Otari MTR-90 maintenance 2 (too) !!! SOLVED !!! !!! UNSOLVED !!!

hi
i am trying to figure out a problem with a otari mtr-90 mkIII
have had some help from some very kind people on a few different forums
plimousse from this forum be the most helpful
but there doesn't seem to be many people that have had any experience
with the mkIII

so i am stuck at point and don't know if i should just move on or not

i have got down to 6.1.9.3 and got stuck there because of the strange
mechanical pulse in the supply side tension arm

we replaced the bearings in the tension arm stands and tension arm rollers
replaced bearings in the two idler rollers but not in the servo or capstan rollers
they seem in good shape
what i have is a mechanical pulse towards the front of the machine in the supply
side reel tension swing arm in rewind mode
here is my scenario

arm tape - tension arms center as they should
play mode - tension arms center as they should tape packs as it should
ffw mode - tension arms center as they should tape packs as it should
rw mode - take up tension arm centers and is solid but - - - - -
supply tension arm has a mechanical pulse in it where about once every
second the supply side tension arm slackens slightly by moving towards
the front of the machine then snaps back to centered position again

then if i use the pad of my thumb and put a little pressure on the supply tension
arm and hold it almost centered the mechanical sound of the machine changes
slightly and the machine rewinds as it should ...... until i release the pressure

so i am wondering if i should move on to see if the rest of the alignment
procedure straightens out the pulse in the supply tension arm

6.1 Transport Alignment
6.1.1 Transport Deck Plate
6.1.1.1 Opening and Closing the Transport Deck 
6.1.1.2 Removing the Transport Deck Plate 
6.1.1.3 Reinstalling the Transport Deck Plate
6.1.2 Head Geometry
6.1.2.1 Reproduce Head Azimuth
6.1.2.2 Record Head Azimuth 
6.1.3 Swing Arm Travel 
6.1.4 Fast Forward/Rewind Damping Solenoid Adjustment 
6.1.5 Swing Arm Adjustment
6.1.6 Tape Lifter Mechanism 
6.1.7 Brakes 
6.1.8 Reel Turntable Height 
6.1.9 Reel Tension Servo Adjustments
6.1.9.1 Upper and Lower Limit Adjustment of Reel Tension
6.1.9.2 Preliminary Center Position and Gain Adjustments
6.1.9.3 Tape Tension Check
6.1.9.4 Reel Motor Tracking with Capstan 
6.1.9.5 Fine Adjustment of Position and Gain
6.1.9.6 Reel Size Detector Adjustment
6.1.10 Capstan Servo Adjustments 
6.1.10.1 Capstan Tachometer Adjustment
6.1.10.2 Adjustment of CAPSTAN CONTROL PCB Assembly 
6.1.10.3 Fast Wind Speed Adjustment 
6.1.11 Adjustment of TRANSPORT CONTROL PCB Assembly 
6.1.12 Adjustment of MASTER CPU PCB Assembly
6.1.13 VU Meter Calibration 

i know that the MDAs can be a problem on these machines

are the MDAs all the same?
should i swap out the MDAs to see if the problem follows the supply MDA?
is there some wave forms i can look at to see if something isn't getting a proper pulse?

thank you in advance,
lance

Defective servo potentiometer? Bad mechanical coupling to servo pot?

Is the error pulse appearing only at the pot viper, or also at top/bottom of pot?

Jakob E.

hi  gyraf
i don't really understand your reply
servo pot? where is that?

the pulse i see is in the supply side tension arm itself
a mechanical pulse where the tension arm has a slight
pulse where it moves towards the front of the machine
about once every second

lance

the two tension arms controls servo potentiometers that detect arm position and adjusts reel MDA's accordingly

i will recheck those pots
i did reset those pots and am pretty sure they are stable
in the set up of the tensions, upper/lower position and reel size
settings both swing arms responded well and setup easily
within spec

the pulse in the supply side swing arm is only and only in rewind

maybe pulse is the wrong term because that denotes electrical
in rewind mode the supply side swing arm has a slight jump in it
the jump is only towards the front of the machine and only in
rewind mode

thank you
lance

hey gyraf

have you worked on, as in maintaining one, a mtr-90 mkIII?

because around here there is no one that we can find and the people
at otari japan don't seem to really know much about these machines

lance

Can u make a little video of what's happening?
Is it an big, abrupt movement?
Sounds like the tape tension / motor gain's not quite right or like gyraf said a bad spot in servo pot.
You could try reducing the tensions/gain generally and see if that stops it?

i will try to get down there today to make a video
again this is only in rewind and only on the supply side
and i could not detect any dead spots in the pot either through resistance or voltage
also i got stuck at step 6.1.9.3 maybe by over focusing on this issue and since i have no one to talk to directly about the set up
now i am wondering if one of the steps i haven't gone over yet  6.1.9.4 - 6.1.13  will address this issue

thanks for any and all help
lance

hi
let me know if this is of any help:
https://drive.google.com/file/d/1iYDi_1ylaZA3hqikhgl3m8RoTCd1-i57/view?ts=5a9b6b02
and i need to reiterate:
i am wondering if one of the steps i haven't gone over yet  6.1.9.4 - 6.1.13  will address this issue

thanks again,
lance

Hi Lance,
I've watched your video...
For me, as show, you should increase gain on the both side...
But, you d'ont have any scotch on the tape ???
Cheers,
Pascal

hi pascal

when we last communicated you had me raise the gain on the supply side but i only
did the supply side not both, then started at zero again  (6.1.3) just to be sure

i'm sorry but i don't quite understand:
But, you don't have any scotch on the tape ???
do you mean make sure that i don't have any scotch tape on the tape ?

