Motorola SK-29M Restoration

[Brettzky99]

Nice job there are some paper caps in the pre amp section and more 12ax7''s

[stbasil]

Preamp finished up. I didn't see any paper caps, unless those fat brown ones are disguised culprits. The two in the power amp, and the ones in the preamp are apparently working OK. I did test a few, they were OK.

The one electrolytic can (10 uF @ 400) was going to be a real pain to replace, 4 resistors and a wire terminating on its single pin. But it tested about 20uF with reasonable ESR, so I left it alone, and all voltages are good, no ripple. However, after running both amps for a while, that cap is too hot, so I guess I'll have to replace it anyway

[TC Chris]

Nip the cap's single pin off, leaving all wires attached. Re-stuff the can and run the new cap's lead to the old pin and its collection of component leads.

Chris Campbell

[electra225]

Or you could cut the can in half, take out the old guts, then put a new cap in the can. Drill a hole in the bottom of the can, run the wires thru to the original connections. You don't have to cut the single pin off that way...Two different ways to accomplish the same thing. Good luck.

[stbasil]

Yep, I cut that sucker off, put the cap negative lead through a hole, and tacked the positive lead to the stump of the post inside the can. I'll glue the can back on and wrap with clear Gorilla tape to stiffen it up.

When I first powered up the preamp, the right channel was weak. After some checking around with the DVM, I remembered the connection issue with these wafer tube sockets. Even though I had deoxed them, and the 12AX7 tube pins, sure enough, at least one pin was loose. Tightened them all, which fixed the bad channel.

Can't figure out why they put the power switch on the balance pot, necessitating adjusting the balance every time you turn it on! Also, that control has only about a 90 degree travel. And the function selector has three phono equalization options, should be fun to play with. All these little quirks of the wild and wooly days of early stereo and record equalization!

Now to get the changer working along with its new Tetrad cartridge....

[electra225]

Magnavox attaches their power switches to the treble control. It's an equally silly setup as Motorola's method. The upline, Series 200 Magnavox tuners get a dedicated power switch, a vastly superior setup. You wear out a control by using it with the power switch. Aluminum HVAC tape wrapped around the filter cap can makes an almost invisible repair. I have a Motorola ST-82 stereo with the power switch as part of the function switch, an indescribably horrible setup.

[stbasil]

I hate to cover up the cool Motorola logo on the side of the can, so that's why I was considering the clear tape. Of course, no one will ever see it again, at least not for a long time! I used Elmer's glue to put the can back on, but I don't trust it to hold permanently. The Gorilla clear tape is only rated up to 140F, the HVAC tape much higher, of course. What do you think?

[electra225]

Looks fantastic to me! You have to look real close to see it's been worked on....

[TC Chris]

If you're worried about durability, the old favorite J-B Weld is a gray color that would not look bad, especially if applied carefully and then the excess is trimmed before full hardening. Make sure you scrape off the Elmer's.

Chris Campbell

[stbasil]

Yeah, I forgot about JB, don't have any on hand, but even our grocery store has some!

[stbasil]

Cleaned off the Elmer's (it looked nice but not very secure), used JB weld instead. The preamp is now working great!

Thanks to assistance via my post in the Changers section, I got the roller bearing unstuck, so the changer is now working perfectly in all aspects.

I replaced the broken Sonotone 8T with the Tetrad, and it sounds great! Apparently it's a good match to this Motorola preamp. It's tracking well at about 3.5 grams.

[William]

I think I need to contact Gary and get that cartridge for my Motorola SK52W. My Sonotone, I think it is a 9T. It is the gold cartridge that Motorola used, is shot.

Bill

[stbasil]

In testing the new cartridge, I noticed very loud rumble, about 70 hz at 33 RPM. The platter bearing and washers are clean and lubed, so I thought maybe it was the idler wheel, even though it was driving the mechanism OK. I removed the idler, and powered the changer motor, spinning the record by hand, with the stylus on the record. Hard to tell, but it seemed that the rumble was gone, or at least a lot less.

