Help with my Nakamichi TA-3A

[proch]

Hello... I have a Nakamichi Receiver that has been a pride and joy for (wow) almost 20 years now. Granted, it's needed repairs more than once, but it's well worth it.

So my latest problem is the tone control button seems to be broken such that it causes the volume in the whole system to fade in and out. It's a real drag because I keep the tone either OFF or on and zeroed.

I'm looking for advice, I could:
1) Take it somewhere for repairs. Where do people take these things for repairs these days?
2) I've got it in pieces: Has anyone attempted to bypass the tone control all together
3) Where could I get replacement parts? I suppose I could buy a TA-1A off ebay and use that to replace the tone control board...

Any other suggestions are welcome...

[bfalls]

Hi proch. Usually the tone control is a dual potentiometer (wound variable resistor). You might see if you can spray some contact cleaner inside the pots. The spray will clean carbon which builds up from arcing, or rubbing between the wires and wiper (adjustment arm) causing a higher resistance. It's even possible the carbon is causing several of the windings to short resulting in less/variable resistance. Pots are usually well marked, so if the cleaning doesn't help, you might try getting the resistance and wattage reading from the pot to find a replacement. You shouldn't need to part out a receiver to find one.

[proch]

Hi BFalls... I know what you mean - I have other audio equipment with bad pots, although I never knew there was a cleaner designed for them - where can I find contact cleaner? Radio Shack? In this case, the malfunctioning part seems to be the switch that turns off or on the whole tone control in the first place. maybe the contact cleaner will work for that in the same way as the pots...

[Kevio]

Where can I find contact cleaner? Radio Shack?Try Google.

Does wiggling the switch or the knob slight change the sound is the warbling unaffected by jostling?

You can probably bypass the tone controls but you'll first need to find a schematic for the unit. Google might be of service there too.

[proch]

Yeah, wiggling the switch totally modifies the effect of the problem at hand, that's why I'm sure it's the switch and not the knobs. For a long while, I've been able to bypass the problem by having the switch 'on' and just leaving the treble and bass neutral. I don't even know why they have those on this unit since the variable loudness acts as a boost for both ends of the frequency spectrum - so a bypass is a completely acceptable solution.

I found the service manual online and took the thing apart. The problem is that the switch is not simple - it has like 12 leads coming off of it and are soldered to the motherboard. I tried some simple logic testing and couldn't figure out how the switch works, but maybe I just need to get the board out completely for better inspection. The service manual doesn't tell me much other than the proper way to get the thing apart...

[Kevio]

Two options:

Find a schematic - it will show you which of the 12 terminals need to be bridged to force it into the "off" position.

Get some contact cleaner and squirt it into the switch.

[proch]

Ok, I got the board out and did some better continuity testing on the switch. If you number the pins on the switch like most electronic pins are numbered (in this case 1 through 12 clockwise), pins 2, 5, 8, 11 are ground, and the swich being OFF or OUT connects the following pairs 1-2, 4-5, 8-9, 11-12. ON or IN connects 2-3, 5-6, 7-8, 10-11. It makes mechanical sense after you realize it.

I'd love to try the contact cleaner before I make semi permanent changes, but it's a pain in the ass to take this thing apart. Can anyone with a NAK TA receiver just verify that the IN position is ON?

[proch]

What do people do? Bridge with a tiny piece of copper wire? Or just use a blob of solder to connect the two contacts?

[bfalls]

If the two terminal point are close enough a blob of solder joining them should be fine. I think it would be preferable since you would have one solder joint instead of two using a piece of wire. Just make certain all joining pieces are hot to avoid a cold solder joint.

[proch]

It's a great plan, but I forgot how much I suck at soldering

[Kevio]

You can use the lead of a resistor or capacitor. Tack the tip to one terminal. Let it cool. Bend it to touch the other terminal. Tack it there, let it cool and then cut off the excess.