Help needed for Nakamichi TA-3A stasis receiver

[routhun]

Greetings to all,

Few days back I've picked up this receiver in non-working state. The receiver will not come out of protection mode. After some investigation I found that output of left channel stuck at -ve Vcc which is -54.3V. I've checked all the transistors in that channel, but did't found anything bad. I've tried to compare the voltages with working channel, but this is next to impossible as the PCB routing for one channel is completely different from another channel. Also the PCB routing is complex and it is not easy to trace back the schematic from the PCB. Can somebody help me in fixing this receiver? I will greatly appreciate if somebody can provide me the service manual or schematic of the power amplifier.

Thanks in advance,
Nageswara

[anatech]

Hi Nageswara,
There is a power resistor that overheats commonly in these. It supplies the reference for the current sources (off the negative rail). Replace both with a higher wattage.

Now that is the common fault (wish I had the manual still to pin point it). There may be other faults as well.

-Chris

[routhun]

Hi Chris,

Thanks for responding. It looks to me that there are couple of current sources in this amp, if you can hint me about which one, I can look at that one. Also the components are crammed and accessing them is very time consuming. If you remember the value of the resistor, please tell me this also helps alot.

Thanks,
Nageswara

[anatech]

Hi Nageswara,
Yeah, it's no fun working under the tuner PCB. I no longer have access to my service manuals or I'd give you all that information.

I think it was a 22K 1/2 W. Use a 1 watt metal oxide resistor to replace it with. There is one ccs per channel supplying the diff pair. That's the feed resistor.

-Chris

[routhun]

Hi Chris,

Thanks a bunch!!! Hats off to your memory. The 22k resistor is indeed the problem. Once I replaced with 22K, 1W the amp worked like a charm. I've replaced the resistor in the other channel with 1Watt one. The receiver sounds great, it has punch and very good highs too. It has lot of detail some time it gives an impression that the highs were artificially boosted, and its sound is almost as sweet as my Luxman R-1120 receiver.

Thanks again,
Nageswara

[anatech]

Hi Nageswara,
The Luxman is yet another good sounding amp.

-Chris

[jcro]

Originally posted by anatech
Hi Nageswara,
Yeah, it's no fun working under the tuner PCB. I no longer have access to my service manuals or I'd give you all that information.

I think it was a 22K 1/2 W. Use a 1 watt metal oxide resistor to replace it with. There is one ccs per channel supplying the diff pair. That's the feed resistor.

-Chris

Thanks, Chris from another TA-3A owner. Same problem. Same Solution.

I documented my repair (1/2 watt 22K Resistors R309L and R309R replaced with 2 watt equivalents) with a lot of photos. If anyone's interested, I'll be glad to post. I bought the service manual PDF online, so anybody, feel free to ask questions.

The TA-3A comes apart easily enough ... no tricky hidden screws or clips ... it was easy to pull the top boards to get at the main PCB ... easy to remove the bottom too.

I got my TA-3A free from our local Craigslist. A nice guy who wanted the receiver to end up with someone who appreciated it enough to repair it. It came with a CR-4a cassette deck too, although that has a bad left record channel ... my next project. The deck and receiver are linked with a DIN cable allowing control from one remote.

Having spent the last few hours enjoying the clean sound of the STASIS amp, I'm pretty pleased. In many respects it reminds me of my Yamaha RX-596 when operating in Pure Direct mode, although the midranges on the Yamaha are not quite as clear, at least on the baby Advents I'm currently using. Sometime this week I want to check the Nak out on speakers with a bit more bass, but so far, so good.

Thanks again. Maybe two years from now Google will send someone else to this thread, so I'll make sure to give it some nice keywords like Nakamichi TA-3A TA-3 receiver protection circuit power light blinks no sound ... there that should work.

-Jack

[urbinab2]

Hello Jcro:
I have the same problem with the protection circuit Nakamichi TA-3A, and want to be able where to find R309L and R309R in the amplifier and change them.

Thank you.

Urbina

[urbinab2]

I need help to locate the resistances R309L and R309R that must change in order that the protection circuit does not fail.

With the manual of service or orientation probably could achieve it.

Thank you
urbinab2

[jcro]

They are on the main (big) pcb ... you need to move the tuner pcb and the control pcb out of the way to see them.

The circuit board should be marked with the resistor names .... look towards the left front of the circuit board for one of the resistors and towards the left rear for the other.
The numbering is fairly consistent, so if you see things like C308L you know that R309L is somewhere close.

If I locate a diagram I will post it.

-Jack