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Old 13th Jan 2019, 8:32 pm   #1
JamieEC
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Default Ferguson 3V29 Alignment/Interference issues

I posted a while ago on here regarding my 3V29. The tape path was out of alignment. I have tried with/without a scope, using several different tapes, and cannot get this to align correctly. The trace on the scope is all over the place. The only adjustments that have been messed with are the 2 tape guides that look like this -O-
I manage to get it close to alignment, but then I put in a different tape and its off by a way.
Heads have been cleaned. Is there a chance it could be bad? Or there is another mechanical/electrical issue other than alignment?

Any advice would be appreciated.

Jamie
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Old 13th Jan 2019, 10:59 pm   #2
rambo1152
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Default Re: Ferguson 3V29 Alignment/Interference issues

First and foremost, does the machine play back its own recordings OK?

I assume your drum and capstan servos are locked, back-tension looks about right and everything is clean.

I'll let you into the way I did alignment in the field with no test equipment whatsoever except a pre-recorded tape that I trusted was accurate.

You won't see this in any service manual

Instead of concentrating in getting uniform FM carrier off the tape, endeavour to get uniform noise.
Adjust the tracking control for maximum noise, if there is insufficient range, move the control head laterally with the adjustment cone.

Adjust the L & R inclined guides for uniform noise. Don't make the mistake of having both guides too high so you are reading the track above, the tape should be sitting on the ledge of the lower drum.
When you have it right you should be able to adjust the tracking control too and fro and see the picture emerging uniformly from the noise with no banding. If you see narrow bands that walk up and down the screen with the tracking control, you are way out.

Of course, then you'll want to look at the FM envelope on the scope and admire what a good job you did.
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Last edited by rambo1152; 13th Jan 2019 at 11:09 pm.
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Old 13th Jan 2019, 11:08 pm   #3
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Default Re: Ferguson 3V29 Alignment/Interference issues

You are a fox that used to be Professor of Cunning at Oxford University but was appointed to the United Nations as High Commissioner for Cunning, and I claim my five pounds!

Did you discover that in practice, or do a bunch of scary maths?
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Old 13th Jan 2019, 11:21 pm   #4
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Default Re: Ferguson 3V29 Alignment/Interference issues

No, I rather expected to be castigated (ooh er missus), by a proper Engineer such as your good self, for adopting such an empirical method.
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Old 14th Jan 2019, 1:30 pm   #5
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Default Re: Ferguson 3V29 Alignment/Interference issues

Quick and dirty alignment method:

Make sure that the upper and lower drums are clean and that none of the guides or poles are bent. Then adjust the entrance guide (left hand side) downwards until you just see the edge of the tape begin to curl on the beginning of the rabbet (the inclined ramp machined into the bottom of the lower drum). Shining a small light across the tape will help you see the onset of the curl. Then adjust the guide upwards until the 'curl' disappears. Do the same for the exit guide at the point where the tape leaves the rabbet. I've used this method many times for 'record only' decks (e.g. Sony CCD-M8) with 100% success.

If a known good tape then plays almost correctly but with poor frame sync, adjust the entrance guide upwards slightly until the sync locks. If you still can't get good results the upper drum may be faulty of the lower drum worn, but check things like the back tension (not a traditional 3V29 weakness) and the impedance roller (next to the full erase head) first. The impedance roller falling apart was a common problem with the Hitachi VTRs before the VT-11.

You can also play a known good tape and adjust the azimuth of the audio / control head for the sharpest sound, that should ensure that the control track is being read properly. If this is miles out, check that the pinch roller hasn't gone barrel-shaped or that its bracket isn't bent.
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Old 14th Jan 2019, 7:28 pm   #6
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Default Re: Ferguson 3V29 Alignment/Interference issues

Quote:
Originally Posted by Studio263 View Post
The impedance roller falling apart was a common problem with the Hitachi VTRs before the VT-11.

