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


Michael Dunn <mdunn@...>
 

At 5:13 PM +0000 2000/11/02, jlamesch@pop2.restena.lu wrote:
Hi,
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. 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!

BTW, the Sept 18th Electronic Design has a design idea circuit that's very similar to the Tek design, but modernized and simplified. Quite a coincidence!

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jlamesch@...
 

--- In TekScopes@egroups.com, Michael Dunn <mdunn@c...> wrote:
As for the six missing GaAs diodes in the sampling bridge and
elsewhere, I got some SMT Schottky diodes as hopeful subs. The
unit
is now working somewhat - there are some triggering and offset
problems. But, with the right settings and input, I can get a
valid
trace!!! Whether these probs are a result of the Schottkys, I
don't
yet know. All I can say is, it's VERY cool to scroll over a 200MHz
waveform at 35ps/div! (yes, 35ps. 0.035ns!) Though a bit
useless,
as the risetime of the thing is *only* about 300ps...
Hi,
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


Michael <mdd@...>
 

Sometime on Fri, 06 Oct 2000, you wrote:

-is now working somewhat - there are some triggering and offset
-problems. But, with the right settings and input, I can get a valid
-trace!!! Whether these probs are a result of the Schottkys, I don't
-yet know. All I can say is, it's VERY cool to scroll over a 200MHz
-waveform at 35ps/div! (yes, 35ps. 0.035ns!) Though a bit useless,
-as the risetime of the thing is *only* about 300ps...
Congratulations!
:)
Michael


Michael Dunn <mdunn@...>
 

Yoohoo. I'm making progress repairing my 1S1 1GHz sampling plug-in. The biggest problem was a kaput power supply filter cap - totally dead - well, many, many kohms ESR. Replaced the big old can with a part about 1/6 the volume, yet almost twice the capacitance, and much better quality to boot! Semiconductors aren't the only technology that's improved in the last 35 years!

Also paralleled the smaller final power supply output stability caps with new ones, again much smaller, yet more C's!

As for the six missing GaAs diodes in the sampling bridge and elsewhere, I got some SMT Schottky diodes as hopeful subs. The unit is now working somewhat - there are some triggering and offset problems. But, with the right settings and input, I can get a valid trace!!! Whether these probs are a result of the Schottkys, I don't yet know. All I can say is, it's VERY cool to scroll over a 200MHz waveform at 35ps/div! (yes, 35ps. 0.035ns!) Though a bit useless, as the risetime of the thing is *only* about 300ps...