Date   : Tue, 18 Aug 2009 01:44:59 +0200
From   : rick@... (Rick Murray)
Subject: Floppy drive cleaner

Mick Champion wrote:

> Best to move the head drum by hand rather than power it up to be 
> honest.

For somebody who has never tried this method, that would be wise. It
ought to come with a HUGE DISCLAIMER attached. :-)


> It's 1500-1800rpm by the way (25-30 frames per second). I think 
> you have doubled your speed calculation based on 50 fields per second 
> whereas each field is read on opposite heads on the drum so 1 rotation = 
> 1 frame (2 fields). 25 frames per sec x 60 seconds = 1500 rpm. Well I 
> think this is correct?

I'm crap at maths, so I'll give you the benefit of the doubt there! I
actually went off the fact that 50Hz generators run the engine at
3000rpm; but yes, opposite heads for opposite fields would indeed mean
1500rpm is a more logical figure.


> When on pause it is likely that only one field / head is being read. So if 
> one out of the two heads is very dirty, when on pause you could 
either see
> nothing but white noise, or a perfect picture

It is my experience, from three different lower-end VCRs that all the
fancy image fanangling is disabled in pause - perhaps because simply
spinning the one set of heads around on a fixed place means it is
difficult to sync exactly (you may often see this in tearing in the
picture when paused). In any case, on my decks the pause picture is
often worse than playback, so I use that to judge how well I've cleaned
my heads - if it is nothing but noise, clean some more. If it's a crappy
version of the normal picture, situation normal. :-)

BTW, I said "set of heads" as surely you would need to switch from field
to field? Cheap VCRs won't have the ADC/DAC nor the memory to memorise a
field (and if they did they could slacken the head and output a perfect
still from memory), and you'd surely see black lines if it just did
nothing for the second head pass. So the second frame head will switch
in and read the first frame data. Well, it's a lot more logical than
just trying to ignore it!


> (that's if your VCR did beautiful pauses in the first place)

Only had one that did. It buffered to some sort of memory and slowed the
head down and slackened the tape slightly. If you paused for more than
about five minutes, it would stop the head completely (while keeping the
static frame on-screen). Was the only VCR I met that would do
slow-motion stepping in either direction. Sadly it suffered a SYSCON
failure which led to it engaging REC mode and running the tape through
at about 3x speed when you pressed the standby button. Cocked up a few
tapes like that before I decided to scrap the thing.


> I personally would not clean the heads with a tape inside, but I know 
> you have had success with your method, so who am I to knock it. :-)

Well, it isn't as if I'm dumping isopropyl in there. That *would* be silly!


> When you say felt, do you mean soft or abrasive?

Umm. Felt. Like the stuff you might have glued to bits of cardboard in
kindergarten? It feels nice and soft, but it is anything but smooth.


> Don't forget to also clean the erase and ACE(audio control erase)
> heads, plus guides and capstan.

Don't forget also the audio head (looking into the deck, usually to the
lower left of the drum, say 5 o'clockish?) needs to be cleaned at the
EDGES. The centre is empty, that's where the picture lies on the tape.
However the top and bottom both have functions - you'll see if you look
with a torch. I don't recall which is which, but one does the linear
audio and the other does the tracking pulses.

Symptoms: No audio at all, or very muffled, out of HiFi mode.
           Deck can't tell if the tape is SP or LP, plays LP at SP speed
           etc.


> Wow, that's a great result. Did / does it read your old discs or only 
> write read new ones?

It prefers its older discs. Writing new data could be read on the other
machine, but it sometimes took a few retries to get it to read it back
itself. Don't ask why!


> I thought it was incredibly hard to get the heads aligned properly.

This one had little notches, so it was easy to put it back in the right
place. Without those, I don't think I'd have wasted time trying.


Best wishes,

Rick.


PS: Apologies to Mick who will have seen this twice. I *will* remember
     to change to reply TO to the mailing list. I *will* remember to
     [repeat until false]

-- 
Rick Murray, eeePC901 & ADSL WiFI'd into it, all ETLAs!
BBC B: DNFS, 2 x 5.25" floppies, EPROM prog, Acorn TTX
E01S FileStore, A3000/A5000/RiscPC/various PCs/blahblah...