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Author Topic: Otari MX5050 BII repair questions  (Read 18486 times)

Offline Indyguy

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Otari MX5050 BII repair questions
« on: June 20, 2009, 10:09:54 AM »
Greetings All
My first post to the forum!  After years in the DAW world I've decided to plunge back into RTR.  I picked up a Otari MX-5050 BII in fair condition from eBay (I know) that was sold "guaranteed to work and recently checked out" that arrived with several issues.  First, on power on both VU meters max out and do not light up.  After being on a couple of minutes the meters slowly fall back to ~-10 (but never all the way to the left).  The machine plays back fine.  Also, the rewind and ff doesn't function.  I just acquired the maintenance manual (minus schematics) so trying to look thru and see if I can pinpoint the issues.  Contacted the seller to see if these were working before shipping but you know...  Are the VU meters internally lit, i.e would have to be replaced, or is there a panel illumination outside of the meters?  Don't know about the high on readings - something misaligned during shipping?  As far as the rewind/ff, guess it could be must the microswitches worn out or bad tape lift solenoid?  Any help appreciated.  This is my first non-consumer deck and it really is well-built.  But apparently a fixer-upper (lots of razor scratches on the splicer so probably very well-used).  Thanks everyone  - Jim

Offline Indyguy

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Re: Otari MX5050 BII repair questions
« Reply #1 on: June 20, 2009, 11:45:47 PM »
Okay - no responses.  Well the light issue I can attribute to all 4 LU2049s being burned out - maybe from the shipping?  And the VU meters not resetting - again maybe a shipping issue and just need to adjust the meters.  But the rewind/ff has me stumped.  Hard to imagine both switches being out, but I guess its possible.  I'll check them tomorrow with a voltmeter for conductivity.  Other than that a bad solenoid? 

Offline ironbut

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Re: Otari MX5050 BII repair questions
« Reply #2 on: June 21, 2009, 09:18:07 AM »
Hi Jim,
Welcome to the forum.
Unfortunately, I can't help you on your issues with the Otari, but just to let you know, things tend to get a little quiet around here on the weekends and downright "dead" on a holiday one.
Be patient, I'm sure one of our many Otari users will chime in soon enough.

In the meantime, it sounds like an ex-radio station machine (they were very popular in that arena).

Some general things that your machine could probably use;

It's a good idea to use some contact cleaner on all of the switches and pots. Don't go overboard with the cleaner (it's better to do it twice than to drown it) and don't force a pot that seems to get stuck.

Do a check to see if the VU is behaving the same way in play and record (it is a needle movement type rather than the light bar type isn't it?). I'm guessing that it's not the VU but some noise (hum) that's being introduced to the input circuit. Listen with the selector on source and record for a bit when the machines is still cold and listen to the tape.

When you try and engage ff and rewind, does it do anything or is it just dead stick? Listen closely to the reel motors to be sure that the motors aren't trying to get going.
Do this with and without a tape on. Lots of tests are just easier and more telling if you do it without the influence of the reels of tape. You need to fool your machine into thinking there is tape threaded by either taping the tension levers down or covering up the tape sensor (whichever your machine has). You can run through all the functions. If you pass through stop, it behaves more like it would normally (except faster).

Sometimes, old machines just need to be exercised to loosen thing up and find where the old grease has hardened and is grinding (very common). Don't go adding light oils to try and get things working. Know that it's the right thing to do before you lube anything that you're not prepared to replace (sometimes adding oil will just move the hardened grease so it can jam things up even worse).

I suspect you ff/rewind problem is electrical rather than mechanical. It's probably a bad contact in there so after using some contact cleaner on the switches (pretty unlikely I'd guess) check the wiring connectors on the control boards. There may be an internal fuse or two but it probably wouldn't work in play either. Worth checking though.
While you're in there, use a light an be sure there's nothing like loose boards, obvious burned or leaking components or animals living in there.

