Lazy capstan solenoid

T

technoplayer

Recovering Gear-aholic
I have rotated my Teac A-6300 back into use and find that the capstan solenoid has become a bit lazy. What I mean is when i engage play, the brake solenoids release sharply but the capstan solenoid( in the same circuit loop) does sort of a "stutter click" when engaging and rather than sharply indexing the pinch roller over is a bit slow.
In the auto revere mode, it sometimes does not activate at all....no activity from the solenoid. But it is not consistent. I have cleaned and gently lubed the solenoid plunger, and its travel is free. I can manually move the linkage with no binding.

I do not believe the solenoid itself is at fault. There is a diode across the coil and a capacitor in there on some other terminals. Why so many wires to this unit?

Anybody (Cory?) have any idea/suggestions on what to look for? Polling all you smart people before i jack up a beautiful machine by poking around......
 
I would start with the relay that powers the solenoid. I’m not familiar with that machine, but any corroded internal contacts/connections in plugs and switches could cause the symptoms you are experiencing. And then the relay. Same thing. Those are hard contact switches basically and if the contacts are oxidized/carbonized or otherwise corroded you can get intermittent results, or with the higher impedance in the circuit from bad contacts the relay action will be sluggish with the lower power, or the solenoid might not latch up because there’s not enough holding voltage. Usually there is initial power that comes from the switch through the relays, and when the relay contacts close there are other contacts the close to provide the holding power to the solenoid so that the solenoid stays powered even when you release the switch.

Do you have the service manual?
 
I have the manual and schematics. I can see the relay that triggers the capstan solenoid, Just need to id it in the machine. Teac does a nice job of burying them.
Would it help to measure the voltage at the coil??
 
Yeah it depends on the machine how hard stuff is to get to.

If I get a chance I’ll see if I have that manual set somewhere so I can look at it alongside you.

Yeah it’s a good idea to measure the voltage across the coil to support your determination it’s not a mechanical issue. I’m assuming it’s powered by a 24VDC supply but you’ll want to check that in the manual, and then measure when it’s under load. It should be at or close to the power rail’s intended voltage under load. If it’s not it can be a power supply fault but you say your other transport functions are okay so it’s *probably* safe to assume it’s not the supply, but it would *also* be a good idea to verify that when the pinch roller solenoid is powered. If the power rail looks good but the voltage is lower across the pinch roller solenoid coil then it’s something in between. You could also compare the voltage across other solenoids (brake and...is there a lifter solenoid?) to really get to the determination “yup, it’s something in between the power supply and the coil specific to the pinch roller solenoid.”
 
I cannot see anything i the manual indicating the voltage for the solenoid. My measurement across the coil was something in the range of 8 volts which seems low.
The Brake solenoids are even lower than that but all 3 solenoids fire and when they are pulled in are pulled in firm.
I guess my reference is my other TEAC machines (2340 and 3340) where the capstan pulls in hard when the play button is activated and the 6300 has a slight lag.
But when its in its in firm...I mean I cannot pull the pinch roller back manually so it must have good hold voltage.
The capstan delay is not killer but just a bit like a tic or a random squeak in a car...annoying but not impeding function.

I am lately wondering if i need to exercise my machines on a more frequent basis......
 
I'm not sure if you're describing the common problem with these machines -I have something with my A-3340 as well.

Here, it's the pivot post that the pinch roller assembly moves on, the grease in the thing has hardened over the years. Some machines have locked up seriously, some have varying degrees of problems with movement. The fix is to take the assembly apart, there is a YouTube video to illustrate for at least one of the 3??? machines. Take apart, and refresh the grease.

Mine still works, but needs a little manual help to engage correctly. Once the machine is warmed up, then it operates a little better, so your reference to 'exercise' may be relevant.

Does this sound like it might be relevant?

Geoff
 
Thanks Geoff. I've had that assembly off in the past. When I got the machine many years back the prior owner had crudely modified the linkages in there, perhaps to have some sort of tape lifter defeat.
I sourced the correct parts from a donor machine and restored all the mechanicals correctly, and got it all moving freely. It all still moves free, even in 'cold' state. Just has that lag in engaging the solenoid, and *sometimes*, randomly, it either does not pull in or doesn't pull in entirely. The relay is actuating, and the brake solenoids which appear to be in the same circuit drop out sharply. Which makes me feel the relay is ok......

