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Author Topic: [Troubleshooting] - Issues with an Otari MX-5050 BII-2...  (Read 19682 times)

Offline rerunmedia

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[Troubleshooting] - Issues with an Otari MX-5050 BII-2...
« on: March 10, 2011, 02:18:14 AM »
I have an Otari that was sold as a "parts" deck... but after cleaning it up a bit and looking it over, I'd rather bring it back to life than part it out. I have the regular manual (as usual, minus the schematics), but it doesn't seem to shed much light on the issues that this deck has.

Some fixes were easy-- the reel tables needed adjusting (though there was much more available play in the take-up reel table than the supply reel table), both appear to turn freely now; the tape path has been cleaned, years of dust have been blown out of the nooks and crannies, etc... but there are still a few nagging problems:

First of all, a missing part-- the polished chrome covering of the capstan is missing, and all that is currently there is the raw unpolished metal shaft-- anyone have any ideas of where to get a replacement? And for that matter, how does the outside chrome cap attach to the metal shaft? There appears to be a dimple in the top of the shaft, but it doesn't really look like a screw hole.

One of the adjustable tape tension arms has apparently been bent at one time or another... it looks like someone tried to bend it back into shape (reasonably successfully), but I have my doubts as to how true it is... another replacement part needed.

Now the biggie-- there are some dysfunctional functions that need some solutions. The main problem seems to be that when the machine is powered up (and it **does** power up OK), the reels do not operate. None of the function panel buttons have any effect, and the capstan doesn't spin. When the tape is threaded through the path and both tension arms are engaged, the relays do not click into operation as the tension arms move back and forth. Additionally, though it may or may not be a symptom of anything, the pitch control light does not come on at all, either when the button is pulled out or pushed in.

This led me to believe that the transport system might be totally dead. However, after experimenting a bit, it turns out that when the button on the front panel of the machine is set on "HIGH" speed, and the "EDIT" button is pushed, the internal relays begin to click, the capstan motor engages and begins to spin, and the function panel buttons now appear to work... though only one tape reel motor engages, to spill tape, as the manual indicates. This **does** however, show that there are signs of life in the transport area, and that there's a chance that both reel motors actually work.

Is this one one those situations where I should open things up to see if a card is seated properly? I also seem to recall that something to do with the "HIGH/LOW" function could possibly fix this problem though I can't remember if the fix referred to the selecter button on the front of the machine, or the lever on the inside that controls the 3.75/7.5 ips or 7.5/15 ips choice.

The amplifier functions appear to work-- the VU meters light up, and the generated test tones caused movement in both in of them, which was controllable by turning the input volume knobs (as expected).

So, these are a few of the more immediate things... can anybody out there take pity on a repair newbie, and help bring this warhorse back to life...?

Thanks for any help...!

- Kevin

Offline docb

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Re: [Troubleshooting] - Issues with an Otari MX-5050 BII-2...
« Reply #1 on: March 10, 2011, 07:53:42 PM »

First of all, a missing part-- the polished chrome covering of the capstan is missing, and all that is currently there is the raw unpolished metal shaft-- anyone have any ideas of where to get a replacement? And for that matter, how does the outside chrome cap attach to the metal shaft? There appears to be a dimple in the top of the shaft, but it doesn't really look like a screw hole.

The matte finish shaft is the capstan, no chrome cover.

Re the other problems you might go inside the machine and pull the controller card under the take up motor, and clean the contacts. Then turn the machine on and let it sit overnight to see if any caps that may be leaky reform and restore function.
Dan "Doc B." Schmalle
President for Life, Bottlehead Corp.
Managing Director - retired, The Tape Project

Offline rerunmedia

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Re: [Troubleshooting] - Issues with an Otari MX-5050 BII-2...
« Reply #2 on: March 10, 2011, 08:22:03 PM »

First of all, a missing part-- the polished chrome covering of the capstan is missing, and all that is currently there is the raw unpolished metal shaft-- anyone have any ideas of where to get a replacement? And for that matter, how does the outside chrome cap attach to the metal shaft? There appears to be a dimple in the top of the shaft, but it doesn't really look like a screw hole.

The matte finish shaft is the capstan, no chrome cover.

I'd say "You're kidding", but I've read enough of your writing to know that you don't joke about stuff like that, Doc...  Boy, that is one **ugly** part!  How it is able to be cleaned up for use if it oxidizes or just becomes a non-smooth surface over time?

Thanks for the hint about the controller card-- I'll try that next.

