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Author Topic: MX5050 B II 2 R/P issue(s)  (Read 4549 times)

Offline ed

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MX5050 B II 2 R/P issue(s)
« on: November 14, 2011, 06:47:58 PM »
Greetings and THANKS for being here!
I've finally found a machine and - for the price, it's ok. The big issue I'm having right now is REC/REPRO level in Ch. 1 (Lt. if you will). Using the internal osc. it plays back ~ -10VU compared to Ch. 2 - with the out pots "equal". On a tape made w/my X2000 of tone (from TDK calibration CD) at "0", it plays at ~ -7VU compared w/Ch2 - pots equal and 4trk. selected. I've soaked, sprayed and pulled most conn. & pots & switches per usual. NO changes. I discovered the 6 (blue) caps on the rear bd. to be leaking (see pic if it posted). Could ?? be cause?? They'll be changed asap.
Not sure if I'm chasing an ele. issue or head issue(s).

I haven't found a method to cal. the PB from  the pdf. I downloaded and it says to do THAT before cal. the REC. Presumably, I'll need a 'standard' tape to set this. Correct? But the procedure would be helpful also.

Thanks in advance. -Keep 'em rolling!

ed

Offline ironbut

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Re: MX5050 B II 2 R/P issue(s)
« Reply #1 on: November 15, 2011, 01:05:27 AM »
Hi Ed,

Welcome to the forum.
Those caps certainly look questionable but it appears that they're on the power supply board so a channel imbalance is less likely than some in the signal path but still not out of the question. They will however need to be replaced sooner or latter but don't count on that fixing your current issue.

It would help if you could give us an idea of the general condition of the machine and maybe some history if you know any.

I'd start with the usual suspects such as head wear, a speck of crap on the head or guide(s). Sometimes it's tough to see something that's resulting in spacing losses on the left channel since it's hard to see that side of the head (outermost). It might be worth your while to remove the headblock so you can really get a good look with a strong light and a magnifier.

Another check you should do is to record a test tone from your cd on the Otari and try playing it back on another machine. If that sounds okay than the problem is probably on the playback side of things. When you're recording the test tone, be sure and monitor with the Otari set to both "source" and "tape".
You've probably already read posts regarding the 1/2 track-1/4 track switch. That's a very common problem. Try listening to a tape while switching back and forth. If that switch is the issue, you should be able to hear the levels balance every now and then.

Regarding the test tape, you can obtain them at MRL Labs in San Jose Ca. Here's the link;

http://home.comcast.net/~mrltapes/

You should follow the instructions for your machine in the owners/service manual. MRL also has tons of info regarding the use of their tapes and everything related to magnetic tape.
I suggest that you don't try and calibrate a machine that may have other issues. Until you rule out other issues, trying to align a machine that's otherwise out of whack will only make things worse and could ruin the tapes you play on it (including the test tapes which aren't cheap and are useless when damaged).

If you haven't already, check out the "Beginner's Guide" to find out more regarding heads etc.
steve koto
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Offline ed

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Re: MX5050 B II 2 R/P issue(s)
« Reply #2 on: November 15, 2011, 09:16:03 PM »
Thanks, Steve. All great suggestions.
Let me start with my creds: been working in electronics for ~ 40 yrs. w/ audio specifically about maybe half that; last position was at a well-known NPR affiliate in the NW where I did the care & feeding of most studio equipment (while lusting for the analog gear sleeping in the corner [i.e. 3!! A807's]:-(((. I've acquired gear as $ allowed on a public radio salary, but still manage to have 3 DAT's four RtR's and about 4 CD burners/players (down to 9 spkrs from ~26.)

The deck was thoroughly 'used' in a commercial AM/FM sta. in Maine for many yrs and is slowly responding to the tlc coming its way. It needs feet, control buttons and most urgently: hub adapters.
When I >>>record a test tone from your cd on the Otari and try playing it back on another machine.<<< the level was down ~7vu compared to Ch.2. The heads do have some wear - I suspect they have been replaced at least once... VERY well cleaned several times.

Oh yeah: & the pitch control pretty much stalls out any forward motion of the tape.
I'll re-do the tone tests in both directions and make critical notes. IT WOULD BE 'NICE' IF IT TURNED OUT TO BE A SWITCH... BUT I've really sprayed the crap out of them (usual suspects). Perhaps I can get my camera's macro to actually work & I'll post some head shots! They can be quite a challenge to get in focus & w/o glare.