Hope this helps,..
steve koto
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Offline Indyguy

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Re: Otari MX5050 BII repair questions
« Reply #3 on: June 21, 2009, 09:23:01 PM »
Hi ironbut and thanks for the tips!  I reseated some of the connectors on the boards and now the VU meter seems fine.  I tested the rewind and ff switches with a VOM and they are fully functional.  This machine is nicely built, but has about 30-40 multi-connectors on it, so I suspect one may be slightly loose from shipping.  I have the service manual and schematics but it's still slow going.  Maybe someone with one of these beasts will chime in.  Most of the pots and switches are clean but a couple are a little scratchy - someone on another forum suggested WD-40 works just as well as contact cleaner - any thoughts?  Haven't had a chance to look at the heads closely but it did play a tape that I had on for a moment and at least it played!  Nice, simple transport and easy to work on - not like the Sony TC-580 that's sitting in the corner (that's another story...)!
     Sorry for my exuberance - - I see those reels spinning and I just can't control myself!!  Beats staring at a computer screen.  Kind regards - Jim

Offline Ki Choi

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Re: Otari MX5050 BII repair questions
« Reply #4 on: June 22, 2009, 12:09:19 AM »
Hi Jim:

Sorry to hear about your unnecessary excitement with your "new" Otari.  It's not rare to have issues with R2R machines purchased from eBay.  Some are lucky but all the Otaris I had bought from eBay in my early days of R2R collection, I have not had a single machine arrived at my house without either the plastic legs broken off or the entire alumninum frame chassis broken, etc.

The filaments in the bulbs might have worked before shipping but probably have reached their end of life and strong jolt it received during shipment may have done them in.

One of the first things I do when I get a "new" recorder is to measure its power supply outputs with O'scope if possible.  Since you have the schematics, check out the PS outputs first.

Although I still have 6 or 7 Otaris in my house still, it has been a while since I troubleshot any of them.  Joseph at Award Music is very familiar with the Otari BII models.  Try to send him a message.  Joel from this forum knows Joseph well and also is an Otari owner.


good luck,

Ki
Ki Choi

Offline ironbut

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Re: Otari MX5050 BII repair questions
« Reply #5 on: June 22, 2009, 01:20:33 AM »
There should be a bundle of wires leading from the transport buttons to a control board. I'd check that connection first and then the rest of the connections on that board. Sometimes the board will have edge connectors where it plugs into the chassis. Make sure that the board is well seated in it if that's the case.
steve koto
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Offline Indyguy

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Re: Otari MX5050 BII repair questions
« Reply #6 on: June 26, 2009, 07:16:08 PM »
Thanks ironbut and Ki Choi for your feedback - much appreciated!  So I went around and reseated all of the connectors (there's about 30 of 'em) - none of which looked loose - and voila!  The rewind/ff buttons work!  Must have jostled in shipping.  This is the kind of repair I like (price was right too).  Now if I can just find that set screw for my hub adapter.....
Jim
« Last Edit: June 26, 2009, 07:18:42 PM by Indyguy »

Offline ironbut

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Re: Otari MX5050 BII repair questions
« Reply #7 on: June 26, 2009, 07:43:50 PM »
Over the years those kind of connections get a little iffy. They usually have a couple of spots on the pin where the connection is good and the rest of the pin gets gunked up with smog, smoke, pet dander (just joking but you get the idea). So when the pin/socket connection moves a tiny bit from shipping, it can sit on one of those gunked up spots which would normally be cleaned by the friction of inserting it.

I'm glad to hear you're up  and running!
steve koto
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Offline miroslav

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Re: Otari MX5050 BII repair questions
« Reply #8 on: July 01, 2009, 01:44:19 PM »
Greetings All
My first post to the forum!  After years in the DAW world I've decided to plunge back into RTR.  I picked up a Otari MX-5050 BII in fair condition from eBay (I know) that was sold "guaranteed to work and recently checked out" that arrived with several issues.

Hello to everyone!
This is also my first post.
I was bouncing around the Internet looking for Otari info, and found this great website and forum and I just joined up.
I too just recently picked up an almost-new Otari MX5050 BIII-2 on eBay.
The unit was apparently a spare at a radio station but was unused. Upon receiving the deck, I could easily see that the machine had NOT been used, except maybe for a basic tryout.
The guides, rollers, heads...every square inch...looked factory-fresh.
It powers up fine, transport works as it should...I even played back a prerecorded tape using the additional/included 4-track playback head, and that too was fine.
Then I tried recording on fresh tape using the 2-track 1/2-track heads....and that's when I found that the Left channel is either not recording or not playing back (tonight I will do more detailed tests).
I have great sound in Source, but when I hit the Tape monitor, the Left channel goes 100% dead.

