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Old 1st February 2017, 03:36 PM   #1
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Join Date: Feb 2017
Default Nakamichi TA-4A

Hi everyone

I Have one TA-4A who refuse to start, just blink the green power led.
Replace the Q-250L, Q-251L, R-252L and R-260L. Can´t see other bad component, the rest of the transistor measured.
Please any help welcome.
Thanks in advance.
Regards.
Sergio.
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Old 2nd February 2017, 12:27 PM   #2
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Location: Silicon Valley, California
There is an internal 3V backup battery for the microcontroller that could be so discharged that operation will not happen. Measure the voltage across the battery.
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Old 2nd February 2017, 01:13 PM   #3
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Hi James, Thanks for reply !!

I check the battery and is OK

Regards.
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Old 5th February 2017, 03:13 PM   #4
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Hello everyone

After a hard battle, I finally came back to life this amp!
The problem was apart from the damaged components, bad welding, wire harnesses with the wire cut (this method of connection I do not like)
Now I have some minor problems, as if I set the speaker selector to "A" .It does not work. Yes the system "B" (I think it is a bad relay output). During this operation, the display will not show that the speaker is working, and when you press the mute button, it lights up on speaker "B" on the screen ...
Sounds like a bad connection (the cables from the front panel straps or the front switch selector in the wrong position?) I will investigate.
When the amp came back to life, I did one test, remove the battery and the amplifier did not stop, as if nothing had happened (a myth?).
Any suggestions would be welcome.
Thank you
Sincerely¨
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Old 6th February 2017, 08:07 PM   #5
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I guess you had the bad solders in the power amp section, most likely around Q254L too Q257L as these often needs to be reflowed on the TA models (my experience). Right?

As for the parts you replaced, to make those resistors blow someone must have made a damn serious mistake.
I guess you got it in that condition?

As for speaker A not working, it can be a few causes.

1. Speaker selector is badly oxidized in A position.
2. Someone has done a shoddy repair work and cut a cable or two.
3. One or more of the following transistors are bad, Q272, Q274 or Q508. The first two are on the main board, last one on control board.
4. Relay might be broken, RY250, but that doesn't explain why [A] doesn't lit up on the display.

As why [B] only lits up in muted is peculiar, gotta think about that.
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Old 6th February 2017, 08:31 PM   #6
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After looking some more, Q508 is only used when setting the speaker selector in the "Remote" position.

The only cause i can see for [B] lighting up in muted, is if CN-22 from the display has been connected to CN-6.

But if that where the case sound wouldn't be muted when mute button is pressed.
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Old 6th February 2017, 08:55 PM   #7
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Well, the more I look at it, it makes sense if connector CN-6 and CN-22 has been switched on the control board.

Sound would be totally muted with speaker in A position and partly muted in B position.
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Old 6th February 2017, 11:00 PM   #8
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Dear Mannegizen.

You're right!!! The connectors were changed. Now the mute control works fine (I can only hear, at a very low volume when pressed)
Now the display is displayed correctly and the "A" output lights up when the switch is on the "A" speaker and you know what? Output "A" now works, when I connect the speakers !!!
That was the problem to solve.

Thank you very much for your contribution.
Best regards from Argentine.
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Old 6th February 2017, 11:03 PM   #9
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Join Date: Feb 2017
Hi Mannegizen

You're right!!! The connectors were changed. Now the mute control works fine (I can only hear, at a very low volume when pressed)
Now the display is displayed correctly and the "A" output lights up when the switch is on the "A" speaker and you know what? Output "A" now works, when I connect the speakers !!!
That was the problem to solve.
Thank you very much for your contribution.

Best regards from Argentine.
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Old 6th February 2017, 11:28 PM   #10
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It had bad welds in the section of the power amplifier and in the control board.
Almost the entire control board had poor welding from the central sector to the part of the input connectors. Probably in the assembly phase of the board, it was not well positioned (horizontal) in the wave welding station.
In the amplifier, poor welding in different areas.
For doubts check and resolded everything.
I agree with you, this amp was with another technician before me.
Provisionally replace 2SK389BL with two BF245 to test. I know it is ********, but here in Argentina it is difficult to get 2SK ...
I bought two originals 2SK389BL and matched on Ebay.
They come in two weeks.
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