27 Oct
2015
27 Oct
'15
6:10 a.m.
Hi folks,
ROM problems aside does anyone know of a way I can test the actual CRT?
Last night I borrowed the screen from another PET just to see if I get a
garbage pattern from the board I'm repairing, but this one stays similarly
dark so I need to sanity check both of them.
Back when I was fixing my broken TRS80s I could use the CRT from a B&W TV,
is there anything oddball about the PET CRT that would stop me going the
other way and putting the tube in one of my spare TVs?
Ta!
--
adrian/witchy
Owner of Binary Dinosaurs, the UK's biggest home computer collection?
www.binarydinosaurs.co.uk
27 Oct
27 Oct
6:33 a.m.
ROM problems aside does anyone know of a way I can test the actual CRT?
By 'CRT' I assume you mean the evacuated glass thing. The term is alas also
misused to mean 'monitor'
[...]
Back when I was fixing my broken TRS80s I could use
the CRT from a B&W TV,
is there anything oddball about the PET CRT that would stop me going the
other way and putting the tube in one of my spare TVs?
There's nothing odd AFAIK about the Pet CRT. I am pretty sure it's one of the
common
ones with a modified B7G base (7 pins) and a 12V-ish heater.
Before you go to all that trouble, why do you think it has failed? In all my time of
working
on classic computers I've had exactly one mono CRT fail (and no colour ones). Fail
meaning
'gives nothing on the screen' -- I've had a few with phosphor burn, or with
low emission. But
those gave an image, albeit a dim one.
It is generally a lot quicker to see if the CRT is getting sensible voltages (and if it
is, and you
still get nothing to then suspect the CRT) than to swap it out. Also make sure the heater
is
glowing (you can generally see the glow from the back end of the electron gun either
through
the side of the tube neck, or in the pinch-off tube in the middle of the socket
connector)
-tony
Ta!
--
adrian/witchy
Owner of Binary Dinosaurs, the UK's biggest home computer collection?
www.binarydinosaurs.co.uk
7:38 a.m.
On 27 October 2015 at 13:33, tony duell <ard at p850ug1.demon.co.uk> wrote:
By 'CRT' I assume you mean the evacuated glass
thing. The term is alas also
misused to mean 'monitor'
Indeed, the glass thing.
Before you go to all that trouble, why do you think it
has failed? In all
my time of working
on classic computers I've had exactly one mono CRT fail (and no colour
ones). Fail meaning
'gives nothing on the screen' -- I've had a few with phosphor burn, or
with low emission. But
those gave an image, albeit a dim one.
Purely because not only do I get nothing on screen but if I turn both the
brightness and sub-bright up full I can't see any glow or raster lines.
I've got at least 3 monitor 'units' that do this, one of them also smokes
but we'll leave that one for now, I guess it's old enough :)
The PSU is giving 22VAC for the screen and the monitor pins on the
motherboard give sensible voltages IIRC, The heater on one screen glows so
that's the one I'm using.
One problem at a time I guess, tonight I'll double-check the CRTC since I'm
assuming if that's dead I'll definitely not get even the garbage on screen.
--
adrian/witchy
Owner of Binary Dinosaurs, the UK's biggest home computer collection?
www.binarydinosaurs.co.uk
3344
days inactive
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ard＠p850ug1.demon.co.uk -
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