BVH-2000 guide retraction

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Tuner2
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BVH-2000 guide retraction

Post by Tuner2 » Sun Nov 19, 2017 5:02 pm

Not sure if I have the common terminology, but here goes. I have very light engineering skills, though started in video in the mid-'70s soldering a computer together, then worked in broadcast and post-production for decades, so have a few skills, but am definitely not a pro tech by any means (so no drum replacements being done by THIS guy :) ).

I have a BVH2000 manufactured around 1983 and well-maintained until around 1992. It's mainly been sitting indoors since then, with only occasional light use, maybe one 30-minute tape per year. Up until a month or two ago it played normally whenever tested: braking fine, auto-braking at EOT, guides closing up normally after threading a tape, and auto-retracting (after the EOT stop) when spinning a tape off. All seemed well.

Threaded a tape yesterday and the guides did not close up when I put the machine into standby, then play. No warnings, no flashing lights, display warnings, they just didn't close. I'm thinking a tape presence sensor of some sort may have failed; there looks to be one right down between the audio heads and the pinch roller. I don't have engineering manuals for the 2000.

Any hints, suggestions or outright statements of where to look first?

Thanks in advance.

grich
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Re: BVH-2000 guide retraction

Post by grich » Mon Nov 20, 2017 11:17 am

Check for slipping belts. Any VTR these days is going to be suspect for cracked or deteriorated rubber parts.

Common on the old MII decks we had...it would get to the point where the pinch roller would try to snap in place, but the belt would slip until it timed out and unthreaded.

Gregg

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PID_Stop
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Re: BVH-2000 guide retraction

Post by PID_Stop » Mon Nov 20, 2017 1:40 pm

What you're after, Sony calls the threading motor, and there are no belts involved: it's a gearmotor assembly that slowly spins a metal wheel with an offset pin that pulls the guide linkage out and pushes it back. If memory serves, the wheel also has a magnet attached to trip reed switches to tell the control system when the guides are open or closed.

Given the age of the machine, I would say the greatest likelihood is that oil has hardened so that the motor can no longer turn. Start by removing the front covers (first the plastic over the audio head assemblies, which just pulls off, then the beige plastic around the head drum (several captive screws), then finally the blue plastic with a handful more captive screws). You will see the threading motor just above the entrance guide -- you're looking for a metal wheel about the diameter of a nickel with a large slot cut across the diameter, and a linkage to the guide assembly connected to a pin on the wheel.

With the machine's power off, use a large flat-blade screwdriver in the wheel's slot, and try turning it counterclockwise. It normally is fairly stiff, but as you keep turning it, the guide assembly will move in and out. I'd give it several rotations to see if it just needed to be broken loose a bit, then turn it on.

Here's where we have a bit of fun: make sure there are no reels mounted on the machine (which there wouldn't be if you've just removed the front panels), and turn on the power. Raise the control panel (if it's a freestanding machine) or open the dropdown door (if it's console mounted) so you can see the circuit cards; find the CD-17 board, which is about 3/4 of the way toward the right. With a small screwdriver, set the three rotary switches so they read 5 - 7 - 0 from top to bottom. There's a little black pushbutton below the bottom rotary switch; press it, and the machine will go into a thread motor test loop. The machine will start beeping (you can silence that by hitting the STOP button on the control panel), and the guides should open and close continuously every several seconds. If my guess is right, letting it run for a bit should loosen things up.

You can take the machine back out of the test loop by switching the card back to 0 - 0 - 0 and pressing the button again, or by powering the machine off and then on again.

If this didn't help any, you can isolate the problem by disconnecting the guide link from the motor wheel and running the test again to see whether it's the motor that isn't turning, or if the guide assembly itself is stuck.

Finally, if you're really bored and want to watch the machine do something unusual, set the CD-17 switches to 5 - 6 - 0 and press the button... that's the complete motor and solenoid test cycle, and goes through a loop of running pretty much every mechanical thing that can be controlled.

This ought to either solve the problem outright, or narrow down where the problem is.

Jeff


p.s.: After you've finished with any of the self-tests, it's a good idea to put the rotary switches back to 0 - 0 - 0. I've never had a machine spontaneously go into a test mode, but I don't want to test the idea that it can't happen, either!

p.p.s: I doubt that it's the tape presence sensor (that's an optical interrupter near the capstan) -- if that isn't working, absolutely nothing will happen when you hit PLAY or STANDBY. On the other hand, a problem with the threading motor will let the drum start and will allow tape motion, but with the guide open (rather like what happens just before the tape rewinds off the end of the reel). I am assuming that this is what you're seeing...
Last edited by PID_Stop on Mon Nov 20, 2017 2:05 pm, edited 1 time in total.

