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Sony BVH2000PS tension adjustment.

Posted: Fri Feb 09, 2018 11:50 am
by karol96
Hello everyone.
It is my first post there.
For couple of days I'm repairing the Sony BVH2000PS machine.
The biggest problem I have are those unadjusted tension arms.
As it is written in the service manual, I should use special "tension adjustment tool", but I haven't got this tool. So there is my first question:
Could anyone tell me, how much those weights should weight?
My second question is about so-called slant quides. Should they keep moving after the tape is out? Or should they stop in fully opened position?
Greetings from Poland,
Karol

Re: Sony BVH2000PS tension adjustment.

Posted: Fri Feb 09, 2018 9:52 pm
by Shane
Hello, Karol, and welcome to the forum.

I think you’re in the right place. There was some recent discussion about this machine and it’s cousins in this very forum (Ask the Engineers) not very long ago, so it should be easy to find. Seems they went over some of the same things you are needing help with.

I was able to find the thread by searching for ‘Sony’ from the home page.

Re: Sony BVH2000PS tension adjustment.

Posted: Sat Feb 10, 2018 1:55 am
by karol96
Hello
I have just made quick research for topics including "Sony". Some of them were pretty interesting, but there is no answer for my questions.
I wish someone could give me information about those weights.
Without using them, it is pretty difficult (or even impossible) to do the calibration of tension arms.
Karol

Re: Sony BVH2000PS tension adjustment.

Posted: Sat Feb 10, 2018 8:58 am
by NECRAT
Jeff Hartman is our "on board" expert with tape decks.

He should see this.

Re: Sony BVH2000PS tension adjustment.

Posted: Mon Feb 12, 2018 10:24 am
by PID_Stop
Good morning!

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:

Image

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!

Jeff

Re: Sony BVH2000PS Slant Guides

Posted: Mon Feb 12, 2018 10:40 am
by PID_Stop
karol96 wrote:
Fri Feb 09, 2018 11:50 am
My second question is about so-called slant quides. Should they keep moving after the tape is out? Or should they stop in fully opened position?
Just to be clear: you are probably referring to the entrance and exit guide assemblies to the right of the drum. Without tape threaded, they should remain in the open position; when you thread tape and put the machine in standby mode, the drum will rotate and the guides will close. During rewind, when the tape approaches the end, the guides will automatically open to protect the drum from having damaged tape ends getting stuck between the guide and the drum.

Except for a special test mode, the guides should either be fully open or fully closed -- they should not keep going back and forth. If I remember correctly, there is a magnet attached to the rotating portion to which the guide linkages are attached, and the magnet trips reed switches at both the opened and closed positions. If the guides keep moving, it might be a bad reed switch, or the magnet has become detached (less likely).

By the way, what many people call the "slant guide" is the machined groove that is part of the lower drum, which guides the tape diagonally as it wraps around the drum... since the lower drum is fixed, the slant guide doesn't move.

Jeff