Audio Systems: Sony Stereo system MHC-GNX70, output transistors, output transistor

Question
I have a MHC-GNX70 Sony Stereo system.when I turn it on it stays on for 3 seconds then turns off and the power light flashes red and green.Ive taken the entire stereo apart to its individual parts to look for any signs of burning out but to no prevail.the only possible solution i could think of is that I had my stereo connected to my computer and when you first turn the computer on it makes a noise through the speakers as if the wires were touching then goes away.But one day the speakers were up on full volume and the noise went through the speaker and it turned off and started with the problem. Can you help? If So Can The Part I need be replaced? When I plug the stereo into the wall the display comes up and all the flashy lights and stuff work but as soon as you turn it on 1..2..3..OFF!

Answer
You can download a service manual for this model at:

http://www.datasheet4u.com/html/H/C/D/HCD-GNX60_Sony.pdf.html

if you wish. It has all schematics, board layouts and parts lists.

The problem is most likely either the power supply (check voltage outputs with a voltmeter) or the audio amplifiers have shorted down with the big audio spike they get from the PC.

Since the display comes on it means the whole power supply is not bad, but maybe some section of it.  However, under the circumstances of the failure it seems most likely the problem is in the audio section.  

The audio failure could be output transistor failure or a hidden fuse or just about anything; there are many parts in that section.  Trace the wires back from the speaker output connections to locate the output transistors.  To test them you need to pull them out of the board or off the heatsink (depends on how they are mounted). No, I just checked; sorry, this model uses an IC block for main audio amplifier.  It is part number IC600 and is found on page 45 of the manual.  I would say there is a good possibility it has failed.  But, there are other components that could have failed instead of or in addition to the IC.

Do you know how to use a voltmeter? If not, you will be better off taking the unit in to a shop for repairs.  If you can use a voltmeter you can purchase one for under $10 at Home Depot or Walmart.  Walmart has two models; one in automotive and one in electrical department. The electrical department one is the best one for electronics work.

Hope this helps you troubleshoot the system.

As a BTW connecting home electronics equipment to a PC is always a dangerous matter due to the feed lines, grounding problems an in general in compatible design goals with no guarantee of inter-connectivity between the two from the manufacturer.


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