VCR 1981 Ferguson 3V23 - VHS

Hi Chris, you don't need to take the cassette loading tray out, but that is fairly straight forward, it was just a photo looking under the cassette carriage to remind me what mechanism it was. Nothing fancy or detailed. I think you will find most of your faults are rubber related. Excellent having the training manual, was handy as in my case as machines would appear from other from other "engineers" where they had tweaked everything and undone things, they should ask first. In the Broadcast Environment I have had to set things up that would never normally need attention due to little understanding of what they were doing and not willing to learn. On the VHS front I could never understand why an engineer called to a fault would tweak the tape guides and a few pots thinking it would fix a problem? I have a story to tell about a VHS that had no colour playback, just good monochrome. It was two hours before I found the problem, story for another day.

Posted by: @hurty

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it was just a photo looking under the cassette carriage to remind me what mechanism it was

Here you go.

That is fine Chris. The machine looks very clean and low mirage. I would take the idler and the two reel table rubbers off and clean them with a bit of fine grain sandpaper to bring them back to a nice matt shine, not to hard and see what happens. There used to be a clear service cassette housing you could buy which allowed you to see what was going on under the cassette.

Update to this thread.

Moved this post from the capstan wanted thread.

This should leave folk with no doubt as to the problem the 3V23 has.

I somehow knew this would be the symptom, I remember it from way back but can't remember what caused it (what a silly old fool!). The 3V23 has a very complicated processing circuit whereby sound appears "normal" in search facility, but speeded up so to speak (I think it was the 3V23). Naffin' things!

Capstan motor is a darned good place to start though.

Good luck Chris, a motor is on its way.

Mick.

@mickmcmichael That was the BBD bucket brigade device. This corrected the audio pitch digitally when playing back at X2 so the audio didn’t sound like Pinky & Perky.

I think it was some Sanyo models which could give intelligible audio in search and snippets of audio in FF.

Posted by: @crustytv

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This should leave folk with no doubt as to the problem the 3V23 has.

It's full of Aquaphibians?

I received the 3V22 capstan motor from Mick today, installed it and I have exactly the same condition. Highly improbable, both capstans are faulty. It would seem I have a circuit fault.

Back to the drawing board, at least we now know.

That’s disappointing, I’m not really sure where to start here. For all it’s complexity in normal service life thankfully the electronics gave very little trouble. Need to put my thinking cap on.

If there's a servo loop controlling the motor (which I expect there is), I'd be looking at small electrolytics in the loop filter - it sounds like the servo is chasing its own tail. Long shot, but could you temporarily feed the capstan motor from a bench PSU just to see if the wobbly audio disappears?

The only other time I've heard "watery" audio was when a pinch roller was very much the worse for wear.

I look at the servo block diagram and die inside ....... 😲 

Well, as a first point I'd look at pin 7 of IC13 and I'd hope you'd see a smooth DC level there - similarly, on the pins feeding the motor itself. If it's all wibbly-wobbly, I'd just have a quick peek at C39 and C40, which are part of the aforementioned loop filter.

What does the manual suggest? As I said, a drastic one would be to measure the volts across the motor whilst playing and then substitute a bench PSU. You'll most likely not get locked pictures but if the audio sounds okay, it does point to the servo.

And yep, that's one of the scariest servos I've ever seen but as any electrical engineering graduate will tell you, servo theory is utterly evil - AC servos doubly so.

There's a bit more going on there than just a servo or two but at least you can see far enough into it to work out what is happening. Largely because it replaces much of the complexity of gears, cams, pulleys and belts that would previously been in there. Most of the complexity of this design (which has to allow for safe tape handling) was subsequently replaced with software, so count yourself fortunate!

Having just recently designed a test jig for the factory where my boss said "Do NOT use an Arduino!" and so having to revive my long-dormant discrete logic design skills, I find it quite interesting!

Posted by: @cathovisor

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Well, as a first point I'd look at pin 7 of IC13 and I'd hope you'd see a smooth DC level there - similarly, on the pins feeding the motor itself. If it's all wibbly-wobbly, I'd just have a quick peek at C39 and C40, which are part of the aforementioned loop filter.

What does the manual suggest? As I said, a drastic one would be to measure the volts across the motor whilst playing and then substitute a bench PSU. You'll most likely not get locked pictures but if the audio sounds okay, it does point to the servo.

Thanks, Mike, that at least gets me to the starting block, I'll try these suggestions later this morning. 👍 

To familiarise myself with the landscape, I located the appropriate section in the manual, it's the Tuner & Timer PCB. I have located IC13-7 on the diagram which appear to expect 5.1V, and found all the components in the "Loop Filter" except C40. Either I have been staring at the diagram too long and have now developed PCB blindness, or it's a revision deletion, or like the recent Sharp TV, it's located elsewhere. I seriously doubt the latter and expect that I'm just not seeing it.

Anyone else care to have a look, here is the snippet from the data.

Remember to view the above image at full size, click on the thumbnail, then right click and open in new tab, then use the mouse (+/-) to zoom in/out.

I've uploaded the entire manual to our data library if anyone wishes to look deeper.

Well, that PCB layout diagram bears no resemblance to my physical layout. Looking at the board I instantly found R77 (1M), R78 (27K), C39 & C40 all within the vicinity of IC13. Both C39 & C40 are 10uF 16V tants, both in-circuit measure 21uF and have good ESR of around 2R.

Be careful, all PCB component references start at IC 1, C1 etc. You need to look carefully at the board you are working on, the layout for Servo 1 which contains most of the capstan servo circuitry is on page 8-17. Might be worth hooking a scope to look at the DC drive to the motor and see what the frequency of ripple is if there is any? Connect across pins 81 & 82 of the servo-1 PCB.

OK, I had the correct physical board but the incorrect PCB diagram, makes sense now.

Posted by: @cathovisor

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And yep, that's one of the scariest servos I've ever seen 

That makes me feel so much better. Vast majority of faults were usually just motor drive bridges.

With tape running, IC13 pin7 has 7.4V on it, should be 5.1V. The scope shows the DC pulsing up and down, see video below. The million-pound question is why? I guess that's the cause of the watery audio

Posted by: @jayceebee

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Connect across pins 81 & 82 of the servo-1 PCB.

Meter shows 7.9V across this