Sony BVH-2180-PS: Servo Error

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DolbySR
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Re: Sony BVH-2180-PS: Servo Error

Post by DolbySR » Fri Mar 04, 2016 4:42 pm

Hi Jeff

I wasn't far off. I tried to remove this cover and it turned out that it is secured by three screws in total. The one you showed and two on the front. Even if I removed all of them, I won't be able to just slip the cover off. So I will have to remove this bar to which the module is attached to. By looking at your picture, I asked myself whether your machine has the card rack lowered so that it sits below the control panel on the front? I changed this on my machine to bring it down in height a little bit as it stands on a table with coasters. Also I don't think that the enclosure on the right is present in my machine. I will have to recheck, but I think there is a fan attached to the card rack blowing air towards the drum servo.

This machine can get really hot. Oh yes. No wonder there are so many fans blowing air in every direction imaginable. The power supply itself is a bit of a "hottie" as well. It's the first machine in my collection too to have a heat pipe attached to some power stuff in the top of the machine. Really proper design engineering. It simply oozes quality.

Regards
Patrick

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Re: Sony BVH-2180-PS: Servo Error

Post by DolbySR » Mon Mar 07, 2016 3:17 am

Hi Jeff

I did some further investigation yesterday and found some strange results. First of all, I found the AP Board :wink: As I thought, there is a fan right next to the enclosure. In your picture, there's an other can...

Image

I then simply disconnected the connector CN356, which has the CTL track signals on it to and from the card rack. Interestingly, the machine still runs perfectly "fine" when not receiving any CTL track pulses. I reconnected the connections and set the machine to record. This meant that I could scope the monitor head output for the CTL track at the WFM output. I double checked at the connector CN356 and I saw a CTL signal, but it was very very weak. I left my USB stick with the scope sreenshots at home, I will add them tonight. The amplitude though was about 200-300 mV. The machine therefore records a CTL track, but the level is way to weak. On replay though, I couldn't see a signal at all. I ran a bit out of time and didn't manage to get the AP board out of the machine without disassembling almost everything or removing the card cage. There are simply too many cable looms in the way... :cry:

On record, the machine lit up the CF Lock LED

Image

and all 4 LEDs on the RL card turned on

Image

...but only on record.

Do you have a clue why the signal is so weak? Wrong bias level adjustment? I turned the CTL monitor level potentiometer on the CD card, but I didn't get the level up significantly. I wanted to take the AP board out to inspect the relay, but as I ran out of time, I postponed this for now.

And I really hated that I didn't take the extender card with me when I picked up the machine... :evil: Is there a possibility to source such a card? Or to make one myself? I would need the connector specs and ideally a source for those card holder brackets... :roll:

Regards
Patrick

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Re: Sony BVH-2180-PS: Servo Error

Post by DolbySR » Wed Mar 09, 2016 1:03 pm

... the promised Scope Screenshots:

This is what I see from the Monitor Head when recording a tape:
Image

This is what I get at the record head:
Image

Sure, there's quite a lot of BIAS present, but the signal is clearly visible as a short pulse. I'm sure there's some sort of alignment procedure for the rec level and bias level, right? Might this be wrong? But then I still don't get a signal from the R/P head when in Play mode. I guess this AP Board will have to come out no matter what.

That the recorder still works fine with the DT head even when it doesn't get a CTL track signal _AT ALL_ still surprises me... :roll:

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Re: Sony BVH-2180-PS: Servo Error

Post by PID_Stop » Wed Mar 09, 2016 4:28 pm

I'm increasingly liking the relay as a culprit here. And yes, there probably is a setup procedure for the control track levels... I'll have to research that.

The question about why you can play back video with the DT head even without functional control track is something I can answer, and it gets into the theory of how the servo system behaves: it's quite different depending on which head you are using.

The mission of the BVH-2000's drum servo is to position whichever head tip is relevant at a particular angular position that corresponds to which line the reference video happens to be at. During recording, the R/P tip wants to be exactly pointing to where that line should be on the tape; during playback, the R/P or DT tip will be advanced a few degrees so that the demod video will arrive at the time base corrector roughly in the middle of its memory window (8 lines for NTSC, and 12 lines for PAL, if I remember correctly). In playback mode, servo operation doesn't care which head is selected, except that the servo moves the drum 120° further around its arc to get the DT head in place, compared to the R/P head.

