Re: S-4 issues

Chris van Lint

Hi Jim,

Great!!!  I was going to suggest checking out the tants, as I know  that they have habit of going bad and shorting.  I have not used any of the 7S11 gear for over 10 years.  I still use my 7L13 and last year it went up in smoke.  The beauty is that often the culprit can be identified visually.  Anyhow, to be on the safe side I replaced all tants and presto it is running fine.

I am somewaht better, no more pain. However I am still not allowed to hold my head up and have to sleep on my tummy for at least another week.  This why I now can use my note pad (not a PC screen).
 At that time I will know to what extent the sight in my left eye has been saved.

Glad that all turned out well.

Sent from Samsung tabletJim Ford <> wrote:Yea!  That was indeed the problem; 3.3 uF tantalum C45 on the preamp
board was shorted, pulling +15 V down.  I replaced it with the closest
value I had, 10 uF, and now it works!  I considered putting another 10
uF in series, but there really isn't room for two caps.

Thanks, Craig!


------ Original Message ------
From: "Craig Sawyers" <>
Sent: 9/15/2018 3:07:34 PM
Subject: Re: [TekScopes] S-4 issues

So, I have two S-4 sampling heads, one of which works fine, and the
other I just obtained from a
TekScopes member.  The 2nd one causes the screen to stay blank when I
plug it into my 7S12 in my
7904 scope.  Is it shorting out a pin in the 7S12 and dropping the Z
axis to nothing?

Besides ESD discipline, which is drilled into my head at my defense
contractor employer, and the
V limit on the tunnel diodes, is there anything else I need to be
aware of before I open up both
First thing I guess is to look for visibly obvious shorts, and then
I'll poke around with a DMM.
one DMM last night in ohms mode with another DMM in volts mode: 3 V
maximum when open
circuited, so no problem there.

Thanks for your help in keeping me from inadvertently damaging a
precious S-4 with (fingers crossed)
just some silly fault and not dead tunnel diodes.

The bridge diodes are not tunnel diodes  - they are conventional low
capacitance Schottky barrier chip
diodes die bonded onto a ceramic substrate and wire bonded to the

I seem to recall that a problem with one of my S4's (or it might have
been an S2 or S6) is a black
tubular tantalum going short. Not the usual bead type that dies.

Worth checking before pointing the finger at the bridge diodes.


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