Repairing an HP3421A (Signature Analysis)

Philip Pemberton classiccmp at
Thu Jun 4 16:10:24 CDT 2009

Dave McGuire wrote:
>   And actual HP signature multimeters show up everywhere, and tend to be 
> cheap.

Of course, if they're not cheap enough, you can always build a signature 
analyser out of a couple of LSTTL chips. If memory serves, the core of the HP 
5004 analyser is an LS86 XOR, a pair of LS164 shift registers, and some logic 
to drive the displays. If you can live with having to do some hex -> 
signature-code conversions (it's basically a quick substitution of the letters 
from one to the other), then four TIL311s will work nicely as a display. If I 
didn't have any TIL311s to hand, I'd probably program an EPROM to do the 
conversion, and use a couple of 7-segment LED displays.

Rik's right though, the May 1977 HPJ tells you just about all you really need 
to know to clone a HP signature analyser...

classiccmp at

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