Power Circuit Board Mystery, Harman Kardon HKTS220 SUB/230

Yoake10

New Member
Here is a power circuit board mystery to solve!

For 3 months now I have been trying to repair and error search Harman Kardon 220 sub power circuit board without any luck at all. Therefore I need some more electric minds and brains to solve this problem. I will attach the schematic below with the replaced components and voltage measurements.

Anyone have any idea whats going on?
The problem started with R23 burning out and recitifer bridge BR1 broken. It should be 35 VDC at DN4 and 3,3V DC at CN2.



 
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They are connected, the first is main power supply board and the second standby power, both must work. Just replaced with recommended repair parts and components i had at home. The problem started with R23 burning out and recitifer bridge BR1 broken. It should be 35 VDC at DN4 and 3,3V DC at CN2. Which goes to the amplifier circuit board.
 
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The first page shows part of a switched-mode PSU - the drive for the power switching stage should come via transformer DT1 & if that drive signal is not present there will not be any output.

With the second page, the fact that there is voltage on the VCC pin and an output on the "15VS" point shows the PSU is basically working.

The lack of the 3.3V supply has to be due to a failed component somewhere between pins 5 & 4 of the transformer and the output, or the output is overloaded / shorted.
 
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That's the point - why are you messing about with both?, it's HIGHLY unlikely both have failed.

Make sure the standby supply is working properly, before starting trying to fix the main one.
 
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Thanks for a superb and informative answer, I will take a closer look at the components between 5 & 4 and come back with a answer and more information.
 
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I have now checked all the components (D1, C5, C6, L1, R10 and C7) between pin 5 & 4 of the transformer, they are all OK. When CN2 is not connected i get a shifting voltage between 2,6-3,1V and when CN2 is connected i get voltage between 0,5-1,5 V. Why not constant 3,3V when not connected?

And I read 0 VDC at J6 (should be 12V), dont understand why because I read 19VDC at (D4) which are connected to R12 and goes from there to 15VS1 and then to Q2 which provides J6 and CN3 which is control board for the DT1.
Is it because the Q2 isnt letting it through? What happens with the 19 VDC at D4?

Here is the full schematics if needed. https://servlib.com/harman-kardon/audio/hkts-220sub.html
At the bottom of the page there is also pictures on circuit boards and the subwoofer itself.

Pleased if you can help me further and have ideas.

 
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I found a n alternate, downloadable service manual here:

Elektrotanya for electronics experts

Electronics forum for electronics experts to repair defective appliance.
elektrotanya.com

It needs the PS/ON signal (CN2 pin 4( to go high to enable the main power supply. The "high" could be anything from 2V - 5V at a guess, with less than 0.6V being low level / off.

It switches on 15VS1, which in turn feeds the 12V regulator using Q2, which gives the 12VS power to the main PSU control IC.

The other stuff near that fed from point A is overload shutdown that can force Q2 off.

It looks like CN2 goes to CN6 on the main circuit board. Check on there for a short between pins 1 & 2 or 3 & 2??
 
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@rjenkinsgb
I understood your last message as it was this area below I should check for a short. As I understand it those non-polarized capacitator prevent DC current from GND. Does these readings on the picture below say you anything? There wasnt a short but some kind of diode threshold voltage?

I also find it strange that it is 350V AC at C28 when the capacitator is marked for 250V AC.

@Nigel Goodwin
I havent got the tools until early next week to test Q1, I need to screw the circuit board loose and Ground it with two wires to be able to read Q1 because it's placed underneath.

Correction: CN4 should read +47V, not +35VDC as I stated earlier.


 
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I have now made some more measurements, this time when CN2 is connected to main circuit board and power connected/on.

(Extra information: CN4 has 8VDC when turning on the power, but goes to zero after around 15-20 sec.)

CN2
Pin 1 = 0,5-1,7 V
Pin 2 = 0 V
Pin 3 = -2,4-2,8V
Pin 4 PS/ON = 0-0,2V (Which means as you told me, that its too low to switch on Q1 FOR 15VS1).

Q8
1 = -2,4-2,8 V
2 = -3-3,3 V
3 = -3-3,3 V

Q1
1 (Emitter) = 19 V
2 (Collector) = 0,3-0,9 V
3 (Base) = 19 V


1. When CN2 is not connected to main cricuit board the pin 1 gives 2,6-3,1 V. Can the lack of constant 3,3V at CN2 1 cause problem when CN2 is conncted (as for example the MPC82L54AT not working as intended, cuz it needs 3,3V, lack of power)? Or is it just as you said, output shorted.
2. When you told me that it has to be a failed component between pin 5 and 4 that causes the "not" constant 3,3V, do you include those components in the red circle? Like the TL432?
C5,D1,L1, C6 is replaced, C7 and R10 (SMD) is hard to measure but atleast no short.


3. What are the next step, I'm all ears and motivated to solve this! I think its about to narrow down now and we might soon be able to locate to problem.


Thanks in advance!
 
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Nigel Goodwin said:
Presumably this comes from the control micro-controller?.
Click to expand...
Which in turn appears to run from the standby 3.3V supply, which is not yet working.

Yoake10 said:
3. What are the next step, I'm all ears and motivated to solve this!
Click to expand...

The problem with the 3.3VSB rail from the standby PSU needs sorting out before any other problem can be solved.

That not being correct while the 15VS rail has power is odd...

What is the voltage on pin 1 of the TL432? It should be close to 2.5V if the standby PSU is working?
 
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Hi, @rjenkinsgb

Greteful to recieve more of your advice.

I have measured TL432 as you instructed (both with and without CN2 connected), see the two pictures below.

There is a also strange phenomenom happening after around 1 min and 15 seconds when CN2 is connected, which makes the voltage change at a few places. I have done measurements and will present it to you graphically in the two pictures below. The first picture is without CN2 connected and the second with CN2 connected. I hope this makes it easier for you to get the whole picture.

What do you think? Any new ideas?

....Without



......With
 
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