RCA 1861, NTSC and a DEC VR-201

From: Ethan Dicks <ethan_dicks_at_yahoo.com>
Date: Fri Sep 24 14:43:34 1999

--- Tony Duell <ard_at_p850ug1.demon.co.uk> wrote:
> OK, you are sure you're giving it 12V still (the VR201 takes its power
> from the system unit when used in a standard DEC configuration).

Yes. I've got a PC PSU attached via my cable (which, again, works with an
Amiga 2000). I even hung a 3.5" HDD off the PSU to ensure a minimum load
on the +5V line to ensure proper +12V on the +12V line.

> Do you get _anything_ on the screen at all, even if you turn up the
> and contrast controls?.

Yes. I get background signal and a retrace image if I turn it all the way up,
whether the VIP is plugged in or not.

> What does your composite output from the RCA VIP
> look like on a 'scope?

I can see some negative pulses, a stronger line at 0VDC, some schmutz that
looks like video data between the sync pulses. It has the general appearance
of NTSC mono data. When I attach a Commodore 1084S to the VIP, I get exactly
what I expect: digital block noise (from random memory garbage in the VIP at
power on) and 1" tall numbers when I tap commands on the keypad.

> Can it drive the 75 Ohm input impedance of the VR201?

Dunno. How can I tell? I have the VIP schematics. Is there something I
can do with this?

> Is there a large DC offset on the signal?

How would I spot it? The sync pulses are below the 0VDC base line, there _is_
a baseline and the noisy stuff is above the base line. Is that what I'm

There is a mention in the manual about tuning a resistor or two for the sake
of certain brands of RF Modulators. Perhaps the signal isn't hot enough to
tickle the VR-201?

> The VR201s I've looked inside use a standard TDA1180/TDA1170 circuit.
> They should be able to lock to 15720Hz (in fact I think I've had them locked
> to 15625Hz, which is the UK TV horizontal frequency). Even if they
> couldn't, there would still be something on the screen.

There appears to be a beam; there is assuredly heat on the cathode, there is
no VIP data on the screen.

This VR201 works with my DECMate II perfectly well. It also works with an
A2000 w/my custom cable. The VIP works with its own cable to another
composite monitor. The only combination that does not work is my custom
cable between a VIP and the VR-201; that path is what I'm trying to debug.



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Received on Fri Sep 24 1999 - 14:43:34 BST

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