The capstan servo lives to position the tape so that the head tip lines up with the track recorded on the tape. Advancing or delaying the capstan will have the effect of moving the track on the tape with respect to the head. When you're playing with the R/P head, the capstan servo locks to the control track pulses (which have a physical spacing relationship to the video tracks); if you pull the tracking knob and rotate it, you advance or delay the capstan servo, and you will see the playback RF level change as the head tip follows the recorded track more (or less) faithfully. This is actually how most VTRs operate, and is pretty intuitive.

Dynamic tracking ignores the control track altogether; instead, the capstan servo is driven by the trace control system on the DT-04 board. The trace control starts by assuming that the piezo element on which the head is mounted is in its neutral position; a small sine wave called a wobble signal is applied so that the head actually moves back and forth slightly across the track. The system looks at the RF level as the head wobbles, and adds a correction signal to the piezo drive so that the RF is at its maximum between the wobbles. (Imagine walking with your eyes closed along a sidewalk with a noticeable crown: if you purposefully drift from side to side as you walk, you can tell pretty easily where the center is, and self-correct your overall course.) In addition to the feedback from the RF system, the DT-04 also has feedback from the time base corrector that tells the system when it's in the right place. That's particularly relevant during variable speed playback, when the head occasionally has to jump from track to track (for instance, to repeat a given track during slower-than-normal speeds, or to skip tracks during higher-than-normal speeds).

There's more to the dynamic tracking -- we spent a full day on just that one topic during the training class, partly because the DT-04 operates differently during different speed ranges. But the bottom line is that your machine is behaving with the DT play head precisely because it doesn't use the control track at all.

Oh, I guess a caution is in order here: calibrating the DT head (that is, the DT-04 board) is not simple or obvious, and the manual ranges between merely misleading and flat-out-wrong, depending on which edition of the manual you have. It's something you don't need to worry about unless you replace the upper drum, or if there's an out-and-out component failure -- and even then, replacing the failed part generally gets things back where they belong.

-- Jeff

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Re: Sony BVH-2180-PS: Servo Error

Post by DolbySR » Thu Mar 10, 2016 3:41 am

Hi Jeff

Thanks a lot for your explanation! So setting the servo system in Dynamic Tracking mode regenerates the required information about where the individual tracks are positioned on the tape by wobbling the head across the tape and determining which signal has to be applied in order to follow the maximum RF strength or the center of the track most of the time. Amazing. Truly amazing. Given that there isn't a ton of DSP power in this machine at all!

So by looking for the center of the track, it is also possible to set the capstan speed correctly. I assume the head drum will rotate at a fixed speed derived from an internal reference and will command the capstan via the DT system to move the tape so that the tape speed is correct. Is the capstan able to keep up with fast changes in speed? I would imagine that with the idea described by me, the capstan will have to be able to adjust the tape speed rather quickly in order to sync up with the commands from the DT system. It's a massive chunk of motor, that's for sure.

This relay will be checked out very soon. When I picked up the machine, the guy said to me that the machine would not play back tapes from other recorders and that it was "non-standard". I never got what he meant by that as everything works just fine in DT mode. But thinking of that, why does the machine have a "normal" mode at all? When dynamic tracking might be far superior than the normal head servo mode? As a backup?

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Patrick

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Re: Sony BVH-2180-PS: Servo Error

Post by PID_Stop » Thu Mar 10, 2016 10:28 am

Hi Patrick,
DolbySR wrote:So setting the servo system in Dynamic Tracking mode regenerates the required information about where the individual tracks are positioned on the tape by wobbling the head across the tape and determining which signal has to be applied in order to follow the maximum RF strength or the center of the track most of the time. Amazing. Truly amazing. Given that there isn't a ton of DSP power in this machine at all!
Pretty much. One thing to bear in mind is that each video track is narrower than a human hair -- 130 microns -- but it's quite long, about 41cm. Tracks are separated by a 52 micron guard band. What's the point? It takes very little wobble to get the head centered. Chuck Hintz, our Sony instructor, used to say that the level of precision implied by following such a narrow track over such a long distance is comparable to driving a car from New York City to San Francisco without ever touching the steering wheel, and yet staying in the lane.

