Unbalanced Nakamichi Receiver 1

[johnferguson]

This receiver seems to work ok except the balance. The balance control will balance speaker output if it is racked almost all the way to the right.

I had a similar problem with a Receiver 2. It turned out to be weak channel within the Tone Mode switch. It worked ok in the tone-mode off position so that's what I set it to.

This didn't work on the Receiver 1. I thought it might be bad contact in CN-14 connector. I cleaned it up without success.

Balance circuit involves +12v and -12v rails. I'm going to check those next.

In the mean time, since I get satisfactory output with the balance control set to the far right, can any of you see anything wrong with just running it?

On the service manual question, the main board looks very much like the one in the Receiver 2.

I bought what I thought was going to be a Receiver 1 manual from Norma, but what I got was an RE-1 manual.

Although many of the circuit elements are similar - at least the main board on the RE-1 is not at all like the equivalent Receiver 1 board. The Receiver 1 main board IS very similar if not THE same as the Receiver 2 board for which Service Manuals are readily available on line.

 

[Binkman]

G'day Welcome to A.K.! Hopefully others will chime in.
This Serv. man. has come up before and possibly schematics are avail? I dug up some threads on the search box but haven't dug through results.
https://audiokarma.org/forums/index.php?search/55526686/&q=Nakamichi+Receiver+1&o=date&c[node]=13

 

[johnferguson]

The main board and the printed circuit image in the Receiver 2 Service Manual look the same. I'm guessing that either the +12 or -12 rail is off. there is a local power supply on the main board which produces these. I have to build up my nerve to probe them. thanks for the note.

 

[johnferguson]

It looks like the problem was the audio muting transistor on the right channel. I'll report back when the two I've ordered show up and the thing works right. There was nothing wrong either with the main power supply or the "local power supply"

And yes, at least for the main board, the Receiver 2 manual is just fine for the Receiver one.

 

[johnferguson]

It was the Q204R transistor. It's driven by the line mute circuit which I assume is part of the FM tuning setup. In any case I replaced both Q204R and Q204L. It now works great.

And even better, I discovered that the speakers in the shop where this thing is going to live had been hooked up to the previous receiver out of phase. I always wondered why Nakamichi configured their speaker connections the way they did. I guess to confuse me.

In any case, the speakers I thought were junk aren't.