so on that note, the scotch tape one, i have been told by a few people
not to even have a fold in the tape when you attach it to the reel.  just
that will upset the system.  in thinking about this today, that when i
viewed the video (which i didn't take) that there was jitter in both supply
and take up swing arms.
i was on that machine for a couple of hours and there had been no jitter in the
take up swing arm but when i was rolling the tape off i was messing with things
and the tape became very loose then re-tightened out of alignment and put a big
divot/rumple in the tape.  well i  just realigned things and kept rolling the tape to the
take up reel.  so, when watching video it surprised me to see the jitter on the take up
swing arm but the crumple would be on the take up side at the time the video was taken

do i need to get the machine completely settled at this point? (6.1.9.3 from list above)
in rereading the manual it seems that some of the other adjustments will
interact with this step

how far can i take that gain setting?
i have them set as per the mkIII manual to +/-3.5V so a 7V
swing from end to end for a 10.5 in. reel

i know in the mkII the voltages were higher

thanks for even more help

lance

You might try contacting Terry Howard he's in the L.A., Ca, area.
He was my Otari Mtr-90II  tech for years.
He actually worked for Otari in the developement  of the MTR90 series machines.
Try Googleing him for possible contact.

i don't think he's available
he's mkII did nobody work on the mkIII

Hi Lance,

I will try to remember how I made all these adjustments, and to rewrite them.
I will send asap to you this by private mail.

Please, remember where are you located ?
Cheers,
Pascal

ok now
new video

https://drive.google.com/open?id=1_kv_A2nGrzLw49I6xJE0_rS7qiB9AjDk
the only way i could get the video to play is to download it

i went in and spliced out the rumple i had caused in the tape, that straightened out ffw
what a finicky system
what you don't see in the video is that in rewind when the jitter is at full scale
the VU meters dim slightly -  so it is pulling that power rail down considerably

when i first saw the machine it would bounce so far as to blow the +/- 24V circuit breakers

thanks to pascal
and all those who have helped me so far
sincerely
lance

I used to service these machines,  but few mk3 among.  I don´t see many MTRs these days .
I suspect that much of the mk2  knowhow applies too.
Wind system - to accelerate all the mass in FF and RW , 
the MTR machine introduces a tension  imbalance by a separate  solenoid pushing outwards  the tension roller of the  side (left in rw) taking up the  tape,  so left motor voltage (tension)  is higher,  until  fast wind speed is attained, then the tension roller  goes back to normal. 
see if there are 2 solenoids on each tention arm , one for latching at Arm  and one for this wind tension.
re video- you machine is quite noisy in the bearings,  I think. 
try looking for the reason the machine does not run fast in RW ,  motor voltage

thanks musiklab for your input

but

i had four different set up documents and there are some significant differences between the mkII and mkIII
so out of the four i chose the official published otari "operations and maintenance manual"
which did not help this machine much

luckily i happened upon plimousse here and after overcoming some linguistic  hurdlers he sent me a document by
J . S t e v e n  S m u l i a n and at every turn when i checked the voltages to set them up as smulian describes the voltages
from the setup where i used the "the official otari manual"  were wrong, so i was just chasing my tail using the otari manual

the smulian setup has the machine running silky smooth

one of the main differences is that the mkIII does not have the second
solenoid  the mkIII uses an air pot for dampening not a second solenoid
another being the way the upper and lower swing arm pos. is set up
yet another is the voltages used at every turn are slightly different

so if any of you mkIII owners are having problems maybe i can
help you just like the other kind people here have helped me

just let me know
peace
lance

digitall2000 said:

luckily i happened upon plimousse here and after overcoming some linguistic  hurdlers he sent me a document by
J . S t e v e n  S m u l i a n and at every turn when i checked the voltages to set them up as smulian describes the voltages
from the setup where i used the "the official otari manual"  were wrong, so i was just chasing my tail using the otari manual

so if any of you mkIII owners are having problems maybe i can
help you just like the other kind people here have helped me

Click to expand...

I recently got a mkIII, it's not having any major problems but I'm still getting familiar with it and trying to iron out any little kinks.  Could you send me the Smulian document?

EDIT: never mind, I think I found it.

it is
Otari_MTR-90mkIII_TransportServo_Alignment_jss_1990.pdf

ifin ya need it let me know
lance

digitall2000 said:

it is
Otari_MTR-90mkIII_TransportServo_Alignment_jss_1990.pdf

ifin ya need it let me know
lance

Click to expand...

Got it, thanks.  One question, what did you use as a block to hold the tension arms at center position?  Just cut a block of wood to size? (I got a kick out of "2.999 inches")