>>> I am tearing it apart to get at that relay just to be sure. Unfortunately Teac found it expedient (cheap) to solder the cube relay directly to the board rather than use a socket.
 
And i DID have that sticky problem on my 3340S as well, but it was rectified by cleaning and re-lube as you indicate.
 
Techno, just to be sure, is there a rubber washer to provide cushion when the solenoid plunger retracts? I suspect you considered that and ruled that out already, but those washers can turn to sticky goo just like other rubber parts and glue the solenoid in the retracted position causing it to extend slowly against grip of the tacky tendrils. Any chance that’s at play here?
 
All good there. I replaced the gooey one when i rebuilt the mechanism some years back. I have pretty much discounted any mechanical hangups.

>> Interesting note: I did a test with the pinch rollers on my 2340S, 3340S, and the 6300. If I hold the pinch roller to keep it from pulling in when i activate the play mode, when I let go none of them will pull in.
BUT, on the 2340 and 3340, if i then push the pinch roller up to the capstan (engaged position), the solenoid "grabs" and locks the roller in tight, suggesting a good "hold" current.
On the 6300, that does not happen. The solenoid does not appear to have the current to even try to hold the puck in place.

This befuddles me.
 
So that’s something I was wondering about. Voltage is one thing, but current is another. You can 500V but if there’s only micro amps of current it can’t do much work. Conversely you could have 10V but if there’s 150mA of current, well, that can do some work.

Does your meter have the ability to measure current? “A” or “mA”?

I suspect you may have a bad solder joint somewhere or we’re back to the relay being a problem. I know you mentioned the relay is soldered to the PCB. Can you otherwise get to it? Does it have a removable cover so you can service the contacts? Note that’s really only typically a temporary solution...once the contacts have started to carbonize, the deposits quickly build up again once the contact starts to go. Any way you can put up a pic of the relay?

I really suspect the relay. Particularly if it isn’t a sealed or potted type relay. If you can see the guts through a clear plastic cover, I would have that as my prime suspect.
 
sweetbeats said:
I really suspect the relay. Particularly if it isn’t a sealed or potted type relay. If you can see the guts through a clear plastic cover, I would have that as my prime suspect.
Click to expand...

On my Otari MX-80...when you engage PLAY, there is a cover that is supposed to pop-up to protect the tape/heads area.
Over the years, it too has become "lazy". If I manual push on it, it releases instantly. Sometimes it releases with the PLAY engagement without issues, over and over...then suddenly it won't.
I to have come to the conclusion it is the solenoid/relay issue....most likely due to age. I actually have a spare one, I believe (somewhere I have a couple of boxes full of spare parts)...but in my case, being just the safety cover that I can easily engage manually...I've just let it go.
It does seem that during a longer session...it kinda gets better the longer the machine runs....so there is something to not letting these devices sit around for too long unpowered and unused, even under the best storage conditions.

Anyway...that doesn't help you, I just wanted to mention a similar "lazy" situation... and I know the capstan misbehaving is a bigger PITA for you.
 
I'm no expert on relays when it comes to tape machines.....but I did spend more than 20 years in the field as an electronics tech working on all kinds of machines with solenoids....small and large.....of all different voltages etc...etc. The basic solenoid is a coil that either is intact continuity wise or is not. Not saying they can't be intermittent......but not likely it could act "weak". I'm 100% sure you guys know that of course. I've never found a solenoid coil that caused weakness....or slow actuation on it's own. All the mechanical solenoid assembly problems you've already outlined are common to age and you guys have covered most of the ones I've ever come across. I assume the arm and plunger are adjustable to some degree and different adjustments have been tried. I do recall a series of solenoids that had been installed by a tech with the plunger arm and base not adjusted quite right. He had installed and adjusted all of them to the same incorrect specs for the arm and plunger assy. It did cause intermittent problems with plunger and actuation timing. The adjustments were not far off............just enough to be faulty from time to time. The adjustment caused the plunger to enter at just a slight angle.....enough to hang up upon momentarily upon signal from time to time. To the naked eye.....it was not obvious. Are all the solenoids powered by a single power supply? If so......all of them would display similar issues right? You mentioned that the power across the solenoids was different.

Ok...sorry for the rambling on here......and not solving your problem. I've been following this thread as an old analog tech.......wondering what the solution was going to be. If I had to guess......as sweetbeats has mentioned (and maybe others)......the relay is the prime suspect......followed by a board trace or cold solder connection.

Anyway.....good luck and let us know what you find.
 
SOLVED IT!!


The general consensus seemed to point to the lack of current and possibly the relay contacts being oxidized or burnt. BUT I was hung up on the fact the the reel brake solenoids, which are in the same circuit worked fine.

Looking closely at the pinch roller solenoid I noted that in the actuated position there was a very slight discoloration on the protruding shaft outside of the coil. Sort of maybe a wear pattern??
And then noted that the coil is affixed to the front plate by three screws, and the holes are slots. I loosened the screws ( they were very tight) and slid the coil body over a few millimeters so the plunger started out further into the coil.

BINGO!!!

The pinch roller now actuates instantly and sharply!! Apparently in the stop mode the plunger was not far enough into the coil for the magnetic field to reliably and firmly pull it in.
I continued to adjust, making sure not to bottom the plunger out in the coil. ALL GOOD.

It did not appear then the solenoid coil position had changed over the years. I suspect that the thin metal fork that attaches the plunger to the pinch roller and tape lifter mechanisms was slightly deformed, holding the plunger a bit too far out of the coil for reliable operation.
I didn't come up with that conclusion until after I did the coil adjustment, which is just as well, as i would have run the risk of breaking something if i tried bending the fork. The coil position is the safer adjustment.

I feel stupid for not catching this earlier, but 20/20 hindsight is my specialty.

Thanks to all who lended a hand here.Your knowledge was much appreciated
 
I'm going to at some point take a look at my tape guard mechanism...because I too have wondered if it need some adjustment or cleaning, it was just never all that critical, like a capstan would be. I mean, we are dealing with 30+ year old gear....lots of time for things to go wonky. :D
 
technoplayer said:
Particular thanks to Mickster for steering me back to a solenoid adjustment!!
Click to expand...

What got me to thinking was that you mentioned that the assembly had been monkeyed with before you got the unit. Human error is usually 99% of....well......lots of problems. Glad you got it fixed!!!!
 
You are approaching this all wrong. Solenoids do not have a history of failure. Power supply caps do yet people ignore that all the time.
Recap the power supply, clean and regrease the pinch roller mechanism without loosening the pinch roller solenoid. Your problem is completely
one of grease gone bad. I have dealt with hundreds of them. Forget looking at solenoid voltages as they are about 26Vdc at start and go to 10-12 V to hold. The grease I have used for many years is Lubriplate 105.
 
skywaveTDR said:
The grease I have used for many years is Lubriplate 105.
Click to expand...

Thanks for the tip on the Lubriplate 105. I just got a tube of it and will use it to lube some of the moving parts on my MX80, though most certainly the tape guard mechanism, since I'm pretty confident the intermittent response is mechanical and not electronic...it's just not been a critical thing, so I just engage it manually if the PLAY button doesn't...but always after a couple of hours of recording use, it responds more regularly.

I've used a variety of lubricants over the years that were originally meant for some automotive/motor use...but ended up being good for audio use too, but I've not seen/used the Lubriplate 105 before.

For the Otari users our there that need to occasionally oil the capstan mechanism, where the manual calls for a specific Otari branded oil...you can use Hammond Tone Wheel oil. I confirmed this with some folks, and the Hammond oil is perfectly fine....I've been using it for awhile now. If you get it in the small Hammond tubes, they come with a long, skinny tip and a little rubber cap...so it's easy to get the tip close to the capstan shaft to put a couple of drops on the felt pad.

I have a good supply of the original Hammond oil...which to me (and my nose) seems a bit different from some of the more current production stuff that is labeled as "Hammond" oil. I'm sure it is OK, since it is sold by organ suppliers who deal with old Hammonds...but I find the new stuff has more of a stronger automotive oil smell to it...where the original Hammond oil has an almost aromatic sweetness to it. :D
It's probably nothing...but I have both the old and new, so I noticed that.
 
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