want to buy DEC VR241 monitor

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Wed Aug 13 21:27:37 2003

> Need DEC VR241 monitor, dead or alive. (Dead is no
> problem.)

It is if you have to repair one... The VR241 is a horrible Hitachi design...

Basically, there's a switch-mode PSU which is driven off the flyback
transformer (the signal is passed back across the isolation barrier to
the mains side of the PSU via a little pulse transformer). So the PSU
supplies the horizontal deflection system, which provides the signal to
run the PSU.

How does it all get started? There's a little astable on the mains side
of the PSU that runs the chopper for a few seconds (it's disabled when a
capacitor charges up) to get the whole thing running.

Which means that if there's any fault in the PSU or horizontal system,
the darn thing won't keep running, so you can't check voltages, etc. A
right royal pain!

Add to that the fact that 90% of the deflection system, including the
control IC and the vertical output stage are on a thick film hybrid
circuit in the middle of the deflection PCB...

And the fact that the darn thing is almost impossible to work on due to
the arrangement of the PCBs around the CRT.

No, this is not one of my favourite designs...

-tony
Received on Wed Aug 13 2003 - 21:27:37 BST