Hello all
This 1988 VCR has had a fault with random noise and poor dropout compensation for some time now.
The main problem is the manifestation of white specks on the screen, and sometimes there are black streaks off the right side of dark-to-light transients on the picture.
My gut instinct is head wear, as it seems to have most of the hallmarks of head wear except the fact that it performs better on some tapes (Rocky Horror) than others (Top Gun). Admittedly, both tapes I tried in this example are ex-rental tapes (Top Gun and Rocky Horror Show respectively). However, ex-rental or used blanks don't matter, the fault is worse on some tapes than others. This even applied to the machine's own recordings.
Playback of the machine's recordings on other machines there are slight symptoms of head wear.
I have checked for dry joints on the main board and the drum board* and thoroughly cleaned the tape path, but no difference whatsoever. Also the tracking seems "thin" - as in when adjusting the tracking, much less of the "cycle" of the electronic tracking of these is clear picture - if you can get it sparkle-free that is.
*The drum has no wires protruding from the top, the head drum wires being sealed into the head drum assembly.
Please see attached photos.
First is RHPS, last is Top Gun.
I have had little use of a scope. To test this head on my scope, would I need to Earth my scope or not?
Donkeys years since I worked on one of these. It looks more like drop-out compensation rather than head wear. I did hear of a fault caused by faulty electrolytics (surface mounted types) on the lower head drum motor PCB that caused this sort of problem. Not sure if this machine uses that sort of lower drum though.
Rich
That VCR has got "white tadpoles".
They can be seen swimming from right to left.
I fixed a 3V16 piano key set for these and it was the mechanical earth on the head drum motor shaft situated on the under side of the chassis.
thanks guys, I'll try both of those suggestions.
Yes Rich, it does have surface mounted electrlytics - lots of them! How do I test the ESR on a surface-mounted capacitor?
I did suspect that, Rich, but as it was a while since i did a VCR, i thought that that was the arm touching the top of the drum 
it does have surface mounted electrlytics - lots of them! How do I test the ESR on a surface-mounted capacitor?
Well if you have an ESR meter, you test them exactly the same way as you test a leaded component, assuming the test prods of your ESR meter can make reliable contact. Personally I wouldn't bother. Normally those associated with the lower drum motor don't amount to that many and I would replace them with carefully mounted standard electrolytics. How about some pictures of the relevant parts?
Rich
The SM cap in question on this range of machines is a 3.3 uF SM elec. cap on the drum motor stator board.
This can be replaced with a conventional leaded cap with the legs cut short if care is taken, when we first got this fault SM elec caps were not generally available from the various wholesalers (they were later), also observe correct polarity.
However when this cap is faulty you usually get part of the picture blanked or missing, and this missing/blanked part is usually in a different place each time play is selected.
In extreme cases you get no/blank picture at all, or grey lines and what looks like the line hold is off speed (incorrect drum speed), or sometimes complete deck shutdown (depending on machine), this cap is part of the drum motor PG (Phase generator) circuit.
The picture tends to improve as the longer the machine plays (warms up) in the early stages of this fault.
Is the back tension band okay ?, and as the others have said check the drum earthing strap/bracket.
Trevor is correct about the much later JVC (and Philips clone) with the horrible earthing ring/bush which was a PITA to change.
I have cleaned the Earth contact arm, to a little improvement. However, when the head Earth arm assembly is removed, the picture is greatly improved, but still not perfect. A fault on Earth?
I will check the back tension band and the amp stages.
Another point to look for on these machines, is to check that the supply pole base ass'y (lefthand tape guide, viewing from the front of the machine) is located in the 'V' block correctly, this can be intermittent.
Also check the deck itself is properly grounded to the electronics.
Well the first problem sorted itself out but now it's developed another. The loading belt was a bit slack and the deck developed loading issues, so I replaced it. Unfortunately, a circlip on the worm gear went missing and the mode switch was moved accidentally while doing this. So, with a missing circlip, I timed up the worm gear as best I could. The ribbon cable attaching the capstan board with the mode switch assembly snapped, so I replaced it with wires.
So now the idler motor just spins for 15 seconds and then the deck just shuts down. Any ideas?
Disconnected IR sensor? Or IR LED that illuminates it.
Well the first problem sorted itself out but now it's developed another. The loading belt was a bit slack and the deck developed loading issues, so I replaced it. Unfortunately, a circlip on the worm gear went missing and the mode switch was moved accidentally while doing this. So, with a missing circlip, I timed up the worm gear as best I could. The ribbon cable attaching the capstan board with the mode switch assembly snapped, so I replaced it with wires.
