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Power Issues Nakamichi SR-4A
Power Issues Nakamichi SR-4A
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Old 16th February 2014, 06:24 AM   #21
Mooly is offline Mooly  United Kingdom
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Power Issues Nakamichi SR-4A
The 13.9 volts in normal, its just the unregulated supply before the reg. Its alos quite common for service manuals to be less than accurate when quoting voltage. There is no problem with that voltage.

If all the PSU voltages are correct. that's the 5.6, 12 and 30 volts (and the unregulated supplies will be higher/lower/different to what is marked) then you need to look further in now.
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Old 16th February 2014, 08:07 AM   #22
Mannegizen is offline Mannegizen  Sweden
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The 10V on CN12 is for the Volume motor control circuit.
If you can operate the volume with your remote it's OK I guess.


TP2, This is a measuring point for the phase comparator circuit, used for both AM and FM, and I have no Idea on how that works.

But I measured the voltage at TP2 on mine SR-4E.

FM 87,5 MHz 1.6V
FM 108.0 MHz 7,5V

AM 522 KHz 1.6V
AM 1611 KHz 22V

Seems like the voltage at TP2 is depending on tuned frequency.
(I guess this is what is also called the "voltage pump"?)

If your tuner isn't behaving like mine, there might be some issue with the phase comparator or voltage pump if that is what it's normally called.

The feeding voltage, 30V, for the voltage pump on your unit seems to be OK though.

Could be something simple, like the CN1 connector is badly seated or have a bad solder in one end.
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Old 16th February 2014, 11:37 AM   #23
Max Headroom is offline Max Headroom  Australia
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Check the 30V rail.....this supplies the varactor tuning voltage.
If that is down, don't expect it to tune any stations.

Dan.
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Old 23rd August 2017, 12:59 PM   #24
d2k is offline d2k  Indonesia
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Dear all,

I have Receiver Nakamichi SR-4 but I've similar as power problem. The green indicator on power switch is on, but I didn't hear relay sound. Anyone can suggest to me t fix it.

Thanks
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Old 21st September 2017, 05:23 PM   #25
Mannegizen is offline Mannegizen  Sweden
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Originally Posted by d2k View Post
Dear all,

I have Receiver Nakamichi SR-4 but I've similar as power problem. The green indicator on power switch is on, but I didn't hear relay sound. Anyone can suggest to me t fix it.

Thanks
Only the power indicator that is on and the display is black?

If that is the case I would first check if there is 5.6V on pin 1 (marked relay) at Connector CN-20 (found on the control board).

Secondly I would check for bad solders on the power supply board. Especially on and around relay RY402 (it is next to the transformer on the power supply board).

Third would be to replace the relay driver Q404 (just south of the relay) and the fly back diode D414 (next to RY402) .

(I have a unit that worked for a while after replacing Q404 but after a few weeks the issue reappeared.
After replacing Q404 again and the D414 it has been working fine.
My guess is that the reversed voltage from RY402 at turn off, killed Q404 after a while when the faulty D414 didn't do it's job.)
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Old 15th October 2017, 02:18 PM   #26
d2k is offline d2k  Indonesia
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Dear Mannegizen, thanks alot for your advice..
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Old 18th April 2019, 03:39 PM   #27
Mannegizen is offline Mannegizen  Sweden
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My problem with Q404 returned once more, after digging around I found that not all 2SA733 are created with the same specs.
Some can handle 500mA and effect of 625mW while others are just 100mA and 250mW.



(The issue with dying Q404 can be something differently, like that I have bad batch of those but the power supply board is iffy to work with and I am lazy.)



So this time replaced it with a KSA1013YTA.
No smoke or fireworks, just a working SR-4E once more.
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Old 20th July 2019, 04:40 AM   #28
martytoo is offline martytoo
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Quote:
Originally Posted by Mannegizen View Post
My problem with Q404 returned once more, after digging around I found that not all 2SA733 are created with the same specs.
Some can handle 500mA and effect of 625mW while others are just 100mA and 250mW.



(The issue with dying Q404 can be something differently, like that I have bad batch of those but the power supply board is iffy to work with and I am lazy.)



So this time replaced it with a KSA1013YTA.
No smoke or fireworks, just a working SR-4E once more.
I found this thread after finding the 2013 thread concerning your replacing the Q404. If this board can't be accessed from the bottom of the receiver, how do you do the work? Must you unscrew it from the case and then partially move it into a position to get to the offending component solder pads? Even reading the voltages must be hard if it can't be seen from below.
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Old 21st July 2019, 12:28 PM   #29
Mannegizen is offline Mannegizen  Sweden
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Originally Posted by martytoo View Post
I found this thread after finding the 2013 thread concerning your replacing the Q404. If this board can't be accessed from the bottom of the receiver, how do you do the work? Must you unscrew it from the case and then partially move it into a position to get to the offending component solder pads? Even reading the voltages must be hard if it can't be seen from below.

From memory:


Remove top cover, 4 screws
Remove front cover ( can't be completely removed because of attached cables.) 8 too 10 crews or so.
Detach power switch, 3 screws.
Detach earth cable from power switch, 1 screw.
Remove the 4 screws on the power transformer.
Remove the 6 screws on the power supply, 4 on the bottom and 2 on the side.


Now you can flip transformer and power supply over to the back and get access the bottom of the power supply.


Be ware of potential short circuits you might have created if you are going to power the unit on in this state. (I recommend that you don't.)
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Old 21st July 2019, 04:10 PM   #30
martytoo is offline martytoo
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Originally Posted by Mannegizen View Post
From memory:


Remove top cover, 4 screws
Remove front cover ( can't be completely removed because of attached cables.) 8 too 10 crews or so.
Detach power switch, 3 screws.
Detach earth cable from power switch, 1 screw.
Remove the 4 screws on the power transformer.
Remove the 6 screws on the power supply, 4 on the bottom and 2 on the side.


Now you can flip transformer and power supply over to the back and get access the bottom of the power supply.


Be ware of potential short circuits you might have created if you are going to power the unit on in this state. (I recommend that you don't.)
Thank you and thank you.

The other question that I have is how hard it is to read the voltages on the transistors and diodes before the disassembly. I am very much in with the idea of no power to the unit when in a state of disassembly, but short of replacing everything on the power supply board I need to have a plan to tackle diagnosis concerning which components to replace.

Another question - can you access the main board from the bottom if I open it up from underneath? I want to replace the two large (green on my unit) capacitors just to the right of center on that board. They look like they are slowly melting away.

Thank you again! You give me hope that I can get the tuner working again on this very wonderful sounding unit.
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