Nikko Alpha II no idle current left channel - diyAudio
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Old 18th February 2015, 02:05 PM   #1
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Default Nikko Alpha II no idle current left channel

Amp powers up and operates. Realized one heat sink was hot while the other was cold during idle. Check of the idle current on the left side measured 0mV. Adjusting R714 1K pot makes no change.

Though I was able to confirm that the pot is adjusting by monitoring Q1 base and watching Q1 emitter.

Can anyone help in what can be suspect?
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Old 18th February 2015, 02:25 PM   #2
rayma is offline rayma  United States
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Quote:
Originally Posted by rfitts46 View Post
Check of the idle current on the left side measured 0mV.
Maybe one of the 0.47 Ohm emitter resistors is open.
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Old 18th February 2015, 04:58 PM   #3
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Rayma, it looks like 2ea .47 ohm emitter resistors in parallel bringing the resistance to .24 ohms. If one opened the emitter resistor value then becomes .47 ohm? Can these be checked for open without having to remove from the board?
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Old 18th February 2015, 05:20 PM   #4
rayma is offline rayma  United States
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Quote:
Originally Posted by rfitts46 View Post
Rayma, it looks like 2ea .47 ohm emitter resistors in parallel bringing the resistance to .24 ohms. If one opened the emitter resistor value
then becomes .47 ohm? Can these be checked for open without having to remove from the board?
Sure, there's no need to unsolder them. After the power supply is discharged, just measure the resistance directly across both pairs of emitter resistors.
The meter should read 0.24 Ohms or so. Zero the meter first because of the low resistance.
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Old 19th February 2015, 12:34 PM   #5
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Good news. Tested the emitter resistors for resistance.

left channel .5 ohms
right channel .5 ohms

the resistance of the clip leads is .26 ohms

so that puts the resistance at .5 - .26 = .24 ohms, half of the paired paralleled .47 ohm resistors.

Decided to give the wire wrapped connections on the left channel amp board a twist using the needle nose pliars.

Now have idle current and was able to adjust to proper setting of 19mV 3mV.

Let it sit for 20 minutes and each heatsink was warm.
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