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PostPosted: Fri May 11, 2018 1:20 pm 
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Location: Montréal, QC, CA
Update

I bought the tuner... to acquire some knowledge. :mrgreen:

I didn't open it yet, but just check the functions.
I'm not a judge, I mean I won't put a blame on anyone, I'm just analyzing the facts.

The tuner IS defective. The narrow function doesn't work properly...
In fact, it doesn't work at all. By at all I mean once on narrow, almost no sound at all, and no signal.

Here in Montreal, CKOI FM is the most powerful radio station in all NA, 307 000 watts.
On wide selectivity, the signal strength is maximal at 5 bars.
Once on narrow... nothing... then, something is wrong.
Attachment:
ts-108 wide.jpg
ts-108 wide.jpg [ 44.73 KiB | Viewed 1025 times ]
Attachment:
ts-108 narrow.jpg
ts-108 narrow.jpg [ 42.69 KiB | Viewed 1025 times ]
For CKOI FM (or other powerful stations), the narrow mode is not necessary.
But using some weak station near a powerful one could be a problem.
It's why there's a button to choose selectivity. Then, it must work.

On wide, the sound is good and surprisingly warm.
But there's an obvious distortion problem on high frequencies, surely a bad cap.

So, the tuner got a free pass to my bench.

I will update... once I'll know what's going on.

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PostPosted: Mon Aug 27, 2018 12:38 pm 
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I forgot to post the result, sorry.

Knowing the narrow function wasn't working, I took a look at the ceramic filter.
First thing, I checked if it was short. It was !

I removed it, but unfortunately, a lead was broken. Before inserting a new filter, I checked the circuit to be sure there's nothing wrong.
Guess what, the reading showed me a short. What the... ?!? I followed the traces, only 2 others parts in the path; I measured them, they are good.
That makes no sense at all.

I took a magnifier to look closely at the traces, looking for a solder drop that could have shorted 2 traces (that happens, sometimes).
What I saw is very very rare...
Attachment:
cer1.jpg
cer1.jpg [ 172.8 KiB | Viewed 582 times ]
The center pin is the normal pin ground of the filter (blue circle).
But look in the red circle...

Pin 1 is also grounded !
This is an error from factory.

According to the circuit, the fact that pin 1 was also grounded (read pin 1 and pin 2 of the filter were shorted together),
that was making the filter to act as a capacitor, making the narrow function not working but ALSO the wide function to not work properly.

I then just cut out the erroneous small trace, put back a new ceramic filter and now the tuner is working perfectly on both wide and narrow mode.
Attachment:
New CF onboard.jpg
New CF onboard.jpg [ 305.08 KiB | Viewed 582 times ]

Attachment:
Wide-strong.jpg
Wide-strong.jpg [ 245.88 KiB | Viewed 582 times ]

Attachment:
Narrow-strong.jpg
Narrow-strong.jpg [ 242.79 KiB | Viewed 582 times ]

Although it's been months, it took me only 15 min to fix the tuner.
This is a very good sounding tuner. It largely deserves the 18th place at fmtunerinfo... :mrgreen:

Settings
Local oscillator: no adjustment, 99.8% on
Meter: set to 99%, was 92%
Quadrature: set to 99.5%, was 97%
Separation: set to 98%, was 89.5%
VCO: set to 99.7%, was 97%


Mik

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PostPosted: Mon Aug 27, 2018 1:09 pm 
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Location: dundas, ON, CA
Nice tuner and good detective and repair work enjoy.


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PostPosted: Tue Aug 28, 2018 11:20 am 
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Location: Montreal, QC, CA
@Nakamichel, thanks for these fascinating and very comprehensive posts. Some of us must have been wondering what was up with that tuner.


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PostPosted: Tue Aug 28, 2018 4:32 pm 
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Wow, nice work Mik...not many would recognize a factory defect in the board itself....I know I wouldn't. :shock:
Toby wrote:
@Nakamichel, thanks for these fascinating and very comprehensive posts. Some of us must have been wondering what was up with that tuner.
+1. How many of these tuners are known to have this problem?

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PostPosted: Tue Sep 11, 2018 6:52 pm 
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ripblade wrote:
How many of these tuners are known to have this problem?
Sorry for the late reply Glenn, I still can't see any new thread where I posted. I have to do a search... :?

