Re: 7854 fixed, now for some newb questions
Chuck Harris <cfharris@...>
The USA market for USA made test equipment back then was essentiallytoggle quoted messageShow quoted text
unlimited. The European market was just a little extra greed. So,
the bean counters wanted it, but the engineers doing the designs didn't
spend much time thinking about it.
As a result, things like using 120V safety caps that though rated to
handle 240V were used... even though the safety margin was much reduced
of what you would like to see in 240V land. And the biggest offense
was treating 50Hz as if it the 16% reduction if frequency wouldn't matter
to 60Hz power transformers and fan motors.
Not a conspiracy, just greed and indifference of USA engineers.
Solid state scopes from the discrete component era usually have a
some method to affect a slow increase in intensity on power up. My
7854 doesn't start bright, but rather the intensity ramps up to just
As far as I know, all 7854 keyboard units have sticky switches. It is a
simple clearance issue. Tektronix made the holes in the aluminum front
panel too close tolerance to the plastic buttons. Further, the buttons
are tapered so that they are narrow at the front, and wide behind the
panel... Only, the holes in the panel are punched square.. not tapered.
If you file the squareness into a taper by relieving the hole on the back
of the aluminum panel, you can improve the situation without making a
noticeable change to the panel. It must be disassembled, which isn't
hard at all.
Lubrication won't do the job.
There is a lot of very fast digital circuitry, packed very tightly, into
the 7854. It needs the air. Do not put a reduced capacity fan in this
Also, it is easy to have the fan rotating the wrong way. It has a plug
with no key, and it is a DC fan. The fan should suck the air out of the
case, not blow air into the case.
The RAM in the 7854 is not low power stuff. It will suck a big battery
down pretty quickly, which is why the older scopes had the ability to use
a large external battery. The last version of the scope had more modern
memory, and tektronix decided to use an internal battery... but I would
bet that it would be shot lived too, as they put a switch to disable the
battery on the back of the scope.
One of the nicest features of the scope is the standard GPIB interface
on the back. It works very well. But, by now, the address selection
DIP switch will be dirty, and the address might not be what the switch
says it is. You should replace it, or clean it, and verify its function.
The 7B87 has an ability to trigger the scope's waveform memory at any
point in time after the 7B87 is triggered. That way you can record
with great fineness an event that occurs later. You don't really need
it, but it is nice to have.
Single shot events are not the 7854's forte. It is only capable of
50K samples per second in that mode. The 7854 is really a sampling
scope with storage, that doubles as a 400MHz 7000 mainframe.
Nenad Filipovic email@example.com [TekScopes] wrote: