The oscilloscope will show you the actual driving waveform. You can then see the level of the spikes
Kindest regards, Doug Jackson em: [email protected] ph: 0414 986878 On Tue, 25 Nov 2025 at 10:48, Rob Jarratt <[email protected]> wrote: > > > > -----Original Message----- > > From: Doug Jackson via cctalk <[email protected]> > > Sent: 24 November 2025 23:04 > > To: General Discussion: On-Topic and Off-Topic Posts < > [email protected]> > > Cc: Doug Jackson <[email protected]> > > 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: [email protected] > > ph: 0414 986878 > > > > > > > > > > On Tue, 25 Nov 2025 at 09:52, Peter Coghlan via cctalk < > > [email protected]> 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. > > > > >