THANK YOU again for your thoughtful suggestions and time.

ed

Offline ironbut

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Re: MX5050 B II 2 R/P issue(s)
« Reply #3 on: November 16, 2011, 02:18:23 AM »
Regarding your pitch control issue, have you cleaned the internal Hi/Low speed switch? It seems to get oxidized and can cause mysterious speed control issues on 5050's.
steve koto
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Offline ed

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Re: MX5050 B II 2 R/P issue(s)
« Reply #4 on: November 16, 2011, 01:20:11 PM »
yeah, I've pretty much shot all sw. & pots except trim pots w/deoxit... wouldn't hurt to do it once more.
Thanks,

ed

Offline ironbut

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Re: MX5050 B II 2 R/P issue(s)
« Reply #5 on: November 16, 2011, 01:55:01 PM »
If you've cleaned and worked the pots, switches and connectors I don't think there's any point to do it again (you don't want to drown them).

It might be time to do some voltage checks. It could be that somewhere in the left channel, the bias voltage is getting dropped.
I'd start with the power supply since those caps a questionable. If the voltages out of it are reasonable, switch to the amp section (after the test oscillator) and compare the right/left channels till you find the area where the voltages are off. Examine the caps and any trim pots there. There's usually a trimmer that adjusts the bias to the transistors. Those can go bad too (I have a couple of trimmers in my Technics that I keep meaning to replace and they just barely pass enough voltage).
steve koto
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Offline Listens2tubes

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Re: MX5050 B II 2 R/P issue(s)
« Reply #6 on: November 16, 2011, 09:40:37 PM »
After changing the caps on the power supply board of deck 2 I think the goo seen around the electrolytic is a glue used to hold them to the board and not something leaking from the caps. I have 5 decks with similar looking caps.
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 ed

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Re: MX5050 B II 2 R/P issue(s)
« Reply #7 on: November 18, 2011, 02:53:39 PM »
It seems I may have 'overlooked' the azimuth: from straight on the angle is not quite the same as perpendicular to the tape path - listing some ??15-20?? degrees port!! With no tape and o'scope, I'm not sure I want to mess with alignment of that nature. AND OF COURSE I didn't down load the pix yet from the cam, but will & edit them in for y'all's opinion.

Many thanks for all the helpful replies.

ed 

Offline ed

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Re: MX5050 B II 2 R/P issue(s)
« Reply #8 on: November 18, 2011, 02:59:56 PM »
Regarding your pitch control issue, have you cleaned the internal Hi/Low speed switch? It seems to get oxidized and can cause mysterious speed control issues on 5050's.

Seems I hadn't bothered w/the pitch pot since I started dealing w/the levels issue. Lots of exercise and some deoxit got - not only the LED to work, but the speed seem to be functioning well, also!
So, it's on to the heads...  Wish me good luck!

Offline ironbut

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Re: MX5050 B II 2 R/P issue(s)
« Reply #9 on: November 18, 2011, 03:22:51 PM »
Hey Ed,

One thing you might consider is sending your headblock to JFR for lapping.
If you can feel a ridge on any of the heads with a fingernail (be super careful not to scratch the surface) and the heads seem to be out of alignment, it may be wise to just send it off to be serviced.
Even though the alignment can only be done to the elements that you send, it will be a matter of spending a little time to check that the guides/tensioners on the machine are aligned with the headblock (which will be your reference).

Here's JFR's linky;

http://jrfmagnetics.com/

BTW, since the output from the internal oscillator is low on the left, getting the heads worked on probably won't solve the channel imbalance. You still need to track down where that channel is not providing enough gain or that gain isn't reaching the outputs.

« Last Edit: November 18, 2011, 04:42:08 PM by ironbut »
steve koto
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Offline ed

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Re: MX5050 B II 2 R/P issue(s)
« Reply #10 on: November 18, 2011, 10:58:59 PM »
I'll probably send heads out after the holidaze ($$).

The osc. output IS consistent  in both ch. (monitoring SOURCE w/meters), it's the REC out that seems deficient
« Last Edit: November 25, 2011, 08:41:51 PM by ed »

Offline danh

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Re: MX5050 B II 2 R/P issue(s)
« Reply #11 on: December 06, 2011, 04:41:09 PM »
I came across the complete calibration manual from Otari. It contains information on adjusting the bias levels on the amplifier. The pdf is too large to attach, so here's a link: otarialignmentprocedures.pdf


Hope this helps..
Daniel J. Hodd
WFUV Radio, New York
http://audiodork.com
http://dhodd.com

Offline ed

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Re: MX5050 B II 2 R/P issue(s)
« Reply #12 on: December 07, 2011, 02:29:48 PM »
MANY thanks Dan and I'll keep y'all posted as to the successful resurrection of another MX5050!
The community radio sta. I volunteer at also has a B II 2! (imagine that...)

Peaceful and Safe Holidays to ALL


ed