Nakamichi SR-4E power up issue

kylerhea

Member
Hi Nakamichi experts,

my Nakamichi SR-4E does not power up.
When switched on there is a steady orange light (which should indicate standby ) and it does not even try to go further.
I have already changed most of the caps on the power supply board and the diodes across the relay coils and Q404 and Q405 (no replacement of zeners yet). There is still no change.
Is it possible to "force" it out of standby? Could it be possible that it would just need an "on" impulse through the remote control (unfortunately not available) or any other switching circuit and if so, how could it be generated?
There is ca. 5.8V at CN-20 and ca. 49V at the rectifier after T2. The relays for all further voltages just do not engage.
Any idea about which other parts or problems could be causing the problem?
The amp was stored for some weeks and was working before.

Thank you so much for any possible help!
 
The normal start up on a SR 4a (american version) is red flashing LED for 5 seconds and then it turns green, and speaker protection relay close. I have seen bad solder joint on the protection relay pins, that can cause no output. The steady red points to something else though. If the unit never comes out of protection, check the value of the 22K 1/2 watt resistor, on the main board 1" or more from the Heat sink near the bias trimmer adjust. Being as you had this stored, you may not know how very good this unit is. It has a killer MC and phono section. NEVER USE THE LOUDNESS CONTROL (always full clockwise is off) AKer Manziger will be along soon, he is a top notch NAK guy!
 
Hello!

You say that you have 5.8V on CN20, is that the voltage coming from the transistor Q406?

The connector CN20 has the following purposes:

1. +5.6V Powers IC604 on the control board (along with some other stuff.)
2. Ground
3. AC Connected to the reset pin on IC604 and what looks like a clock circuit for IC604 (above my knowledge what it does)
4. Relay This is should be around 5.6V in order to turn Q407 and Q409 on for relay RY402 and RY401

The RY402 turns on the rail voltage over the coil for the RY401 via the resistor R407, this a soft start circuit to limit the current rush trough the transformer. When it works the relays should should turn on almost simultaneously.
If only RY402 turns on, the resistor R407 would be fried in a few seconds.


The normal startup sequence would be like this.

Flashing green power indicator led for 5 seconds (the relays RY401/402 should engage immediately).
After the 5 seconds you should have a solid green on power led and speaker protection relay would go on.


Startup sequence with a fault in the power relay circuit.

Flashing green power indicator led for 5 seconds. No power relay action.
After the 5 seconds a solid green or solid orange.


Startup sequence with a amp fault that stops speaker protection from turning speaker relay on.

Flashing green power led for ever. Power relay goes on


Startup sequence you have?

Solid orange directly? No relay action.

If this is the case, you have a problem that I've never seen before.
Even if the receiver is put in standby mode, if you switch power of and on it would leave standby mode.
.
 
A possible fault for the receiver to go into standby directly after power on, (with out any flashing green), is if the capacitor C628 on the control board is shorted. (1uF 50V)

Tested it by shorting it with a screwdriver, and the power led goes directly to orange.
 
Another fault for orange power led on start up is missing AC on CN20 ( around 41V DC on my unit.), could be broken cable or fault on diodes D410 and/or D411.

If that is the case, you should be able to turn the receiver on by shorting between leg 1 and 8 on IC604.

It could also be that Q611 and/or D630 is broken, there should be around 5,6V at pin 8 on IC604.
 
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Hi, Freddymac2 and Mannegizen!

Thank you very much for your ideas.

My situation is exactly the steady orange light when switched on and nothing else.

I will try your suggestions, check voltages and report back if one of these solutions helped.
 
Just to make sure: how do I measure AC on CN20 (between which terminals)? It seems that there is no voltage. I have checked the wires for continuity and they are fine. Have also replaced D410 (not yet D411 since it measured ok). No success yet.

I have also measured ca. 5.0V (too low?) at pin 8 on IC604.

Would it be safe to try to turn the unit on by shorting between leg 1 and 8 on IC604?

Thank you very much again.
 
You could either measure between ground pin on CN20 or any grounded area, I usually hold my black probe at the big heat spreader.

5V on pin 8 is correct, I was thinking about pin 26 which is around 5.6V in on mode and 0 when in standby.
As you have 5V on pin 8 you should have a sufficient voltage on the AC pin on CN20 (unless you measured on pin 7 which is 5.1V on my unit.)

Shorting between pin 8 and 1 on is safe to do, but actually easier to short between 8 and 7.

So go ahead and short between 7 and 8, if it turns on it's great but I don't think low voltage on pin 8 is the problem any more..

Then check voltage on pin 26, should be 5.6V, but as it's stuck in standby it's probably 0V or around 10mV.

Then check voltage on pin 1, in on mode it should around 100mV, in standby around 5.6V.

But if pin 26 is 5.6V and 1 is around 100mV, then the transistor Q608 might be shorted between collector and emitter.
Pull out CN18, power led would go out but the receiver might go on.
 
There is 2 jumpers, J22 and J23 next to IC607 on the control board, these are connected to pin 1 and pin 26 on IC604.

If I short them together with a screwdriver when my unit is in standby mode, it will go on.
(I didn't check if I got any sound from it, so it can still be in some form of mute mode as I saw that the "Audio Mute" led turned on at one try and I couldn't turn that of by pressing that button. the one next to the volume knob.).

And don't short J22 and J23 for any longer period with CN18 connected (power led), as both green and orange will be turned on at the same time, dunno if the led can handle that for a long time. It's just a test if it turns you unit on.
 
