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

[plimousse]

Never !!!
Cheers,
Pascal

 

[digitall2000]

yes ...  yes ... yes ...
i used the block method
i used some very fine lam plywood cut at an angle to match the swing arms angle
when it is at the center of it's travel and rounded to fit the corner of the deckplate
i did everything that smulian said to the very last and the machine runs smooth,

lots of interactive adjustments

ferget the otari manual in regards to to the swing arm and motor speed
alignments i went through that three times and well you saw where i
ended up (last video) there is a place in the smulian setup where you
have to hold the swing arms in the mid travel point, which is where the
two dots align.  that alignment is equal to 0 volts on some test points
which tell this bi-directional closed loop servo system to stand still
which i think the mkII did on it's own with 2 solenoids

always remember and never ferget to disengage the reel size detector

i also have the official
"operations and maintenance manual" and schematics ifin someone needs them

lance

 

[digitall2000]

hey pascal

why never?
there are some, what appear to be minor changes from mkII to mkIII but
they do affect the setup fairly drastically at least in my experience with
this machine and i would of never of figured it out without you pointing
me in the right direction and giving me the proper documentation
and the block is in the smulian docs that worked for me

pascal thanks again

peace
lance

 

[digitall2000]

hi

today while checking the record and erasure operations on the mtr-90  mkIII i started
havin problems again with the MDAs or some other part of the tape drive "gizmos"

after going through hell trying to set the tensions, servo voltages and adjusting
feedback system as per the otari mtr-90  mkIII manual plimousse turned me
onto a document by steven smulian on the proper way to setup the
" MTR-90 MKIII transport bi-directional , closed- loop servo system "
and the machine came to life and had been running smoothly

today the machine was consistently, when in rewind mode, popping the
- 40V  breaker on PSU and pretty slow to start up into play mode (2-3 sec.)

if when in stop mode,  i pull the supply swing arm forward slightly the machine
starts rewinding the tape slowly and gradually speeds up the rewinding over time
and none of the transport controls have any affect on the machine in this state
i have to push the swing arm back toward the supply reel until the tape stops

does that point to the MDAs, PSU, tension, drive gain?

also

gyraf and others have stated that if one of the transistors on the MDA is bad to
replace them all, all on the board that test bad or all on all the boards?

thanks for all yer help so far
and for any future help and advise

lance

 

[radardoug]

When the servos are properly balanced, you should be able to move the takeup or supply rollers slightly in either direction and the servo should respond accordingly. Pulling to the front of the machine increases tension on the side you pull. Pushing lowers it. Letting go, the machine should stop. If it doesn't your servos are not operating correctly.
When changing power transistors, change the whole set, supply or takeup.
Check for loose parts in the coupling to the servo pots.

 

[digitall2000]

thanks radardoug

yeah i have learned theses points over the last year chasing this "ghost in the machine"
i was just hoping someone with experience on this machine would have some grand insight into this particular
issue which reared it's ugly little head on the day i fixed all of the erasure issues on said machine
there just seems to be very few people that have much experience on the mkIII -- otari doesn't have a clue
we put in new bearings in the swing arms and rollers and set up the electronics for the tape path/closed loop servo system
plimousse has been very helpful to me in giving me a document by steven smulian  that is the correct way to set up the tape path
i have the official otari mtr 90 mkIII service manual and the setup in there is either incomplete or something is wrong in it
it did not work, went through it three times thinking i missed something
but with the steven smulian way all seemed good, the machine was acting properly

so today i pulled all the power transistors and am checking them tonight

thanks again to all of you that have helped me along this crooked path
lance

 

[digitall2000]

i pulled all of the power transistors on the MDA's on this mtr-90 mkIII they are
2SD552 BJT-NPN  and  2SB552 BJT-PNP
none are shorted or dead but the hFE on the NPNs are all low and one is below spec
the PNPs hFE are all high and one being above spec

could this be what is causing the -40V breaker on the PSU to pop?
i am assuming that i can substitute MJ21193/MJ21194 comp pair for these also

should also change out the driver transistors?

thanks for any help offered
lance

 

[mrclunk]

i am assuming that i can substitute MJ21193/MJ21194 comp pair for these also

Yes, they work fine. Recently used them in a friends Otari.
Change them all tho, don't mix.
You'll need a good amount of heatsink compound and new shims as well. Messy business!

 

[digitall2000]

what about the 4 driver transistors?

 

[mrclunk]

what about the 4 driver transistors?

I didn't change them. Machine's been fine since.