MR80 with problems...worth picking up?

Great work!!....:thmbsp:
I'll bet your a very pleased with your efforts as you well should be...
The MR80 is a very complicated unit....

This will serve as valuable information for others who may have the same issues....
 
Thanks Kev & Caddy it was a challenging and rewarding adventure! I hope my troubleshooting write up will help those with similar problems.

Caddy I haven't experienced the warm up preset drift but I don't think that it has anything to do with the touch functions. The button selector control circuits are digital CMOS logic circuits that merely engage the analog preset tuning circuits. My guess is that the faults lie on board 9 which contains the analog circuits and the preset tuning pots. That board and those circuits are located right behind the incandescent lamps and right below the top panel vent slots. It would make sense that the area would experience a fair amount of thermal change as the unit warms. Is it just the presets that drift or does the tuner drift from a tuned in station upon warm up? Do all of the presets drift? Let me know if you decide to dig into it I'd be happy to lend a hand.
 
Wow! Nice work on that. It will sound especially nice to you now that you've made it right. Enjoy the music.
 
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MR80 power supply boards with original filter caps on bench.

I picked up a non operational MR80 from the same audiophile who I got my main components from. This weekend I decided it was time to see what was wrong. On power up the display read "175.3" all the time. Started getting ready to measure ps voltages and noticed the rectifier unsoldered itself (ouch -hint!)

That 1000mfd cap (the middle of the left three gold caps on the smaller board in Gregory's photo) was shorted. Dropped in a new one and bingo, up came the display but no sound. Figured out the mute control needed to be switched off or way down and with a dipole I was pulling in stations like crazy. The scan up and down works fine but one of the presets is not operating now. I'll try cleaning up the springs and ensuring they make good contact. If this unit is a good example of an MR80 I would give it the edge in a comparison with my MR77. The Service Manual on the other hand was not as friendly as the one that came with the MR77 IMO.
 
Picked up the unit today, here's a quick pictorial...

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Clean as a whistle under the bottom panel. This one was definitely a non-smoker. :D


Looks like a hackluster power supply recap job. What a strange collection of electrolytics! I'd not fool around with a bunch of miscellaneous caps. Best to order and install replacement Nichicons of the correct value, size, and form factor. The newer caps are physically smaller. Sometimes you can increase the voltage rating one notch and it will still fit nicely on the PCB.


Can you see that ok? Lol, where's my damn glasses!?

MR80_Nich_VZ.jpg




These tuners (especially the digital MR80, IMHO) need to have the PS's updated right away (and a few other caps) before running them any longer.



-Greg
 
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The service manual is a almost 3/4 inch thick notebook......14 sections with maybe 60 pages of three page layouts.

Looked at it when I got to the shop.
 
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Removed the glass...

The "Lock" and "Stereo" bulbs are missing, so that's an easy fix.

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Preset 3 & 4 leds are always on. The front panel circuit board has some char marks from what appear to be a smoked and replaced R501 resistor. The etches look fine but something definitely smoked.

Will dig deeper tomorrow.

Thanks Max! You are correct it was Ren & Stimpy and I knew that...memory failed me in my exuberance!

Just bought an MR80 and narrow band bulb is out...this is my first Mcintosh piece. Is the only way to fix it is by removing the glass?

Thank you
 
When my MR-80 came back from Audio Classics for repair it was better than new it seemed to me. I had one button frozen up and some other minor issues that needed correcting. It sounded Better than my 78, for sure when it came back. Remember Audio Classics has the designer of Mr 77, 74, 78 on staff for repairs and further updates if you wish. And what he and other techs can do with MR-80's is amazing. Is it worth the cost, only you can decide. They will give you an estimate. All I can say is you will have one the best analog tuners ever when they finish.
 
Just bought an MR80 and narrow band bulb is out...this is my first Mcintosh piece. Is the only way to fix it is by removing the glass?

Thank you

Narrow band bulb?
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Or do you mean the panel illumination for the selectivity settings?
 
Sorry...yes. The Selectivity bulb. Long day yesterday!

The good news is that the faceplate is easily removed for bulb replacement.

The bad news is that you run the risk of screwing up all the touch-button controls when you do. Don't ask me how I know. Talent & expertise on a whole different level when working on an MR80. Not a unit for the amateur to get his feet wet.
 
This may sound simplistic but if the tuner works fine RF wise and the display works, why not just use it like an MR78?
 
The good news is that the faceplate is easily removed for bulb replacement.

The bad news is that you run the risk of screwing up all the touch-button controls when you do. Don't ask me how I know. Talent & expertise on a whole different level when working on an MR80. Not a unit for the amateur to get his feet wet.[/QUO

Thank you
 
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