Otari MX-70 Restoration 8-track 1" (with Pics)

M

MusicWorks

New member
Hi everyone!

I have spent some time away from the forums, had a ton of work to do! Glad to see you are all still around :) I have also posted this at Gearslutz, so everyone has updated info.

However, happy to announce I am about to start work on my recently purchased Otari MX-70 (as I have some time on my hands) and will update with detailed descriptions and pictures throughout the process!!



mx70_01.jpg




mx70_02.jpg




Luckily, this is a fine example of a machine with *really* low hours on it (check out the heads below, and tell me what you think :-) It was sitting in the "B" Studio of a small privately owned Studio in the south of Spain. Apparently, they got it for movie soundtrack post-production, but clearly saw little -or no- use as they sold it to me when they started signing movies for audio post and decided to shift to digital.

Actually, could any of you give an estimate on how many hours it may have? Just tell me what you think! heppy


mx70-heads_01.jpg




mx70-heads_02.jpg




mx70-heads_03.jpg



The transport is 100% aligned, even after shipping (which I did myself personally, it is one heavy beast!!!) and edge of the tape is incredibly sharp. It's in fully working condition, all functions, and recording/playing all 8 channels.

In spite of it being in working condition, it has developed noise because of relay leakage (the famous clear-sealed relays that are prone to fail in the MX-70 and MX-80 models).


Work I will be doing to the machine:

- PCB work to replace all 3 relays in each card (8 channels x 3 = 24 components)

- Pinch Roller rebuilding

- Power Supply Voltages maintenance check & PCB inspection -checking for bad caps, etc.

- Head Demagnetizing

- Record & Playback Calibration with MRL tape



As you can see its the high-speed pair version model - FH. (30ips and 15 ips).



mx70_03.jpg



Will try to complete restoration in one month :)


Stay tuned if you are up for a detailed restoration guide!!



Carlos K.


P.S Price I paid for this machine is listed in Analogrules.com (Current Market Prices for Various Recorders, check out year 2011)
 
Nice. I have the 16 track version and love it. Yes, those relays suck. Not that big a job to replace them. Power supply rebuild is a good idea too. Where are you going to get tape? Luckily mine came with three unopened cases of Quantagy 499.
 
Thanks for the replies you guys!! :)

Talldog: Cool! Would love to see that 16-track too! I hope changing the relays is easy, I have experience soldering but not desoldering components. Have been thinking about rebuilding the Power Supply, but it's in such good shape I think I am not going to touch it.

Regarding tape, with the machine I got 3 sealed Ampex 406 (no shedding) and 1 used Ampex 456 (terrible tape shedding syndrome, I threw it out) and a few empty take-up reels in great shape. I have been studying RMG tape options, and I will be recording my project with RMG 468 (based on the beloved PEM 468 -Otari's love this japanese tape formulations, and 468 sounds great anyway!)

hungovermorning: thanks! come back for updates!
 
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By the way, would any of you know a replacement for the MX-70's VU meter lamps???

Each VU has two of them (mine has a total of 16, two of which are not working -in channels 7 and 8).

Thanks!!
 
I am in Europe, do you know if the small lamps can be replaced individually or the whole VU needs to be replaced?

Will be ordering the OMRON relays this week, and will probably start desoldering components ASAP. :-)

Carlos
 
MusicWorks said:
Actually, could any of you give an estimate on how many hours it may have? Just tell me what you think!
Click to expand...

It looks like this machine has done a fair bit of rewinding / forwarding, based on the rather good amount of ware on the tape lifters. It's tough to judge heads and tape guides tho but I'd say an average used machine you have there. Not overused but not lightly used either.. BUT FOR 400 EURO (ABOUT 500 USD) IT'S AN AMAZING DEAL!
 
Good call on the lifter wear, Daniel...I didn't even notice...I was so mesmerized by the shiny heads. :eek:

Purty-purty.

Yeah, I concur it has seen some use but I'd call it a "below average miles" machine for sure. Lots of life left, and my goodness it looks super clean. DEFINITELY a good deal for 400EUR!

I'd have to see what the lamps look like...when you can, post a pic of one of the lamps. Maybe someplace like 1000bulbs.com has something...
 
Wow, nice machine! I don't think I've seen an Otari MX in that configuration. Hard to beat 1" 8 track far as cost/sound quality--sure you get the same thing x2 with a 2" 16 track machine, but the tape costs double too! I've been running an MCI 1" 8 since the beginning of the year and I'm loving it. Congrats on your machine and have fun!
 
Hey, I have an MX-70 too, congrats on the finding this one for such a great price. I'd highly recommend getting the Athan pinch roller if you've got room in your budget: Department
Also, if you wanted to save a bit more money, you might be able to get away with leaving RL-3 alone and just replacing the other two per channel. I believe RL-3 is only used for noise reduction switching.
A tip: it's dead easy to rotate those tape lifters so you'll have a smooth surface and much less tape shedding (dry normal shedding that is) during fast winding.
 
