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Tech info about JumpFree from the designer



        Amongst the products I designed at Cintel in my years there were
JumpFree & LowSpeed. When I left Cintel to work for a post-production
company, Soho 601, one of the things I started to look at was the ocasional
hop, or jump. JumpFree had to be the most unfortunate product name ever
when it turned out that it wasn,t. 
        One thing did become clear from my 2 1/2 years watching real film
go through was how stable it really was. At Cintel I had some reasonable
35mm test film but no decent 16mm. I could measure 35mm to be at least
twice as good but could only really tell that 16mm was better. We couldn't
really be bold enough to put a figure on it. With proper film it became
clear how stable it really was, despite the occasional hop. 35mm is easily
4 times more stable than the original servo with a good bit of film.
        I now have no commertial interest in the product so I offer this
info for the benifit of the many users out there.
        I about two years ago I did some modifications to the JumpFree
phase servo 102133 to speed up and latch some of the inputs of the timer
PAL, IC12. The reason for this is to overcome something called
metastabililty (pun unavoidable). Metastability is a problem that happens
when latching asycronous inputs, (frame pulses, tacho pulses) with a
flip-flop. Basically if the flip-flop is clocked while it's input is
changing it it possible to 'balance' the flip-flop. Speeding up the slew
rate of the transitions of the asycronous inputs helps, as this reduces the
chance of clocking the flip-flop on the edge. Trouble is, the flip-flops in
question are inside the PAL, which is fairly slow Cmos technology, so even
if the PAL (ic12) recieves a nice fast edge externally, by the time that
edge reaches the flip-flop inside the PAL it's a slow edge again. External
fast latches are required and fast schmitt trigger buffers to speed the
edges feeding the fast latches.
        The signals that require this treatment are framepulse (FP) and the
two tacho pulses (01 & 02) and the parts required are one 74act14 and one
74act574. Send each signal through two stages of the 74act14 then latch
them with the 74act574. Now send these nicely latched signals to where they
used to go. TOUT1 from the MPU is the required clock signal for the
74act574, (also IC12,pin35 or IC11,pin1).
        This worked great for about a year, no complaints, then we moved
the telecine. In fact we moved the whole company down the road. Suddenly we
had racking problems and jumps again, but they different. The racking
problems turned out to be the little tacho pulse buffer box you get with a
Pogle that plugs into the back of the servo rack. It contains a 7805
regulator chip with no decoupling on its input. It is powered from the
Pogle rack and we had extended the cable so every now and then the thing
would burst into oscillation and put RF every where, upsetting the framing
board.
        Next, static. I saw a MK111 do a 'JumpFree' jump once with a
standard servo. The operator just said you get that sometimes and did an
edit. There are two sourses of static in a Cintel tube based scanner. First
is the film and I've seen numerous ways of dealing with this. I have heard
very good reports on the Alpha particle attachments you can get to go with
PTR rollers.
        Second static source is the 25KV supply. Remove it on its tray,
unbolt it from the tray, remove the insulating washers, reassemble it all
without them, and put it back in. Then, using heavy duty earth braid, earth
the tube package to the metal work around the EHT box and PSU's.
        I hope the above is of use, what ever servo you have. If anyone
else has anything to add please post it and add it the the list.
        Stuart Hunt ITK
        PS. The JumpFree/LowSpeed hardware is capable of any speed you
like, with any number increments and was designed for high speeds too. It
just needs programming up and the store control to do the right thing, but
I thought everyone had disk recorders these days anyhow!

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