ALIGNMENT OF THE MCI 2 INCH TRANSPORT
BY MICHAEL BLACKMER
The MCI/ Sony 2″ transport is based on a rather subtle design philosophy. Really, these principals should apply to any 2″ transport, but many do not have provision for some of the needed adjustments and rely on a more brute force approach. I must express thanks to my dear friend Greg Hanks for sharing his knowledge with me on this subject (and many others!). I also wish to thank the fine people who taught me at MCI school. This goes way back to the ’70s and ’80s.
1) Keep your machines at a constant temperature. If possible the zone thermostat should be located near the machines. Do not change the thermostat around, as a few degrees can and will make your alignment, both mechanical and electronic, wander. A 10 degree change can be a disaster. MCIs were designed to be run at 68-70 degrees F. Always leave your machine on. This is very important, even though it costs some money. The transport, and indeed, the whole machine, is made out of many dissimilar materials in contact. These expand and contract at differing rates with changing temperature and ratchet into new positions as temp cycles. Often things do not return to exactly the same position when the temperature cycles back. Temperature changes also make the electronics age more quickly, as solder joints fracture and screws work out.
The screws that hold the transport deck plate into the case should be a bit loose to avoid torquing the deck plate.
2) The height of the upper surface of the supply reels’ bottom flange is the basic height of the tape path, so it is particularally important that this flange be in very good condition, completely flat and solid, without cut-outs. Find one good reel and label it as THE supply reel that stays with the machine. Even if you receive a tape wound “head out” you must wind it “tail out” and then rewind it onto the supply reel. This is important. If the supply flange is bent, the high end, especially the high frequency Azimuth Sum of all tracks, will bounce at the rate of the supply reels’ turning. If the tape is seen to be bouncing up and down in the path look to the supply reel first. I have seen badly slit tape, the other likely cause, but not very often. The Supply side hub first gets shimmed to the correct height, which is just high enough to lift the tape off of the bottom edge of the incoming roller guide, so that it is just kissing, not being guided by, it. This height ajustment is done by shimming under the reel table.
3) The tape path faces must all be parallel, including the capstan (which is tricky to shim), the dancer arm and even the reel motors, so the tape naturally runs in the right place, without touching the guide edges. When it is right you see a tiny sliver of silver above and below the tape. You will need a set of MCI surface blocks, or functional equivalent, to do this set of ajustments. (You want to be very careful about what you lay on the contact mirror face of a tape head and how you do it! Rock the blocks corner to corner very gently and do not slide the block around.)
If the tape is being “guided” by any edge but the supply reel bottom flange something is wrong, especially if there is tape residue accumulating on that edge. This statement is true for any wide tape transport. The tape centering on its path should not rely on the fine detail of the slit tape edge, which may wander from the true path.
NOTE: If you can get your hands on a JRF Magnetics (jrfmagnetics.com) “Pro-Mix” head stack mount for your MCI or Sony 16 or 24 track, by all means get it! This is a very well engineered assembly that has knobs on the top to set the record and play head heights, so you can adjust your machine easily to itself and to tapes from other, even badly misaligned, machines. The Pro-Mix is also much more temperature stable than the stock MCI block.
Eventually the stationary guides get grooved and gunk starts to accumulate. You can get several uses out of one guide by rotating it in several partial turns. Rotate only as much as needed, planning ahead to maximize the number of steps. Replace anything that has become so worn that it presents sharp edges to the tape, including the tape lifter. The tape lifter can also be reused a several times by unscrewing it and adding shim washers of differing thickness to set how far it screws in and thus which face is presented to the tape.
4) After the parallels are set then the guide heights get ajusted as needed using various combinations of MCI shim washers. When the tape is correctly centered you can record some 10-15k, turn the tape over, play in sync mode and not be able to raise the reproduced levels by skewing the tape up and down. If you get a rise while skewing make note of how much you needed to skew and raise or lower the head half that distance. After the record head is centered in the tape path the repro height gets set with the machne in record to peak when directly downstream. The tape should appear centered between the undercuts on the head and you should have to skew it equal amounts up and down to see the edge of the pole pieces. You will almost certainly need to reset the parallels and azumuth if you change head height. Set azimuth by summing all channels and playing the 15k band of the repro tape in both repro and sync, ajusting for the very clear peak. I would say do not try to ajust 2″ azimuth with a scope.