Your observation about DSP power is interesting: the DT control system, at its essential core, is really analog. There's plenty of digitally derived input, but ultimately most of the comparison and drive work is done with op amps and similar circuitry. That's why alignment is such a chore: you have trimpots to set starting points for different speed ranges, wobble levels, piezo drive shaping and amplitude, and so forth. My Tektronix 2445 scope gets a real workout!
So by looking for the center of the track, it is also possible to set the capstan speed correctly.
Speed is a relatively crude measure; as a practical matter, the motor is pretty well up to speed immediately. The servo system actually thinks more in terms of phase: a phase shift of a few degrees is more useful when you're talking about advancing or retarding the tape position a matter of microns.
I assume the head drum will rotate at a fixed speed derived from an internal reference and will command the capstan via the DT system to move the tape so that the tape speed is correct. Is the capstan able to keep up with fast changes in speed? I would imagine that with the idea described by me, the capstan will have to be able to adjust the tape speed rather quickly in order to sync up with the commands from the DT system. It's a massive chunk of motor, that's for sure.
Since we're dealing with relatively small amounts of phase shift, the actual speed variation is quite small... which is good, because any speed (or phase) change also winds up becoming time base error in the video, which must be corrected. The motors, incidentally, are not traditional DC motors -- they are multi-phase jobs, essentially very smooth steppers. This makes it very easy to control both speed and phase, because both are set by the rate at which the motor drive circuitry changes the drive phase.
When I picked up the machine, the guy said to me that the machine would not play back tapes from other recorders and that it was "non-standard". I never got what he meant by that as everything works just fine in DT mode. But thinking of that, why does the machine have a "normal" mode at all? When dynamic tracking might be far superior than the normal head servo mode? As a backup?
There are several things that will potentially make a type-C machine like this non-standard. Incorrectly set drum phase, incorrect guide position and height, excessive wear on the slant groove on the lower drum, incorrect position of the audio head stack, and so on. It's a rather odd comment, because all of these cause the machine to make non-standard recordings; the whole purpose of the servo system is to be able to play back tapes from a wide number of recorders with varying setup errors.

The purpose behind the 'normal' mode is that it's (usually) the most reliable and highest quality mode. When you deliberately force the playback head off the center of the track, it degrades the RF signal to noise somewhat; also, the dynamic tracking system has a lot more moving parts, both literally and physically. And from a production point of view, if you can't make recordings that are playable with a normal R/P head, there's a serious problem that needs to be corrected before you start sending commercials all over the place (we used to do a lot of commercial production on these machines).

Ahhh... time to go back to the mines.

-- Jeff

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Sony BVH-2000 Tape Motion Timeout Errors

Post by PID_Stop » Tue Mar 21, 2017 7:37 am

I just received a PM from a gentleman in Germany, who posed this question:
I have a BVH 2000 PAL and have a Servo Problem. The machine displays always the red "Servo" lamp on the left. When I insert a tape and press "StandBy" i can play or shuttle the tape for about 15 seconds, then the machine stops and the red "System" lamp goes on and on the RL-12 board a D6 error LED goes on....When playing back I can see an image from the video output, but it is not stable. Do You have any idea what I could do ?
As it happens, I encountered this very problem several months ago... and it's exactly the sort of thing one starts to see with older machines, so I'm adding this to the thread for the benefit of anyone else who might encounter it. It's also very easily and inexpensively fixed.

When the machine is in play, record, jog, or variable speed mode, a solenoid on the right side of the transport pulls the pinch roller down against the capstan; this forces the tape to move according to the speed and position of the capstan servo. If the pinch roller doesn't come down or engage the tape with enough pressure, the tape won't move at the right speed or stay in the correct position compared to the video head, and the servo system will eventually give up and stop the machine.

You can prove whether this is the problem by pulling off the plastic cover over the audio heads and pinch roller; press the PLAY button and press the pinch roller bracket down so that the roller makes good contact with the capstan and tape. If this is the problem, the machine will play without error.

The problem is caused by oil and dirt in the linkage and bearings for the pinch roller. If you have Volume 1 of the manual, take a look at sections 3-18 and 3-19, where it describes how to replace the pinch roller and the solenoid (you aren't really going to be replacing anything, but they show how to take those parts of the linkage apart). Take the assembly apart (carefully -- there are lots of small parts!), and clean everything with isopropyl alcohol. In my case, most of the binding was between the bracket that holds the roller, and the metal post on which it rotates. Once you have cleaned everything and put it back together, you should be able to push the roller bracket down fairly easily, and it will pop back up without being sluggish. You don't necessarily have to take everything apart -- start at the roller end, and work your way through a step at a time until you have fixed whatever is binding.

Two related possible causes for this error: the pinch roller might not be spinning freely (you can generally clean the bearings with alcohol), or the rubber on the roller has deteriorated to the point where it can't grip the tape. If it's the roller surface, you might be able to scrub it enough with alcohol to make it work... otherwise you will need to replace it.

