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? Regards, David Partridge

Hi David, I looks like the gate before TP3 gets a signal from off the PCB, how clean is that? first I would put a .1u to .22u small ceramic cap between power and ground of 403 then I would look at where TP3 signal goes to, does it feed off the PCB to anywhere else? a ring below ground means an inductive kick. HCT is even faster, so it might give a bigger kick? Wrinkle > From: david.partridge@perdrix.co.uk > To: volt-nuts@febo.com > Date: Wed, 30 Jan 2013 21:32:07 +0000 > Subject: [volt-nuts] Improving Solartron 7071 and 7081 > > 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? > > Regards, > David Partridge > > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there.

The input signal is reasonably clean. I need to probe all the outputs of this chip I think. It looks like this output ONLY goes to the test point, which is somewhat odd! Regards, David Partridge -----Original Message----- From: volt-nuts-bounces@febo.com [mailto:volt-nuts-bounces@febo.com] On Behalf Of m k Sent: 01 February 2013 07:43 To: volt-nuts@febo.com Subject: Re: [volt-nuts] Improving Solartron 7071 and 7081 Hi David, I looks like the gate before TP3 gets a signal from off the PCB, how clean is that? first I would put a .1u to .22u small ceramic cap between power and ground of 403 then I would look at where TP3 signal goes to, does it feed off the PCB to anywhere else? a ring below ground means an inductive kick. HCT is even faster, so it might give a bigger kick? Wrinkle