So now the idler motor just spins for 15 seconds and then the deck just shuts down. Any ideas?
Oh dear!
It could be many things, these decks do this when mistimed, either the mechanical timing and/or mechanics to electronic timing (mode switch), or alternatively you could have a supply missing (CP OC ?).
Without actually physically seeing the machine it is anyone's guess where the new problem lies.
I would recheck the wiring to the mode switch. also check that the mec is actually fully loading.IE are both loading arms reaching the end of travel?
Rob T
Well the first problem sorted itself out but now it's developed another. The loading belt was a bit slack and the deck developed loading issues, so I replaced it. Unfortunately, a circlip on the worm gear went missing and the mode switch was moved accidentally while doing this. So, with a missing circlip, I timed up the worm gear as best I could. The ribbon cable attaching the capstan board with the mode switch assembly snapped, so I replaced it with wires.
So now the idler motor just spins for 15 seconds and then the deck just shuts down. Any ideas?
Oh dear!
It could be many things, these decks do this when mistimed, either the mechanical timing and/or mechanics to electronic timing (mode switch), or alternatively you could have a supply missing (CP OC ?).
Without actually physically seeing the machine it is anyone's guess where the new problem lies.
In case it offers up any clues, before I realised there could be a timing error, the loading motor did spin.
The cables to the loading motor did also come loose early on but these were correctly re-soldered.
Before my attempt to re-time the mode switch (using another machine with same deck as reference):
The idler & idler motor motor span for 15 seconds from switch-on, the feed reel span with them. After about 5 seconds of power, the loading motor would then suddenly spin up, then shut down 10 seconds later with the rest of the machine
After I timed up as best I could and re-soldered the ribbon cable: The loading motor doesn't move and the idler motor spins for 15 seconds and idler moves into gear but the idler and the feed reel don't move at all.
I would recheck the wiring to the mode switch. also check that the mec is actually fully loading.IE are both loading arms reaching the end of travel?
Rob T
Bioth loading arms are not locked but don't budge when the machine is on - I can move them with my finger quite freely.
Bioth loading arms are not locked but don't budge when the machine is on - I can move them with my finger quite freely.
Well this is wrong for a start, the arms should not be free to move under any circumstances as they are driven by a metal sector gear which is in turn driven from the control cam which itself is driven by a worm gear.
For those not familiar with this machine, it is (I believe) the nearly all metal JVC deck as used in the Ferguson FV21R etc., the one with the tiny loading belt and the separate reel drive motor.
This is the Deck that used the dreaded black grease that sets solid.
If you post a picture of the underside of the deck to confirm I have the correct mechanism, then I have the Manual for the FV21R and can post the small amount of timing information for you.
Located the problem - the white latch on the metal sector gear wasn't down, so the gear was out of position.
Moved it into place and the load motor/mode switch assembly fits fine now - it didn't quite go in properly before.
Now the loading motor twitches slightly twice and the idler motor moves the feed reel for about 15 seconds. I'm thinking this is some kind of "servicing mode" for the machine when the deck is disassembled?
No, this machine does not include a service mode per se, there were unofficial means of disabling the end of tape sensors and the carriage to allow the deck to be ran without a tape and the cassette housing being present though.
How about a picture of the underside of the deck to make sure I have the correct manual ?, I am nearly sure the Fergy FV21R is the nearest equivalent to this machine.
No, this machine does not include a service mode per se, there were unofficial means of disabling the end of tape sensors and the carriage to allow the deck to be ran without a tape and the cassette housing being present though.
How about a picture of the underside of the deck to make sure I have the correct manual ?, I am nearly sure the Fergy FV21R is the nearest equivalent to this machine.
The mech is exactly the same as that series of machines. I will take a photo later anyway.
This mechanism was one of the best ever designed in my opinion - when it works.
Hi.
I was about to reply, R2B though beat me to itRe servicing mode, indeed there is no servicing mode as such. Servicing mode on these is a Biro lid, black tape, and an empty VHS cassette. You can get clear plastic skeleton "Tapes" these allow the machine to load up they give you access to reels and idlers, very useful
Thanks trevor - where would I get one of these skeletal tapes as a search on CHS and Donberg reveals nothing.
see through vhs tape
http://www.ebay.co.uk/itm/150893718297? ... 1423.l2649
rob t
