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Old 31st Mar 2014, 12:38 pm   #1
ben
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Default JVC HRD140 (Thorn 8947, Ferguson 3v44/45 etc) cam

Picked this up so long ago I can't recall where from!
Now it has come off the roundtuit pile. The symptoms were: power ok, cassette mech stuck in the fully laced position, load motor /belt slipping as trying to unlace but jams after a couple of revs of the worm gear.

Dismantled the load motor sub assembly and discovered the cam has a broken track end, see third photo. This allowed the pinch roller follower arm, which is under considerable spring tension, to jam up the cam.

Now, my question is, where on earth am I going to find another cam? I think I chucked all my scrap chasis for these models ages ago. I doubt a repair of the cam would be feasible given the forces involved, but I'm all ears!

Incidentally, the date on the motor says Feb 86. So, pushing 30 years old, not surprised the plastic gave up the ghost.
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Old 31st Mar 2014, 12:45 pm   #2
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Default Re: JVC HRD140 (Thorn 8947, Ferguson 3v44/45 etc) cam

If you have a part number PM me,just in case i have a NOS one. Just had a look through one case of spares and no cams but i know i have some around if i can find my other vhs bits.

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Last edited by HamishBoxer; 31st Mar 2014 at 12:51 pm.
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Old 31st Mar 2014, 6:32 pm   #3
Maclee62
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Default Re: JVC HRD140 (Thorn 8947, Ferguson 3v44/45 etc) cam

Here is an idea for repairing the old one, but obviously you will have to make sure that there is enough space available in the mechanism that the repair will not interfere with anything. I know nothing about these mechanisms so you will need to check this yourself.

Since the end of the track has broken, but you still have that piece of plastic, perhaps you could remove it, clean the cam assemble thoroughly with alcohol and then glue the broken piece of plastic back in place with a tiny drop of general purpose glue.

Obviously this will not be strong enough for the job, but if there is enough space in the mechanism and nothing to get in the way, you could then fill the void outside of the cam track with epoxy resin, such as Araldite. Once cured, the resin will support the tiny piece that you glued back in place, and it, in turn, will have prevented the resin from flowing into the cam track.

As I said, obviously you will have to clean off every trace of grease, (and it would probably be wise to abrade the area that is to be filled with resin to give it better adhesion).

Worth a try perhaps?
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Old 31st Mar 2014, 9:40 pm   #4
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Default Re: JVC HRD140 (Thorn 8947, Ferguson 3v44/45 etc) cam

In the original JVC manual, and the Ferguson/Thorn manual there is no part number for the Cam, it comes as a complete ass'y including the loading motor, belt, worm gear, and bracket etc.

Edit: that is not to say that Thorn/JVC never offered the main cam as a spare part, they very well may have done at some point, just that the manual does not show it as a seperate item, and the chances of the usual suppliers having one is virtually nil.
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Old 31st Mar 2014, 10:04 pm   #5
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Default Re: JVC HRD140 (Thorn 8947, Ferguson 3v44/45 etc) cam

Unusual to see a grey one, I've only ever seen white nylon ones. Not that that makes any difference to your predicament, just an observation. The filling of the void is a good idea although I'd have a go with that plastic metal stuff as it's quite hard when cured.
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Old 31st Mar 2014, 10:22 pm   #6
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Default Re: JVC HRD140 (Thorn 8947, Ferguson 3v44/45 etc) cam

Thanks so much for the replies and especially the useful tips. Looks like a repair as suggested by Maclee62 is the way to go. Will buy some araldite tomorrow if time permits. I don't want to scrap this one if it can be avoided, as although it's only a 2 head mono unit it is exceptionally well made compared to what came later. It also brings back good memories from when I was learning VCR repair in the early 90s - armed with a few manuals and plenty of visits to the local traders and tip!

This afternoon I had a quick look in the scrap box, but could only find a complete carriage mech for this model. Isn't it always the way - you junk the bits you end up needing, and keep bits you don't!
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Old 4th Apr 2014, 2:38 pm   #7
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Default Re: JVC HRD140 (Thorn 8947, Ferguson 3v44/45 etc) cam

Repaired the cam, reset and timed everything, hand cycled, and tried it out.
The load motor keeps trying to return the deck to the fully laced position and when it reaches the end, just grinds away.
I have hand cycled the mech to half-laced and fully unlaced and plugged in again, but the same thing happens no matter whaere the mech is at in its cycle.
The cassette basket is in the up position. No other motors come on, even when the unit is fully laced.

Anyone recognise this problem before I start digging and taking measurements?
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Old 5th Apr 2014, 3:10 pm   #8
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Default Re: JVC HRD140 (Thorn 8947, Ferguson 3v44/45 etc) cam

I was actually wondering if you may have had "other problems" when I saw how the cam was damaged.

The load/control motor should be stopping as the cam follower gets to the end of the spiral, the way that cam was damaged suggested that it was over running.

It looks like mode switch type problems, also check the earthing of the small PCBs with the mode switch and end sensors etc. that are fixed to the deck, this deck, and others in this range, relies on the fixing screws for the chassis return connections for the various deck sensors.

As always with JVC/Thorn machines of this era, check for any O/C circuit protectors.
If I get a chance I will dig the manuals back out later on.

Just thought, this machine uses an optical mode switch, and you may have a similar problem to the one that Ian had in an earlier thread, the optical mode switch is more than likely faulty.

This optical switch senses the fully loaded/unloaded position, provided the timing is correct this would account for the damaged cam gear.
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Old 7th Apr 2014, 3:12 pm   #9
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Default Re: JVC HRD140 (Thorn 8947, Ferguson 3v44/45 etc) cam

Took another look. the only area that is earthed is the very motor assembly I've been working on and both the leads are fine. I cleaned and refitted them - no joy. The other pcbs on deck underside are secured with screws, but there are no earthing lands or straps visible.

I was secretly hoping it wouldn't be the mode switch -it is a Sharp assembly ref. PU57650. Needless to say I've cleaned the IR diodes already.
I haven't yet checked the PSU outputs, I suspect something may be amiss as the cassette basket does not respond at any time. The Standby LED and clock are the only things that work apart from that load motor. Though I suppose that could be down to the micro not issuing the required commands.
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Old 10th Apr 2014, 10:18 pm   #10
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Default Re: JVC HRD140 (Thorn 8947, Ferguson 3v44/45 etc) cam

I still have a few of these optical mode switches if you need one.

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Old 11th Apr 2014, 12:16 am   #11
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Default Re: JVC HRD140 (Thorn 8947, Ferguson 3v44/45 etc) cam

That's very good of you, Roy. When I get a moment I will first measure the voltages to rule that area out before troubling you. I may well be in touch!
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