Strange Nakamichi tuner issue

[JHanko]

Hello all!
First time poster here, so please be gentle... I've owned a Nakamichi TA-4A receiver for a few years and absolutely love it. Alot of equipment has come and gone over the years, but this one always ends up cranking out the tunes. A few months ago, the tuner quit working with similar symptoms as in this thread. I got tired of not having the tuner, so I purchased a new Yamaha R-S700 to replace it. It seemed like a great recever, but it honestly was no match for the Nak. Side by side listening revealed the Nak was more powerful and had better bass, even though they're rated at the same power. The Yamaha was boxed up and returned. I decided to repair the tuner and enjoy it a few more years. With the help of the service manual, I tracked down the problem to the voltage regulator supplying the tuner board. I got that fixed and replaced the backup battery. The tuner came back to life and works perfect, except for one thing. The digital display shows .1 mhz higher than actually tuned. If I want to listen to 93.1, tuning to 93.1 will result in no lock and no stereo. Tuning to 93.2 will result in a lock and stereo. When scanning in auto, all of the stations grabbed are even numbers, always displayed .1 too high (93.2, 98.0, 103.6, etc). It does this throughout the entire band. I'm really stumped on this. There is no mention of any adjustments in the service manual. Any suggestions would be appreciated...

[JHanko]

Wow, 47 views and no suggestions. Looks like this isn't getting fixed...

[geraldfryjr]

There are a number things that can cause this.
Possibly a shift of frequency do to the repaired voltage regulator or the reference oscillator crystal has shift out of tolerence which is highly unlikely but it does happen.

Set the tuner to your desired frequency say 93.1mhz and try tweaking the local oscillator coil very very gently until it locks on the signal.
It is possible the the coil got misaligned slightly during the repair job causing the phase lock loop circuit to make up the difference and causing an improper display.

I could verify this procedure for you on my Technics tuner if you wish.
Once I determine which coil is the local oscillator coil as I don't have the schematic for it and will have to do some searching to find it. jer

[geraldfryjr]

Here is some more info.
It suggest that the discreminator coil could be misaligned.
This is correct and not the local oscillator coil.
Sorry for the misinformation it has been quite a long time since I have worked on any receiver circuits as they rarley go bad.

If you try adust the LO coil the PLL will just compensate for the change and the results will remain the same.


Denon Tuner Problems - Please help

[geraldfryjr]

I found the discreminator coil on my receiver but don't have an alignment tool to fit in the tiny square hole in the slug.
As soon as I find or make one, I will verify that this procedure works. jer

[geraldfryjr]

I would not suggested messing with it if it works as I just shattered the slug by turning it to far.

Don't worry I will fix it as it was just a spare tuner and a freebe any way.
It is not the first one I have broken from not having the proper tool. jer

[anatech]

Hi JHanko,
These Nakamichi receivers had a circuit modification that dealt with that fault. I no longer have my service manuals, but an ex-Nakamichi service center would be able to perform the changes you need.

Do not fiddle with any adjustments! That is not your problem, you have a circuit failure. BTW, I am using a TA-2 in the bedroom and agree with your findings about the sound quality with the Nak. Because it is a Stassis type output stage, you absolutely do need about 6" clear air above this receiver.

Hi geraldfryjr,
Please tell me you are joking! Everything you just posted here is not simply pure silliness, it's just plain wrong! Never mess with any adjustments without having the proper tools and service information.

To properly adjust a tuner, you're going to need far more test equipment than an accurate meter. The odds are great that you'll really degrade the performance of the tuner, and the charges to put it right can easily be high.

Possibly a shift of frequency do to the repaired voltage regulator

Huh?

or the reference oscillator crystal has shift out of tolerence which is highly unlikely but it does happen.

This is an extremely rare event, and probably caused by something else entirely.

Set the tuner to your desired frequency say 93.1mhz and try tweaking the local oscillator coil very very gently until it locks on the signal.

Ahhh, no.

It suggest that the discreminator coil could be misaligned

Good Lord! No!!!! Never mess with adjustments when a device stops working properly. They don't drift that far with time for one, and never change suddenly for two.

This is correct and not the local oscillator coil.

STOP. Do not adjust your tuner either.

Sorry for the misinformation it has been quite a long time since I have worked on any receiver circuits as they rarley go bad.