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By the way, have you replaced C628 on the control board, capacity ain't that picky, 1uF to 22uF will not make any negative difference.
The purpose of it might be to filter out noise on the reset pin and/or create a small delay before voltage on reset pin, (pin 8), goes high, 5V.
The purpose of the reset is to restart the IC604 after it gets powered up if the theres is any noise on the 5.6V supply during start up that could put the IC604 in a strange mode.
So if C628 is out of spec, in other words capacity, is much lower, the reset might come too early. (pure speculation from my side tho.)

The IC604 is a small microcomputer with ROM (programed at manufacturing), RAM and other stuff, the pdf I've downloaded didn't give so detailed information.
The sole purpose for IC604 is to execute remote control operation. (if it's bonkers you can bypass it easily, but there is more to test.)
 
Mannegizen, the effort and help you provided is just fantastic.

The problem has been solved: with the help of your directions I was able to narrow it down to a broken PCB track on the power supply board (from D410 / D411 to "AC" on connector CN20). Bridged that with a wire and it immediatley went out of standby and worked.
I am sorry that I could not identify that before.

I am planning to do a full restoration on that unit.

Which parts (besides most caps) would you consider critical for replacement with regard to sound quality (usually just use the main amplifier and phono (important) section)?

Thank you so much.

Marc
 
Gratz, broken traces can be hard to spot.

I usually do replace all caps that has something to do with power supply, tone board, power amp, protection circuit and phono.

Power supply and protection circuit caps feels to be the most important, better to be safe than sorry I think.

As for other parts, I replace the original trim pots for Bias adjustment with Bourne multi turn pots to make adjustment easier.
The battery for radio station memory.

On the smaller cousins SR-2/3 and TA-2, I've so far replaced the differential pair and the drivers to lower DC-offset and getting tighter bass reproduction. But for the SR-4E I did it on, just drivers tho, it gave a minuscule difference in DC-offset, around 5mV. Was around 12-15mv to begin with, which was great as it was.

And of course, spray all switches and selectors with Deoxit, Dexit FaderLube for the Volume/Tone and Loudness pots.
Input selector and tape monitor selector is the ones that most often cause distortion when they get oxidized on the SR series.
The speaker selectors on SR-4 are not in the signal path, same with TA-4, they control the speaker relays, so really no need to spray those.

And check the solders on the TO220 transistors for the +/-18V supply, they run hot and their solders will inevitably fail at some point and when you loose one rail, the result is silence.

All I could think about right now.

Enjoy it ;-)
 
Recommendations anybody for the electrolytics critical for sound?

Would prefer to use the original Nichicon Muse (KZ) series, but they are not available in these values.

Options would include:

- Nichicon FG series or other Nichicon for audio
- Elna Silmic
- Elna Cerafine
- maybe Panasonic FC for the bigger ones in the line / phono amp power supply ( 2200 / 35 )?
- or ?

Any actual experience with one of the above as replacement where Muse caps were used originally?

I am aware of the suitable replacement for the big PSU caps.
 
Recommendations anybody for the electrolytics critical for sound?

Would prefer to use the original Nichicon Muse (KZ) series, but they are not available in these values.

Options would include:

- Nichicon FG series or other Nichicon for audio
- Elna Silmic
- Elna Cerafine
- maybe Panasonic FC for the bigger ones in the line / phono amp power supply ( 2200 / 35 )?
- or ?

Any actual experience with one of the above as replacement where Muse caps were used originally?

I am aware of the suitable replacement for the big PSU caps.
Tons of threads on capacitor replacement, also lots of fights on capacitor replacement on this forum. Check them out. My two cents: I've used all types that you listed and more. I use Panasonic FC/FM everywhere possible, Nichicon PW if those are not available. Long life, low impedance.
 
Hi ivandezande,

thanks for your thoughts.

I did not want to start a new capacitor debate.

Maybe I should try to be more specific: does anyone know from actually trying which one of those well known and well debated good quality caps is as close to the original Nichicon Muse sound characteristic as possible?
I would like to maintain the original character of the SR-4.
 
Hi ivandezande,

thanks for your thoughts.

I did not want to start a new capacitor debate.

Maybe I should try to be more specific: does anyone know from actually trying which one of those well known and well debated good quality caps is as close to the original Nichicon Muse sound characteristic as possible?
I would like to maintain the original character of the SR-4.
Gotcha, I would just use the highest series possible of the Muse series. If it KG, then FG, if not FG, then KW. Also keep in mind they have 105 rated caps that will last a lot longer (KT, KA).
 
One last question concerning the signal routing:

would it be an option to connect CN-39 directly to CN-41 (skipping the Pin Jack and Loudness / Volume PCB)? Would this be electrically the same as original, only removing the loops on the back and the loudness out of the circuit? Or does bypassing those parts parallel to the signal alter it in any way?

I know I can try it and listen but I dont want to undo and insert the connectors more often than necessary.

My loudness knob shows quite a strange behaviour: when turned towards the left (it is of course always fully clockwise at "normal") the volume goes down to (almost) zero.

So I thought I could just simply bypass it and shorten the way of the signal, too.



Thank you,

Marc
 
Hi!
My original intention for writing this follow up was to report on the results of recapping the SR-4. But something went wrong...

I have replaced almost all the caps on the mainboard with Nichicon FG series and FW on the power supply board. I am quite confident that I soldered well and did not create any shorts etc..

The problem now is: when pushing the power switch not even the orange stby led will illuminate. Nothing is happening at all.

Checked the fuses, they are ok. There is 236 VAC at the power switch and beyond and also at the input to the power supply board.
Measured CN-20 again: AC is at 44 V, but no voltage at the 5.6V pin.

Any suggestions on which parts, connections or voltages to check?

Thanks.
 
I hope you did not get the caps from Ebay. Check all the fuses, you are dropping voltage somewhere. I have seen bad solder joints on the 4 pin rectifiers, that fail if the boards are flexed at all.
 
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