To do tension adjustments, you ordinarily need the Sony weight kit, an extender board, and a digital meter. The supply weight is 85 grams, and slides directly onto the supply tension arm; the takeup adjustment uses two weights: 135 grams and 240 grams, but it's less obvious. Take a look at this picture:
The top portion depicts the supply tension arm; the bottom is the takeup arm. You need to screw a threaded support standoff into the chrome trim on the right; a piece of 1/2" (12mm) tape is attached to this standoff, passes to the left of the tension arm, rests on the timer idler wheel, and supports the 135g (or the 240g) weight. If you're handy with machine tools and have a scale, you should be able to make the weights pretty easily.
Once you have the weights, here's how to do the adjustments:
SUPPLY TENSION ARM
1) With the power off, remove the RL-12 card, plug the extender board into that slot, then plug the RL-12 board into the extender. Turn the power on and let the machine boot up.
2) Put the 85g weight on the supply tension arm.
3) With a test clip lead, short extender board pin 9B to pin 10B.
4) On the RL-12 board, measure test point TP-12 with respect to ground, using a low DC range. Adjust variable resistor RV-12 to get 0 volts, +/-10mV.
5) Remove the test clip. The voltage on TP-12 should read 0 volts, +/-30mV; if it is outside that range, slightly loosen the two lock screws and turn the eccentric screw a bit to bring the voltage close to 0. Tap the weight slightly to make it settle whenever you make an adjustment; the reading should approach zero. Tighten the lock screws and make sure you are still reading near zero volts.
6) Remove the weight. The voltage on TP-12 should go to —2.6V; if it isn't, find circuit board TT-01 (it's on the transport, above the tension arm) and adjust RV-1 to get —2.6V.
7) Without a weight, the tension arm should clear the stop by 0.2 to 0.4mm.
TAKEUP TENSION ARM
1) Set the weight as shown in the picture.
2) With the test clip lead, short extender board pin 12B to pin 13B.
3) On board RL-12, measure TP-13; you want 0 volts, +/- 10mV. Adjust RV-13 to get the voltage within this range.
4) Remove the test clip. You want to see 0 volts +/- 30mV on TP-13; if the reading is outside the limits, slightly loosen the lock screws and adjust the eccentric to get the voltage close to 0. Again, tap the weight slightly every time you make an adjustment to make the sensor settle into its new position. When you get the voltage down around 0, tighten the lock screws and make sure you still have close to 0 volts.
5) Remove the 135g weight and put the 240g weight in its place, threaded the same way.
6) The voltage on TP-13 should now be 1.4V; on board TT-01, adjust RV-2 to make it so.
Two things to remember: first, the mechanical adjustments and electrical adjustments interact a bit, so you might need to go through the process several times until you get the proper readings with the 85g weight and no weight (on the supply side), and with both the 135g and 240g weights (on the takeup side). Second, always give the arms a small tap and let them settle to get the most accurate voltage reading.
Best of luck!