BVH2500_BVT2000 Interface_Performance

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GRP
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BVH2500_BVT2000 Interface_Performance

Post by GRP » Mon Jan 15, 2018 6:35 pm

Greetings,
Just retiring after running a studio for 44 years I'm archiving from a variety of formats. Presently I'm on to the 1" shelves . . I have a BVH2500 and BVT2000. They are connected via the multi cable with advanced sync from the TBC to the 2500 . . output from the video out of the TBC to my record. The image locks up properly but is loaded with sparkles similar to head switching but not at the bottom. It seems way too much for just dropouts. I've tried several tapes and they all do it. I noticed there is nothing on the video/RF meter of the machine as well. I don't exactly remember how to interface the DOC and have no manual. The "off tape" light on the TBC doesn't stabilize on green - keeps bouncing to "advanced". Nothing I am transferring is all that critical but if I can bypass something or test to see where the sparkles are coming from it will help . . . any suggestions welcome. I'm not an engineer but been around this enough to understand most of it on a non-component level.
Thanks!!
Greg Rike
GRP Studios

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PID_Stop
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Re: BVH2500_BVT2000 Interface_Performance

Post by PID_Stop » Tue Jan 16, 2018 1:09 pm

Greg,

That kind of sparkle is commonly caused by bad sliprings or brushes. On a BVH-2000/2500, power for the preamp mounted to the inside of the upper drum, plus control signals to the dynamic tracking actuators, goes through these brushes. Try changing from the "PLAY" head to the "R/P" head -- the latter doesn't depend on the drum-mounted preamp, so if it's a slipring problem, the video should clean up.

The video/RF meter is controlled by a toggle switch on the front of the modulator card -- on a BVH-2000, it's called a MD-14 board, and it's a similar designation on a 2500. With the switch in the upper position, the meter reads the RF coming from the video head; in the center, it's reading input video, and in the bottom position it's reading the RF from the sync head. If you're looking for an RF level off the tape, you'll want the switch in the top position.

If the video isn't totally stable, chances are good that the servo isn't quite locked -- which will result in the TBC not running in the center of its correction window. There are also other reasons, but that comes immediately to mind.

The dropout compensator is built into the BVT-2000 TBC, and the handshaking signals for it go through the large cable... so you shouldn't have to make any special connections to make it work. One thing to check -- and it would also affect the signal advance -- check the capstan/drum servo card (it's should be named something similar to CD-17)... there might be a toggle switch labeled "ADV", with positions for "BVT", "OFF", and "BKH". Make sure it's set to "BVT", or else the machine's servo won't interact with the TBC.

We had an early revision 2500 for a number of years (from the serial numbers, we literally had the first control panel off the production line), and I did PM on several in Rochester... but those were so outnumbered by 2000s that I really have to stretch to recall all of the differences.

Best of luck!

Jeff

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Re: BVH2500_BVT2000 Interface_Performance

Post by PID_Stop » Tue Jan 16, 2018 1:33 pm

Okay, here's an update after taking a look at the remains of our old 2500...

1) The switch I was thinking about to get rid of the sparkles is called "R/P MODE", and is to the left of the fluorescent readout on the control panel. The setting to try is the bottom "CONFI HEAD", which is the equivalent of the R/P head on a BVH-2000.

2) The modulator board on a BVH-2500 is called MD-22, and does in fact have the meter select switch.

3) Forget the idea about the BVT / BKH switch... that only applies to the 2000. I had forgotten that the 2500 uses the slots that would accommodate a built-in TBC on a 2000, for the additional record trace control logic.

4) Also on the front panel, make sure the SERVO REF switch is in AUTO mode... and that the VTR and TBC have valid reference video.

Memories of the 2500 are a bit slow to come back after 20+ years... :?

Jeff

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Re: BVH2500_BVT2000 Interface_Performance

Post by GRP » Tue Jan 16, 2018 1:35 pm

Jeff,
Thanks so much for your input . . . I'll make some evaluations and let you know where it lands!!
Cheers!
Greg

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Re: BVH2500_BVT2000 Interface_Performance

Post by GRP » Tue Jan 16, 2018 3:45 pm

Jeff,
Playback from the confidence head is really ragged . . more than sparkles . . looks like tape damage from that head. The switch on the MD-22 board did the trick for the meter. I added a black burst generator to the TBC . . . still just the adv sync to the machine from the TBC (do I need to send sync from the sync generator to ref of the machine too?). Sparkles might be a bit better but still there - they seem to live consistently in the same lines . . not totally random. would brushes/slip rings look fairly consistent?
Cheers!
Greg

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Re: BVH2500_BVT2000 Interface_Performance

