Seven Segment Displays

[Tony Duell]

> 
> > One of my VCR's has a load of LED 7 segment displays
> 
> My family's first VCR had a mechanical timer (not too much different than
> an alarm clock) and a knob-tuner (obviously using the same tuner mechanism
> as knob-tuned TV's) for selecting the channel.

I have a VCR with a mechanical timer -- and it is one of the first 
domestic VCRs, a Philips N1500. The timer driven by a synchronous motor 
from the AC line (I think via a dropping resistor, maybe also using the 
mains transformer primary winding as an autotransformer). It has an 
analogue clock face with a coloured band you can move round and adjust in 
length (up to 1 hour, the longest tapes that were made for this machine). 
There's another control on the clock that selects whether it will trigger 
on the first or second time the hour hand gets to the coloured segment 
(i.e. giving a total range of up to 24 hours in the future).

The tuner, though, is electronic. There's a set of interlocked buttons on 
tope, and the same number of multi-turn presets under a flap. In fact 
much of the tuner/IF circuitry is the same as in Philips TVs of the period.

It's a strange machine. The cassettes have the 2 spools stacked on top of 
each other, there's a complex dual concentric drive spindle. One result 
of this is that the head drum is almost -- but not quite -- parallel to 
the deck surface.

That machine is now about 33 years old. In that time it's needed nothing 
more than a new set of belts, a repair to the threading pulley, and one 
new transistor in the audio mute circuit. 

The machine with the 7 segment LEDs is also a Philips -- a VR2022. This 
is one of the later V2000 machines, taking a flipover cassette with up to 
4 hours recording per side. The video heads are mounted on piezo crystals 
(with a set of brush contacts on top of the head drum), which allows them 
to be servo-tracked along the video tracks -- a bit like a hard disk head 
(to get this towards being on-topic ;-)). You can therefore have a 
noiseless freeze-frame -- one of the problems with other vcr systems is 
that the apparanet angle of the recorded track to the edge of the tape 
depends on the tape speed, so if you stop the tape for a freeze-frame, 
the head wanders off the edges of the track. The V2000 machines apply 
some amazingly large (over 100V) waveforms to the actuator crystals in 
this mode, but the heads stay on the video tracks.

It's also a machine with very few mechanical parts. The only rubber part 
is the pinch roller. The capstan, drum, and both reels are directly 
driven by their own motors (there's a 5th motor for lacing up the tape). 
There's no back-tension band, back tension is applied by a small current 
through the rewind motor.

Oh, and the electronics is all on plug-in boards, apart from the tuners, 
RF splitter and modulator, which are soldered to the backplane PCB. There 
must be about 20 such boards, including half a dozen for the various 
servos. The service manual (I have it, of course), documents each board 
sepaarately, and also explains the complete machine.

I'd love to find the diagnostic tool for it. This was a box containing a 
ROM and an address latch with a bit of ribbon cable coming out of it 
ending in a 40 pin DIL clip. You clipped it over the 8048 on the syscon 
board and it disabled that chip's intenral ROM and ran the program from 
the external ROM instead. It would let you do all sorts of useful things.

I'd also like to find the baseband I/O adapater. There's a 20 pin 
non-standard plug on the back that this connects to. It gives composite 
video and (mono) audio I/O, a remote pause facility, etc. 

Oh well, enough off-topic rambling...

-tony