Need help with Sony BVH2500P

It's just radio with pictures! :)
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djmk1988
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Need help with Sony BVH2500P

Post by djmk1988 » Sat Jul 21, 2018 6:52 pm

Recently got into the possesion of this Sony BVH2500P 'C' type video machine. Worked for a couple of hours but than the disaster happened. The machine went into fault mode- wouldn't rew/ff , but it does work on pb if i hold the left reel to keep the tape tensioned. I do have knowledge of servicing electronics, however I don't seem to get any voltage for the left motor. All drive transistors are OK, however I got lost when it got into IC's. Did take me a bit of time to understand a small part of the diagram and got to a MB7051 8842 M40 TTL-PROM . While I don't have a good oscilloscope ( i think it goes max 10mhz) I did manage to see that 1 or two input frequencies are missing hence not working properly (On the 3 outputs for the motor drive I get a constant 4Vpp - on the working motor section it swings between 0 and 4Vpp) and so I need to search further. But I might be very wrong! Never serviced one of these before and I feel pretty lost. If someone has the knowledge to guide me would be amazing, or even the manual will help, I didn't manage to find it. All the help and advice would be more than welcome. All the best , Mario.

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PID_Stop
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Re: Need help with Sony BVH2500P

Post by PID_Stop » Mon Jul 23, 2018 7:06 am

My first guess is that the problem is not really with the motor driver or motor, but rather with the servo system -- in particular, the supply tension sensor. Here's a quick way to eliminate the motor and driver:

1) Mount a full reel of tape on the supply hub, and make sure the end of the tape is securely taped down. (Do not thread the tape!)

2) Find the capstan/drum servo board (it's called a CD-17 on a BVH-2000, I don't remember if there's a different variant for the 2500). It will be the third card from the right.

3) You will see three rotary selector switches on the CD-17 board. From top to bottom, set the switches to "2", then "0", and "0".

4) Make sure nothing is near the reel (hair, fingers, or anything else you don't want to get caught).

5) Below the CD-17's bottom rotary switch you will find a black pushbutton (it faces to the right... you have to stick your finger between boards to reach it). Press the button for a moment.

If the motor and driver are working correctly, the motor will spin in one direction up to full speed, then slow down and reverse direction, reach maximum speed, then slow down and stop. The alarm buzzer will sound, which is okay. You can silence the buzzer by pressing STOP -- it won't affect the test.


Some background: on BVH-series machines, the reel motors are not traditional AC or DC motors, where the voltage would be in proportion to the intended speed; rather, they are three-phase stepper motors. The three motor windings share a floating common point; each phase either floats (no drive voltage applied), is switched to V+, or is switched to ground. What you're measuring is not necessarily abnormal.

I've serviced several dozen BVH-2000s and three 2500s over the years, and I have never encountered a problem with the motors (other than worn bearings) or the motor drivers. I have had a number of cases where the potentiometer for sensing either supply or takeup tension has developed a bad spot. The tension sensors play a major part in telling the servo how much torque to apply, so a sensor problem will wind up looking like something strange is going on with the motor. The diagnostic I gave above is the only case you will find where the motor runs without input from the sensor -- so it's a really good way to isolate where the problem is really coming from.

Regards,

Jeff

djmk1988
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Re: Need help with Sony BVH2500P

Post by djmk1988 » Mon Jul 30, 2018 3:32 pm

Hello Jeff and thank you very much for replying back to me.
I did the test as well and you were right. Not only that but thanks to you the issue is now solved.
I can't possibly say how thankful I am for your help. Without you I would have been lost in this case for months probably as I don't have big experience
with vintage broadcast equipment.
I wish you the best of luck and may God bless you for for the happiness you brought into my heart to get this fixed.
Thank you very much again.

All the best, Mario Alessandro M.

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PID_Stop
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Re: Need help with Sony BVH2500P

Post by PID_Stop » Tue Jul 31, 2018 10:06 am

It's my pleasure! I think most of us around here get a real kick out of helping people keep vintage equipment going, and it's nice when practical experience comes in handy.

Jeff

djmk1988
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Re: Need help with Sony BVH2500P

Post by djmk1988 » Mon Sep 17, 2018 3:04 pm

Hello again.
Sorry to say but my BVH2500P failed again- a few weeks back but was very busy and didn't had the time to post here.
As I was mentioning at the begining of this thread, the left motor failed. As Jeff said, I did the tests and it work
But while playing a tape it stoped.
Powered on, did the test, the left motor wouldn't spin at all.
I did repeat the process several times, couldn't get it to move
I realy don't know what to do, this machine is becoming a pain.
I don't have the manual either so I'm kind of lost over here.
If anyone would be able to help with any ideas, it would be great.
Massive thanks again to all of you

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