Mcintosh MR78

L-82

Super Member
Hello all, just picked up a Mcintosh MR78 in beautiful shape inside and out. All the lights are on but it does not find stations, basically nothing happens. The frequency and strength gauges are still. I will probably will have to send it out for servicing but my question is, what can cause a tuner to fail at the antenna or at the reception
Cheers and thank you for your input.
 
My guess blown cap in the power supply. Seems to be common problem. On underside small board with heat sink, and a few caps. Service manual available to hifiengine.
 
My guess blown cap in the power supply. Seems to be common problem. On underside small board with heat sink, and a few caps. Service manual available to hifiengine.
Lol that means it will need serving, thanks
 
We discussed this in the Mac Forum. Early Mr78s had a tantalum cap filtering the power supply feed to the MPX board. Since then it has been discovered that many tantalum caps fail by shorting out and causing the voltage regulator to also fail. A part of the SOP of a proper restoration of these now 45 year old tuners is to replace with a 10 mfd electrolytic.

Restored and realigned these tuners can again jump to the front of the line for tuner DX performance.
 
We discussed this in the Mac Forum. Early Mr78s had a tantalum cap filtering the power supply feed to the MPX board. Since then it has been discovered that many tantalum caps fail by shorting out and causing the voltage regulator to also fail. A part of the SOP of a proper restoration of these now 45 year old tuners is to replace with a 10 mfd electrolytic.

Restored and realigned these tuners can again jump to the front of the line for tuner DX performance.
Thank you !
 
The offending cap is on the MPX board, I believe it originally was a 6.8 mfd blue maybe green teardrop tantalum. I do not remember the schematic number but follow the 24 volt supply.

When it shorts out it usually takes out the TO66 transistor used as a regulator.
 
Keep it. Especially if it is in great shape otherwise. Awesome classic that was the flagship of the McIntosh family. Unless you count the MR80 which was fantastic when it worked but could be temperamental. Send it to DeWick.
 
So I’m still looking for a capable repair shop in Montreal, if not I’ll drive to NY and give the guys at classicsaudio a visit.
 
Audio Classics? Yes, I hear they are good. I sent my Mac gear to Terry DeWick (mcintoshaudio.com) in Tennessee and highly recommend him! He is THE McIntosh Guru! He always has a pretty good back log (for good reason) but he does a fantastic job and was very reasonable. If you have any questions, he is the one to ask. He did my MX110 and MC225. I think he posts sometimes on the McIntosh board.
 
[Mod Edit]

I am in broadcast engineering. Stations I engineer for have a lot of MR 74 FM tuners installed as air monitors. NIkko is good. But it is no McIntosh. And if a MR 74 doesn't sound good, chances are it needs servicing and/or alignment. The ones in my care sound superb, and meet or exceed new performance limits.
 
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There are several Japanese tuners that I'd like to play around with - most notably the high end Sansuis. I've tried to buy the TU-9900 from @motorstereo has but he won't sell it to me. It's presently shelved in his collection in favor of a Mc (possibly even an MR78 - I forget).

Sorry Tony the aligned and modded TU9900 left here last winter while my stock MR80 stayed put. The 9900 was nice no doubt; just not quite MR80 nice.:king:
 
I would drive it down to Audio Classics. The drive through Vermont, past the 6th Great Lake (ha, ha) and upstate New York should be spectacular come the color change. You could even arrange a tour of the McIntosh factory.
That’s a great idea, I’ll take my C33 at the same time for a check up...
 
62 caddy has had local connections with AC, it might be possible to prearrange a 24 hour turn around, he might know. I know the factory service is too backed up most all the time but it would not hurt to ask AC what they might be able to do with their service.
 
62 caddy has had local connections with AC, it might be possible to prearrange a 24 hour turn around, he might know. I know the factory service is too backed up most all the time but it would not hurt to ask AC what they might be able to do with their service.
I will ask, I bought a few things there maybe caddy will jumpin..
 
Moderation Note: Thread-crapping in this thread has been stripped out, and the topic has been dragged back to what the OP originally set. Let's keep this thread on topic. This thread has nothing whatsoever to do with opinions on Mac tuners in general, or Mac equipment in general. Let's fulfill the OP's request for information and help, regarding issues he has with his tuner..

Rich P
 
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That’s a great idea, I’ll take my C33 at the same time for a check up...
When you go to Audio Classics, you might see if Richard Modafferi is still doing his magic on MR78s. You might have already heard of him. This is from the AC website:

Richard Modafferi
Inventor and independent consultant to Audio Classics, Rich Modafferi has established himself as one of the world's foremost authorities on tuner and loudspeaker design and development. He holds Masters degrees in Electrical Engineering and Computer Science from the NJ Institute of Technology. A Senior Engineer at McIntosh Laboratories from 1968-74, he designed the MR77 and MR78 tuners and the famous "Rimo" filter. The MR78 tuner has received world wide acclaim for its State of the Art performance. From 1974 to the present, Richard has been a self employed inventor at Modafferi Acoustical Systems, Inc. He has been granted a United States patent for Phase Shift Bass Loading and for the Infinite Slope Crossover. These patents are currently being licensed to Joseph Audio of White Plains NY for use in their speaker systems. Richard also serves as a writer, reviewer and test lab for Audio, Audio Critic, The Sensible Sound.
 
The MR 78's best attribute for me is it's RF section. One of the most selective tuners out there when it was introduced. Many FM DX fanatics loved them, and adjacent channel reception on super narrow is a joy when you need it. That adjustable IF was a great idea, and the RIMO filters really work well on tough reception jobs.
 
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