[volt-nuts] Improving Solartron 7071 and 7081

David C. Partridge david.partridge at perdrix.co.uk
Wed Jan 30 16:32:07 EST 2013

One thing I have noticed in my digging around in Solartron 7071s and 7081s is that there is a nasty ringing of around 100mV pp or more every 0.66uS in all the power supplies.   As far as I can determine this appears to be caused by a big spike as IC403 (74LS02 on the earthy processor board) switches.  You can see the spike at TP 3 on the earthy processor board.  This spike goes  below ground by about 1.4V every 0.66uS.

I'm wondering what I could do to reduce this problem.  Would adding local supply de-coupling help, or would a different logic family (e.g. HCT) help, or what?

David Partridge

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