Power Issues Nakamichi SR-4A

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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.
 
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.
 
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.)
 
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.
 
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.
 
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.)
 
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.
 
What kind of issues do you have?

I just bought this on Friday and knew the tuner wasn't working. Once I got it home I very much enjoyed the amp hooked up to a CD player. The amp is ultra quiet and seems amazing.

After playing with the tuner I was able to get a weak sounding AM audio response from a local 50,000 watt AM station. The AM station was listenable but not very pleasant.

But the FM letters don't light up in the display and even though there were two FM stations that I could almost tune in (seeing their dim frequency numbers in the display) the audio was a very static filled distortion.

The memory function seems to be working.

Other owners of this receiver(including a post that I think you made years ago) seem to look to the power supply as the cause of FM trouble and thus I want to measure the voltages there as a start in diagnosis.
 
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