Sony BVH2000PS tension adjustment.

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karol96
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Sony BVH2000PS tension adjustment.

Post by karol96 » Fri Feb 09, 2018 11:50 am

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

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Re: Sony BVH2000PS tension adjustment.

Post by Shane » Fri Feb 09, 2018 9:52 pm

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.
Mike Shane, CBRE
---Omaha---

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Re: Sony BVH2000PS tension adjustment.

Post by karol96 » Sat Feb 10, 2018 1:55 am

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

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Re: Sony BVH2000PS tension adjustment.

Post by NECRAT » Sat Feb 10, 2018 8:58 am

Jeff Hartman is our "on board" expert with tape decks.

He should see this.
http://www.necrat.us

"Arguing with an engineer is like mud wrestling with a pig. After a couple of hours, you realize the pig likes it"

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Re: Sony BVH2000PS tension adjustment.

Post by PID_Stop » Mon Feb 12, 2018 10:24 am

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

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Re: Sony BVH2000PS Slant Guides

Post by PID_Stop » Mon Feb 12, 2018 10:40 am

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

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Re: Sony BVH2000PS tension adjustment.

Post by karol96 » Sun Mar 04, 2018 3:52 pm

Hello
Sorry, that I didn't reply before, but I hadn't got any time to make any experiments.
I made the 3 weights: 85g, 135g and 240g. I also made an extender board.
But I have got still some problems.
First of all, I tried to calibrate the T-tension arm.
So I screwed a weight post into a metal frame and put the first weight (135g) and set voltage on TP13 to 0V. After tapping the arm, I still got the same 0V. As a next step I did, was changing a weight to 240g. At TP13 I got -1.2V insteed 1.4V. I tried to set it to proper value with RV2, but I didn't reach the 1.4V. Te max. voltage I got, was only 0V.
Nearly the same thing was with a S-tension arm. When I got 0V on TP12, I pulled of the 85g weight and the voltage was about 1.1V. It was impssible to get -2.6V.
Could you tell me, what probably did wrong?

P.S. Refering to the original manual, that I have, those movable guides (entrance and exit guide assemblies) are called "movable slant guides"
Karol

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Re: Sony BVH2000PS tension adjustment.

Post by PID_Stop » Tue Mar 06, 2018 9:52 am

That's very strange: it almost sounds like you're measuring the opposite test points. TP12 on the RL-12 board comes the supply arm, and tends to go negative when the weight is removed; TP13, on the other hand, tends to go positive with the 240g weight threaded.

One thing to double-check is what you're doing with the jumper clip: it's only used to set the sensor amplifier's electrical offset. Basically, for each sensor you're doing three things:

1) Shorting the sensor's input to the amplifier, and adjusting the amplifier offset to yield 0 volts;

2) Removing the short and adjusting the sensor's mechanical position to approach 0 volts (with the weight on the supply arm, or the 135g weight on the takeup arm);

3) Adjusting the amplifier gain to achieve a target voltage with a changed weight (supply: —2.6V with no weight; takeup: +1.4V with 240g weight).

Here's another thing to check very closely: on the TT-01 board, make certain that CN003 and CN004 haven't somehow gotten swapped. CN003 is the supply sensor, and CN004 is the takeup sensor. They're nearly identical 5-pin connectors, and they're right next to each other.

Jeff

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Re: Sony BVH2000PS tension adjustment.

Post by PID_Stop » Tue Mar 06, 2018 12:57 pm

I just realized something from your original post: you're apparently having issues with the guide motor not stopping in the open position, as well as the tension arm adjustment. This could indicate a problem on the TT-01 board -- or maybe a loose connector or a damaged ribbon cable. This one board is where all of these signals for sensors and actuators on the transport come together, and are sent to the main backplane for the plug-in cards. Although I've never seen these problems come up at the same time, the TT-01 is a common point that should be checked.

Jeff

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Re: Sony BVH2000PS tension adjustment.

Post by karol96 » Wed Mar 07, 2018 4:41 pm

[img]Hello
Today I made some experiments.
I followed all the procedure of tension adjustment,which you described.
My results are pretty interesting and strange.
When it comes to the T-Tension adjustment.
With a 135g weight, I reached 0V on TP13. After tapping the arm, I still had 0V.
After replacing the weight (with 240g), the voltage on TP13 was about -1.1V.
As it is written in the manual and in your previous posts, the voltage should go up to reach about 1.4V, but not go down to about -1.1V.
I don't undrestand, why such a thing is happening.
I also checked all connections to the TT-01 board and of course the board itself and I didn't find anything wrong.
Now the S-Tension.
After putting the 85g weight into the arm, I set voltage on TP12 close to 0V. Next, I removed the weight and set the voltage close to -2.6V with RV1 on TT-01.
In the both cases, I also shorted the sensor's inputs to the amplifiers (9B to 10B and 12B to 13B) for setting 0V.
Have you got any idea, what is happening with those strange voltage readings when it comes to the T-Tension arm?
What do you think? Is it possible, that the sensor in T-Tension arm assembly is broken?

