VCR 1981 Ferguson 3V23 - VHS

Posted by: @jayceebee

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I wonder if that sine wave ripple is the same frequency as the capstan FG? 

Looking closer and thinking about it I see one cycle appears to be about 80mS which equates to 12.5 Hz so far too be low to be related to the FG signal. Half the value of the control pulses but doesn't help me much.

@jayceebee Out of interest, what does your Cap FG amp out look like?

Mine again is not stable, it constantly fluctuates between 212Hz and 238.4Hz siting around 3Vpk-pk. The book has it at 225Hz at 3.5Vpk-pk

Now that's interesting, if we are talking about TP4 mine is 8V in amplitude and clipped. It's stable because my motor is stable, you see it's generated by the rotation of the motor and used to generate a speed reference voltage. There is a PCB coil under the capstan flywheel and a magnet attached to said flywheel that generates the FG, that's the problem with servos and feedback loops.

8V! How come yours is so high? The waveform in the manual states 3.5V. The more I deep dive into this VCR, the less I understand, and I wasn't at a good level to start with!

Don't fret about it, I'm struggling to unravel this also. I've just tried an experiment and shorted out the FG coil and there was virtually no effect so possibly the FG is only being used in record mode? With later machines and digital servos remove the FG and the capstan would go at full tilt. Unfortunately there is precious little about the capstan servo operation in the manual, it does say that it was covered in other models but which? I can only think of the 3V16 which I don't have a manual for. Certainly wasn't the 3292/3V00/3V22

Posted by: @jayceebee

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I can only think of the 3V16 which I don't have a manual for

You do now, I've just uploaded it to the Vrat temp library. 👍 

@jayceebee John, out of interest, how does your 3V23 Cap motor +in (TP14) and -in (TP15) compare to the expected on the circuit? Again, mine are as expected wildly off.

Yellow is TP14 motor +in
Purple is TP15 motor -in

Am I to assume the level of noise I have (TP15) is due to the mysterious sine wave? The level of noise here is supposed to be 18mV, I have 160mV.

Noise level at TP15 is barely measurable but my motor seems to need a little higher voltage to run at the correct speed @ 5.4V DC.

I wonder if I'm clutching at straws here, well, I'm at that stage now.

The replacement capstan motor I tried was kindly provide by @mickmcmichael and was a pull from a 3V22 spares machine. When I tested it in the 3V23, I pretty much had the same poor results.

Since then, another member @unit-no-16 has sent me a NOS 3V00. Now, one interesting observation, I've noted, and I've no idea if it means anything, is that if I manually spin the shaft on this NOS 3V00 motor, it carries the spinning momentum for a good few seconds. However, If I try the same action with the 3V22 one, it just stops dead in a fraction of a second.

I can't recall the exact data, but perhaps as capstan motors are recommended to be replaced every XXX - hours, then this type of wear is perhaps one of the reasons, and I should try this free running 3V00 motor.

I did say I was clutching at straws

It's worth a try Chris.  JVC/Ferguson did issue service / overhaul instructions to replace after so many hours for a lot of parts. Other manufacturers didn't issue routine replacement of parts at certain hours you just repaired and serviced as necessary when they failed. 

When we overhauled a VCR we would replace clutches, idlers and belts as a matter of course, but motors, heads etc were only replaced as needed. You could try running both motors from a bench supply and see if the current drawn is different that may indicate wear or tight/dry bearings. 

On later machines with large direct drive capstan motors it was possible to sometimes solve a problem with a touch of light oil on the bearings. This was strictly forbidden according to the manufacturer, you were supposed to replace the motor but often this would mean the machine was borderline beyond economic repair so there was nothing to lose by trying.    

The spin test was something I used with good effect on the pancake type motors used on the FV1x/2x series before brushless became common. A good motor would normally give you several rotations a bad on not even one so go for it. It wasn't due a seizure of the bearing as you could rotate it slowly no problem, give it a fast twist and you could feel it pushing back. Never did dismantle one to see how they were constructed and possible cause, that motor is certainly suspect.

I just removed (I had refitted it) the original 3V23 capstan motor, the one with the brass pulley, that spins nice and freely too, it's just the 3V22 replacement one that stops dead. I'll try the 3V00, but I think it's wishful thinking on my part and it will give the same results, warbled audio. Back in 10mins

Yep, exact same fault, so it is without a doubt some circuit fault. OH well, I think for now the cover is going back on as this complex VCR is more than a little complicated for me.

p.s.

One thing that strikes me odd is the warble with the original capstan installed is far worse than with the new old stock 3V00 capstan, which makes things even more bizarre.

p.p.s

@jayceebee you wondered why none of the controls over on the clock side functioned, I wonder if this has something to do with it? Under the display PCB is the battery backup PCB. I snipped it out before putting the case back on, but I think it had done all the damage it wanted already.

Hi Guys, what are your thought on this. I've been in contact with an ex engineer regarding the garbled audio, here are his thoughts on my fault.

As to the garbled 3V23 sound playback..... if the picture is as mentioned without any error or " issue " ( I do hate this modern phrase ! ) then my initial thought is that if the tape speed is both correct and stable enough to deliver a perfect picture image, then , I am wary that you believe there is a serious electronic error in a sound servo. We must consider that the physical off-tape sound reproduction is akin to a good old Phillips cassette tape, plus our human ears are very sensitive to speed fluctuation causing Micky mouse speech.  You mentioned that you have made a complete swap-out of the belts and I expect the other rubber friction drive parts. I recall there is, was, an often and nasty case of servos chasing their own tail because the 3V23 had received a new set of drive belts. It was a really silly case where the natural resonant frequency of the new and " twangy " drive belts was just about the same as the tracking feedback resonance of the relevant servo loop.  The usual solution was to replace the new belt with a visually identical belt but from a different supplier, which usually made a quick and workable repair. Of course these days how one obtains genuine JVC or Akai drive belts instead of the troublesome " after market " belts is a very good question.  The actual servo loops themselves were double function loops, the first ( outer  )  target of the loop was to achieve the correct frequency of the specific " frequency generator"  slotted disk, then once frequency lock was closed then the control logic switched over to an inner phase lock system. So with an over excitable rubber drive belt with a resonance close to that of the tracking loop, the result is more or less as you have described. John

• This any help??
  

  

   

Hi Michael, I don't think so.

I wouldn't describe the fault as "noisy" or having problems with playback of own recordings. The fault is on sound only and on any type, be it off-air or pre-recorded tape. The previous page of this thread has an uploaded video that clearly demonstrates the audio fault, and a few posts down a waveform capture showing the expected signal riding an unexpected sine wave.