Osborne 1 monitor questions

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Thu Aug 28 17:08:11 2003

> 3) Does the monitor use the +12V line on the connector
> from the CPU board for all its power, including the HV
> converter?

Quite likely it does (I've never seen an Osbourne...) Many mono monitors
run the line output stage (horizontal output stage) off 12V, and the
flyback transformer provides all the higher voltages.

>
> Unfortunately I don't have an HV probe at the moment,
> so I'm being cautious about poking around the CRT.

Even without an EHT probe you can check the electron gun voltages.
Assuming it's a 7 pin CRT (with a 12V supply, I'd expect this, since such
CRTs have 12V heaters). Firstly, I assume the heater is glowing.

The pinout of most CRTs is :

1 : Control grid (expect a -ve voltage up to about -100V here, adjustable
    by the brightness control if there is on (NOT the contrast control)

2 : Cathode (expect about 70-80V here, maybe less)

3 : Heater
4 : Heater (Often one of these is grounded, the other had 12V DC on it)

5 : Control grid (see pin 1)

6 : Anode
7 : Anode (One of these is the 'focus' electrode, the other is connected
to the 'screen' control if there is one. Expect about 400V on the latter
and a bit more on the former).

If the anode voltages are present and look reasonable, then the line
output stage is probably operational.

-tony
Received on Thu Aug 28 2003 - 17:08:11 BST