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Re: BVH-2000 guide retraction

Post by PID_Stop » Mon Nov 20, 2017 1:54 pm

For inquiring minds, here are the different test modes you can get by setting rotary switches on the CD-17 board and pressing the button under the bottom rotary switch:

2 - 0 - 0: Supply reel torque check (must have a new one-hour reel on the supply reel)
3 - 0 - 0: Takeup reel torque check (must have a new one-hour reel on the takeup reel)

(Caution: don't thread the tape for torque checks! Just mount the full reel with the end well taped down. Also, keep fingers well away during the test, as the machine will apply maximum acceleration in both directions.)

4 - 0 - 0: Reel brake check
5 - 1 - 0: Pinch roller pressure check
5 - 2 - 0: Pinch roller cycle check
5 - 3 - 0: Brake solenoid cycle check
5 - 4 - 0: Mini arm (the small guide next to the capstan) cycle check
5 - 5 - 0: IP roller motor rotation check
5 - 6 - 0: Full motor / solenoid cycle check
5 - 7 - 0: Threading motor cycle check
5 - 8 - 0 through 5 - A - 0: not used
5 - B - 0: Capstan motor rotation check (reduced speed)
5 - C - 0: Capstan motor rotation check (play speed)
5 - D - 0: Drum motor rotation check (servo in PG lock mode)
5 - E - 0: Drum motor rotation check (faster than normal)
5 - F - 0: Drum motor dynamic braking check (about 10 seconds)

0 - 0 - 0: Test mode off

grich
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Re: BVH-2000 guide retraction

Post by grich » Tue Nov 21, 2017 11:49 am

PID_Stop wrote:
Mon Nov 20, 2017 1:40 pm
What you're after, Sony calls the threading motor, and there are no belts involved: it's a gearmotor assembly that slowly spins a metal wheel with an offset pin that pulls the guide linkage out and pushes it back...
Why the heck didn't Panasonic think of that? Replacing the threading drive belt in most MII units was a royal PITA.

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Re: BVH-2000 guide retraction

Post by PID_Stop » Tue Nov 21, 2017 12:18 pm

grich wrote:
Tue Nov 21, 2017 11:49 am
PID_Stop wrote:
Mon Nov 20, 2017 1:40 pm
What you're after, Sony calls the threading motor, and there are no belts involved: it's a gearmotor assembly that slowly spins a metal wheel with an offset pin that pulls the guide linkage out and pushes it back...
Why the heck didn't Panasonic think of that? Replacing the threading drive belt in most MII units was a royal PITA.
As far as I know, Sony used a belt for all of their cassette threading systems. On the one-inch BVH-2000 machines, the term "threading motor" is a bit of a misnomer, since it really has little to do with threading. A better name would have been "guide retraction motor". One reason I can think of for not using a belt-driven system is that the guide assemblies are fairly massive, and the linkage presses them firmly against the end stops, in order to achieve consistent precise alignment. I doubt that a belt-driven scheme could summon up enough muscle to last very long in that environment... also, on a machine the size of a 2000, they could afford the space for a gearmotor assembly.

Jeff

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Re: BVH-2000 guide retraction

Post by grich » Tue Nov 21, 2017 12:58 pm

DUH....BVH, not BVU! Yeah, 1" makes a difference. :oops:

I'll shut up and slink into the corner again...

Never had the pleasure of Sony 1". We were an Ampex house...VPR2's.

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Re: BVH-2000 guide retraction

Post by PID_Stop » Tue Nov 21, 2017 3:31 pm

It was striking to see how different facilities were "Ampex stations" or "Sony stations". We went from Ampex quad machines to Sony one-inch; the other stations in town were all Ampex. I wound up getting a fair amount of freelance repair work in Rochester -- for some reason, while TV stations, which had their own maintenance engineers, had Ampex, while the production houses largely had Sony. BVH-2000 maintenance has very little similarity to any other machine -- the procedure for changing the upper drum and setting up dynamic tracking needs special tools,a special alignment tape, a four-channel scope, and is insanely finicky.

So far as I know, I was the only one in the Central New York area to have gone through Sony's two-week class in San Jose... a fluke that ended up being far more lucrative and far more interesting than I would ever have expected.

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