I took a quick look inside by removing one of the panels...and I see that there are plenty of connectors. So I'm wondering if it's possible that during shipping, a good THUMP might have just popped a connector or a board loose...???
Does anyone know for sure if that's possible on these machines...or are the REC/PLAY electronic soldered firmly?

Being that this machine is so pristine...I wouldn?t think that the electronics are blown/burned out...as it probably never saw even an hour of use. On my first inspection last night...it just seems like it might be a loose or broken connection...but I'm not sure yet where to look. I only glanced at the schematics last night. Luckily I also received the full Operations and Maintenance manual with the deck...also brand new...the binding on the spine wasn't even wrinkled!
If anyone is familiar with the guts of these machines?I would appreciate some tips/pointers so that I don?t waste time going down the wrong path. Of course, if I can?t find  the cause?I will probably take the deck in to JRF Magnetics which is only about an hour away from me?but I would hate to spend a nice chunk of cash on repairs just to have them reseat a loose connector or something silly like that that I can do myself.

Oh...since this deck has the additional 4-track head and switch under the head block cover...is it "safe" to flip the switch from 2-track to 4-track with the machine powered up??? I did that without thinking about it and then got nervous afterwards. Same thing for Flux and EQ switches on the back...does it hurt to flip them with the deck powered on?
I?ve never used these Otari decks before?so I?m not sure.

OK...sorry for the long first post!

By the way...I'm a musician and I have a fairly well appointed project studio where I still track to tape.
While I do use a DAW for basic Cut/Paste editing...I've been a tape user for about 35 years, starting way back with the TEAC 4-tracks of the '70s.
The Otari MX5050BIII-2 was going to be used for mixdowns and basic mastering, since I?m not happy mixing back into the DAW. Right now, after I edit in the DAW, I use it as a 24-track ?playback deck? and I mix back out  to analog through a console and outboard processing?but then when I record the stereo mix back into the DAW, I?m never happy with the dynamics, and I hate trying to correct it digitally.
Using tape, I can then get the higher mix levels that many people desire, while at the same time letting the tape do its natural compression instead of using any digital processing.
Bottom line?it just sounds better on tape!

Thanks
Miroslav

Offline ironbut

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Re: Otari MX5050 BII repair questions
« Reply #9 on: July 01, 2009, 08:10:20 PM »
Hi Miroslav, welcome to the forum.

The first thing to be sure of is that the head selector switch is on 2 track when you hit source. You should get some sound from the left channel but it would be much lower compared to the right. Also, many machines have a "record mode" switch that also has to be in the right position (it's kind of a fail safe so you don't record over an important recording).
If you need to find out if it's the record or the playback, it's easy enough to check. Just flip the tape as if it's a 1/4 track tape and see if the silent channel stays in the left (it'll be backwards but it's just a test after all).

If this machines in great condition like you've described, the switches and controls are almost certainly in need of cleaning. If it had been used a little a few times a year and taken in for yearly servicing, that would be the ideal situation. So it would be a good idea to do some routine "tuning up" even if that isn't exactly what needs to get that left channel recording/playing back.
Since you didn't mention it, I'm assuming that the VU was showing signal on the left channel as you recorded. If not, let us know.

And yes, it's ok to pretty much toggle any of the switches that control signal processing or routing while the machines playing. Just don't try and do that with any transport/speed type controls. It's so "ok" in fact that the first suggestion I have is to try shooting a bit of contact cleaner (I use DeOxit D5) into all the signal switches and and pots(start with that head selector switch, just be careful not to get the cleaner all over the heads). If you look at the back of these there's usually a slot or hole in the switch/pot body that you can squirt a bit of contact cleaner in. Don't use too much or you could have the stuff dripping out for ever. Start with as little a spray as you can and practice into a waste basket so you can see how much comes out. They gently work the pot or switch back and forth. If you a lot of resistance when turning a pot, stop and let it dry for a few hours. Some pots don't like these cleaners and forcing it can ruin the trace that the wiper is moving across inside.

steve koto
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Offline miroslav

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Re: Otari MX5050 BII repair questions
« Reply #10 on: July 01, 2009, 10:13:51 PM »
Hi Steve

Thanks for the response.

Yes...all the selector switches and record mode switches are all in the correct positions.
I have everything set identical for Left & Right channels.