P.S.
Here are the descriptions form a manual, how to do a calibration.
But there is nothing about shorting any pins... So how is it with those pins?
T-tension.jpg
S-Tension.jpg


Karol

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Re: Sony BVH2000PS tension adjustment.

Post by PID_Stop » Thu Mar 08, 2018 8:25 am

Good morning Karol,
karol96 wrote:
Wed Mar 07, 2018 4:41 pm
After replacing the weight (with 240g), the voltage on TP13 was about -1.1V.
As it is written in the manual and in your previous posts, the voltage should go up to reach about 1.4V, but not go down to about -1.1V.
I don't understand, why such a thing is happening.
This is indeed strange, and it does suggest a problem with the sensor itself. I'm going to think this through, looking at the schematic for the TT-01 board (it's page C-159 of volume 2).

1) Both the S-potentiometer (RV1) and T-potentiometer (RV2) receive the same reference voltages. These should be around +4.7v as measured on pin 1 of CN003 or CN004, and —4.7v as measured on pin 3. These are regulated by zener diodes D4 and D5, and buffered by the two sections of operational amp IC1. Since the supply arm is working properly, that tells us that there's nothing wrong with these reference voltages.

2) Similarly, a voltage divider formed by R33 and R29 derives the midpoint between reference the voltages, somewhere near 0V. Again, we know that this is good because the supply side sensor works.

3) The sections of IC3 form an instrumentation amplifier, buffering the sensor potentiometer's reading. It's possible that IC3 has failed, but rather unlikely because you are seeing a change in the output (that particular type of op-amp tends to fail with an output going toward one supply voltage or the other, and not changing).

This leads me to suspect a problem with RV2, the potentiometer on the sensor. If you unplug CN004 and do resistance checks, you should see 15k across the ends of the pot (pin 1 to pin 3). With the connector plugged in, if you measure the voltage on pin 2, you should be able to move the arm manually and see the voltage change in a fairly linear way -- that is, as you apply more pressure to the arm, the voltage should keep changing in the same direction. If there's a dirty spot in the pot, you are likely to see wild voltage swings, or the voltage won't change at all when it should.
Here are the descriptions form a manual, how to do a calibration.
But there is nothing about shorting any pins... So how is it with those pins?
One of the things that surprised me during the two-week maintenance class was the number of areas where the manual is either incomplete or just wrong; the instructor gave us a number of improved or corrected procedures as part of the training material (the page I uploaded is a good example). In many cases, the manual was written based on early prototypes, but the training materials were based on factory procedures for setting up actual production machines. This is especially true for setting up the dynamic tracking, where following the manual will often end up making the system much worse.

Documentation isn't just a Sony problem... our Ampex quadruplex VTRs going back to the 1960s had a special hand-typed procedure for setting up the Intersync servo (it was nicknamed something like "37 steps to disaster"); if you tried to do the setup by the manual, the VTR would get so badly misadjusted that it would take many hours (and the special procedure) to get it back into calibration.

Jeff

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Re: Sony BVH2000PS tension adjustment.

Post by karol96 » Thu Mar 08, 2018 10:52 am

Hello
I have just made some more measurements.
The resistance between 1 and 3 pin of T-tension sensor is 15.5k and it doesn't change in time.
When the machine is switched on, voltages on pin 1 and 3 are +4.57 and -4.48.
Voltage on pin 2 depends on arm's position, and it changes lineary with a pressure applied to the arm.
With no weight on the arm, the voltage (directly on a sensor) is -254.5mV, and in a second extreme position is 170mV. (with more pressure applied, voltage is going up).
When I put 135g weight, the voltage directly on a sensor is 30mV. And with a 240g weight, the voltage is 85.3mV.
As I think, sensor is working properly.
But why when voltage on sensor is going up, voltage on TP13 is going down? Or is it a normal situation?
On the other hand, when more pressure is applied to the S-tension arm, voltage on sensor is going down and on TP12 voltage is going up.
It seems, that somewhere is phase-inverting amplifier.
Am I right?
Karol

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Re: Sony BVH2000PS tension adjustment.

