[SOLVED] Sony HCD-CP101 - no sound problem

[Chriss]

Hi!
I'm trying to repair the Sony HCD-CP101 Hi-Fi equipment.
The problem is:
No audio output on the speakers.
Actually there is a very weak sound output on the speakers only if volume max.

It is a Hi-Fi equipment with a TDA7296 amplifier.
The volume is controlled by the LC75342 volume control ic.

What I was tried:
1. checked for shorten of the TDA7296 inputs and outputs - no short
2. checked for sound on the TDA7296 inputs whit a small speaker 8 Ohm 1w. - sound is hearing without any distortion etc.
3. until the TDA7296 checking by method 2 I tried to inc. decr. the vol. button and the sound on the speaker was correctly reacting.
4. checked the LC75342 ic voltages described in the datasheet of the Sony HCD-CP101 which I put the link at the end of this text for download.
5. checked the transistors:
   Q815-Q818 - on the base should be 0v but there is 2.36v. if I play the CD than it should be 6.4v but there is 8v.
   Q313 - on the collector should be 0v but there is 2.36v.
   Q330 - on the collector should be 0v but there is 2.36, on the base should be 4.4 which is correct.
   Q100, Q200 - on the base should be 0v but there are 2.36v.

6. I disconnected the CN501 and checked the transistors from the list above ( list index 5 ) again but the same result.
7. Transistors Q310, Q501 & Q502 checked for voltage as in doc described. Voltages correct.
8. Cut the trace on Q313 on the collector side & checked the collector for voltage, the voltage was 0V but on Q200 base was still 2.3V.
9. Changed the TDA7296 with new but no result.

I have no clue what could be the problem.
Any help would be nice.
I missing something in my repairing but I cant see it. 

Here you can download the Repair manual for this device: https://mega.nz/#!dtdmkKZQ!sX27M022_ZG2Ek7YUCFilRyIHnDkfQUaVtKYYfDEcKQ

Here is the link for the TD7296:
http://www.st.com/content/ccc/resource/technical/document/datasheet/3a/2f/b7/86/30/b2/4b/6c/CD00000198.pdf/files/CD00000198.pdf/jcr:content/translations/en.CD00000198.pdf

I focused on the page 25 & 26 in the repair manual and all testing was done
as it is described in the repair manual at that pages.
Equipment was ON in tuner mode.

I hope for somebody to give me a helping hand.

Thanks and my best regards.

[Armadillo]

The fault is commonly caused by Q330 going open circuit. This transistor is normally biased on and grounds the mute line.
Q313 type KRA102S can fail. This also causes an incorrect voltage level on the mute line.

Replace the 2 transistors.

[Chriss]

Sure, here I made the measurements again on the pins of the two TDA's.

The unit is in "Tuner" mod without speakers on the output.
Measurements are related to GND, see in the repair manual page 26, connector CNP902, pin 7( S1-GND).

The volume is on minimum:
Pin:   U       Pin:   U          Pin:     U
1.      0       6.     15.6       11.      0
2.      0       7.     26.5       12.      0
3.      0       8.     -26.5      13.     26.5
4.      0       9.      4           14.     0
5.      0       10.    4.9        15.     -26.5


When the volume in on max there is a bit diference:
Pin:   U       Pin:   U          Pin:       U
1.      0       6.     15           11.        0
2.      0       7.     26           12.        0
3.      0       8.    -26          13.      26
4.      0       9.      4            14.        0
5.      0       10.    4.9         15.     -26


I don't have these transistors at the moment on hand.
What you think if I would remove the Q330 and short the collector and emitter with a jumper wire
for testing purpose?
Actually I would ground the whole line which is on a wrong voltage and if the Q330 is the failure part
the missing sound problem would be solved, but the muting option would never work until I replace the Q330.

Or I could also make a similar digital transistor as on ebay described from a convectional transistor and two 22k resistors.
And this would serve as a replacement transistor for this device.

Any idea?

Thanks for interesting in my problem.

My best regards.

[Armadillo]

Yeap you could short collector to emitter of Q330;

It is just a general purpose transistor with resistors, you could rig one up yourself.

I think its described as SMD component.?

[Chriss]

Thank you mate!
You helped me so much!

I already shorted it out as described and the unit is working well!
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Jump in!