MTR-90 WON'T GO INTO PLAY MODE

[digitall2000]

hi thanks for any help in advance
i  have tried to scour the existing mtr90 pages but not getting the answers i need
i've maintained other multi-tracks but that was a while ago but am not familiar at all with this machine

trying to help a friend with "tape transport troubles" as he said
to find out today that the machine acted oddly, was shut down, then has been sitting idle for about two years

well last night the machine would only rewind, try to put in stop would bring it to a crawl in reverse
then it would speed up again in reverse until the came off the take-up reel flapping about wildly on the supply wheel
also at this point it seems to be stuck in cue mode (no tape lifters).  the tape tension on either sides of the heads seem to be different as per the position of the tension arms and the machine when in reverse sounds like there is too much on the tape.
if the machine stays in the crawling stall mode (stop mode) it blows the 40v breaker on the psu

took out the capstan servo motor and have both the sine and square wave at the appropriate test points when turning
the capstan by hand so at that point the instructions say initialize the reel servos and "put the machine into Play mode"
and there i am the machine "wont go into play mode"

a few questions to those that may know
1.  anything come to mind that wont let the machine go int play mode?
2.  what drives the capstan servodisk motor  ---  sine wave, square wave, and what  amplitude?
3.  what could i use to check the capstan servodisk motor just to see if it functions?

so tried today with pretty much the same results.  decide to pack it in for the day and on the last rewind the machine is
rewinding at a constant rate instead of speeding up, the tape lifters activate and no odd sound of stretchy tape, as the
tape come close to the end of the rewind it slows down and comes of the take up reel nice and easy like (that's a first)

thanks
lance

 

[plimousse]

Hi,
Please send me a pm. I will try to help you.

Cheers,
Pascal

 

[fazer]

Ya could be those motor drive transistors are blown.  Weird things happen when one of them go out and others are still working

 

[digitall2000]

ok so
go in today and we strip all the skin off the machine and clean things
no sides< no front/back< no deck plate skin
notice the supply tension arm is floppy, find that the pivot nut has fallen off
we replace the pivot nut, reset tension arm travel and center point
Fast Forward/Rewind Damping Solenoid Adjustment, and general cleaning

next - swing arm adjustment -- the tension gauge didn't arrive yet so skip it
then - tape lifter mechanism adjustment:

1. Thread a reel of tape on the transport, activate the solenoids and place
the transport in Stop mode. There should be between 2 mm and 3 mm
clearance between the tape and the closest lifter. If this clearance is
correct, go to Step 3. . . .

no clearance
no lifters  but try it out any way
"load tape" by hitting STOP and all seems fine
FF fine with tape lifters
RW fine with tape lifters
STOP fine with tape lifters
PLAY and wonderful 2" audio coming out of the speakers the first time in two years, but why?
well the owner plays the tape that is loaded FF PLAYING and  REWINDING for about a half hour
lots'a joy now (two years latter)
we are talking as the tape runs off the supply reel for the first time after getting it running
rethread tape "load tape" by hitting STOP and the machine goes into rewind it won't play
only FF and RW and it seem by looking at the tension arms that there is too much tension on the supply wheel. 
when you hit stop it creeps to a stop and the goes into rewind again

"UNLOAD" tape

so i take my can-o-air, turn it upside down, spray the white cold poisonous gas all over the heat sinks for the
motor supply boards, thread the tape, "LOAD" the tape by hitting STOP and the tape loads properly
FF fine with tape lifters
RW fine with tape lifters
STOP fine with tape lifters
PLAY and wonderful 2" audio coming out of the speakers again

so i did notice in the middle of this that of the three motor control cards on the back of the machine that the
middle one was hotter than the other two and when i cooled the heat sink down the machine came back to life.

something going thermal?

packed it in for the day

 

[fazer]

Nice work.  Fix that motor drive card and you golden. 

 

[digitall2000]

by the way this is a mtr-90 III
is there a way to check the transistors on the MDA boards in place?
so as to not to have to pull every single transistor out

 

[gyraf]

We usually replace all transistors, as the ones still kinda-working are known to have taken a beating.

Don't fool around with the capstan motor driving - the motor is prone to blow up beyond repair when driver card fails. There is a protection update that you will want to implement (some heavy power resistors in the harness).

Jakob E.

 

[Matt C]

Don't fool around with the capstan motor driving - the motor is prone to blow up beyond repair when driver card fails. There is a protection update that you will want to implement (some heavy power resistors in the harness)

Can you elaborate on this a bit?  I recently purchased one of these machines so I'm hunting for as much information as I can.  Is there a service bulletin from Otari about this?

 

[gyraf]

Yes, there is a service bulletin for mk2 on this - although I'm not 100%sure if its implemented in mk3 already

 

[Matt C]

I'll search around for it, thanks.  Although mine is a mkIII so might not need a change.

 

[digitall2000]

Matt C
did you have any luck finding that technical bulletin that gyraf pointed out?

lance