I played back some old tapes I had from my 4-track days, so that way I was able to check both the 2-track and 4-track playback heads, and the playback seems to be fine from both playback heads and on both channels.
Also, when in the Input mode with Source selected, the Left & Right channels sound the same, the VU meters are the same, and everything works fine. But as soon as I engage Record...the Left channel just goes dead...nothing. I even tried working the switches and knobs while in Record to see if it was just some dirt...but nope, nothing not even any hiss/scratch. The Left channel is dead silent.

And oh by the way...based on the serial # and what the seller told me, this deck appears to be a 2006 model, so it hasn't been laying around like 10-15 years. Having looked inside and all around?it?s VERY clean. There wasn?t even any of the usual dust you find inside just from sitting around. I bet it was covered the whole time. I got it in the original Otari box.

According to the manual?s troubleshooting section....if there is VU meter action on Source/Input and if the Record button lights up and also the Record select LED lights up...but NO recording takes place...then it would be a bias circuit issue.
However...I'm recording on the Right channel, and I do believe that both channels use the same bias circuit/oscillator (from what I could deduce looking at the schematics)...with only their bias level pots making the difference per channel...so I don't think it's the whole bias circuits, but at this point, I'm just starting to guess.
I had the machine open front and back tonight and I could not find anything out of place or lose or that appeared broken.

I'm at a loss....I may have to find a qualified Otari tech to look at it.  :-(
I would really like to have it working, as the rest of it is in such good shape?I just hope it doesn?t get ugly with all kinds of circuit board replacements and whatnot, because I bet that will cost quite a bit.

Miroslav

Offline ironbut

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Re: Otari MX5050 BII repair questions
« Reply #11 on: July 02, 2009, 11:35:53 AM »
Have you tried going in through the mic inputs rather than the line? Take a close look at the XLR connector. It may have slipped in it's barrel. (BTW you know that pin 3 is hot and 2 cold)
Also, look at the wiring of the record head. It could just be a loose connection or it's always possible that the machine was rewired for 2 track mono (though highly unlikely but with radio stations,.. you just never know).
steve koto
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Offline steveidosound

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Re: Otari MX5050 BII repair questions
« Reply #12 on: July 02, 2009, 12:43:30 PM »
Hi Steve

Thanks for the response.

Yes...all the selector switches and record mode switches are all in the correct positions.
I have everything set identical for Left & Right channels.

I played back some old tapes I had from my 4-track days, so that way I was able to check both the 2-track and 4-track playback heads, and the playback seems to be fine from both playback heads and on both channels.
Also, when in the Input mode with Source selected, the Left & Right channels sound the same, the VU meters are the same, and everything works fine. But as soon as I engage Record...the Left channel just goes dead...nothing. I even tried working the switches and knobs while in Record to see if it was just some dirt...but nope, nothing not even any hiss/scratch. The Left channel is dead silent.

And oh by the way...based on the serial # and what the seller told me, this deck appears to be a 2006 model, so it hasn't been laying around like 10-15 years. Having looked inside and all around?it?s VERY clean. There wasn?t even any of the usual dust you find inside just from sitting around. I bet it was covered the whole time. I got it in the original Otari box.

According to the manual?s troubleshooting section....if there is VU meter action on Source/Input and if the Record button lights up and also the Record select LED lights up...but NO recording takes place...then it would be a bias circuit issue.
However...I'm recording on the Right channel, and I do believe that both channels use the same bias circuit/oscillator (from what I could deduce looking at the schematics)...with only their bias level pots making the difference per channel...so I don't think it's the whole bias circuits, but at this point, I'm just starting to guess.
I had the machine open front and back tonight and I could not find anything out of place or lose or that appeared broken.

I'm at a loss....I may have to find a qualified Otari tech to look at it.  :-(
I would really like to have it working, as the rest of it is in such good shape?I just hope it doesn?t get ugly with all kinds of circuit board replacements and whatnot, because I bet that will cost quite a bit.

Miroslav


Sounds as if you have a issue in the dead channel record path to the head. You have eliminated most other possibilities by saying you have sound through the machine at all times and both meters are indicating, all switches set correctly etc.
One more thing. If you have a piece of junk tape that has sound on both channels, can you erase both channels when you try to record over old material? If the erase head works on both channels the common bias oscillator circuit is working. I might then double check the wiring to the record head and any associated connectors.