- Kevin

Offline ironbut

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Re: [Troubleshooting] - Issues with an Otari MX-5050 BII-2...
« Reply #3 on: March 10, 2011, 09:49:26 PM »
Hi Kevin,

Welcome to the forum.
Almost all capstan shafts aren't smooth and shiny. They need to be able to "grip" the tape without letting it slip while it's between the capstan and the pinch roller. The rotation of the capstan is what controls the tape speed not the reel motors on your Otari.
Some machines (like many Ampex studio decks) have capstans which have a sandblasted surface. When the surface becomes shiny and smooth, it needs to be "roughed up" either chemically or sandblasted.
steve koto
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Offline rerunmedia

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Re: [Troubleshooting] - Issues with an Otari MX-5050 BII-2...
« Reply #4 on: March 12, 2011, 09:31:06 PM »
It's nothing short of miraculous--

I owe a **big** thanks to everyone who helped... after setting the reel tables, blowing off the crud, some copious use of contact cleaner and the sacrifice of a large number of long-handled cotton swabs, the patient is off the operating table, and apparently now fully functional... at least intermittently.

The Otari 2-track is officially coming back to life!  :D
 
- Kevin
« Last Edit: March 13, 2011, 01:45:25 AM by rerunmedia »

Offline Listens2tubes

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Re: [Troubleshooting] - Issues with an Otari MX-5050 BII-2...
« Reply #5 on: March 17, 2011, 06:41:18 PM »
Having 4 5050's and counting there are a few things that have worked for me. First get some contact cleaner, ie; Caig DeoxIT. Try spraying the internal Ho-Low speed switch on the control board. That's the one that folds down. Just cleaning that switch has fixed odd brake and speed/operation problems on 2 decks. Next unplug a re-plug all connectors on the boards. Then clean the front panel speed switch as well as the speed switch on the head block. Try working all the switches 20-30 times, including the switches on the back panel. Look at the capacitors on the control board. Inspect those cans for bulging tops amd or leaking goo. See this thread for tweaks: http://www.tapeproject.com/smf/index.php/topic,2037.0.html Generally if it plugs in pull it and re-seat it. Also the capstan motor should be movable with the deck off and static. If you push down on the capstan it shoud move down easily and spring back up. If it does'nt you need to remove it to clean and oil the assembly. I will be doing this to one of my decks soon. I'll try to document the steps with pix. Enjoy!
Neal - Ampex Fineline F-44, 3 - Otari MX5050BII-2, Revox A77 Mk II , Teac A 4010s, 4070, Sony TC102A, Magnecord 1020, Systemdek IIX/Dynavector Karat 17D2MKII, CEC CD3300 CDP, K Works NanoMax DAC, Van Alsine Transcendence Eight+ tube preamp, Dynaco MkIV amp pair, Paradigm Reference Studio 100 v1

Offline rerunmedia

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Re: [Troubleshooting] - Issues with an Otari MX-5050 BII-2...
« Reply #6 on: March 17, 2011, 11:48:15 PM »
I have to admit, I think the Caig DeOxit is probably what did the trick for me-- I had concentrated on all three of the speed switches that you mentioned with regular contact cleaner (and yes, after reading up a bit more, I now know that you shouldn't use contact cleaner on a switch!), and that seemed to help; but after hitting all of them again with the Caig & some Faderlube, the machine appears to be working **much** more consistently.  Indeed (dare I say it), it appears to be fully and regularly functional again!

I think the thing that threw me the most about this BII was that I kept expecting the right tape guide (the one under the take up reel) to trip a relay when it was moved into position-- it doesn't, but that's what my 4-track Otari does, so I suppose I thought that all Otari models had that same behavior.

I'll oil the capstan soon, and there do appear to be a few capacitors in the amplifier area that could stand replacing (mostly the ones that look like tan-colored Chiclets), but overall, this machine appears to be in pretty good shape for its age.  Overall, they truly are built like tanks-- and even in stock form, they sound pretty good, too!!

- Kevin

Offline Teeg

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Re: [Troubleshooting] - Issues with an Otari MX-5050 BII-2...
« Reply #7 on: March 18, 2011, 05:22:00 AM »
  The 'tan-colored Chiclets' are probably OK, film/tantalum/mica caps rarely go bad. It's the electrolytics, the cylindrical 'soda can' looking guys you should check. And these are polarized, their orientation in the circuit board matters. Replacements should match the originals for capacitance and rated working voltage.
  That being said, unless you have some experience working on printed circuits, avoid fixing something that is probably not broken.

Tj
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Offline rerunmedia

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Re: [Troubleshooting] - Issues with an Otari MX-5050 BII-2...
« Reply #8 on: March 20, 2011, 03:38:22 PM »
Anybody have any ideas on this one?  I suspect the problem is electronic...

If I have a tape threaded up on the machine, and leave it plugged in for a while (but switched OFF), I can then start the machine up and it will be fully functional  (i.e. - capstan starts turning when the machine is switched on, the HIGH/LOW speed switch works, all PLAY/REW/FF functions are fine, etc.).

But, if I **don't** leave a tape threaded up on the machine, and then attempt to start it up,  the capstan doesn't spin, and the machine reverts back to the "...will only [partially] function when in EDIT mode" behavior that I wrote about in my first post.  If I attempt to thread a tape up and play it while the machine is in this state, nothing happens.

I can however, leave the tape threaded up on the machine, turn off the machine and come back a little later (approx. 1/2 hour), and the machine is fully functional again.

It sounds as though having the tape on the machine allows some crucial relay or electronic part to fall into place, which in turn charges something in the transport functions.  Once the reel is taken off the machine, that circuit disengages, and whatever was charged (some caps, perhaps?) dissipates the necessary stored charge over a relatively short period of time.

Any ideas?  Does this sound like a reasonable interpretation?

- Kevin

Offline bobschneider

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Re: [Troubleshooting] - Issues with an Otari MX-5050 BII-2...
« Reply #9 on: March 28, 2011, 02:18:41 PM »
Anybody have any ideas on this one?  I suspect the problem is electronic...

If I have a tape threaded up on the machine, and leave it plugged in for a while (but switched OFF), I can then start the machine up and it will be fully functional  (i.e. - capstan starts turning when the machine is switched on, the HIGH/LOW speed switch works, all PLAY/REW/FF functions are fine, etc.).

But, if I **don't** leave a tape threaded up on the machine, and then attempt to start it up,  the capstan doesn't spin, and the machine reverts back to the "...will only [partially] function when in EDIT mode" behavior that I wrote about in my first post.  If I attempt to thread a tape up and play it while the machine is in this state, nothing happens.

I can however, leave the tape threaded up on the machine, turn off the machine and come back a little later (approx. 1/2 hour), and the machine is fully functional again.

It sounds as though having the tape on the machine allows some crucial relay or electronic part to fall into place, which in turn charges something in the transport functions.  Once the reel is taken off the machine, that circuit disengages, and whatever was charged (some caps, perhaps?) dissipates the necessary stored charge over a relatively short period of time.

Any ideas?  Does this sound like a reasonable interpretation?

- Kevin

The right hand tension arm is connected to a switch, to prevent the transport from operating if there's no tape loaded, or loaded improperly.  This is to prevent tape spills, and save wear and tear on the deck.  Try turning the deck on without any tape, and then manually pull up on the right hand (take up side) tension arm.  The capstan should start turning (a handy trick for cleaning the capstan), and you should be able to get the reel motors to begin turning by pressing the transport buttons.  Release the tension arm, and these should all stop.

If that's the way your deck behaves, you have normal function.
Bob Schneider

Offline rerunmedia

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Re: [Troubleshooting] - Issues with an Otari MX-5050 BII-2...
« Reply #10 on: March 28, 2011, 11:19:17 PM »

The right hand tension arm is connected to a switch, to prevent the transport from operating if there's no tape loaded, or loaded improperly.  This is to prevent tape spills, and save wear and tear on the deck.  Try turning the deck on without any tape, and then manually pull up on the right hand (take up side) tension arm.  The capstan should start turning (a handy trick for cleaning the capstan), and you should be able to get the reel motors to begin turning by pressing the transport buttons.  Release the tension arm, and these should all stop.

If that's the way your deck behaves, you have normal function.

Well, as I suspected, that appears to be the problem... my **other** (4-track) Otari works exactly that way... but this 2-track doesn't.  I went over and took the tape off the machine-- it started right up with the capstan turning and every button functional (until the stored charge dies off, at least).  This includes the transport buttons, since the motors engaged and the reels spun when the PLAY/FF/REW buttons were pushed-- even with no tape on the machine!

As for the right tension arm of this 2-track, for whatever reason, there is no "bump" or click or any feeling (or sound) of a relay engaging when the arm is moved into the play position.  The machine is fully functional, even when the tension arm is in what should be its "OFF" position.  Moving it in or out of position has no effect on anything.

And sure enough, after turning the machine back off for about 25 minutes with the reel off, the stored charge has dissipated.  When turned back on, the motors do not engage, and the capstan does not spin.  This initially looks like normal operational behavior, but as before, moving the right tension arm has no effect.  The machine only (partially) functions in the EDIT mode.

I'm guessing that this means that the switch or relay connected to the right tension arm is not functioning, or has been removed or bypassed, for whatever reason.  There's obviously still some sort of circuit contact there, since keeping the tension arm in the "ON" position (by leaving a tape threaded on the machine when it's powered off) makes a difference, by allowing enough charge to pass that the machine will start up when powered on... which at least allows it to be fully functional, if in a somewhat roundabout and atypical manner.

So I'm curious as to what to do about that tension arm switch or relay.  Historically, were they routinely bypassed, is it is more likely that this one is just dirty or worn out?  Any repair ideas?

I feel like we're most of the way there-- if this problem can be licked, then the machine will truly be able to function properly.

Thanks to everyone for all the help so far, by the way...!

- Kevin
« Last Edit: March 28, 2011, 11:39:07 PM by rerunmedia »

Offline jeri

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Re: [Troubleshooting] - Issues with an Otari MX-5050 BII-2...
« Reply #11 on: March 29, 2011, 11:37:34 PM »
Hi Kevin,

As Bob noted, the right tension arm is mechanically attached to a microswitch.  This switch is a safety switch which automatically stops rotation of the supply and takeup reels when there is no tape.  Even with power off, you should be able to feel and hear the switch click when you move the tension arm back and forth.

Since you don't feel or hear anything, the switch is malfunctioning.  It can't be absent, since the reels sometimes move.

I'd guess that the switch has become full of crud after years of service and is sticking internally.  When you initially thread tape, it takes a while for the switch to make contact inside.  So the reel motors won't run at first.  If you turn the machine off and remove the tape, the switch stays as-is for a while so the reel motors will still run even without tape.  But the switch s..l..o..w..l..y opens as the internals push back through the gunk inside, and then the reels no longer turn.  Evidently this takes about 25 minutes or so in both directions.

I have no idea if the switch can be cleaned or not to see if it might be the culprit.
Jeri

Offline rerunmedia

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Re: [Troubleshooting] - Issues with an Otari MX-5050 BII-2...
« Reply #12 on: March 30, 2011, 08:30:05 PM »
**Very** well-reasoned and logical, Jeri...!!   I've now hit that switch with some Caig (as best I could... there are what look like just a couple of small openings on top of it, and it's mounted pretty close to the capstan motor); while it's drying, I'll alternate leaving the take-up tension arm in and out of out of "play" position for 20 minutes at a time over the next couple of hours-- that should give the internal switch in the microswitch an opportunity to move back and forth a bit.

And now I tend to think of that microswitch as a "kill" switch, rather than an activation switch... makes more sense to me that way.

Thanks for everyone's help-- I think we're definitely on the right track with this...!

- Kevin
« Last Edit: March 31, 2011, 01:26:13 AM by rerunmedia »

Offline rerunmedia

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Re: [Troubleshooting] - Issues with an Otari MX-5050 BII-2...
« Reply #13 on: March 31, 2011, 01:44:45 AM »
Jeri's diagnosis appears to be exactly right... a sluggish micro switch.   With some patience, and an ear right next to the switch position, I sat next to the machine and waited while I ran an experiment... and heard the switch click after the tension arm had been raised for about 10 minutes.  The switch apparently disengages much more quickly, since after the arm is lowered, I can hear the relay click back out of position after only about a minute and a half (after which you get to wait for 10 more minutes until it engages again when you re-raise the tension arm).  So my earlier report of 25 minutes each way was more than a bit inaccurate, but you get the idea...

And apparently, the indentations in the top of the mounted switch are **not** holes in the casing, since I don't see any evidence that any Caig is actually penetrating into the switch.  I've taken off the side panel and removed the three screws that are supposed to be all that holds the microswitch in place (at least according to the exploded diagram that I finally found), but it doesn't seem to want to be removed for closer inspection.  Anyone know if those micro switches are soldered in place?  And for that matter, where a replacement might be found?

- Kevin

Offline ironbut

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Re: [Troubleshooting] - Issues with an Otari MX-5050 BII-2...
« Reply #14 on: March 31, 2011, 03:47:39 AM »
Hey Kevin,
Have you lubricated the idler pivot?
There's a picture of it linked in the last post (IIRC) in the "Reel to Reel Links" sticky located above the General forum.
It seems to be a common issue with 5050's and it's a free fix.

If it does turn out to be the switch, see if you can locate a part number on it and google it for a data sheet. It should have a picture of the back of the switch so you can see what you might need to do to get it loose. Bear in mind that either the switch or the lever that moves it has to be adjustable (opening or closing the gap). So the switch could be on an adjustable plate that you might need to remove to get at the screw(s) that hold it to that plate.
If you can find a parts number, you have a good chance of finding one at one of the many surplus stores in China. It'll cost 10x for shipping but it could be the only practical choice.

You can also ask if anyone here has a parts machine that could spare a switch (just be sure they're the same).
steve koto
 Sony scd 777es(R. Kern mods)> Vpi Aires>Dynavector XX-2mkll>Bent mu>CAT ultimate>CJ premeir 140>Magnepan 1.6qr(Jensen xover)Headphone Eddie Current Zana Deux>AT ad2000,HD800 ,Metric Halo ULN-2 (battery powered),
 HE Audio Jades