McIntosh MR78 tuner repair

There is no magic to it, although it is a bit tedious to do. Getting an MR apart is not so bad, but putting them back together is complicated by the fact that you can't touch the glass, at least on the inside. Gloves help, but I hate the things. Off topic but, I just got my MR78 back from Richard Modafferi. I am just thrilled with the result.

Cleaned? I assume more than just dusting it out?

How old is the unit? If from the 1960s, have the filter capacitors in the power supply been replaced recently? If not they are overdue.

There is a thread with photos answering your question at audioaficionado dot org slash mcintosh-audio slash 4294-mcintosh-mr78-cleaning dot html.

I think this is exactly what you need.

Perfect! Thanks for the link Kmccarty.

It's really quite easy. I did my mr77 w/o any instructions a few times.

More or less you remove knobs, then the side metal bars, and various screw that hold top and bottom bars that retain glass. You figure it out as it goes. Once apart you will probably have to replace the foam that keeps the lamp light from bleeding. I used the thinnest self adhesive foam from Home Depot or Lowes.

If you encounter noise while tuning the station, the bearings in the tuning capacitors are corroded. They can be sorted out with a contact cleaner like Deoxit- spray into the bearings of the tuning caps and run the cap back and forth a few times.

Ralph, thanks for your good recommendations. Actually just dusty on the inside of the glass. Not sure about the filter capacitors but I'll take a look while I'm in there. No noise while tuning but probably wouldn't hurt to Deoxit the bearings also while I'm in there.

Be careful if you decide to remove the glass- the lettering on the dial can be fragile.

If this really is an older unit get the filter caps replaced! Otherwise your power transformer is at risk and they are not easy to find.

How I can tell the difference between an original filter cap and a replacement?
I've owned the unit some 6-7 years and don't know if the previous owner(s) had any service work done on it.

Replacements will likely have a sticker identifying its brand, pin out and associated values. The originals will have that info stamped into the side of the part.