Yes I had almost forgotten about that design feature!
The brass impedance roller was carried on a plastic insert shaped like a bobbin.
In hot weather (I suppose) the brass would expand and pop off one or other of the "cheeks" of the bobbin. It was a 50/50 chance, but if it was the top cheek it had no impact on operation unless you warned to operate the machine on its side or upside down(!) If you noticed the shim of plastic on the roller when servicing you cut it with snips and removed it.

If the lower cheek cracked then the brass roller dropped so it was only in contact with half the width of the tape and the lose plastic shim/cheek fouled the rollers' rotation. The cure for that was simple, I think we simply turned the bobbin over so the intact cheek was at the bottom. If not, a strategically applied blob of RS adhesive would have cured it.

Sounds like a bodge, but replacing the assembly with a new one just risked a repeat performance.
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Last edited by rambo1152; 14th Jan 2019 at 7:57 pm.
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Old 15th Jan 2019, 10:22 pm   #7
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Default Re: Ferguson 3V29 Alignment/Interference issues

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Originally Posted by rambo1152 View Post
No, I rather expected to be castigated (ooh er missus), by a proper Engineer such as your good self, for adopting such an empirical method.
No, I think it's sound engineering practice! Well, there's a bit of psychology in there too -- the cunning part is making sure the psychology is working in our favour. You say "adjust for maximum noise", but what you are inevitably actually going to be doing is adjusting for maximum (signal plus noise).

Noise is just noise, with no structure to it. It just looks like noise. It will always have exactly as much light as dark in it, no matter how much gain you apply, because that is the nature of the beast: there is exactly as much energy above the line as below, and the average over time is zero. Noise riding on an actual signal looks worse than just noise, because there are still some discernible fragments of structure in it; and these are perceived subjectively worse than just random, structureless noise. So when the noise is as bad as you can get it, that means there must be a good strong signal lurking somewhere nearby. You are basically making the target for your initial search easier to hit -- it's easier to get it right once it's already nearly right, and a broken-up picture with lots of noise on it is more nearly right than just noise.

It's like the old joke about the physicist, the engineer and the mathematician who are all staying in a hotel one night, when a fire breaks out in each of their rooms. Each of them wakes when the smoke alarms sound. The physicist does some quick calculations involving enthalpy of combustion, specific heat capacity and latent heat; then pours on exactly enough water to extinguish the flames, yet have every drop of it evaporate from the residual heat. The engineer keeps pouring on water until the fire is out; then pours on twice as much again, just to make sure. The mathematician yawns, notes that this is identical to a previously-solved problem, and leaves it as an exercise for the reader .....
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Old 16th Jan 2019, 4:18 pm   #8
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Default Re: Ferguson 3V29 Alignment/Interference issues

I have used the method posted by Studio263 with success, especially useful when the customer had been twiddling first!
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Old 16th Jan 2019, 7:53 pm   #9
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Default Re: Ferguson 3V29 Alignment/Interference issues

In fact Tim's 'quick and dirty' method often produced better results than the 'correct' method, especially on a well-worn machine.
To get back to the OP, I'd check the guides are going home - it's possible for one to be one tooth out and not fit snugly into the V-block. Also, if someone's been there before you then who knows what's been twiddled or broken, so maybe back tension issues might not be so far fetched.
Now Tim, you surely wouldn't align a B&O like that, would you?!
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Old 17th Jan 2019, 10:25 am   #10
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Default Re: Ferguson 3V29 Alignment/Interference issues

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Originally Posted by Welsh Anorak View Post
Now Tim, you surely wouldn't align a B&O like that, would you?!
With the Beocord VHS82 and VHS82.2 (Philips DMP deck) you sometimes had to!
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Old 17th Jan 2019, 3:15 pm   #11
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Default Re: Ferguson 3V29 Alignment/Interference issues

We still don't know if this deck plays back its own recordings OK. As rambo1152 correctly suggested this is essential info.

I once had a similar problem with a Fisher unit. Turned out the plastic tracks for the roller arms had fractured and occasionally impeded the travel fully home into the V blocks. Ended up scrapping it as it was past its use by date by then anyway.

