BVH-2000 playback muting to grey screen

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oldtvgear
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BVH-2000 playback muting to grey screen

Post by oldtvgear » Sun Sep 02, 2018 5:16 am

So i have been working on a Sony BVH-2000ps

Initially the machine was missing an SV-43 card which did not allow it to complete booting.

Putting a known good SV-43 card from another machine in allowed it to boot, however on playback had a weird b/w image though recognisable it was pulled to one side - this was only visible on on pause or jog etc and when switching to the DT heads unstable scalloping weird patterning- if you went into playback it muted to grey screen.

Swapped the SV-43 with another one, and miracles of miracles i now had a color image and stable DT - (but only in pause or jog), in playback it still muted to grey screen.

So i swapped the internal PR-63 TBC card with a known good one - amazing! now it no longer mutes to grey screen - all functions appear normal and a happy machine.

Questions:
- why out of two known good working SV-43 cards, would it be only happy with one? (version numbers or something on chips?)
- What would cause the PR-63 TBC card to mute to a grey screen, (but otherwise perfectly functional on pause/jog etc?)

also, if anyone has a spare SV-43 card available or knows where i can obtain one it would be useful for troubleshooting - however are those NTSC/PAL machine specific?

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PID_Stop
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Re: BVH-2000 playback muting to grey screen

Post by PID_Stop » Tue Sep 04, 2018 9:00 am

The SV-43 card is common to both NTSC and PAL/SECAM models; it is the gateway between the main system controllers (SY-79 and SY-80), and the analog servos for the reels, capstan, and drum. When you hit the PLAY button, the machine goes through several modes before it gets to the point of being completely locked:
  • First, the servos give an initial shot of current to get the drum and capstan motors moving;
  • Second, the analog servos take over to bring the motor speed roughly where it belongs (this is called FG, or Frequency Generator control);
  • Third, the analog servos switch to PG, or Position or Phase Generator mode (depending on who you talk to), which gets the tape lined up so that the head is actually scanning the recorded track;
  • Finally, the system switches to full SV-43 control, where the computer is in charge of coordinating each of the servos with incoming reference and feedback from the timebase corrector to produce a stable, color-framed picture. This is especially crucial when you're using the DT head, because there's even more interaction based on variable tape speed.
The ability to keep the head centered in the recorded track depends absolutely on the SV-43 being in full control; functions like manual and dynamic tracking and skew control only come into play when the SV-43 is in the loop.

The timebase corrector looks for information from the servo system about the current operating mode, in order that the TBC can apply the most helpful correction... so if the SV-43 board is sending the TBC weird input, it would not be a big surprise to see it go to grey. Another possibility is that the bad SV-43 is never getting the drum positioned quite onto the track, so that there's no RF to demodulate... hence a grey screen. Unfortunately, I went to school on the machine back when the large external BVT-2000 timebase corrector was the only option... the four-card BKH was a future option back then, and even though I have a machine with the BKH, I never did get the manuals for it.

This is a very difficult type of problem to troubleshoot, because it involves looking for patterns in data; the only type of failure I would expect to spot in the field is one of the data I/O lines on the SV-43 being stuck either high or low... which would point to a logic buffer failure (as a rule, most logic signals leaving a card are buffered). I'd say you best shot would be to put the working SV-43 on an extender board, and take a look at the main data buses with an oscilloscope; then take a look at the non-working card, and hope that you find one or more lines that isn't showing similar data activity. If you are really fortunate, you'll be able to trace back to a buffer or gate where the output doesn't match up with the input...

Best of luck,

Jeff

oldtvgear
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Re: BVH-2000 playback muting to grey screen

Post by oldtvgear » Tue Sep 04, 2018 8:30 pm

Thanks for your reply!

I do not think the SV-43 is at fault since the one that appeared faulty still functions fine in its original BVH-2000 that has an ext TBC

After swapping the SV43 card from another machine that also has internal TBC it functions fine.

The problem was then that the screen is muting to grey on playback but perfectly fine on pause or jog/shuttle, this fault was isolated to the PR board on the internal TBC card set, as swapping for another cured it.

I have seen this similar grey screen muting before on a betacamSP deck but never solved it, in this case since i do not have the manual for the internal TBC card set it makes it difficult to fault find, as you do not know how it all interacts on a schematic.

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PID_Stop
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Re: BVH-2000 playback muting to grey screen

Post by PID_Stop » Wed Sep 05, 2018 7:57 am

Bear in mind that the interface to the external BVT (via the round multi-pin connector) doesn't necessarily use the exact same handshaking circuits that the internal BKH timebase corrector uses... so there are credible cases where the fault could still be in the SV-43 board. One thing that could tell you a lot about what's going on: set the toggle switch on the MD-14 board up to RF (V), so that you see the playback RF level on the right-hand meter; put the machine in PLAY using the R/P head. Pull out the tracking knob and give it a turn to see if you can get a peak out of the RF level... and if playback video replaces the grey screen when you hit a peak. That would tell you that the servo isn't centering the head on the track, and that the demod isn't locking to anything.

The other thing I'll ask... the top toggle switch on the CD-17 board is in the down "BKH" position, right?

Cheers,

Jeff

oldtvgear
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Re: BVH-2000 playback muting to grey screen

Post by oldtvgear » Thu Sep 06, 2018 12:27 am

From what i am looking at so far, its appearing more likely its a software version mis-match - both the machines with internal TBC's are much more recent serials, where as the one with ext TBC is much older.

What remains unanswered is if this was the case also with the TBC cards themselves.

Yes, i had tried toggling the tracking and looking at the RF (when the good SV card is installed). But it does not make any different to the muting to grey screen.

Yes! - i checked all the switches first thing in case anything was incorrect, but they are all in the right places, especially that BKH one (which btw seemed to be absent from the SV card that did not work in there - suggesting it is much older probably before those internal cards were even available).

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