29 Apr
2017
29 Apr
'17
9:48 a.m.
Hi Jon,
I can hear a light crackle but not a whine.
Are you referring to Q202? The centre pin is 11v, the other two are at
0v.
Thanks,
Aaron
Jon Elson writes:
On 04/29/2017 08:34 AM, Aaron Jackson via cctalk
wrote:
The heater and control pins appear to be giving
sensible voltages. The
logic of the board is fine, I can type on the terminals keyboard and I
get the correct characters on the other end of the serial cable. The PSU
is putting out 31v which seems fine?
I'm used to discharging the tube before fixing things inside CRTs
(usually I only attempt to fix simple things like a broken toggle
switch), but I have not managed to get a spark off this monitor. The
tube doesn't seem to get charged up at all.
If everything is working, even a
small monochrome monitor
should give a bit of a crackle (might have to listen closely
in a quiet place) and you should be able to feel the
electrostatic field on the hairs on the back of your hand
for a few seconds after powering on.
I've measured the
capacitance of nearly all caps and they seem fine, diodes seem to be
working fine. Does this mean it is most likely the flyback transformer?
Since it doesn't smoke, I'm thinking the horizontal sweep
transistor may have gone out. It may have shorted, which
then may have burned up the primary winding in the flyback
(if left on long enough). I'd check that transistor for a
short, and then you can trace a few traces to identify the
primary terminals on the flyback and see if they are an open
circuit.
Jon