24 Nov
2025
24 Nov
'25
5:14 p.m.
The oscilloscope will show you the actual driving waveform.
You can then see the level of the spikes
Kindest regards,
Doug Jackson
em: doug(a)doughq.com
ph: 0414 986878
On Tue, 25 Nov 2025 at 10:48, Rob Jarratt <robert.jarratt(a)ntlworld.com>
wrote:
-----Original Message-----
From: Doug Jackson via cctalk <cctalk(a)classiccmp.org>
Sent: 24 November 2025 23:04
To: General Discussion: On-Topic and Off-Topic Posts <
cctalk(a)classiccmp.org>
Cc: Doug Jackson <doug(a)doughq.com>
Subject: [cctalk] Re: Hot Video Shift Register on VT100
Another test would be to disconnect the output and see if that runs the
device cooler. Maybe the load, while not a short, is simply too great
for the
device.
I think I can try this, the DC012 it drives is socketed.
But I am leaning towards the inputs containing spikes that need to be
dissipated as heat in clamping diodes. A decent CRO on the device input
pins
while it is out of circuit will show that as
well.
I guess CRO means Cathode Ray Oscilloscope? Not sure what you are
suggesting I try here?
Kindest regards,
Doug Jackson
em: doug(a)doughq.com
ph: 0414 986878
On Tue, 25 Nov 2025 at 09:52, Peter Coghlan via cctalk <
cctalk(a)classiccmp.org> wrote:
> >
> > Sorry if I wasn't clear in my earlier reply, but there were some
> > answers inline. The summary is that Vcc looks fine, there does not
> > seem to be any short on the outputs of the shift register and the
> > chip seems to be
> working
> > correctly. It just gets hot and I wonder if this could be due to the
> > CLK input being a bit spikier on the VT100 than on my VT102? Could
> > this be
> why
> > later revisions of the VT100 introduced an inductor on the DOT CLK
> > output from the DC011?
> >
>
> Perhaps one way to test the hypothesis would be to insert an inductor
> like those used on the later revisions in the DOT CLK output and check
> whether
> a) everything still works and b) the shift register runs cooler?
>
> Regards,
> Peter Coghlan.
>