MR80 power supply recap

This is something you can do between 8:00 and 11:30 AM and that includes getting your tools and chemicals out.. and the tuner on the bench.


Getting started around 8 AM

Here we have the MR 80 on the bench. That's the reflection of the tripod in the front panel. Damn.. the camera lens is speckled!


MR 80 Tuner on the bench prior to a power supply recap. A very fine instrument with proven performance.


Bench arrangement

Now the tuner is turned over and pointed to the LEFT to keep the glass from being damaged and the bottom cover removed. Being right-handed.. I always use this arrangement. Another kudo for the kitchen counter.


MR 80 upside-down on bench with front panel off the bench to the left. This is my standard servicing arrangement.. glass off the LEFT edge.


Removing PCB #1

The inline PCB connectors can be TIGHT! Using latex gloves like the Mrs. has, help a lot in getting a firm grip. You wouldn't pry on those plastic housings with a screwdriver.. would you?


Location of Power Supply PCB #1 connectors and mounting hardware. Eight-pin inline connectors are very tight. A firm grip is needed to remove them.


Removing PCB screws

The MR 80 is built well and relatively easy to service. In removing PCB #1 fasteners, one of the tiny screws was VERY difficult to turn. Unfortunately the threads were destroyed. The good news is.. the standoff was fine after testing it with the other `clean´ screw. It may have been cross threaded during assembly? Let's not speculate. No problem really.. because I tend to replace OLD screws with stainless in the McIntosh units anyway.


4-40 x 1/4" mounting screw with threads destroyed. Luckily it came out.. and without ruining the standoff. Time to order a box of black 4-40 stainless Phillips.


Removing PCB #2

Next to remove is PCB #2. I started unhooking from the far end and worked toward the center. Most of the connectors come off easily by rocking them end-to-end. The one LONG inline was tough. It takes more force but comes off ok. There are two #4-40 board screws into standoffs, and three #6-32 bracket screws through the back panel.

Best to inspect solder joints underneath and re-flow at least the end pads (or two) for the longer 8-pin connectors.


Power Supply PCB #2 connectors removed starting from the side wall, and working toward the eight-pin in the center of chassis.


Your tuner will look like THIS

The wire harness is tight and leaves little room. PCB #2 must be coaxed and navigated out from under with patience.


MR 80 with power supply boards removed. PCB #2 (rear) took some skill and patience to jockey from underneath the harness.


Here are the two original Power Supply boards on the bench..


Power supply PCBs on the bench before original axial electrolytics are removed. Radial caps will be replaced when parts arrive.


and another view... I see the Light!!




Replacing capacitors

The fun part is replacing caps! Here is PS board #1. Looks GREAT!! and what satisfaction to do the work yourself.


Power supply PCB #1 with new axial caps installed. These Nichicon VX series should easily be superior to the originals.


The recapped boards next to each other with six new axials installed. Also there are a couple Muse ES 10uf in the output signal path of PCB #2... and the old parts bag. Of course the radial caps will be replaced... that is after UPS arrives.


MR 80 power supply boards #1 and #2 with new axial caps.. and old parts bag. Don't forget to inspect the solder pads under the connectors!!


Summary

That's about it for today. The tuner will sit there until the second Mouser shipment arrives... probably on Monday.

Can hardly wait to get it back together and try it out.


-Greg

Look like you had fun with the update. I have same tuners as you and recently had them updated by Terry DeWick. They really sing now.

Nyycebro said:

Look like you had fun with the update. I have same tuners as you and recently had them updated by Terry DeWick. They really sing now.

Click to expand...

Yeah.. I enjoy tinkering and detailing a lot. The radial caps came in yesterday instead of the estimated delivery on Monday, so PS boards will probably be done today. Look for Part 2 soon. :yes:

Ordering replacement screws will delay power-up by a few days. OTOH the PCB screws could easily be replaced by removing the cover.

Both tuners could use an alignment, but I'm not the FM Dx'er like years ago. The MR 80 is a superb tuner with proven performance. There was something awkward about the digital tuning function now and then, and I recently found a 16V PS cap in place where a 40V should go.


-Gregory

The MR 80 Power supply is a wrap!


Radials installed

Another task completed in the morning hours.

The axial caps were installed on Jan 4th. The radials, which came in on a separate order were installed today Jan 6th.


Let's get right to it.

Here are the completed Power Supply boards




Nichicon caps

Nichicon VX and VZ caps were installed. Here is their cap line-up: http://www.nichicon.co.jp/english/products/alm_mini/pict_f.htm


Below is a new VZ radial that is smaller by a good measure than the original. The VZ is rated at 105°C and the at VX 85°C.




Recap complete

Some close-ups... really delighted with how it came out!! Caps are nice and small. Some are tiny like slivers.

Left side..




Right side..




Smaller PS board.. EXCELLENT!




Circuit side prep

Good thing we're discussing desoldering methods. Solder Wick is ok but it can burn your fingers. I tend to PRESS too hard and damage the insulating coat. Usually try and drag the wick slightly over the pad, and in a direction off the end of the trace lengthwise. Was practicing for when the C33 is on the bench. That unit must NOT get damaged. I like the idea of a spring-loaded solder sucker.

Missed a spot there on the right.




Solder joints are fine. They get a swipe with a stiff acid brush and acetone before and after new components go in.




Old parts bag

That's the old bag all right! Didn't bother to count em'.




Summary

Yeah.. been posting a LOT lately and must chill soon, but there are four or five projects going on almost at once. The MR 80 power supply recap is complete and it should be back together in a day or three. Will be pulling this activity back into the "MR 80 display ranging" topic.

Another very kool and satisfying Mc project in the books.


-Greg

very good job Gregory !
I use the same cap here ! :thmbsp:

very nice...will update my MR80 in the near future as well...sub'ed