No sound out of MX110 tuner

J

joss2178

New Member
So my MX110 is now recapped (basic recapping) and have no more smoke on 220ohm resistor (R152) (other thread).

Now, there is no sound coming out of the tuner - not even noise - switched in/out the muting switch. nothing.

There is a slight movement in the tuning visual indicator when I roll the the tuning knob.

MPX light indicator is turn on when I turn on the MX110, then slowly light off.

Just got NOS 6AB4 and 6CS6 yesterday, but it is not better.

Do not wanna buy a full tube set for the tuner just to find out my problem, could however try to swap similar ones to see if something happen.

I don't know where to start to fix the tuner. I suppose if the MX110 was not aligned, I would still get at least some noise, no ?
 
Illumination and fade of the MPX STEREO lamp on initial startup is normal. Can't comment on why no sound otherwise.
 
After you recap, you have to, absolutely have to, make sure you have the correct voltages going to the right places. Have you checked the voltages?
 
That what they created pockets for....a place to keep one hand while you measure tube circuits!

Of coarse inside some of the big Mac transistor amps there is enough high current DC to light you up also.
 
Sounds like the local oscillator isn't working, 6AB4 or the mixer 12AT7. Agreed, if the tuner worked prior to the recap, suspect a mistake somewhere in the rework.

First quick pass is to check the plate voltages on all the tuner tubes. They need to be in spec called for in the Service Manual. You didn't pull out that little metal tube, 6DS4, did you? That's the first amp stage for FM.

Lastly, if you don't know what a local oscillator and mixer do, take it to someone who does. You've waded into some deep doo-doo in tube tuners.

Cheers,

David
 
Thanks for everybody that responded. Seems like the plot thickens, but slowly finding my way through.

Went thru most of the tuner circuit, looking at voltage, bad connections, blown resistor or leaking capactor. When I got at the 6D10, I didn't understood why there was nothing connected to pins 2, 3 and 11 - then from TP2 to S2 Rear, there was a few differences in the way things are looking compared to the schematics.

So before going to work this morning, I tought that maybe I was not using the right schematics, and look through all the files I downloaded on the net for the MX110, and bingo, found a schematics that was matching - not using the 6D10 for the radio.

I was using the schematics from the service manual that is easily found on the web - seems to been dating from 1.24.63 from a similar schematics. However my MX110 seems to be dating from end of 65.The matching schematics to my MX110 is from 11.22.65.

I had time to look a bit through the difference in the schematics and it seems that beside the 6D10 not being used, there is a lot of differences around the 6CS6 that looked like it was responsible for the smoking resistor that I had. I saw that the 10mfd C38 capacitor is not there anymore. However, on my MX110 there is a 10mfd at position C38 - and the look of the font is not the same as all the other capacitors in the preamp - so I wonder if during previous servicing, the tech guy did the same mistake as me by not using the 1965 schematic, but previous one, and installed a "missing" 10mfd at C38 ? Anybody have a MX110 late 65 or later and can see if capacitor C38 is there ?

By the was, lots of voltage are off as I replace the selenium bridge (I have around 55v at pin 1,2 and 7 of 6CS6, old schematics is showing 29v, newest is 10v). Also, lots of the lower voltage change when i turn the tuning knob (I suppose that is a good news).
 
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Not that it helps, but did you take notice that the MX110 is unique in that it utilizes both a Compactron (the 6D10) and a NuVistor in its design? I've never seen that in another audio component.

Back on topic ...
 
damacman said:
Not that it helps, but did you take notice that the MX110 is unique in that it utilizes both a Compactron (the 6D10) and a NuVistor in its design? I've never seen that in another audio component.

Back on topic ...
Click to expand...
Nuvistor is a vhf friendly metal/ceramic minitube with almost no available shelf reserve supply and no equivalents.
6D10 is a triple triode color crt gun driver Compactron type tube. Fair number of them still available, great as a single envelope Mullard driver. Nobody makes them anymore either.
 
damacman said:
Not that it helps, but did you take notice that the MX110 is unique in that it utilizes both a Compactron (the 6D10) and a NuVistor in its design? I've never seen that in another audio component.

Back on topic ...
Click to expand...

By George you're 100% correct Tony. Just to be sure, I checked MR67 compliment (and MR71) - sure enough neither sport Compactron 6D10.

All three do have the "NuVistor" though.
 
Like I wrote, it is a MX110 late 65 - so Z.

And just edited my last post as I did mistakingly named the C28, a 10ohm resistor, but it is in fact a 10pf capacitor. Sorry for the confusion.
 
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Thanks 62caddy, but this is for the first version of the Z series , schematic dating from 1963 - if you look between the 6HU6 and the 12AU7, the tuner is going to the 6D10.

If you look at the link I posted, the tuner is not going through the 6D10 between the 6HU6 and the 12AU7 - that new schematic seems to have a lot of changes (that appears on my MX110) and date from 1965. The link I posted, the resolution is good, it is just missing a little part in between the 2 pages and I don't want to screw anything.
 
Thanks again 62caddy, but the schematic in that manual is the same or really similar to the links you sent previously (first version of Z series)
 
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