Technics RS 1700 reel motor problem

[rjones5296]

Hello
Im new to this forum, so here goes. Score 1 technics RS1700 at the local thrift, in good shape but has a problem
The issue is the supply reel will not start unless i give it a twist, or at least does not start like it should.
The motor is not tight just will not start on it's own, turning counter clock wise I feel weak cogging.
Playing a tape the left tensioner just bounces, this is because the motor dosent supply smooth reverse torque, just the cogging effect.
Also rewind will not start, again if i give the motor a nudge it will spin,
What I notice is turning the motor it cogs, almost like a selector switch when i turn it by hand, I'm used to smooth resistance in reel motors, in this motor i feel the poles, I count 6 for 1 revolution.
If i give it a spin it will accelerate, but really dosent have any torque to speak of.
Im thinking this has to do with the reel motor control board, I have a service manual but it dosent really give an explinations of how the reel motor system works.
Checking the take up reel motor it is as smooth as silk.
Any ideas out there ???

bob
   

[Studer Fool]

I would definitely suspect the mechanicals of the deck before the electrical circuits! 

I do not know the Technics R2Rs very well, but I'm suspicious about the reel brakes, at least as one place to start looking.  Of course that means going inside the machine to see.  You may prefer to find a technician to give a look-see.

cdw

[docb]

Yeah, brakes might be a good place to start. They are the weak point on a Technics and mostly they loose efficiency rather than getting grabby. You can see the drums of the reel motors if you remove the top panel. There might be some areas where the black paint that covers the drum has been worn off. That can cause uneven or jerky rotation of the reel motor if the brake is engaged - which it will be in counterclockwise rotation on the supply reel motor when you turn it by hand. The brakes only come off when play or fast wind are engaged.

For starters try cleaning the drum with alcohol. IMO the best solution is new pads of a different material since you can't hit the brake tension figures in the manual with the stock brake pads, even if they are new. If the stock pads aren't glazed or worn off they can at least be adjusted to give a little better performance. Adjustment directions are in the service manual. Doing the adjustment right requires a tension gauge and a half full reel of sacrificial tape. But you can use the approximate method of setting an arbitrary gap between two pieces in the brake assembly as they show in the manual to get the machine running.

[ironbut]

Yeah, I think Doc and Chris are right, it sounds like a mechanical problem. Brakes are the nightmare on these machines and I'd check them first as the previous posts indicate. One other thing that you might check (and it does sound like you're not new to reel to reel since some of this can be tricky) is the reel table adjustment. There's a section in your service manual about this adjustment. To raise the table, you loosen a nut and turn the screw at the end of the reel motor axle. If it's adjusted too high, the motor will begin to seize. I tried to adjust this myself on my 1500 to center the tape wrap on aluminum 10.5" reels without the spacers I have. I was able to adjust the take up reel enough but not the supply reel. And when I went too far on the supply reel, the motor acted similarly to what you described. It could also be that the supply reel tape holder received some sort of impact and the axle is damaged. So, while you're in there checking your brakes,  lower the reel table a little and see if that helps.
If the brakes and motor axle seem OK. I'd go ahead and pull the motor out to see if it cogs when completely free. Be careful not to jerk the wires to the little circuit board that the motor connections are soldered to. Those can come loose but usually the motor won't work at all. Examine those connections and the circuit board for cracks.
I've never seen a 1700 so I don't know the mechanisms that trigger or allow the autoreverse. If everything seems to check out, you might describe that mechanism to us.
BTW Welcome to the forum Bob.

[rjones5296]

Guys
Thanks, got the problem solved with the help of Will, he recommended cleaning and lubing the motors, I did so, also recommended checking the reluctor ring, once this was done the motor works like a champ.
I didnt see any sign of gunked lubricant, so im thinking the reluctor ring was the problem.

