I LIKE MUSIC
Super Member
Yes, very well done!
kevzep
Its all about the Music
Commandeered the Wife's craft table for my set up.
To remind all because it's been like a year, the task was replacement of a dual n-FET (the "mixer" FET103) since it was 3 ohms drain to source and presumably shorted.
Acquired Signetics 40673 on the recommendation of dr*audio. Did final check (is this really the right transistor? where am I in danger of screwing something up in the tight space?) and then desoldered the original 3SK-39, trying hard not to break anything else. It was non-trivial... some of the coil wires, particularly, are really tiny. This was right after I desoldered the drain...View attachment 1234764
The old FET had a plastic jacket, likely to isolate the can from other circuitry (the can is and is supposed to be shorted to the source, near as I can tell). I removed it and fitted it to the new FET... probably didn't matter, but why not?
Followed instructions to attach source first, then drain, then the gates (plot twist: the schematic showed gate 1 attached to what was in the actual stereo the gate 2 circuitry... I followed the actual stereo connectivity, obviously--based on what I could discern it shouldn't matter, but it would actually have been a more complicated deal to slavishly try to match the schematic, so why do so?).
The soldering went okay. One thing that went wrong near the end was on reattaching the L103 coil wire: can't tell if it broke or if the insulation melted and flowed over the end of the wire, but I had to strip the insulation back in a space where no wire strippers could get. Ended up cutting it with my fingernails and pulling the insulation snippet out using two pairs of pliers [shudder]. I think it's shorter now, but what're ya gonna do?
View attachment 1234778
Best I could do. Made sure I checked all solder joints with my ohmmeter to verify they were getting connectivity on both sides. Checked drain-to-source resistance: 115 ohms. Much better than 3. Checked overall tuner power supply to ground resistance: 143 ohms. Better than 83 ohms (previous value).
Time to add power... I plugged the 5000X in, set to AM. Verified the expected 14V at AM incoming, then grimaced as I turned the Selector to FM, half expecting popping noises and to see the magic smoke released. Nothing. So far so good. Checked incoming power to the tuner. 14V... if you'll recall, before the FET replacement, it was like 6V. Yet another small victory.
Turning the tuning dial gave me very little on the signal dial... but wait, was that a fluctuation? Eff it, speaker time... and lo and behold, real actual sound. Plugged in an antenna (okay, so it was just a couple of alligator-clipped wires), and... tears of joy...
View attachment 1234790
She works, folks. It's a lovely thing, and I have you guys to thank for the inspiration and guidance.
I still have some stuff to do... while the FM STEREO indicator fluctuates in and out, pressing the FM STEREO ONLY button in basically kills any station, even if it's at Signal 4 or above. Would love some advice there; suspect it's either some kind of alignment issue or something in the demux circuitry...
But overall, I am proud to flip the middle finger at the service shop guys.
"Unserviceable" my ass. Unserviceable no more.
There you go!! Excellent job, I can see you exercised some patience and were thinking about what you were doing every step of the way....
Everything is serviceable, if you have the motivation!!
So good to see you nailed it..
I'd say you need a bit of an alignment which would probably bring back the full stereo function..
I like seeing this sort of thing happening......just brilliant!!
I did find two stations on the dial which were apparently good enough to keep working even with FM STEREO ONLY depressed, so i'm sure you're right.
Just don't have the right signal equipment for an alignment (signal generators).
Still, it's a delight to hear right now. It's so clear!
kevzep
Its all about the Music
FM Mono has extremely good performance, when I was aligning my G9000 tuner, in Mono I had the distortion down to 0.03%THD, insanely clean pure sound, of course when its stereo, its more like 0.1% at best....
Yes aligning is a bit of an Art, I have now been through my "apprenticeship" with alignment, and I am pretty fluid and confident aligning tuners now, and yes, you need the right gear, and especially with Sansui sometimes you need to devise your own methods for certain parts of aligning, like the discriminator for example, Sansui love you to use a Genescope, which is a fairly rare beast these days, so I do it with distortion, you can null the DC from them as well, or you can use a sweep Gen but has to have markers so you can get a visual on the scope....But it just takes a bit of experience to know what and how to do certain parts.
I think in your case here it might just be the RF sensitivity that needs looking at, all you need is an RF Gen that can modulate a 98mhz carrier with a 400hz audio tone and a scope...