Jeff

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Re: Sony BVH-2180-PS: Servo Error on VHS 2000

Post by MartinKuhnert » Thu Mar 23, 2017 8:24 am

Hallo,
even as the Pinch Roller now moves much better, the machine still stops after 15 seconds of Play or Shuttle or VAR.... The Servo lamp goes on as soon as I press "Standby" and the drum starts to rotate. After 15 seconds the red System lamp goes on and the machine stops. On RL-12 board a D6 error is indicated by a LED. Ref. signal is good and I tried Sync via CVBS and REF inputs to a color bar signal. Has anyone an idea what may cause the problem ? Many thanks!
Martin

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Re: Sony BVH-2180-PS: Servo Error on VHS 2000

Post by PID_Stop » Thu Mar 23, 2017 11:55 am

MartinKuhnert wrote:
Thu Mar 23, 2017 8:24 am
...the machine still stops after 15 seconds of Play or Shuttle or VAR.... The Servo lamp goes on as soon as I press "Standby" and the drum starts to rotate. After 15 seconds the red System lamp goes on and the machine stops. On RL-12 board a D6 error is indicated by a LED.
On the RL-12 board, D6 tells you that the drum servo is not locked. This can be caused by a number of things, so I'll quote from the manual (volume 1, section 4-12-2):
  1. When the tape is stuck around the drum by condensation etc., and if the VTR is placed into the STANDBY ON mode (SERVO alarm lamp will light up), the drum motor will perform drive/release operation 3 times at intervals of about 1 second, and if the tape does not become unstuck, the VTR will go into the error mode.
  2. When the drum servo lock is lost continuously for about 16 seconds.
  3. When the drum rotation decreases less than 80% of normal speed after the drum servo locks.
From what you're describing, it sounds like you're experiencing the second condition.

The drum servo is mostly contained on the CD-17 board; you might try pulling it, making sure all of the chips are fully in their sockets, and replacing the board in its slot. (This is a long shot, but I have had rare cases where this was the problem.) There are several operating modes for the drum servo, depending on whether the machine is in record, play, or some other mode, but it sounds like it might not be seeing feedback from the drum position generator (which tells the servo where the drum is). Here's something to try:
  • Thread a work tape on the machine.
  • Power up the machine.
  • On the front edge of the CD-17 board, you will see three rotary switches; from the top going down, they are S4, S5, and S6. With a small screwdriver, turn the top switch S4 to point toward position "D".
  • Press the little pushbutton below the bottom rotary switch for at least half a second.
  • Press the STANDBY button on the front panel.
The drum should start rotating; you will hear some clicking and several lights will be flashing (don't worry, it's normal for this test mode). Take a look at the LED numeric display on the SV-43 board; it shows you a reading of how fast the system thinks the drum is spinning. It should read "FD", "FE", "FF", "00", "01", or "02". This value typically varies a little bit; touch your finger lightly to the drum's cover, you will should see the reading change. If the servo system isn't seeing feedback from the drum PG (position generator) sensor, the reading won't change at all -- and it might very well give you another error.

If you see evidence that there's no PG feedback coming from the drum to the CD-17 board, and if you have an oscilloscope and an extender board, take a look at the signals on TP12 and TP13 on the CD-17 card. Run the same test mode I just described to turn on the drum motor; you ought to see pulses that vary according to the drum speed. Depending on whether you see the pulses or not, you will need to trace backwards toward the sensors, or forward into the servo logic.

You can get out of the servo test mode by hitting the reset button on the SY-80 board, or by shutting off power to the machine. Don't forget to turn S4 on the CD-17 board back to the "0" position.

Jeff

Edited to correct a typo: the drum speed test needs to have a tape threaded.
Second edit: I forgot to include the step of pressing STANDBY.
Last edited by PID_Stop on Mon Mar 27, 2017 9:17 am, edited 1 time in total.

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Re: Sony BVH-2180-PS: Servo Error

Post by MartinKuhnert » Thu Mar 23, 2017 3:16 pm

Hallo,

many thanks. I tried this out and when I set S4 to D and press the button below, nothing happens. the drum does not start to rotate. When I press "Standby" the drum starts to rotate, On the indicator on SV 43 I can see some changes when I touch the drum..... On the CD 17 board I have, there are no chips in sockets. They are all soldered. I have another CD 17 board here, but it is an NTSC version ( 512 ) and in my machine is a 602 ( PAl ) Board. so with the NTSC board - of course - nothing works...But maybe it is good for spares... Many thanks, martin

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Re: Sony BVH-2180-PS: Servo Error

Post by MartinKuhnert » Fri Mar 24, 2017 5:32 am

Hi Jeff,
as I do not have an extender board, i just soldered cables to the TP12 and TP13 and there are very good pulses visible on the Oscilloscope. So it must be an error on the CD 17 board... Maybe You have an Idea...I checked the board visually and can not see something suspicious. The capacitors look good and all ICs are soldered.

