31 Aug
2015
31 Aug
'15
3:18 p.m.
Hi,
I traced the 18Khz signal all the way from the moment it enters the
logic board until the video board (attached to the neck of the CRT).
The signal is there (it has different shapes but it is 18KHz). The
output of both transistors is 18KHz and so is the output of the
transformer. I traced it across resistors and capacitors as well. The
voltage (Vpp) does change as expected but the signal is present. Pin 6
and 7 have the 18KHz signal too on the CRT connector. However they
only measure 7 and 10V respectively.
Regards,
Vlad.
On 31 August 2015 at 02:26, tony duell <ard at p850ug1.demon.co.uk> wrote:
Hi Tony,
I have checked the horizontal signal from the MDA using an
oscilloscope. It is pin 8 like you mentioned. I get a regular 18KHz or
so signal out of that. Pin 9 gives the vertical signal at roughly
50Hz.
OK. Your PC and MDA card seem to be OK.
Now trace through the horizontail circuit in the 5151. IIRC there
is a driver transistor, the collector load of which is a transformer
which couples to the base of the horizontal output transistor
(sorry, I am doing this from memory, I don't have the techref
in front of me). Do you get the 18kHz on the collector of
the driver transistor?
Are both transistors good?
-tony