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NEC T-710 Tuner
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jurb...@gmail.com
Jan 18, 2015, 12:46:41 AM1/18/15
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Looking for some info on this. Internet searches come up with very little. Normally a tuner I would just ditch the bitch (you know a divorce lawyer used that phrase in his advertising ? lol) but I see one went on eBay for like $79. That is alot for a tuner on eBay. I notice it has selectable IF bandwidth as well. I've only had one or possibly two tuners in my life that had that. I know what it does and that it takes a little doing to put it in as a feature. So maybe this thing is worth fixing.
It does not use any of the usual front ends I recognize. The front end is not integrated PLL from what I see. It is bigger than the usual and it has terminals marked "Vt" and I think "Fosc" or something like that. That indicates the PLL is not in there.
There is very little out there on this thing, one sold on eBay, and there is a monitor or something with the same or similar model number that polluts the web results. So I decided to attack the chipset. What I can see is an LA1247 AM IC, LA1235 FM IF/detector IC, LA3450 stereo decoder IC, two M5218L OP AMP ICs near the audio output jacks and two "c1163" right near the front end. (obviously upc1163)
I can get nothing on these for some reason. Web searches indicate it is equivalent to a Sony 8-759-111-72. They're only a seven or ewight pin SIP through hole. I believe they are probably just OP AMPs but it wod be nice to at least know their pinouts with them being right next to the front end.
Symptom is it pretty much tunes nothing. One time as I am hitting the up button and the display is incrementing though the stations it got something weak but it was at more than one station. Bottom line is that it is not tuning what it is supposed to be tuning.
None of these chips I see are a microprocessor. It might be a surface mount on the bottom of the board or it is might be on the front panel. Thing is I don't see any shielded cable running up there to feed it the local oscillator sample.
That leads me to believe it could be a surface mount on the bottom of the main board.
Why are those obviously unsophisticated ICs right by the front end ? Are they the active filters for the digitally generated tuning voltage ? Perhaps one for AM and one for FM ? Anyone know WTF a upc1163 is ? Or the pinout ? I doubt they are for AGC, but then we are talking NEC. Sometimes they did things a little different. If this tuner is of the vintage I think, they did a little different in it.
The fact that it got a station on multiple station settings, when supposedly being a PLL, means the L in PLL ain't there and it is therefore not Led. Any idea about what I should expect on a scope fron the "Fosc" or whatever that terminal is ? (don't have the unit in front of me right now)I popped the lid and I don't see any ICs in there so I really doubt there is a prescaler of any kind. It is probably a direct sample. Hell, we are talking less than 20 mHz here. It must, however be somehow unloaded from the local oscillator so it can run. That is especially true if they pipe it all the way to the front panel.
I do not even know what year the thing is. Information is that scarce, at least to my searches. The year is not marked on it, rather a date code. Of course that is not the holy grail either, it could have surface mounts on the other side or even be those hybrid boards where they cover the IC with a blob of epoxy type stuff.
I can't say this is a labor of love, but it is something I will do in spare time. It would be nice to have a high end tuner. My one Pioneer tunes really well and I have a Technics that pulls in IHF 0.95 uV. Not that I use it. This, or that or whatever will probably go to my sister because I accidentally cut the dial string in her vintage Marantz. I mean really vintage, not the junk ones. A 2225. I have to order all the lamps for it and figure I'll put it back together so she can at least use the amp for now. So it would be nice to have a tuner. (hmm, there is an Onkyo T-4055 around here she could use that we can't sell because of cosmetic issues, but I still want to fix this thing)
Either way, I am not as concerned that the resale value isn't all that high, I think it might be one hell of a good tuner. If it rivals the tuner in my SX-850 which has been teaked and can pick up a stick in the mud from China, and it has this IF bandwidth doohickey on it, I want it. Why not ? I got three turntables in the house and about five records. No, four, one is on loan from someome else lol.
But this might turn into REAL troubleshooting, and I might find a one meg resistor open or some shit. Like the old days.
Any info you got is appreciated. Even comments unless they are, well you know.
Thanx in advance.
It does not use any of the usual front ends I recognize. The front end is not integrated PLL from what I see. It is bigger than the usual and it has terminals marked "Vt" and I think "Fosc" or something like that. That indicates the PLL is not in there.
There is very little out there on this thing, one sold on eBay, and there is a monitor or something with the same or similar model number that polluts the web results. So I decided to attack the chipset. What I can see is an LA1247 AM IC, LA1235 FM IF/detector IC, LA3450 stereo decoder IC, two M5218L OP AMP ICs near the audio output jacks and two "c1163" right near the front end. (obviously upc1163)
I can get nothing on these for some reason. Web searches indicate it is equivalent to a Sony 8-759-111-72. They're only a seven or ewight pin SIP through hole. I believe they are probably just OP AMPs but it wod be nice to at least know their pinouts with them being right next to the front end.
Symptom is it pretty much tunes nothing. One time as I am hitting the up button and the display is incrementing though the stations it got something weak but it was at more than one station. Bottom line is that it is not tuning what it is supposed to be tuning.
None of these chips I see are a microprocessor. It might be a surface mount on the bottom of the board or it is might be on the front panel. Thing is I don't see any shielded cable running up there to feed it the local oscillator sample.
That leads me to believe it could be a surface mount on the bottom of the main board.
Why are those obviously unsophisticated ICs right by the front end ? Are they the active filters for the digitally generated tuning voltage ? Perhaps one for AM and one for FM ? Anyone know WTF a upc1163 is ? Or the pinout ? I doubt they are for AGC, but then we are talking NEC. Sometimes they did things a little different. If this tuner is of the vintage I think, they did a little different in it.
