How to replace a motor run capacitor on your R2R like a boss!

PART ONE OF TWO

I bought a vintage 1967 Roberts 1725-8L (not the more popular 1725-8L III) on eBay the other day from a local seller. This was one of the last units that Robers (actually, Akai) built with vacuum tubes. It has a built-in 8-track tape player/recorder in the base (not on the side like some later units). The 8-track unit was built in the USA by auto parts maker Lear in Detroit; the rest of the unit was built in Japan, of course. The tube lineup is NEC 6CA4, NEC 12AT7 (x2), and Telefunken ECL82 (6BM8) x 2. It has two internal 5x7 speakers, quarter-inch jacks for external speakers, and pre-out / record in RCA jacks.


100_4051 by Wigwam Jones, on Flickr

Worked great for a couple hours. I noticed that the volume and tone controls were very scratchy (not uncommon), and then in the morning when I went to turn the unit on, the power came on but the motor for the reels was not running. This is not uncommon. I opened the back access cover and noticed that when I put the unit in fast-forward or rewind position, the fan 'tried' to start and did not start spinning. That is also a common indicator of a failed motor-run capacitor. Another common symptom is when the tape plays but the motor really seems to drag, or it speeds up and slows down. Sometimes this is thought to be a bad belt, when it is really the motor-run capacitor. Fortunately, they can be pretty easy to replace.

A motor-run capacitor is used on many single-phase motors such as refrigerators and washing machines and overhead fans. They require a special kind of capacitor to keep them going; if the capacitor fails, the motor won't run.

Fortunately, I had ordered a couple replacement caps for another reel-to-reel that I have, and I had not yet used them. I determined that the old capacitor was a 2uf unit, and I had two 1uf and one 3uf motor run capacitor. I could have put the 3uf in series with a 1uf and gotten 2uf, or I could have put the two 1uf capacitors in parallel and gotten 2uf; I elected to do the latter. The important thing is to try to get as close as possible to the original value. If necessary, go over slightly, but not under. Also, have at least the voltage value of the original; it is better to go over, but not under. Mine are rated at 400VAC, which is nearly double the original rating. That's fine. I got them off eBay, they were very cheap. Couple bucks.

You will need a few tools, besides the replacement capacitor. A couple screwdrivers to remove parts, a soldering iron and solder, some electrician's tape to make the new solder joints insulated from short-circuit. Needle-nose pliers are good to have handy, as well as something magnetic to pick up tiny parts. It's a good time to do other maintenance work like cleaning the heads and capstan and other metal parts in the tape path, so you'll need alcohol and swabs for that. The faceplate of the unit has to come off, and you'll want to clean that up too; great time for it.

Observe safety precautions, of course. Unplug things. Use safe practices, remember that enough voltage lurks inside this unit to kill you stone cold dead. Large capacitor store energy. That means they can zap you and murder you and then your widow has to sell your crap for next to nothing at a garage sale and your neighbor whom you hate will be flipping your stash of Telefunken tubes on eBay while your widow eats cat food and who wants that? So be careful, goofy.

First you have remove the inspection panels on the back.


100_4052 by Wigwam Jones, on Flickr

The motor-run capacitor is located next to the motor, labeled 'MP'.


100_4053 by Wigwam Jones, on Flickr

Here are the tubes, ain't they pretty? And Telefunkens? SWOON.


100_4054 by Wigwam Jones, on Flickr

Another view of the motor-run capacitor.


100_4056 by Wigwam Jones, on Flickr

The front panel has to come off to get access to the bracket that holds on the motor-run capacitor, so first I have to remove all the knobs and the plate over the heads and the pinch roller. Don't worry, none of the parts are spring-loaded, nothing flies off and runs under the damned sofa or gets eaten by the dog.


100_4057 by Wigwam Jones, on Flickr


100_4058 by Wigwam Jones, on Flickr


100_4059 by Wigwam Jones, on Flickr

Here is what it looks like all naked. Don't worry, you don't have to deal with any of this stuff.


100_4060 by Wigwam Jones, on Flickr

In the four corners of the frame are four screws. Remove those, and the whole unit tips out. Don't try to remove it entirely, it is attached with some wires (the are plugs, you could pull them out and replace them later if you wanted to, but there is no need) and a mechanical linkage (I think for the record setting). I could have removed the plugs and the linkage, but that's a hassle I did not need. Once I removed the screws, I just carefully tip the unit forward to expose the bracket for the motor-run capacitor.


100_4064 by Wigwam Jones, on Flickr

So there it is, that rat-bastard. Again, be careful here. This thing can hold a whole lot of charge and could end you fast and easy. Don't be a dead guy, it's not really any fun.

Here are my replacement caps. Not really the same form-factor, but they do the same thing. Remember, I'm going to put them in parallel to create a total of 2uf value.


100_4066 by Wigwam Jones, on Flickr


100_4067 by Wigwam Jones, on Flickr

Old dead cap.


