Nikko Beta 20 help needed

[J English]

Hey, AKers, my Nikko Beta 20 stopped making sound today, was working yesterday. Reading as to likely cause of a no sound issue, discussion seems to center on the reed relay / muting circuit. I see that relay is an old Fujitsu MX2 12vdc relay, part number FRL-644Z212/2AS-05. It is an 8-pin relay. Is there a drop in replacement for this old relay, or would it be better to just de-solder and bypass the relay?

 

[arts]

Do not bypass the relay. It is there to mute the nasty (and perhaps loud!) noises made during power on and power off.

It is extremely unlikely that the relay has failed. Verify the coil continuity to be sure.
The fault is much more likely in the drive circuitry, specifically C901 or Q901.

 

[Dingman]

I got my hands on this Nikko and really, the root cause was corrosive glue. There were a couple other minor issues but it really the glue had eaten thru several leads.
And then I made it worse, the first voltage test on a diode broke the corroded lead and I shorted out the C2275 output transistor.
While waiting for a new transistor sub from digikey, I pulled glued components (mostly resistors), cleaned the board, reflowed some (not too bad) cracked solder joints, just a little deox into the controls (not the volume, it's sealed).
Installed the replacement transistor today, unit is working but I did upsize the 4700uf power supply caps to 6800 on a 2a rectifier and it takes a loooong time to charge those caps on power up. It's about 60 seconds and it's too long, the old caps actually test good (I can't do high voltage leakage test) so I might put those back in. It was a bit silly to upsize those caps on a preamp anyway.

 

[loudnoises]

These relays are a common issue with the nikko preamps. I chased it in my beta ii for a while then just jumped the relay. That was about 10 years ago. It doesn't produce any noise on startup or shutdown.

Besides, amp off first always.

 

[Dingman]

These relays are a common issue with the nikko preamps. I chased it in my beta ii for a while then just jumped the relay. That was about 10 years ago. It doesn't produce any noise on startup or shutdown.

Besides, amp off first always.

Sure, relays need attention sometimes. And it appears the volume control is flakey on the left channel so I'm gonna pop that out and see what I can do with it. I'll take the relay out and see if I can easily get it open to clean the contacts.

 

[Dingman]

Update on the this Nikko unit.
As mentioned, the biggest issue was corrosive glue. I did end up replacing quite a few components, not all were affected but once I pulled something out to check, I put in a new part rather than the old.

After getting this unit working, I was testing and found the reed relay introducing some distortion into the audio signal. I don't know how this happens and I couldn't find a direct replacement and so I bypassed the relay entirely. I should have taken a screenshot, any steady freq sinewave showed the distortion. If y'all have any insight into that, let me know.

Unfortunately while testing, I had pulled too hard on the scope ground jumper. Naturally, the grounded jumper fell right on the powered board and blew both the output transistors. I'm just not careful enough sometimes. So I had the pleasure of replacing both the output transistors, and the gain on those replacements are about double of the OEM's. I checked the input vs. output gain, and it's all right on - but that being said - it's spec'd to do 1v output at full volume and man, that's high. I can only get the volume control to about 9 or 10 o'clock before the db's are quite high.
So I'm looking at how to attenuate that signal output (like the carver C-1) and the unit should benefit from a lower noise floor. And I'll get back a bunch of useable volume knob control.

The pictures show all that nasty glue cleaned off and new components installed (more than really needed but we like to strike while the iron is hot!)
Oh, last pic shows the beauty mark this unit has. I like it.

 

[loudnoises]

The beta ii has a pad circuit, button on the front.


Could implement on the 20.

 

[avionic]

A man, outstanding in his field. Great job Dingman.

 

[painttoad]

The beta ii has a pad circuit, button on the front.

it does. but he has a beta 20 and it doesn't

 

[loudnoises]

it does. but he has a beta 20 and it doesn't

But the circuit is similar, it's just a resistor change and a switch. Would be pretty easy to add it to the circuit. Switch isn't required but would allow you to choose.

 

[Dingman]

But the circuit is similar, it's just a resistor change and a switch. Would be pretty easy to add it to the circuit. Switch isn't required but would allow you to choose.

Ya, I didn't even see that on the other version. I'll take a look at that, and sure, I might recreate that circuit.
Thanks for that.

A man, outstanding in his field. Great job Dingman.


View attachment 3833184

"Sometimes I sits and thinks.
And sometimes I just sit."

 

[painttoad]

But the circuit is similar, it's just a resistor change and a switch. Would be pretty easy to add it to the circuit. Switch isn't required but would allow you to choose.

ahh...i see now.. the text you added under the pic blended into the pic.

 

[Dingman]

The beta ii has a pad circuit, button on the front.

View attachment 3832982
Could implement on the 20.

I am going to use that as the guide, it fits right in with what I see on the Beta 20. And no switch for me, I'll just have one output at normal levels and the 2nd pre out at the attenuated level. Then a nice little sticker on the back because in 10 years, I won't remember. I maybe 2 years. Or the next person with the unit.
It will have wait a bit until my basement dries because we got 6.75" of freaking rain in the metro over the last 12 hours and.... there are issues all over town. Dayum.