I see what you mean about brakes, there are 2 worn spots that look like the pads sat on them for years.
I am wondering, do you re finnish the brake drums ? they appear to be steel with a glossy paint finish.
I can get new brake pads, and will have to, the originals are useless.
Also the tension arm bearings are toast, I have a set of replacements coming, but for now she is working like a champ other than a few bugs to work out.
Im figuring, much cleaning, new bearings, brakes,cleaning the noisy switches.
Sound wise this deck is one of the best I have heard, my everyday recorders are Revox A77 and G36.
One thing about the 1700 is, when you hit stop, it reverses the motors almost stopping the tape before the brakes apply, VERY NICE! very smooth tape handling.

Thanks for the info, im sure ill be posting about changing the brakes in the next few days.

bob

[ironbut]

Great Bob, I'm always glad to hear when another Technics is back on it's feet and running. I've never pulled the reel motors apart (probably should have considering the number of times I've had them loose). So, I'm guessing that the reluctor ring is inside of the reel motor assembly? I'm guessing that there may be more than a couple of decks out there that are sitting in closets from these kinds of problems. That's what happens when there aren't enough experienced repair guys out there. Speaking of which,.. who's Will?
Personally, I'd appreciate any posts describing repairs or restoration tips that any members could make.
BTW,.. I don't think that there's any reason to repaint those brake drums unless they've become scored or damaged somehow. I would guess that the only reason they're painted is to provide a nice consistent surface for the pads to ride on. If you look at most raw aluminum with magnification, you'll see how pitted and irregular the surface usually is.

[docb]

Hey Steve, you're the first hero member (500 posts) - I think that means you buy the next round of drinks.

[ironbut]

Wow,.. I knew I was the leader in spreading disinformation around here but "Hero"? I guess that'll show those folks that thought I'd never amount to anything!
Well, I know what you're drinking Dan,.. what about the (240+) rest of you guys?

[xcortes]

tequila reposado with a beer.

gracias esteban!

[rjones5296]

"So, I'm guessing that the reluctor ring is inside of the reel motor assembly?"
Yes the reluctor ring is inside the reel motor, if you look linide you will see a copper ring, looks more like a cap that is a just barely snug fin on the rotor, with slots or cutouts around the diamater.

Will is a bud that is very knowledgable about reel to reels. and one sharp tech.

So far I have lubed the motors, replaced the tension arm bearings with ABEC 5, the reverse idler bearings with ABEC 7.
I have found a brake pad felt that is similat to the original, so I'm going to re do the brake pads.
And the plan is to start replacing the electrolytics with hand selected 105c caps, starting with the power supply board.
I'm also planning on using audio grade electrolytics on all the signal boards.

But so far she is playing like a champ. no complaints except for the weak brakes, she stops fine but the tension arms are relaxed, opening up the switches.
I have to tension the tape up before hitting play.

bob

[ironbut]

Thanks for the info Bob.  Jennifer Crock (Jena Labs) is raving about the Elna Silmic ll caps over on the Studer list. That's one tough crowd over there and if she's anything like me, she wouldn't suggest something there unless she was pretty sure about 'em. Not crazy $$$ either. I'm planning on trying some in a little project I have going.
You're lucky to have a pal that knows r2r. It sounds like you know your way around a circuit board yourself but it's nice to have someone with experience. One of the members here upgraded a 1500 a while ago and seemed to like the results. Hopefully, he'll see this post and give some suggestions.
One thing that you might think about is to bypass the playback electronics and replace them with a Bottlehead Seduction. You probably know this stuff already but it might not cost much more than you're planning to spend upgrading. You can check it out here;
http://www.bottlehead.com/et/adobespc/Seduction/bottleheadtapeheadpreamp.htm
It's a huge improvement and I seriously doubt that upgrading the stock circuits could ever equal.
Hey, I noticed the Perreaux in your signature. I've got a PMF 2350 laying around here someplace.

[rjones5296]

Thanks, Good info there Ill look into those caps for my 1700.
I cant beleive I have over looked this deck for this long, I have always been a Revox guy and while I love the Revox range, the Technics I feel is about the best prosumer deck out there.
A little tougher to service than Revox but worth the effort.
I have been working on/messing with hifi since I was a kid, 50 now so I have seen or own, owned a ton of stuff.
The Perreaux 1150b I have I bought for a song, and I have to say I love the thing, it's one of my favorites.
If I see another, well ill smuggle that home too........
bob