Re: 1S1 repair news :-)


 

replacing the GaAs diodes with Schottkys sounds extremly
interesting. Could you write which type of Schottky diodes you
used? I think a lot of (potential) sampling plugin repairers
would appreciate this information, at least I would.

Thanks a lot,
Laurent Lamesch
Giving you part numbers would not be too useful, since the 1S1
still has the offset problems I mentioned.
maybe due to a unmatched set?


I got a couple of
different types through Digikey. If you want to experiment, I
expect
it's best to look for low-capacitance parts, say, 1-2pF. I'll get
back to the 1S1 when I have time. It *is* a weird circuit, and
difficult to troubleshoot, even with the manual!
I have tried a hp HSMS28xx (I don't remember the number but i can
have
a look, its a bridge-connected 4-diodes in one SMD housing) and a
(matched set) hp 5082-2815 in a a 3S76 a time ago,
as i mentioned in the tektronix-forum(@reprise.com) last year.
The balance and offset is ok, i have not checked the risetime and
aberations, because it was only a test. (My original sampling diodes
are OK)
I have tried those diodes because i have studied some service manuals
from samplingbridges in (vector-) voltmeters by hp. The HSMS28xx was
used up to 2 GHz in a hp VV-plug in, the 5082-2815 was used to 1 GHz
in 8405 VV and 3406 Sampling Voltmeter.

Jorgen
dj0ud

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