Sony TA-AX5 power supply, No Output, Please Help - diyAudio
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Old 16th March 2015, 01:14 PM   #1
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Default Sony TA-AX5 power supply, No Output, Please Help

Hi All,

This is my first post. I have some very basic perhaps inadequate - trouble shooting skills, so please be patient.

As a matter of course, I have replaced all the electrolytic capacitors C906, C911,C912, C913,914, C915,C916,C917,C918 but there is still no output from this supply. Voltage across coil L901 measures 330v DC (320V DC)

All resistors R901,902,903,904,905,906 measures ok out of circuit and Transistors Q901,902,903,and 904 measures ok in circuit.

It seems that the oscillator has started but oscillation cannot be maintained. The final voltage across C and E of Q902 is 14.3mv (40V) and C and E of Q901 is 0.665V (31V)

The voltages in parenthesis are reference voltages from the Sony TA-AX4 which uses a almost similar power supply.

The value of the installed R906 is 30 Ohms and not 22 Ohms as indicated in the circuit diagram, I do not know if this will cause the problem.

The amplifier did power up intermittently, approximately 1 time out of 100 power ups. During the time that it powered up normally, all the voltages in the power supply measures correctly.

Thanks for reading and any help appreciated.
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Old 17th March 2015, 04:06 PM   #2
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Anyone ???
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Old 17th March 2015, 04:53 PM   #3
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As I was the owner of an Authorised Sony Service Centre for almost 30years, Sony did not recommend repairs for this type of power supply as there is a serious safety issue involved with repairing these unless highly qualified to do so. There was no technical backup and a replacement item was recommended. That was many years ago so I doubt there is any working stock left.
All I can suggest is check capacitors and the feedback loop Q902/2 etc. Mind your fingers as the capacitor (C419) stays charged with a lethal voltage, for some time!
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Old 17th March 2015, 07:42 PM   #4
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I recommend pulling and testing all semis out of circuit. If I recall, high voltage transistors of this era were not so good, and a common cause of failure.
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Old 29th March 2015, 04:44 AM   #5
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Default Power Supply Repaired

Thanks to those who replied and sorry for the late response as I was waiting for parts from farnel.

For those who are interested, two film capacitors (C907 and C908) were replaced and the power supply can now maintain oscillation

Click the image to open in full size.

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Old 29th March 2015, 10:43 AM   #6
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Interesting. How did you come to this conclusion?
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Old 1st April 2015, 02:42 AM   #7
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Default Sony TA-AX5 Power Supply

Originally Posted by Welcome View Post
Interesting. How did you come to this conclusion?
Simple, I came across this site and learned that the two capacitors were responsible for the oscillation of the power supply:
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Since both of them were .33uf, there were basis for comparison and I found that one of them were faulty using the capacitance range of my trusty sanwa analogue meter

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Old 8th May 2015, 04:45 PM   #8
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Default TA-AX5 resetting system and freeze problem

Hi all, i have the same model, my problem is when i turn on the unit, powers on normally, but when i turn the volume up and reaches certain level (aprox -30 db) resets and the volume go down to -60 db and passes automatically to tuner input. If i try to volume up several times the display turns off and the unit freezes, i have to power off and wait 5 minutes to turn on again. Ive checked the service manual and all button functions goes directly to the IC701 sony upd553c-141 which control them but i dont know if maybe is another component (like X701 crystal between pins 1 and 42) which causes this IC to behave wrong! any clues?

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