On 7.2.13 11:42 , Ian Field wrote:


"Martin Brown" wrote in message
...
On 30/01/2013 22:26, DaveC wrote:
80's vintage German printing equipment (offset press industry) uses a
video
plug-in card (made by the manufacturer of this equipment) to generate
parameter display for the operator. The display is a standard
baseband video
tube monitor. (It is possible, being German and sold in the USA
market, that
the video may be NTSC or PAL.)

There is no video signal on the BNC output connector.

This is used equipment being resurrected, so operational history is
unknown.

There is a place on the video card labeled "Q2" that is the right
shape &
size for a crystal can. The pads look like it was ripped off the
board: a
short lead soldered in one pad; a hole in the other pad where a lead was
soldered (poorly, apparently!). (Rough handling is a distinct
possibility:
the client is a used-equipment dealer and the fork lift is their main
tool...).

The board is populated with 80's technology, mainly 74LS' :: the
crystal pads
connect to an 'LS04 inverter/driver and then to an 'LS96
parallel-to-serial
converter. The 'LS96 spec sheet says that it can be driver up to 25 MHz.

The board uses a 8275 CRT controller, and in the datasheet it says:
"CCLK is
a multiple of the dot clock and an input to the 8275."

Maybe these clues will tell someone what frequency this crystal needs to
be...?

What frequency crystal should I be looking for?

I'd try 13.5MHz first but anything in that ballpark and output the
video to a multisync monitor and you should get some sort of picture.

Old monitors don't like being driven too slowly for long periods.


They don't have to be old - just have a CRT.

The scan yoke being an inductor has linear ramp current when the voltage
is applied for the forward scan period, reducing the frequency increases
the period - the inductor has time to saturate and "punch-through" the
scan transistor!


There is another consideration:

The scan system is resonated on the third harmonic to the line rate
to create the S-correction for the scan, slower on the edges and
faster at the middle. This is to compensate for the varying distance
between the electron gun and the screen. This means to keep the
line rate within a few percent of the nominal. The method was
populas with the monochrome tubes, but colour things often use
more sophistacated methods (parabolic correction, etc).

--

Tauno Voipio