Post by PID_Stop » Thu Mar 08, 2018 12:50 pm

There are several things that are not obvious here! If you look at the schematic for the TT-01 board (volume 2 page C-160), you'll notice that the feeds from both supply arm amplifiers are called "X" and "Y". "X" tends to rise in direct proportion to the voltage coming from the potentiometer, while "Y" will drop as the feed from the pot rises. IC2 (for the supply arm) and IC3 (for the takeup arm) are creating a differential output that feeds the RL-12 board.

Things get a bit strange when the signals hit the RL-12 board (volume 2 page C-77). On the supply sensor, "X" feeds the inverting side of IC25 and "Y" feeds the non-inverting side. So the voltage on TP-12 will be inverted from the sensor voltage -- that is, as the sensor voltage rises, TP-12 should drop.

The takeup side is slightly different: "X" and "Y" are reversed, so that "X" feeds the non-inverting side of IC26. And if you measure the voltage on IC26 pin 7, you should see the op-amp's output rise as the sensor voltage rises. But... notice that while TP12 comes right out of the first supply-sensor op-amp, TP13 comes after another inverting stage... so ultimately both TP12 and TP13 should trend opposite compared to the sensor voltage. The big puzzle is why that doesn't seem to be happening in your case... and it has me starting to wonder if there's a problem with IC3 on the TT-01 board, after all.

I just took some voltages from a working machine (though one I haven't calibrated in a while). The ground side of my meter was connected to the silver-colored TPE1 on the RL-12 board (it's toward the back, not far from TP-12).

Supply arm with no weight:
TT-01 CN003 pin 2 (potentiometer wiper): -0.020v
RL-01, extender board pin 9B (differential amp "X" output): 0.000v
RL-01, extender board pin 10B (differential amp "Y" output): —0.046v
RL-01, TP-12: around 0.000v

Supply arm with 85 gram weight:
TT-01 CN003 pin 2 (potentiometer wiper): 0.281v
RL-01, extender board pin 9B (differential amp "X" output): 2.695v
RL-01, extender board pin 10B (differential amp "Y" output): —2.453v
RL-01, TP-12: —2.585v

See what I mean: the "X" output is proportional to the potentiometer voltage, and "Y" is inversely proportional.

Takeup arm with 135 gram weight:
TT-01 CN004 pin 2 (potentiometer wiper): —0.026v
RL-01, extender board pin 12B (differential amp "X" output): 0.000v
RL-01, extender board pin 13B (differential amp "Y" output): —0.049v
RL-01, TP-12: around 0.000v

Takeup arm with 240 gram weight:
TT-01 CN004 pin 2 (potentiometer wiper): —0.085v
RL-01, extender board pin 12B (differential amp "X" output): —1.678v
RL-01, extender board pin 13B (differential amp "Y" output): 1.568v
RL-01, TP-12: 1.411v

Takeup arm with no weight:
TT-01 CN004 pin 2 (potentiometer wiper): 0.190v
RL-01, extender board pin 12B (differential amp "X" output): 6.36v
RL-01, extender board pin 13B (differential amp "Y" output): —6.21v
RL-01, TP-12: (I didn't think to measure this.)


If there's a problem with IC3 on the TT-01 board, you might end up missing the "X" voltage... while the "Y" would end up driving the rest of the circuit downstream in the opposite direction from what you would expect.

Hope that helps --

Jeff

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Re: Sony BVH2000PS tension adjustment.

Post by karol96 » Fri Mar 09, 2018 12:06 am

Hello
I have just found a reason, why such a strange things were happening.
No IC is broken.
It was such a easy reason: the power cables for T-Tension were flipped.
Why, I don't know. I am not the first person which tries to repair this machine.
I am pretty sure, that the man which was repairing the machine before me, flipped the cables.
I spoke with him and he told me even more interesting things.
As I know, he was changing the position of the potentiometers - the one from T-Tension was put into S-tension and this one from S-tension was put into T-Tension.
So, is there any difference between S-tension and T-Tension sensors?
As soon as I changed the cables on T-Tension sensor
and recalibrated it again, the machine seems to be working.
Karol

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Re: Sony BVH2000PS tension adjustment.

Post by PID_Stop » Fri Mar 09, 2018 8:16 am

Hooray! Good for you.

As far as I know, there is no difference between the potentiometers -- they are both 15k linear taper. Reversing the wires is something I would only have thought of if the pot had just been replaced; one of the things I tend to ask myself during troubleshooting is "what's the last thing that changed?".

Having the sensor wired properly and calibrated should make the machine a lot happier now!

Congratulations,

Jeff

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