100_4068 by Wigwam Jones, on Flickr

Continued on PART TWO

PART TWO OF TWO

After cutting the old capacitor off, I stripped the ends of the wires and wrapped them with the wires from my new motor-run capacitor pack. Note that in my case, I had one red and three green wires - or black - I'm color-blind and can't tell. But I can tell that they're the same. Kind of important. So one end of my new caps go to the three green wires and one end goes to the red side. These motor-run capacitors do not have a polarity, so you don't have worry about positive and negative.

I then soldered the ends together and wrapped them with electrician's tape to make sure they would not short against any metal components inside. Shrink tubing would have been the professional way to do this, but I haven't got any. So I dressed the connections carefully with name-brand good quality electrician's tape. Should be fine.


100_4071 by Wigwam Jones, on Flickr

TOP TIP: Put the two bottom screws back in the frame when you're soldering; you don't need the unit tipped out too far, and the frame won't fall out of the case while your hands are elsewhere.

TOP TIP: Magnetized screwdrivers are nice for removing and replacing small internal screws; you can magnetize yours temporarily by drawing them about 20 times across a fridge magnet. How cool is that? Get it? Fridge, cool? I kill myself.

I modified (read, 'cut the crap out of') the original bracket so that I could screw the base of my new capacitors to what had been the old base, then screwed the base back into the side of the motor. When installed, it looked like this.


100_4073 by Wigwam Jones, on Flickr

I was careful to route the wires so they did not get in the way of the fan or other moving parts, and did not get rubbed so no short-circuits would develop later.


100_4074 by Wigwam Jones, on Flickr


100_4075 by Wigwam Jones, on Flickr

Then I put the faceplate back on (all cleaned up), put the knobs and the head cover and the pinch roller back on (also cleaned, and I cleaned the heads and various rollers as well). I mounted a tape and fired the unit up.


100_4076 by Wigwam Jones, on Flickr


100_4077 by Wigwam Jones, on Flickr

And that, ladies and gentlemen, is that. Total time invested was around 1 hour. Cost for the new motor-run capacitor was less than 5 dollars.

I am not an electrical genius. I followed instructions I found on the 'net, and I was careful and methodical. I took photos of before and after so I would know where things went again. I am (not unfairly) often called a klutz. If I can do this, you can do this.

Replace your motor-run capacitor on your reel-to-reel LIKE A BOSS. You can do it.

Good Post---I have 2 AKAI-260D tape decks --both with bad run Caps --but I haven't got the guts yet to tackle them.
Yes I do have the service manual.

JHS2RT said:

Good Post---I have 2 AKAI-260D tape decks --both with bad run Caps --but I haven't got the guts yet to tackle them.
Yes I do have the service manual.

Click to expand...

Probably don't even need the manual, these Akai units are dead easy! Note that my Akai M8 had a multi-cap capacitor for the motor-run; there was a 1uf and a 2.2uf. I believe that one is for voltages other than US and so might be ignored when replacing, but I did them both. This unit (the 1725-8L) only had one, but it did not have settings for multiple voltages, so that might be why. Just make sure you get the right kind of caps and you should be in great shape. These things are dead easy, you should it!

Well shoot! I moved from St Clair Shores two years ago ---if I was still up there --I'd have you over for some on the job training.
BTW ---I believe one or maybe both is a multi voltage unit.

My AKAI 1800 SD (SS, side mounted 8-track, built in speakers) had a bad run cap., it failed while in use, the motor slowly slowed down, the cap did NOT have the rubber end caps, and dribbled a pile of wax onto the chassis below.

I knew I had a 2uF cap. someplace, I looked on my "this looks useful" shelf and It was a metal encased cap. rated at 250 V, so I installed it and the recorder works like new now.

Mark T.

Nicely done, Mr. Jones! :guitar:

Great post, Wig! And I suspect that's a scarce machine you've got there... I was in the hi-end audio service biz for a long time and I'm pretty sure I never saw one exactly like it. I worked on MANY variations of the original Lear 8-Track deck, and MANY Akai/Roberts products, but this particular combination never crossed my workbench.

Nice job Wiggy!

Good job Mr Jones

This is a nice step by step guide. Thanks for sharing your work. My reel is dragging on my Roberts 1725-8L III. The owner said it was working fine when he plugged it but when he moved it downstairs and played it again, the unit started dragging. My unit doesn't look as easy as yours to access the cap.

I have a bunch of 2.0 uF motor run caps if anybody needs some - these are plastic cased with a foot with mounting hole. And if you suspect the cap, wire the new one in temporarily before you dig in to replace the old one. You might even have room to fit a new one in without taking out the old one.

I have a Sony TC-377 that had the same problem. I replaced the run cap and the problem disappeared for a little while.... and now it's back. Occasionally the motor won't start unless I start it by hand. I'm wondering if it's possible I have a dead spot in the motor itself.

Charles.