| 3M M79 FFWD & FRWD PROBLEM [message #20178] |
Sun, 12 September 2004 16:49  |
 bobreghr
Messages: 21
Registered: September 2004 |
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Hello, I am new to this board...hope someone can help here.
I have been hired by a studio to do their tech work...mostly I'm a computer geek that does programing and special interfacing with ProTools and such.
Anyway, the studio I am working at has a couple of 3M M79 24 Track recorders that they want me to maintain. Both machines look absolutely immaculate...hard to believe how old they are! But I am new to tape transports and these machines.
My problem is that one of the machines came from the old Record Plant Mobile Truck and was set up to run 14" reels with the factory mod for this. The studio owner wants this machine put back to the original 10" reel configuration...OK. So replaced the spooling motor 14" adapter plates and put on the original 10" plates and transport deck cover that matches. No problem...very simple so far.
Now the problem that I cannot figure...the Fast Forward and Fast Rewind is VERY SLOW ! Maybe on 25 - 30 IPS. I assume that there must have been a mod to adjust this speed for the 14" reels so as to prevent tape damage with the very intense tape path geometry using those 14" reels.
But for the life of me, I cannot find a way to adjust the FFWD and RWD speed!!! All I see available is the PLAY & STOP TENSION adjustments on the logic board. I see no other adjustments or controls to adjust the fast forward and rewind speeds.
Does anyone have any ideas or know the solution?
Thanks,
Bob
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| Re: 3M M79 FFWD & FRWD PROBLEM [message #20481 is a reply to message #20178 ] |
Wed, 15 September 2004 00:04  |
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John Klett
Messages: 468
Registered: April 2004
Location: Carmel, NY |
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tension will effect wind speed
does the tape wind slow at both tensions setting or only one
CR115 and CR116 set high and low tension limits respectively - one or the other is shorted the wind speed at the corresponding tension setting will be very slow
otherwise you should look to see where R4 and R5 are set
R4 and R5 are big adjustable resistors on the left bulkhead under the deck
from the book...
"For wide tape with the TAPE TENSION switch set to the HIGH position, the sliders on the resistors are set for a measurement of .7 to .8 ohms to ground (1/2 inch tape is 2 ohms, 1/4 inch tape is 6 ohms). When the switch is set to LOW, the measurement should be 2.5 ohms (1/2 in tape is 6 ohms, 1/4 inch tape is 2.5 ohms) ±10%. Operate the recorder from forward to rewind, and from rewind to forward; the tape should pack solidly on the reels. Readjust R4 as necessary"
note that the book has a typo and that the resistance for the sliders with the tension switch set to LOW and with 1/4 inch tape should really be 25 ohms or so...
there could be other problems - even gummy tape residue on lifters will cause slow wind
John Klett / Tech Mecca
http://www.technicalaudio.com
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