[volt-nuts] Improving Solartron 7071 and 7081

[m k]

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 at perdrix.co.uk
> To: volt-nuts at 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
> 
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