Thanks for the comments!!! I really appreciate it, I am aware of the bargain I snatched. But for example I hadn't noticed the tape lifters wear (the shiny heads also have a strange hypnotizing effect on me :))

The lifters "wear" seemed so "clean" I thought tape lifters were actually faceted that way ! xDD -excuse my ignorance.

ethyrvalve: can I just rotate the tape lifters by hand or would I need to open the deck's cover plate to rotate them? would be great to have such an easy fix!!

thanks for the tip :)


1) PCB Work


PB16XA_PCB_ASSEMBLY.jpg


Regarding the third relay (RL-3) I have checked the original diagrams and it's only used when Noise Reduction switching occurs:

rl3.jpg


Considering it's in the center of the PCB, and it's not so easy to reach as the crucial RL1 & RL2 (on the edge of the board) I am not going to bother with RL3. Never intend on using the deck with Noise Reduction anyway :)) -although I might use Dolby A/SR during the mixdown process, it doesn't seem logical (or practical) to use NR with the multitrack deck...would love to keep a certain amount of dynamics, thank you very much!! xD So, I will be replacing RL1 and RL2.




Now, on to something else, I have some stuff for you all.

I scanned a fresh high-resolution copy of the MX-70 Audio Card Schematic (PB16XA) you can download here (4.6 MB).

Also, for the *first time available online*, a copy of the Audio Control Card (PB48DA) schematic, download here (3MB).


Had some time on my hands so I also scanned the coolest thing my eyes ever saw -inside the original MX 70 manual that is! Also for the first time available, the OTARI MX 70 PARTS DRAWINGS:


mx70_exploded_views.jpg




mx70_exploded_views_vu.jpg




mx70_heads.jpg



You can download the full high-resolution set here (9MB). These drawings are really interesting, you can actually see the whole machine inside out!!! -always loved exploded views hehe Now there is a digital copy of these, in case someone needs them in the future..

I am sure some of you will enjoy them!! xDDD


Cheers!

:-)
 
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Re the lifters. I'm at work right now, but I seem to recall that you can access the lifters quite easily if you open up the VU meter panel. There are a couple hex screw to loosen which will allow you to rotate the lifters a bit to give them a fresh surface then re-tighten.
 
Hi guys!


Ready for some updates??? So I started soldering as soon as I received the relays and variable temperature soldering station. Here is what I did:



***BEFORE DOING ANYTHING TO THE MACHINE***



a) Adjust Power Supply Voltages (5V)

As indicated in the manual, before doing any maintenance or repair work to the machine one must check the 5V voltages. Basically opened up the lower rear panel:


psvoltages01.jpg



Cleaned it up a bit, so the PS could breathe a little. Connected DC Voltmeter (+ CP1, - CP3). Adjusted VR1 for 5.0 volts +/- 0.05V. Connected voltmeter to +CP2 and - to CP4, adjusted VR2 accordingly. After this I opened the upper rear panel, adjusted fast wind speed and fast wind offset by resetting the CPU (red button) while measuring TP4 for the positive and TP2 as ground (for 0.0V). Release CPU reset and adjust for +4.5V.


psvoltages02.jpg



After having set all my voltages correctly, now I can start working on the machine -wouldn't wan´t a voltage peak to fry my 200 dollars worth of relays or any other component :)


psvoltages03.jpg



b) Opened VU meter panel front to access tape lifters from the inside, unscrewed hex and rotated the lifter (brand new tape lifters for 0$! thanks ethyrvalve for the suggestion!!) Anyhow it was almost impossible to access the hex screws holding the middle lifter, so I left it -has almost no wear, the important lifter to rotate was the one near the record head.


lifters.jpg




c) PCB Work (finally...)

After some hesitating -it is really scary doing PCB work!! hehe- I received the relays and pulled out the eight audio amplifier cards. I am beginning to think I am a lucky man....SIX OUT OF EIGHT cards had already Otari stock gas-sealed Omrons in perfect working order. I had to swap out the ones in cards 2 and 3 only! -that were the clear-cover relays like this:


relays.jpg



So, a total of 20 solder points to have my Otari MX 70 working 100% - that is an easy to repair machine in my book!!! Everything is clearly laid out and it's really easy to fix this deck. (By the way, got a bunch of spare relays now as I had ordered for all eight cards, if you interested in these let me know)


oldstock.jpg



And


Testing the machine...


testing.jpg



I recorded the same piece of music in all 8 tracks, one at a time, after calibrating the machine using digital tones (I can't afford a stupid MRL). After recording all tracks, I dumped each one to my DAT.

All 8 tracks have no distortion, no measurable noise levels (in the digital world!!!!) and sound SWEEEEEEET! After that I recorded all 8 tracks at once, just to check. Everything is working at 100% now.


:DD


Will be posting Pinch Roller replacement, calibration (when I can get a hold of a calibration tape) and de-magnetizing procedures. So this is a guide to fully restore an Otari MX 70. These machines have certainly aged quite well!!

The insides of this deck look pristine.

Thanks all!


C.
 
Hi musicworks,
I was wondering what is the noise that the relays cause? what does it sound like? Congrats on the 1", thats a real nice score.
 
Hi falken,

The noise is usually described as "wind on microphone" or "ghost noise". Unfortunately these relays are a problem in almost 100% of the MX-70s that have the clear case relays. The rest of the electronics have aged beautifully. When checking out a MX 70 I would look at the cards, and determine the amount of PCB work to be done. There is apparently problems with some output drivers in earlier models...

Hope I cleared it out for you

Cheer,

C.
 
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