I want to say this one more time. You can play tapes fine, and when you are in record mode and rolling tape with the tape source switches in source you hear the input, but when you switch them to tape, you find that no sound is being recorded on the left channel of the tape, correct?
Steve Williams

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Offline miroslav

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Re: Otari MX5050 BII repair questions
« Reply #13 on: July 02, 2009, 04:36:43 PM »
Have you tried going in through the mic inputs rather than the line? Take a close look at the XLR connector. It may have slipped in it's barrel. (BTW you know that pin 3 is hot and 2 cold)
Also, look at the wiring of the record head. It could just be a loose connection or it's always possible that the machine was rewired for 2 track mono (though highly unlikely but with radio stations,.. you just never know).

Didn?t try the Mic inputs?but I did try the line inputs and then of course also the built in oscillator. I?m not sure if the path from the oscillator and Line inputs is one and the same?but will try the Mic inputs tonight.

Yes, I knew about the Pin 3 Hot. I actually switched switch the wires around on the connectors and made Pin 2 Hot as soon as I got the deck just to keep things standard in my studio wiring.

I doubt they rewired the Record head to mono?because the Playback heads are both still in stereo.




Sounds as if you have a issue in the dead channel record path to the head. You have eliminated most other possibilities by saying you have sound through the machine at all times and both meters are indicating, all switches set correctly etc.
One more thing. If you have a piece of junk tape that has sound on both channels, can you erase both channels when you try to record over old material? If the erase head works on both channels the common bias oscillator circuit is working. I might then double check the wiring to the record head and any associated connectors.

I want to say this one more time. You can play tapes fine, and when you are in record mode and rolling tape with the tape source switches in source you hear the input, but when you switch them to tape, you find that no sound is being recorded on the left channel of the tape, correct?

I didn't try the erase test...but I will do that tonight too.

Yes...my pre-recorded tapes playback fine...and I have the same signal on both channels when in Source/Input mode...but when I go to Tape monitor, the Left channel is dead. So...since I already know the Playback heads are OK...it must mean that the Record is not working on the Left channel, hence the dead VU in Tape monitor mode?there's nothing there for the Playback head to reproduce.

I spent about 20 minutes speaking with John French at JRF Magnetics...and he gave me a couple of tests to do to check the continuity going through the head...and he also told me to once again look over the wiring around the heads and connectors in the signal path. But he said if everything looks good and the head passes continuity...then it may be a relay or something in the signal path that is feeding the head...
...or in the end, it might just be a bad Record head.

If I don't find anything over the weekend...the deck is going to JRF on Monday, and John said he's confident whatever the issue, they can repair, and then he'll even realign the electronics and heads if needed....so, I'll have a fine-tuned machine when all is said and done.

The guy who sold it to me tells me that a friend of his who works as an engineer at Hershey PBS is telling him it's a "two minute fix"...something about "needing to task the machine as a multi-track?  because of the added 4-Track Playback head...etc. I'm not really sure what he's talking about...?...don?t see what the 4-track Playback head has to do with the 2-Track Record head?
I asked him to get me better details from his HPBS buddy.

I appreciate all the responses here!
When everything is resolved, I will certainly post up the details so that they can be of help to anyone else with a MX5050.


Miroslav

Offline steveidosound

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Re: Otari MX5050 BII repair questions
« Reply #14 on: July 02, 2009, 06:26:01 PM »
One more idea. The record safety switch for the channel in question. Have you checked it's wiring and operation and is there a relay involved in the path. These are the switches other Steve mentioned that prevent you from going into record mode for a particular channel unless they are engaged. I think though it reverts to playback mode for that channel if not engaged and the record indicator for the channel is not lit?
I am looking at older 5050 electronics and there are 2 record buttons on the electronics with indicators above. This is in addition to the record button on the transport controls. In addition mine has buttons marked sel / rep  next to those. These have to be in the "rep" position for the channel to work. They control whether the playback is being taken from the play head (normal REProduce) or off the record head (which can't record in that mode) to provide SELsync as it's called  for listening to one track and recording another without the associated delay between the 2 heads. Teac called it "simulsync". Anyway, exercise these switches too as they control either directly or through a relay what gets to the record head.
Steve Williams

you don't want to know what equipment I listen to...