For the last VM changer I worked on (in the Moto SK111), I soaked the wheel in alcohol/wintergreen mixture, and it worked wonders, softening up the rubber. So, I tried that on this idler, it's completely different, a two-level design. After soaking for a couple of days, the larger tire disintegrated and came off the shaft. So, I packed it up and mailed it to Gary for the $ swap. If that doesn't fix the rumble, I guess I have a bearing issue.

While I'm waiting for the new idler, I've been cleaning the cabinet. At first, I thought the brassy metal legs were solid brass (magnet doesn't stick), but of course they are just pot metal, chrome plated (now pitted and blistered), with a yellowish wash. I'm not going to spend the bucks to have them stripped and replated. But working them over with Brasso made a huge improvement!

I think they won't look too bad on the final product, but I wish there was a way to remove the pits and bubbles!

[William]

Wow, that is a huge improvement.

Bill

[stbasil]

Washer question:
The new idler definitely helped the rumble, but I can still hear some. In the past, I have always seen two washers under the platter, one above and one below the bearing race, and that's what the service manual shows. But, on this changer, the lower washer is either stuck to, or attached to, the transmission casting, or maybe I'm missing a washer. I tried prising it off, as gently as possible, but it won't budge, so I wondered if it's supposed to be permanently attached, and there should be yet another free washer above it? You can see the silver washer contrasted with the gray casting, that's fresh lithium grease on it.

I don't want to ruin the washer trying to get it off, maybe it's OK like it is?

[TC Chris]

You say silver--if it's polished, like chrome plated shiny, then it's meant to be the bottom race (and probably crimped in place). Look elsewhere for rumble--like maybe worn motor bearings? I have the stand-alone 1200 variant that came on a steel-pan base, an arm with a plug-in headshell (for the GE VR II cartridge), and a 4-pole motor. It was in daily background-music service for a long time and the bearings are a bit sloppy. It rumbles some. I'd love to find new bearings.

Chris Campbell

[William]

Your series of VM changers use two washers, one on top of the race and one on the bottom. And, like Chris stated, the shinny one is on the bottom. Something else to consider is you might have a bad bearing race. If the little balls are not turning it can cause rumble.

Bill

[stbasil]

Thanks for the suggestions. The bearing race was completely devoid of grease when I first disassembled the changer, not even any dried up gunk, which I thought strange. I think I'll go back and examine the race under magnification to make sure there's no rust or pitting. Maybe even temporarily swap it with one from my SK111.

As far as the cabinet goes, after some sanding, I'm disappointed to see that the flaking finish is opaque, fake-grain "mahogany", the actual veneer underneath that junk is poplar. My first experience with that type of finish. I'm convinced now that the nice looking restored one that was on eBay must have had the original finish, which looks ok if in good condition, probably from being inside all its life. The top of this one is terribly stained, even after sanding. I will veneer over it it with real mahogany, for sure!

[William]

I have a couple of items with that same fake finish. The hardest one to do something with is an RCA TV from 1958 in blonde. The front of the TV is real oak, but the sides and top are a Masonite type of thing with a blonde sprayed on finish. The top is pretty much gone and there are missing parts of the finish on the sides too. I have not touched it yet and probably never will. TV's scare me as I have enough trouble with record players and radios.

Bill

[electra225]

An RCA TV is straightforward to repair with all kinds of factory documentation available. Like a Briggs and Stratton or a 350 Chevy, getting parts or service expertise. The main service challenge with your RCA TV is that it has one of those reversed chassis, with the tubes sticking thru the front of the vertical chassis, and the PCB on the inside. You have to use "hook and loop" soldering, actually recommended by the factory. I'll bet that if the filter caps aren't shorted and if the CRT doesn't have an open filament, it would somewhat work. It might not work perfectly and might have sync issues, but it should work. That old set was built back when stuff was built to work and last a LONG time. People got tired of looking at them before the set wore out. The blonde Masonite cabinet on yours will be more of an issue to repair than the TV chassis. I'd like to see you get it working. I think you told me that you had a record player to match it. That would make a nice display. Somebody has an idea of what to do to repair the masonite cabinet.

Think of a TV set as a picture radio. An AM-FM radio with a built-in oscilloscope.