
Adjusting RV2 this gives at J8 -0.2v to +0.2v I set this to 0
Adjusting RV3 this gives at J9 0, +0.1 I ser this to zero

tried swapping IC2/IC3 around makes no difference

IC2 (Left channed) still get very hot and no sound even before I attach left channed sk7

I am at a loss…

Can you help

Thanks

4

Proably, the output of the IC is shorted or loaded with a very low impedance.
Remove power and remove IC. Check with multimeter.
If there are no obvious assembly problems, examine PCB tracks for possible etching errors.

5

Yes pin 6 of IC 2 is shorted to GND, but I can’t find out where. I have checked tracks and isolated SK7. I am not able to find prioblem.
Thanks

6

Follow complete path of tracks and components connected to pin 6.
If necessary, remove components.
Check for etching error between track and GND plane.

7

:smiley: :smiley:

Hi,
Sucess I have finally corrected the problem.

For IC2 pin 6 shorting to GND I found a tracking error close to R31.

Also for IC3 pin 3 was shorted to GND. I eventually foound where the track error was for this, but had to take of the ALPS. Taking off compontets doesn’t do the PC track any good so I had to bridge some of the PC tracks with wire.

However now the unit works very sweetly for the PU and CD inputs.(Haven;t used the others)
I also I am driving the power amp for A 28 year old NAD 3020 which works fine. As the preamp for this fried along time ago.

Thanks for your help on this.

Now I have got the kit bug I may purchase the MOSFET amps in the long term, but only when you have widened the gap of the PCB tracks.

Mike