10 Oct
2015
10 Oct
'15
5:57 p.m.
Hi Tony,
On 05/10/2015 16:55, "tony duell" <ard at p850ug1.demon.co.uk> wrote:
I should receive an 8 channel logic analyser on Monday but for now I'm
getting results from the DMM and probe. Socket (empty) for UD11 looks faulty
in that it's VCC and GND pins show nothing. Continuity on the others looks
OK.
--
Adrian/Witchy
Binary Dinosaurs creator/curator
Www.binarydinosaurs.co.uk - the UK's biggest private home computer
collection?
And I would be surprised if you got nothing on the
screen either. Odd bit
rot would mean the wrong patterns for some characters. But still something.
The heater is working in the tube and now that I've got a proper DMM I'm
getting the correct AC voltage across pins 9&11 on the transformer.
Also the blue and brown pins look OK.
This is presumably a large-screen machine with a 6845
on the mainboard.
Is it initialising that (look at the vertical and horizontal sync outputs with
your logic probe, are they toggling)?
No. Only HSYNC is toggling, VSYNC is low.
Is it accessing the kernal ROM? Is the CS/ pin pulsing
low?
Yes. The others are high.
What about the RAS/ and CAS/ signals on the DRAMs?
RAS/ is toggling, CAS/ is high on all chips. VBB is -4.98, VCC is 5.08, VDD
is 12.02
A lot of the
repair pages use a piggyback 6502/ROM/RAM add-in called a
PETvet but all I have is a DMM, logic tester and other working PETs as
sources of chips I can borrow.
I assume the logic tester is a simple logic probe and not a logic analyser,
alas