I reckon Dr Audio might have a few tricks to get you an alignment of sorts, he's a bit of a tuner guru....
dr*audio
Fish fingers and custard!
Great job! A couple of pointers:
Coil wires can be stripped by melting the enamel off with solder. In the factory they just dip the end in a solder pot and the enamel melts off and the wire comes out nicely tinned. You can just touch the iron to the end of the wire and keep feeding solder into it until it melts. I used to scrape the enamel off with an exacto knife until I learned this trick.
You can align the front end for sensitivity by using radio stations and looking at the signal strength meter. Align the coils for the low end of the dial and adjust the trim caps for the high end of the dial. Follow the directions in the service manual, but use stations at the low and high end of the dial.
The discriminator has to be aligned with test equipment, so don't touch it.
You can align the MPX section using a scope and an FM station, adjusting the coils for the max reading on the scope. But leave it alone for now and do the front end. That may fix your problems. The discriminator adjustment also affects how the MPX locks in. Sometimes you can get the discriminator adjustment close by tuning to a place with no signal at all (hiss only, no digital beeping) and adjusting the coil that the service manual says to adjust for centering the tuning meter so that the meter reads dead center.
Coil wires can be stripped by melting the enamel off with solder. In the factory they just dip the end in a solder pot and the enamel melts off and the wire comes out nicely tinned. You can just touch the iron to the end of the wire and keep feeding solder into it until it melts. I used to scrape the enamel off with an exacto knife until I learned this trick.
You can align the front end for sensitivity by using radio stations and looking at the signal strength meter. Align the coils for the low end of the dial and adjust the trim caps for the high end of the dial. Follow the directions in the service manual, but use stations at the low and high end of the dial.
The discriminator has to be aligned with test equipment, so don't touch it.
You can align the MPX section using a scope and an FM station, adjusting the coils for the max reading on the scope. But leave it alone for now and do the front end. That may fix your problems. The discriminator adjustment also affects how the MPX locks in. Sometimes you can get the discriminator adjustment close by tuning to a place with no signal at all (hiss only, no digital beeping) and adjusting the coil that the service manual says to adjust for centering the tuning meter so that the meter reads dead center.
Good to know! This was pretty standard "extra" clear polyethylene (?) wire cover, looks like it was added as an afterthought to make certain if the end of the coil wire accidentally crossed with another lead there'd be no electrical contact. Would have been no problem if there'd been room to maneuver, but the side walls of the tuner shielding box left very little.
Thanks! Will give these a try today!
In other news, I had thought the AM was working on this thing, but I get only dead air (no static). Because who doesn't want to repair both tuners?
Gary Francks
Well-Known Member
Great job!
Hmmm... after making a go at trying to trim using the Signal meter I think I might get this thing professionally aligned. There wasn't much change except for the worse when I tweaked any of the coils, and I just don't think I have the precision to make a play at it without equipment. It's odd... some of the stations which come in heavy on the FM Stereo signal are at about 3 on the Signal meter while several that come in at 5 on Signal won't light up the FM Stereo indicator more than intermittently.
Yeah, wasn't going back there for anything but decent vinyl prices.
I'm in Phoenix, Arizona and was going to try this guy out if no one else has suggestions:
http://www.audiodoctor.biz
I'm in Phoenix, Arizona and was going to try this guy out if no one else has suggestions:
http://www.audiodoctor.biz
Soooooo tempting. En Zedd is on my bucket list.
kevzep
Its all about the Music
There you go!! Solution right there...
dr*audio
Fish fingers and custard!
Dude, I'd like to come and stay there permanently.
What are you using for an antenna? Usually no change except for the worse means it's aligned properly, try using a decent antenna and see what it does with a good signal. If you can get some TV "rabbit ears" they work great for FM.
This is entirely a good point, and I'll pick something up, but the Sansui 800 and 5000A ten feet away are pulling solid stereo with no antenna at all.
Something weird is up, as even when I've got AM selected I get intermittent FM STEREO indicator flashes on the dial.
dr*audio
Fish fingers and custard!
Sounds like an issue with the selector switch.
Hmmm... maybe.
Seems like there's maybe an intermittent or leaky component in the path to the FM STEREO indicator light which keeps it active even when the FM tuner is getting no power.
I'll check to see if anything is miswired or shorted in the selector assembly, then try to trace the lamp signal while in AM.
