PDP-12 Restoration at the RICM (tony duell)

David Gesswein djg at pdp8online.com
Sat Oct 17 09:10:29 CDT 2015

On Tue, Oct 13, 2015 at 08:32:49PM -0400, Michael Thompson wrote:
> > What exactly do you mean by 'glitches'? Are these on a TTL level signal,
> > an analogue
> > output of the read amplifer, or what?
> >
> You can see the logic analyzer trace of many of the TC12 signals here.
> <https://4310b1a9-a-11c96037-s-sites.googlegroups.com/a/ricomputermuseum.org/home/Home/equipment/dec-pdp-12/dec-pdp-12-restoration/LINCtape_Track-3_Problem.jpg?attachauth=ANoY7crnX8o5yLYK_UhrFx_58_SY0L1ogEtncsO6od4NhnEtVA9JazEEolMQZqGO4o8Z5l_z2g8-Bba6EX1OkRVrjpjutMp_JDMRoWSoMRZk6PnpOdywwKqxjdnHEdFO3Roux9LqFkmKG7oqalE7c8EUL-2ecJb99ZQuUsPvbz7I1oZJPppz8zWCG0174_en4Hm5e2Aqc1vzjESaq6SdUyJ9EDKQIRP_uBsR8lw9sq2DYaIUJk1MxHv2K9YoiWaFgm3V0hfE6T3syLwKBtA6GaoNIv667JwhR0fgf6B-FTXrGeWow5TmVfA%3D&attredirects=0>
> The labels at the far left of the image include the backplane slot and pin
> number for the probe location. The signals were TTL level by the time the
> logic analyzer saw them.
Have you hooked up a digital scope to the read amplifier and seen if the
analog waveform has problems when the glitches occur? Seeing both the analog 
and the digital output would help see where the signal is going wrong.

The other is if you have enough memory and channels in your test equipment 
you can trigger off a signal indicating that the block number was missed 
then look back to see how the block number was wrong. If you have it a 
trigger out from the logic analizer can trigger a digital scope to capture 
at the same time to see the head amplifier signal.

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