Many thanks, Martin

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Re: Sony BVH-2180-PS: Servo Error

Post by PID_Stop » Mon Mar 27, 2017 9:31 am

Good morning Martin,

I double-checked the test procedure on the machine in the control room, and discovered that I forgot a step: after you set the test mode ("D 0 0") and press the test button on the CD-17 board, you need to press the STANDBY button on the front panel. Then you can take a look at the 7-segment LEDs on the SV-43 board. The thing I'm wondering is whether the drum speed is far enough off standard that the servo system is seeing it as an error, and shutting it down. There's an adjustment on the CD-17 board for this, but you need the extender board to make adjustment practical. With this test mode enabled and the system in STANDBY mode (drum spinning), adjust RV4 so that the LED display reads FD, FE, FF, 00, 01, or 02 (shoot for FF or 00). It's a pretty fine adjustment, and a very small change in the trimpot setting will make a fairly big difference in the reading you get. There are several revisions of the CD-17 board, but in each case RV4 is about halfway back, and about two centimeters from the top edge. (Don't accidentally grab RV1, which is just above it -- that's the free-run speed for the capstan!)

Another test you can run on the drum is "5 D 0". Make sure there is no tape threaded, select that test code, and press the CD-17 test button. That will spin the drum at its free-run rate, and it's pretty handy if you want to do extensive testing without having a tape threaded.

Jeff

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Re: Sony BVH-2180-PS: Servo Error

Post by MartinKuhnert » Wed Mar 29, 2017 9:49 am

Hi Jeff,
many thanks, now I tried this test. When press the button below the switches on CD-17 and then Standby, the drum starts to rotate but makes a clickering sound... clac clac clac.... about 3 to 4 times per second. this sound is not there in normal operation mode ( 000 instead of D00 ) In D00 and with drum rotating: On the SV 43 board the numbers change so fast ( i assume between 00 and FF ) that I can not read them. I changed the value of V 4 4 turns clockwise and then 8 torns the other way round... ) but nothing seems to change...
Many thanks, Martin

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Re: Sony BVH-2180-PS: Servo Error

Post by PID_Stop » Wed Mar 29, 2017 10:17 am

MartinKuhnert wrote:
Wed Mar 29, 2017 9:49 am
Hi Jeff,
many thanks, now I tried this test. When press the button below the switches on CD-17 and then Standby, the drum starts to rotate but makes a clickering sound... clac clac clac.... about 3 to 4 times per second. this sound is not there in normal operation mode ( 000 instead of D00 ) In D00 and with drum rotating: On the SV 43 board the numbers change so fast ( i assume between 00 and FF ) that I can not read them. I changed the value of V 4 4 turns clockwise and then 8 torns the other way round... ) but nothing seems to change...
Many thanks, Martin
The clicking noise is normal for that particular test mode. Even if the drum speed is right on the edge between FF and 00, you should still be able to read it. Sounds to me like the drive system for the drum motor isn't obeying the servo feedback, and essentially running the drum at a random speed -- which would absolutely cause the shutdown and error. Since you are seeing good pulses coming from the two position generator sensors (they're 90° apart, by the way, which is how the servo system can infer not only the speed but the angular position of the drum), it seems likely that the problem is later in the circuit. It's also possible that the necessary reference-derived signals aren't getting where they need to be on the CD-17 board.

This is going to take some serious troubleshooting, and you will really need to have both volume 1 (with the testing and calibration instructions) and volume 2 (with the schematics), plus an extender board.

I am a bit puzzled about which trimpot you changed: RV4 is a single-turn pot, and is very touchy.

Jeff

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Re: Sony BVH-2180-PS: Servo Error

Post by MartinKuhnert » Thu Mar 30, 2017 12:34 am

Hallo,
thanks a lot, the RV4 I changed has only one screw and I simply tried to change it in one direction to see if anything happens and than in te other direction... So the letters and numbers on the SV 43 are changeing really fast, no chance to read them. I will see if I can get the manuals... I found Vol. 2 as a download, but not yet Vol.1.... will see if can find it anywhere.

Thanks, Martin

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