After many weeks now, the tuner is still working great and sound very good. The narrow function works like a charm.
Note, the CF for the narrow mode is now 110khz, instead 150khz as originally.

Some googling didn't show me anything relative to this problem.
The closest thing I've read is that a guy did a mod to the narrow function for something better.
Is it because he found something weird with that function and couldn't find the problem ?
Or knew the problem but didn't dare to say it loud ?
Or just wanted to improve the sensibility/selectivity for some DXing... I just don't know...

On the PCB, it's marked : REV B made in 91.
So, I assume every REV B would have that error. However, no one's complained about it.
A review of the tuner Fanfare (using the same design but a bit mod'ed) made no mention of this problem.
It could also be just a very few units with that problem. I'm closely looking to see another to sell,
I'll buy it because as engineer as I am, I have to know.

With some mods around all IC's and dedicated supply for each stages, that tuner could easily be ranked
#1 on fmtunerinfo. Another proof that simpler is better, always.

Although there are not many replies in this thread, it has been viewed hundreds times so I guess some of you
should be very interested to know how I proceeded to align the tuner... with just some very cheap "toys".
I'll also explain in details how to check (and what really does the narrow mode).

I will post the "alignment procedure" for this tuner (which is simple) as soon I will have some free times because for now,
my brain is in R&D mode about a certain ACA's power supply... :mrgreen:

Mik

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Nakamichi Dragon/Onix Dac25b, Audio Research SP-9, Spectral DMA-100s/Nakamichi PA-7II, Martin-Logan CLSII/Balance Helicia


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PostPosted: Sat Sep 15, 2018 10:22 am 
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Thanks, Mik....looking forward to reading your alignment tips using "cheap toys" *....and the ACA power supply... :)

* I have an MD 101a I'm hoping can be made to sound as good as it looks. Presently, the Nak ST-7 tuner I'm using blows it out of the water (especially with the Schotz NR engaged), but I can't get past the '80s mid-fi push button interface. I also can't see the buttons in the dark, which has on occasion caused me to erase memory presets by accident lol.

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PostPosted: Thu Sep 20, 2018 5:40 am 
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I have had a FT-101a and I'm remember it was a lot better sounding that a Nak ST-7.
The Schotz is clinical sounding to my ears.

Your 101a needs tech's care. :wink:
Even this B&K sounds better than the Nak.

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PostPosted: Sun Sep 23, 2018 2:19 pm 
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I think I get where you're coming from. When I first tried it I thought some kind of signal processing was going on beyond simple noise reduction. The bass and treble seem to be boosted as well. But, I must admit I like what I hear. I rationalize it by thinking the source is essentially digital anyway, so it should sound clinical. Certainly, the reduced background noise is highly reminiscent of digital replay.

For the quality of material on FM these days, the tuner is relegated to background most times. The greater SNR, frequency tapering and overall spunkier dynamics the Schotz circuit brings helps to pull me in if the music takes a turn for the better.

If only the damned thing had a nicer UI.

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PostPosted: Sun Sep 23, 2018 4:17 pm 
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The noise comes from the digital synthesized tuning.

The thing is, those PLL have pre-fixed voltage for the tuning which can not be ultra accurate.
So instead of 99.500, we have 99.505 or 99.495 or something in between.
Worst part is that it's impossible for us to fine tune the tuning, lol.

However, those tuner still use some varicap, which are very accurate... with the right voltage...
A knob "fine tune" would be of great help here. It would permit greater precision
of the 19khz pilot and thus a lot better stereo separation and then lower noise.

It is easy to see if the tuning is right on. Just hit the mono button.
If there is a big difference (in noise) between mono and stereo,
one can be sure that the digital tuning is not accurate or has drifted, kind of...

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Nakamichi Dragon/Onix Dac25b, Audio Research SP-9, Spectral DMA-100s/Nakamichi PA-7II, Martin-Logan CLSII/Balance Helicia


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PostPosted: Fri Oct 05, 2018 11:06 am 
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The old MD 101a is long in the tooth and sounds very much of its time (late 1980s).
HOWEVER, take it to MD and they can upgrade it and sound much better. At least that was my experience. I have the same tuner and after the upgrades sound quality was improved.


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