Ferguson 3V48 - picky with pinch rollers

[ben]

'...worked hard every day for 27 years'?!!

All bets off re: head wear as far as I'm concerned!

[AidanLunn]

Originally Posted by ben

'...worked hard every day for 27 years'?!!

All bets off re: head wear as far as I'm concerned!

Well, this is the thing, the head wear (if it is that) has been so rapid over the past few weeks that the picture has gone from perfect, to unplayable on other machines' recordings, and this started a good few days after the shampoo incident.

I must stress that it plays back all its' own recordings fine, so it seems to be a gradually emerging problem with tracking in to other machines recordings, to the point where it really struggles to track in correctly.

I have heard of refusal to play back other machines recordings related to board component issues, but surely these are instantaneous rather than gradual?

Without looking, I'm placing my bets on either the pinch roller or mechanical wear, as surely it wouldn't play back its own recordings fine if it was head wear? Or is that totally wrong (aka is it possible that a machine with worn heads can play back only its own recordings fine?)?

[ben]

The heads are borderline. I've found that the onset of compatibility problems /tracking errors on other tapes is common in this scenario. It plays back its own Ok as the tape path is an exact match of the tape. The minute there's some deviation, such as with another tape, it cannot handle it and breaks up the audio etc.

[AidanLunn]

Looking at replacement head drums on CHS, the originals are way past my budget, but there are things listed as "VIDEO HEAD UPPER ALT" - I presume "alt" means "alternative", meaning "pattern part".

http://www.chsinteractive.co.uk/manu...ferguson/3V48/

I take it it would be OK to at least try adjusting the back tension and tape guides, as reading about the effects of these, these sound exactly the same as what I am getting? I did report a few weeks ago that originally the supply guide was slow to react when unloading. I am saying this with the greatest of respect to your knowledge and experience and I am putting your diagnosis in front of my own diagnoses.

*If I can't get my hands on any kind of professional alignment tape, I'd have to try and align from a recording on a known good domestic machine.

[ben]

You could do with a tentelometer to check things are in spec. I think gezza had one for sale not so long ago.

A full tape path realignment - roller guides, A/c head, take up torque and and backtension etc. would be worth a try before ordering heads, but only if you have a new genuine pinch roller installed, so as not to confuse the results /to rule that out.

I have some detailed notes on how to perform this setup without a scope, PM me your email if you'd like a scan.

I do think though, you're clutching at straws a bit, given the age and probable wear now involved. Don't think I'm trying to put you off, but one has to be realistic.

[AidanLunn]

Originally Posted by ben

You could do with a tentelometer to check things are in spec. I think gezza had one for sale not so long ago.

A full tape path realignment - roller guides, A/c head, take up torque and and backtension etc. would be worth a try before ordering heads, but only if you have a new genuine pinch roller installed, so as not to confuse the results /to rule that out.

I have some detailed notes on how to perform this setup without a scope, PM me your email if you'd like a scan.

I do think though, you're clutching at straws a bit, given the age and probable wear now involved. Don't think I'm trying to put you off, but one has to be realistic.

It was Donberg's lack of information regarding their pinch rollers for these decks that led me to believe that they were genuine JVC parts - the 3V48 however, totally disagreed.

Thanks, Ben, I'll look for the tentelometer. I do have a scope, but I haven't used it yet and I'd like to get around to learning how to use it. Would a 20MHz one do (Hitachi), as this one is working (my Gould 25MHz one, is as dead as a Dodo for now)?

[AidanLunn]

Hello all.

This is the first time I've ever used an oscilloscope, it's a Hitachi 20MHz dual-trace scope from around 1990.

For testing of the entry and exit guide waveforms, I connected channel 1 trace to the PB FM test point, and the trigger to the flip-flop test point - there was just two flat lines on the scope. Ext triggering was obviously selected, and the various time divisions were tried, all to no avail. No earth was screwed to the front panel of the scope.

I also wanted to test the heads as well, this way, but I couldn't work out which test points to put them on. I have been using the circuit diagram for the 3V45 as a rough guide, as I don't have that for the 48, as logicially I deduced that the waveforms would be the same, despite the lack of HiFi on the 45.

[Nickthedentist]

Originally Posted by AidanLunn

This is the first time I've ever used an oscilloscope... I connected channel 1 trace to the PB FM test point, and the trigger to the flip-flop test point - there was just two flat lines on the scope. Ext triggering was obviously selected, and the various time divisions were tried, all to no avail. No earth was screwed to the front panel of the scope.

I'm no scope expert, but you need some kind of ground/earth/chassis/0V connection, between the scope and the item under test.

Typically, there will be a short lead with a croc clip on it emerging from the probe, or you can use any old length of insulated wire connected to the earth terminal on the front of the scope. At the VCR end, it should be connected to any sensible nearby earthing point, e.g. the metalwork of the chassis, or the shielding can over the head amplifier.

Nick.

[AidanLunn]

Originally Posted by Nickthedentist

I'm no scope expert, but you need some kind of ground/earth/chassis/0V connection, between the scope and the item under test.

Typically, there will be a short lead with a croc clip on it emerging from the probe, or you can use any old length of insulated wire connected to the earth terminal on the front of the scope. At the VCR end, it should be connected to any sensible nearby earthing point, e.g. the metalwork of the chassis, or the shielding can over the head amplifier.

Nick.

I gather this is what the bendy spike protruding from the cassette housing to contact the metal cover is for?