The fact that it got a station on multiple station settings, when supposedly being a PLL, means the L in PLL ain't there and it is therefore not Led. Any idea about what I should expect on a scope fron the "Fosc" or whatever that terminal is ? (don't have the unit in front of me right now)I popped the lid and I don't see any ICs in there so I really doubt there is a prescaler of any kind. It is probably a direct sample. Hell, we are talking less than 20 mHz here. It must, however be somehow unloaded from the local oscillator so it can run. That is especially true if they pipe it all the way to the front panel.
I do not even know what year the thing is. Information is that scarce, at least to my searches. The year is not marked on it, rather a date code. Of course that is not the holy grail either, it could have surface mounts on the other side or even be those hybrid boards where they cover the IC with a blob of epoxy type stuff.
I can't say this is a labor of love, but it is something I will do in spare time. It would be nice to have a high end tuner. My one Pioneer tunes really well and I have a Technics that pulls in IHF 0.95 uV. Not that I use it. This, or that or whatever will probably go to my sister because I accidentally cut the dial string in her vintage Marantz. I mean really vintage, not the junk ones. A 2225. I have to order all the lamps for it and figure I'll put it back together so she can at least use the amp for now. So it would be nice to have a tuner. (hmm, there is an Onkyo T-4055 around here she could use that we can't sell because of cosmetic issues, but I still want to fix this thing)
Either way, I am not as concerned that the resale value isn't all that high, I think it might be one hell of a good tuner. If it rivals the tuner in my SX-850 which has been teaked and can pick up a stick in the mud from China, and it has this IF bandwidth doohickey on it, I want it. Why not ? I got three turntables in the house and about five records. No, four, one is on loan from someome else lol.
But this might turn into REAL troubleshooting, and I might find a one meg resistor open or some shit. Like the old days.
Any info you got is appreciated. Even comments unless they are, well you know.
Thanx in advance.
mrob...@att.net
Jan 18, 2015, 5:23:29 AM1/18/15
to
jurb...@gmail.com wrote:
> There is very little out there on this thing, one sold on eBay, and
> there is a monitor or something with the same or similar model number
> that polluts the web results.
You may have seen these already:
> There is very little out there on this thing, one sold on eBay, and
> there is a monitor or something with the same or similar model number
> that polluts the web results.
One guy on a forum bought one from another guy on that forum. No tech
info, but pics of it lit up and working.
http://www.audiokarma.org/forums/showthread.php?t=443860
Another guy on that same site was trying to fix one that had a hum
in the audio:
http://mail.audiokarma.net/forums/showthread.php?p=8337075
From that thread...
"I recapped the power supply and found that the glue used with some of
the bigger caps had eaten away the leads of a diode and a resistor.
But it didn't hum, so I don't know...just throwing an idea out there."
There are a couple of images of the boards posted in that thread, but
you have to be a member of the forum to see them.
A "what's it worth" site that has dates of 1987 to 1989:
http://www.usedprice.com/items/audio/nec/tuner/t710-digital-28507.html
Hey, this one has a little bit of technical description:
http://fmtunerinfo.com/reviewsM-N.html#NEC
Quoting the above link:
- Thanks to our contibutor Dave N. for this writeup: "The T-710 is a
- 4-gang, dual-gate front end MOSFET design, that features copper foil
- capacitors. That means that it still sounds like new, after 15 or so
- years, and is very quiet. The T-710 has wide/narrow bandwidths,
- separate mute/mono switching, fluorescent display, auto and manual
- tuning of .2 kHz, calibration tone and auto and preset channel scan.
- [...] The specs include usable sensitivity of 10.8 dBf, S/N ratio of
- 78 dB stereo and 85 dB mono, image rejection ratio of 80 dB and IF
- rejection ratio of 100 dB.
There is apparently a review in Stereophile Volume 12 (1989), issues 9,
10, or 11, but Google Books won't show you the full text for it.
There is also a review in Stereo Review, December 1987 (probably
Volume 52 Number 12), per http://www.roger-russell.com/magrevsr2.htm .
If you get desperate, this place has the service manual for $20 plus
unknown shipping (they don't know how to run a shopping cart):
https://www.agtannenbaum.com/n_cat.htm#NEC
and this has it for $17 + $6 shipping:
http://www.stereomanuals.com/man/rep/nec/
Standard disclaimers apply: I don't get money or other consideration
from any companies mentioned.
Matt Roberds
chuck
Jan 20, 2015, 10:45:17 AM1/20/15
to
the VT connection to the tuner. Gradually raise the voltage from 0 to
12 volts from a well regulated power supply to the VT terminal. If
stations come in during this range, set a voltage for a particular
station and then remove the connection to VT. If the station
disappears immediately, there is leakage on the VT line: probably a
varicap. If the tuner is good, the frequency won't drift for about 10
seconds. Chuck
jurb...@gmail.com
Jan 20, 2015, 12:33:50 PM1/20/15
to
Thanks. I had forgotten that trick. For so long now everything I touched had integrated PLL in the tuner or front end.
Unfortunately, if there is leakage on the Vt line it is curtains for this thing. No way I am changing those diodes and going through the alignment. Not sure I could scare up the right equipment even if I wanted to.
Unfortunately, if there is leakage on the Vt line it is curtains for this thing. No way I am changing those diodes and going through the alignment. Not sure I could scare up the right equipment even if I wanted to.
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