5) Set the erase head by plugging its connectors in place of the record heads and ajusting its wrap for a peak while monitoring in sync the highest frequency that it will reproduce. Be sure to put the connectors back in the correct order!
The height and parallelism of the erase head is set with shims.
6) The capstan should be doing very little work, only metering the tape. When you push the pressure roller away from the capstan while in play the speed should stay the same. If it is off it is better to have it slow down than speed up. This is because the capstan motor has almost no ability to slow the tape down. Also the centering of the tape in the path should stay the same when pushing the puck away.
7) Ajustment of tape tension: After setting up the tape path geometry load the machine with known good record test stock and feed it with 20kHz. With the machine in record, alternately reduce the supply tension in steps and set the record and play head wrap adjustments to peak until the signal begins to become unstable. You may need to lower the take-up tension to balance as you go if it is much higher than the supply. Raise the supply tension until 20k is stable on all tracks and make sure the wrap is peaked. Spool equal pack onto both reels. Now, with the screwdriver on the take-up tension adjustment, and the other hand on the top of the pressure roller, repeatedly push the roller off of the tape and adjust the takeup tension so the tape speed stays the same. Test the balance at both ends of the reel. The tape should not speed up under any conditions. Slowing down a bit is OK. The idea is that the holdback tension should be no higher than needed to maintain good head contact. You might be able to get another 1/4 – 1/2 db at 20kHz out of the machine, but it will be eating head metal much faster. When the heads are new or newly relapped, a JH-24 can run at about 4.5 to 5 oz. (Compare this to something like 12 oz on a Studer A-800 or around 20 oz + on a 3M M-79. Properly set up the MCI transport can be very kind to the tape.) As a flat wears on the heads the tension gradually needs to be raised. It is good economics to keep the transport running at the lowest possible tension for as long as possible to conserve the heads and all other sliding tape path surfaces, as well as the tape itself.
8) Like the tape tension, the puck pressure should be no higher than it needs to be to do the job. Higher just stresses the tape. Pressure is set by a nut compressing a spring around a threaded rod connected to the plunger of a selenoid mounted under the deck plate.
Sometimes the pressure roller (or the brake) selenoid gets sticky and needs to be cleaned. To do this the power must be off. Mark the position of the coil assembly with razor blade scratches, then take out the mounting screws and slide the coil off of the plunger. Clean with 91% alcohol only. It will come out black. Don’t try to get every thing off of the plunger, as it is coated with a graphite compound that is a necessary lubricant Never use any kind of oil to lubricate this, or any, selenoid. Screw the coil assembly back in place aligned with your marks. Be sure that the plunger operates smoothly. Tweek as needed. The plunger wants to bottom during normal, heated up operation. If the pressure ajustment nut is set too far clockwise the selenoid will not bottom and the bressure will be drop markedly. (A selenoid gets weaker as it heats up. Its resistance rises, the current falls for a given applied voltage and so the magnetic field reduces.)
9) Ajustment of the dancer arm: After setting the tape tensions the incoming dancer arm wants to be set so that it is in the middle of its travel during play. This is ajusted by prestressing some bits of multistrand stainless steel wire that act as springs. It may be necessary to remove one of these wires, retain it if you do. You may need to set the rest position of the dancer by loosening the clamp at the top of its axle and rotating it. The dash pot valve (a little hex head screw on the back of the glass cylinder) wants to be set to “critical damping” so that when you disturb the supply side tape tension by hand the dancer arm moves fast enough to track the tape, but not so fast that it overshoots and bounces.
10) The takeup reel needs to be shimmed so that its lower flange is just touching the tape. It should not be dragging on the tape edge. It’s best if it is set a bit low so that bent flanges won’t scrape.
11) After doing mechanicals and reducing tension you should check and touch up the playback alignment with the repro test tape, then do your record alignment. After biasing recheck the record head azimuth by skewing the tape slightly upstream from the record head while recording 15-20k. If you can get more summed level then touch up the record azimuth. I suggest this last step because the bias current slightly affects where the signal sticks to the tape in relation to the trailing edge of the record gap.
Michael Blackmer, Acoustician