Hi,

most of the the older VX7000 decks have a problem with the fast rewind function of the tape.

They were specified for a really fast rewind of the tape, but reality is that the tape sometimes seem to be stuck in the recorder, it does not rewind. Sometime the tape really stops, starts to rewind a little bit, stops again, and then rewinds very slow.

Is this defect known and the reason for it?

Martin  

Hi Martin

I have always believed that you were the expert with these machines and that one day you would reveal the solution to this irritating problem.  It certainly seems to be a wide spread issue and I know that my VX7000 suffers from exactly the same symptoms as yours.  Pity because it works so well from other respects and has many useful features.  I really hope that this thread will throw some light on the problem and I wish you luck with your endeavours.

Regards

Geoff

Hi Geoff,

the VX series is really well known to me, but this bug is still mysterious. It is a bug in the system software.

What i definitly know:

- the voltage for the capstan motor is controlled by software, it is not simply a stabilized power of 13,5V, it is regulated by a pulse-width signal from the cpu to a 4V -13,5V supply according to the function it does. Playback ~ 8,5V, Rewind from 4-13,5V

- the torque of the capstan is also controlled by a pulse-width signal of the cpu, also according to the function.

- and there is a cpu controlled tacho unit of the capstan motor.

- there is also a tacho pickup reel of the tape

- and it has a brake function on the capstan

If i change the power supply to stable 13,5V, the capstan chip controller overheats during playback, but rewinds like hell, veeeeeery fast and stays cool. Surprisingly  it starts rewind with 13,5V and then becomes lower and lower and lower... and then the motor stops. The motor has a tacho unit and when the speed is not enough, it rises the power supply voltage. The torque of the motor becomes lowered.

The next bug is, that it lowers also the torque during the wrong rewind feature. If i change the torque signal manually, the motor becomes stronger or weaker, but this affects also playback, the tension of the tape becomes to strong and it showas up in the picture.

It is a bug in the cpu program, but why does it show up in older VX7000? I have replaced 100% of all caps, not just in this one VX7000, i have dozens of these units and all of them show this bug. But not when they were new.

It was reported, that there could be noise on the 3-state switch unit. I checked it, there is no noise, i also filtered the switch with caps additionally... absolutely no effect, the bug is still there. 

I think, there is a bug in the rewind software section. The VX thinks, that the tape end is near an lowers the speed. This would be logical... but the tape end is far away.

It stays a mystery...

All of this information is very interesting Martin - you certainly go into everything in a lot of detail - way further than my skills would take me.

I was particularly interested in your last line comment.  I have always thought that the slowing down process was simply taking place far too early and that the time indication clock was either wrong or being misinterpreted.  Since the initial winding speed was OK there didn't appear to be anything wrong with the motor or drive mechanics so it seemed logical to me that the slowdown point was simply wrong.  The situation did seem to get worse if one was ejecting and loading part wound tapes or if one switched from full video speed to half audio speed.  In those situations the clock always seemed to get confused.  I was also concerned that the machine didn't have the correct information on the tape length as I was always switching from tapes with 2,3 or 4 hours running time.  This might have been messing around with the clock logic.

I played around with these thoughts for quite a while but nothing seemed to be consistent or make sense.  Eventually, I gave up when digital recording came along and never looked back.  As you say, it remains a mystery.

Thanks for your ideas

Regards

Geoff

This was indeed a common problem with these otherwise super machines.You are on the right track Martin,it is due to noise confusing the computer.The culprits are the reflective strobe markings under each turntable,NOT the ir sensors.Replace the two turntables with new ones(if still available?)Trust me,this will sort the problem.

Regards,

Nick

Hi Nick,

this solved the problem a little bit, it became better. Under each of these two pickup wheels is a silver/black tacho wheel unit for the led speed detection.

These reflectors of the tacho unit become dirty, there is really dusty smoke on it. I cleaned it and the rewind problem is better. This would point also to noise on cpu controls.

But the tape still stops one time on fast forward at ~90% position and during fast rewind at ~ 10%.

Looks still like a software bug for the rewind/fast-forward program.

Martin

You need to replace the turntables Martin.Its something to do with pitting of the chrome type coating on plastic.I've looked at them under a magnifying glass,and can't see the problem,but new ones do the trick!This was a factory recommendation.The tape will slow down towards the ends,this is the clever design to prevent tape breakage.B&O used to tell us to time the wind/rewind,and if it was within spec-it was "good enough"

Clever design,all credit to Hitachi of course,but with B&O refinement.Apparently they were so expensive to get made,that B&O made no profit from them!!

Regards,

Nick

Regards,

Nick

Hi

Nick and Martin are clearly the experts on the VX7000 video machine and from this thread it does seem that one can expect an improvement in fast winding performance if these turntable parts are cleaned properly.  My question is, can this job be carried out fairly easily and what is involved.  A good set of brief instructions from the experts would be a great help, provided that this task is no too involved. 

Thanks for your help

Regards

Geoff

I've never had much luck cleaning the discs Geoff,you have to replace them in my experience.They may not be available any more as new spares now though.

B&O used the same idea to time the door sequence in the Beocentre 9300,and that was problematic too!!

Might be worth asking your nearest Dealer to check if the parts are still available.

Part No's 2726166 (supply reel)

               2726171 (take up reel)

Quite straightforward to replace,just remove the machine top case,then the cassette carriage assembly.The turntables are held to their spindles by small circlips.

Regards,

Nick

Thanks Nick

I will make some enquiries regarding the availability of these parts next week but given my luck in the past, I am not that hopeful.

It does sound as if it is not too difficult to clean these reels so I will probably do that in any case.  Any improvement at all will be a step in the right direction.

Thanks again

Geoff