Post by PID_Stop » Tue Jan 16, 2018 4:29 pm

GRP wrote:
Tue Jan 16, 2018 3:45 pm
Jeff,
Playback from the confidence head is really ragged . . more than sparkles . . looks like tape damage from that head.
I just dug into the BVH-2500 manual, and I would need to do some real study, but it looks like maybe both heads might go through the rotary preamp, not just the play head as on the 2000. So it might still be sliprings.
The switch on the MD-22 board did the trick for the meter.
Hooray!
I added a black burst generator to the TBC . . . still just the adv sync to the machine from the TBC (do I need to send sync from the sync generator to ref of the machine too?).
Both the VTR and TBC need reference. The way it's usually done is to connect black burst to the REF VIDEO connector on the VTR, then connect the VTR's loopthrough to the COMP VIDEO-1 connector on the time base corrector. Turn off the 75-ohm termination on the VTR, and turn it on on the TBC.
Sparkles might be a bit better but still there - they seem to live consistently in the same lines . . not totally random. would brushes/slip rings look fairly consistent?
Yes, that's a classic sign. Since the head drum makes one revolution per video field, a bad spot on a slipring will manifest as a horizontal band of noise or altogether missing video.
If you are handy and want to give it a shot, it is possible to try and clean the sliprings. You normally need a brush with rather fine bristles, but you might be able to get the job done with a can of compressed air (it it's just dust that's gotten lodged). I can give you some guidance on how to go about it, if you want to try... I have several meetings tomorrow, but I should be able to post the info within a day or so.

One other possibility that would also produce noise in a horizontal band, especially around the middle of the screen: dirt on the slanted guide around the lower drum (that is, the part that doesn't spin, particularly toward the left-hand side). If you take a close look, you'll see that there's a machined edge that guides the tape around the drum, drawing it higher as it goes around. If there's a bit of gum or shed oxide and tape binder there, it will deflect the tape a bit in that particular spot... and make the signal weaken or drop out there. A thorough cleaning would be a good idea on general principles; we used to use Freon TF, but that's been banned for a number of years. Pure isopropyl alcohol, like what is used to prepare for medical injections -- not rubbing alcohol, which contains water -- and a lintless cloth are about the best approach nowadays. If there's something really caked on that alcohol won't touch, xylene would be the next solvent to try... just keep it away from the pinch roller. Sony used to include an orangewood stick like what manicurists use as a tool for cleaning this guide, but I've never needed anything quite that persuasive!

Regards,

Jeff

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Re: BVH2500_BVT2000 Interface_Performance

Post by Shane » Wed Jan 17, 2018 12:41 am

Heh. Carbon tet anyone? :lol:
Mike Shane, CBRE
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Re: BVH2500_BVT2000 Interface_Performance

Post by PID_Stop » Wed Jan 17, 2018 9:32 am

Shane wrote:
Wed Jan 17, 2018 12:41 am
Heh. Carbon tet anyone? :lol:
It's stunning to consider the chemicals we used so freely in the control room not so long ago. Isopropyl alcohol, xylene, and Freon TF for cleaning VTRs... carbon tetrachloride for degreasing... and trichloroethane as a carrier for dissolved wax, to clean film and minimize scratches. Acetone, for cleaning projector gates and sprockets. Plus concocted mixtures like PicClear for film, Ethyloid film cement, speaker cone cement, glyptol, liquid PC trace repair compound, ferric chloride for etching circuit boards, and proprietary head cleaning solutions.

And for those of us who had film processors to contend with, there were the lovely substances in the E4 process.

It's a wonder most of us haven't gotten cancer or grown vestigial body parts. :shock:

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Re: BVH2500_BVT2000 Interface_Performance

Post by GRP » Wed Jan 17, 2018 11:43 am

Success Jeff!
I have a service manual for a 2000 and gave the process a look. I just cleaned the slip rings and brushes and it's clean as can be. I can't thank you enough for taking the time out of digital world to take a trip back in time. Digital seems so simple on the surface compared to the brilliance of the brainpower that put these machines together . . . and still work 30 years later. BTW, I paid more for my first BVH-3100 than I did for my first house . . I gave the machine away since it is worth zero . . my first house quadrupled in price . . . guess I got in the wrong biz! Anyway, thanks Jeff

Cheers!
Greg

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Re: BVH2500_BVT2000 Interface_Performance

Post by PID_Stop » Wed Jan 17, 2018 12:10 pm

Hooray!!! So glad that did the trick for you.

You're right about the people who designed these machines -- Sony flew several of them to San Jose for some reason or other, and those of us who were there for the two-week maintenance course (just for the BVH-2000 -- the BVT-2000 course was a third week!) got to meet them. Very impressive gentlemen, with a seemingly encyclopedic knowledge spanning not only Sony's gear, but Ampex's and IVC's as well.

Best,

Jeff

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