They are often out of alignment, some worse than others. This does not cause the tuner to not work. Try using some logic please, especially when advising other people!

If you try adust the LO coil the PLL will just compensate for the change and the results will remain the same.

No it will not. What will happen is the performance will be strongly degraded - if it still functions! I'm now in a state of shock due to your suggestions.

I found the discreminator coil on my receiver but don't have an alignment tool to fit in the tiny square hole in the slug.
As soon as I find or make one, I will verify that this procedure works.

Thank goodness for small miracles. You were meant not to have the proper tool for a reason.

I would not suggested messing with it if it works as I just shattered the slug by turning it to far.

Completely predictable.
Ferrite is brittle and the cores are tight. The slug shattered because the tool may not have been a perfect fit, or you did indeed turn it too far. If the alignment is out, it will not be out by very much at all. Keep that in mind.

Don't worry I will fix it as it was just a spare tuner and a freebe any way.
It is not the first one I have broken from not having the proper tool.

And that's a good reason or justification for trashing another tuner? You may well break the next core as well, and they are not always the same.

When aligning the detector of an FM receiver, one of the things you absolutely need in addition to a good meter is a good harmonic distortion analyzer. You also will need a very good FM generator that can be modulated with a constant tone (1 KHz is a good choice). You also will require a 19 KHz pilot (at 9%) and an MPX modulator to produce a stereo signal with tones.

JHanko has an electrical failure that caused this fault. In no way was messing around with the alignment indicated by anything.

-Chris

[geraldfryjr]

I do sincerely apologize for my misinformation as it has been along time ( 25 years) since I have done any work on receiver circuits. I do know the procedures and consequence's of not having the proper tools.

I normaly don't post any information unless I am absolutely sure it is correct.

I got a little ahead of myself and after doing some research it all started to come back and I had realized that I was wrong,by then it was to late to retract my erronous posts.

I'm very sorry.

I do hope there there is a lesson to be learned to those who don't have the proper tools or knowledge too leave these types of repairs to a qualified tech.

As far my cheapy tuner,I am quite capable of repairing it ,but you are right it would not have been broke had I have had the patients and searched for the proper tool buried deep in my garage.

I am very sorry and I wil do my best not allow this type of mistake happen again as I take great pride in helping others by giving the proper information ,unlike some of the other jokesters in some of these theads.

I'm truley sorry and I hope there wasn't damages done due to my misinformation. jer

[Mooly]

I was going to say I remember a marathon thread of mine on a Nak tuner but see there is a link to it hidden in the first posting. I couldn't remember the exact outcome tbh but see we got there in the end. A lot happens on DIY in three months

As this voltage regulator is perhaps a common problem (as anatech mentions there being a stock fault on these... if that is the fault Chris means) I wondered in a hazy moment if the original "calibration" could be returned by tweaking this supply... either a variable reg or using a 7805 in "variable" mode by adding a pot lift to the ground connection.

Do the two diodes in the original reg arrangement allow for temp compensation to maintain calibration as the receiver warms... does the alignment depend on supply voltage in a critical way.

[JHanko]

geraldfryjr: Thank you for taking the time to help. I'm sure you had the best intentions. No harm done.

anatech: Thanks for the reply. What you say makes sense. It's quite possible that the tuner fault is what caused the regulator to open, but I would think the fuse would have prevented this. The tuner still sounds great, so I guess I'll leave it alone. I can live with that extra digit. It's not like I'm trying to sell it. This receiver lives in my shop, where it runs 8-10 hours everyday. I use the tuner alot. I would love to get it aligned, but I wouldn't even know where to begin looking for an ex-Nakamichi service center.

Mooly: I thought anatech meant that the tuner/display being out of sync is the fault. I could be wrong though. I can't answer if the PS has temp compensation or if the alignment is voltage dependant. All I know for sure is that after the repair, the voltage was well within 5% of the service manual spec. The only adjustment I made was L305 (center voltage), as this is all I have equipment for. This was only off by a very small amount (~30 mv.). I got it set to 0v ±5mv. This made no noticable difference in reception or sound.

Again, thanks to all for the help. If anyone has any more suggestions on how to get this fixed, please reply. If there's no other options, I'll just leave it alone and hope it doesn't get worse...