Another time I read about an impossible to align deck. Turned out someone had replaced the whole drum beforehand, when it was again removed it was resting on a splash of solder, so it wasn't sitting true to the chassis! Another I wrestled with in the end had a bent chassis, I think that was a 1990s Daewoo. As you can see, it can be hard if you don't know the units history!
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Old 18th Jan 2019, 12:03 am   #12
JamieEC
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Default Re: Ferguson 3V29 Alignment/Interference issues

Thanks for the advice/responses, will try out this weekend and get back to you
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Old 18th Jan 2019, 9:56 am   #13
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Default Re: Ferguson 3V29 Alignment/Interference issues

Quote:
Originally Posted by Welsh Anorak View Post
In fact Tim's 'quick and dirty' method often produced better results than the 'correct' method, especially on a well-worn machine.
To get back to the OP, I'd check the guides are going home - it's possible for one to be one tooth out and not fit snugly into the V-block. Also, if someone's been there before you then who knows what's been twiddled or broken, so maybe back tension issues might not be so far fetched.
Now Tim, you surely wouldn't align a B&O like that, would you?!
I've had congealed grease prevent one (or both) of the guides settling into the V-blocks. It led me a merry dance for a while!
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Old 19th Jan 2019, 9:04 pm   #14
JamieEC
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Default Re: Ferguson 3V29 Alignment/Interference issues

Quote:
Originally Posted by rambo1152 View Post
Instead of concentrating in getting uniform FM carrier off the tape, endeavour to get uniform noise.
Adjust the tracking control for maximum noise, if there is insufficient range, move the control head laterally with the adjustment cone.

Adjust the L & R inclined guides for uniform noise. Don't make the mistake of having both guides too high so you are reading the track above, the tape should be sitting on the ledge of the lower drum.
When you have it right you should be able to adjust the tracking control too and fro and see the picture emerging uniformly from the noise with no banding. If you see narrow bands that walk up and down the screen with the tracking control, you are way out.

Of course, then you'll want to look at the FM envelope on the scope and admire what a good job you did.
I have tried this, however when I adjust the tracking the noise bar doesnt disappear completely. Also, different tapes still don't play correctly. It does appear to play back its own recordings perfectly. It also appears to sometimes slip of its path between the pinch roller/capstan and audio head sometimes. Thanks for all the responses.
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Old 24th Jan 2019, 10:09 pm   #15
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Default Re: Ferguson 3V29 Alignment/Interference issues

Quote:
Originally Posted by JamieEC View Post
It does appear to play back its own recordings perfectly.
OK that's what we needed to hear.

Note that if you alter the tracking in extremis , you shouldn't see any noise bands when you play back its own recordings, your goal is to achieve that with your trusted reference tape.

If you are seeing defined noise bars that move up and down with the tracking control, the track angle is still incorrect.
Follow the method described Studio263 to get it as correct as possible, the technique I described is really for a final confirmation, and possible tweak.
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Old 8th Feb 2019, 9:02 pm   #16
JamieEC
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Default Re: Ferguson 3V29 Alignment/Interference issues

I will look at this this weekend,
some tapes seem to move up and down on the pinch roller.

I have only adjusted the guides, not the angle of any heads. There arent any noise bars that move, but they appear and (almost!) dissapear. I have to have the control to the extreme on one side.

Any advice on what to check is appreciated
Thanks for all your help
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Old 9th Feb 2019, 12:52 am   #17
rambo1152
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Default Re: Ferguson 3V29 Alignment/Interference issues

Quote:
Originally Posted by JamieEC View Post
I will look at this this weekend,
some tapes seem to move up and down on the pinch roller.

I have only adjusted the guides, not the angle of any heads. There arent any noise bars that move, but they appear and (almost!) dissapear. I have to have the control to the extreme on one side.

Any advice on what to check is appreciated
Thanks for all your help
It isn't possible to adjust the angle of the head-drum.

The adjustment of the two inclined guides relative to each other has the same effect.

The azimuth of the audio/control head is important, but it only affects the treble sound reproduction, not the picture.
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Last edited by rambo1152; 9th Feb 2019 at 12:59 am.
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