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Old 7th February 2013, 10:43 AM   #1
diyAudio Member
Join Date: Aug 2009
Location: Chandler, Arizona
Default Harman Kardon Signature 2.1

Hi Guys,

First time to post here. I have a HK Signature 2.1 Multi Channel Amplifier. The amplifier suddenly went into protect mode.
After initial troubleshooting, I found out that the right channel is causing the problem while other channels are okay. This is by disconnecting the power supply of the right channel.
I would like to ask the experts there what do I need to start looking at.
I have the schematic and attached it here.
When I look into the right channel, it has history of resistor (R6) replacement.
Thanks in advance for the help.

Best Regards,

Attached Files
File Type: pdf HK Signature 2.1 Service Manual A.pdf (973.6 KB, 83 views)
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Old 14th February 2013, 03:42 AM   #2
diyAudio Member
Join Date: Aug 2009
Location: Chandler, Arizona
Default Harman Kardon Signature 2.1

Hi Guys,

I continued troubleshooting and after dismantling the main amp board, all the transistors of right channel are shorted. Also found 2 diodes that are shorted. History shows that they have been replaced already.

I'm trying to troubleshoot what causes the right channel to fail while other channels are working and no signs of repairs.

I would like to ask the experts there about the wire wound resistors, if this type of resistors easily fail. One channel has 6 0.22 Ohms. 2 0.22 Ohms are connected in series with one end from emitter of 2SC5242 and the other to its complementary 2SA1962 (collector).
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Old 10th June 2013, 04:54 AM   #3
diyAudio Member
Join Date: Aug 2009
Location: Chandler, Arizona
Default Harman Kardon Signature 2.1

Hi Guys, no sure why I cannot see my previous post.

To reply to Gio, I measured the normal voltage range of the step down transformer output and it is ranging from 114-115.5V.

When the indicator is showing low, it is ranging from 103-105V.

I'm using the amp for sometime now after being repaired and so far it is ok. But from time to time I will check the bias measurements how stable it is.

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