VCD wrote: ↑
Wed May 08, 2019 4:55 pm
Yes, this BVH-2000 allows to install 4 cards on it.
Even very early revisions of the BVH-2000 had the four slots assigned for the plug-in TBC, but you would need to modify some of the other cards before it would work. Only a machine above a particular serial number would take the BKH without doing field modifications. Just seeing the empty slots is a bit misleading.
I'm not sure that BKH-2100/2150 kit is even possible to find separately from the VTR (maybe I'm looking in the wrong place?)
I don't think I've ever seen it sold separately from a machine. As you've discovered, a BVH-2000 without time base correction isn't very useful.
I discovered that if I connect a video signal with black fields (Servo Ref switch to "Ext") to the "Ref In" input and then I play the video, colors become a little more stable. I'll try to buy sync generator to make sure.
That doesn't surprise me, but even supplying external reference to the machine will never be sufficient to stabilize the playback. One of the problems that's fundamental to videotape recording is that there is always some mechanical imprecision with the tape and head motion; the playback head will never precisely duplicate the path that the recording head wrote. Minor differences in the slant guide around the lower drum, entrance and exit guide position, drum velocity and phase, head tip projection, and a host of other things add up so that the playback signal recovered from the tape doesn't exactly align in time with how the original video was recorded. These discrepancies create constantly changing delays in the playback signal, which (if extreme) can be visible as horizontal instability; even very small changes in delay become phase shifts at the color subcarrier frequency -- which become drifting hue in the picture.
What a time base corrector does is to store incoming video in a small digital buffer (enough for eight video lines, on a BVH-2000); the sync at the beginning of every horizontal line is compared to your stable reference, and the pointer that's grabbing data from the buffer to play out automatically adjusts to offset the error, so that the feed from the tape is given a correcting advance or delay to compensate for the mechanical error. It also does a much finer correction by comparing the color burst coming off the tape against the color burst in your reference signal, and making the corresponding correction on the output. (If you remember the old Ampex 2" quad machines, the corrector for horizontal error was called AMTEC, and the corrector for color was COLORTEC.)
Doing all this on a BVH-2000 is not a trivial exercise, because the length of the video track is extremely long (about 16"); Chuck Hintz, my instructor at the Sony maintenance training school, used to say that making the playback head exactly scan the same track that the record head laid down takes the same level of precision as driving from New York to LA without touching the steering wheel and without drifting out of your lane. One of the reasons that the machine needs a specially designed TBC is that the machine actually needs to be playing about four video lines early, compared to your house reference (and your other sources). Ideally, your stabilized playback video should be coming from somewhere around the middle of the eight-line buffer memory in order to allow for error in either direction. So the TBC produces an advanced sync reference that drives the tape machine's servos. There are other signals that go back and forth, including information from the demod circuits that trigger the dropout compensator. There's an awful lot going on!
P.S. My DT head is almost dead - the signal output level is less than 80%, still-frames lose color and vertical sync (but they are clean nevertheless). Also, head drum makes strange noises when running on it. The R/P head is more than alive instead.
Don't give up on your DT head just yet. The DT-04 board that controls it depends on a lot of feedback from the time base corrector. If it's not getting that feedback, and if there is no correction going on, the moveable head tip is going to go nuts trying to produce a stable picture -- and it will make a very noticeable chattering noise. Because the control system is sending the head all over the place, it's not surprising that the recovered RF level is low compared to the R/P head. Finally -- if you do get a TBC designed for this machine, DT chattering can be caused by dirty or worn sliprings, which are much cheaper and easier to replace than the upper drum (you need special tools and an alignment tape to replace the drum).
Realistically, I would say your best hope would be to either find a BVT-2000 with the umbilical cable, or another BVH-2000 that already has a BKH card set. A machine with a bad head would still be a good source for the cards (plus other spares).