Re: 2465A channel 2 problems

Chuck Harris
 

When calibration is under computer control, the computer
will automagically set all of the pertinent controls to their
proper settings for you. If the inputs need to be 50 ohms,
they will be set to 50 ohms.

Just like the manual says.

If your preamp attenuators are broken, they won't do what
they are told to do, and calibration will fail.

Two quick ways to kill the attenuators are to give
them a spray with contact cleaner, or to wash them with
water. The manual warns you not to do either. Somehow
everyone knows better than the engineers that designed
this stuff.

The relays are not made to be water resistant, and will rust
solid if you wash them, and their plastic structure is not
guaranteed to be compatible with anything but isopropyl alcohol.

The relays are a latching variety that was devised and made by
tektronix. They are set or reset by giving the appropriate coil
a little pulse of current. They are not strong enough to release
if there is oil (contact cleaner) between the armature and the
pole piece. The surface tension will for all intents and purposes
glue them into one position.

-Chuck Harris

GerryR wrote:

Chuck,
Are you saying that the scope CH 1 & 2 inputs will be in 50 ohm mode for all
the Cal procedures? I did check the inputs in normal mode when switched to 50 ohms,
and they are both OK, right at 50 ohms.. I haven't checked their state when in the
different Cal procedures; I'll be back at it a little later.

Also, I don't hear CH 2 relays clicking when going from the 500 mV to the 1 V
scale; OK from 50 mV to 100 mV. The inputs stay at 1 M throughout the ranges for
both CH 1 and CH 2, but I expect that particular relay isn't being activated for CH
2, so it is stuck in the 500 mV range and showing a "good" 1 M input.

I'll have to look at the schematic and see if I can jumper the proper relay to
activate the 1 V scale change. They are OC Darlington's, so that may tell me whether
it is the attenuator module relays or if the software or the drivers are the
problem. Any other suggestions are welcome!
Thanks.

Gerry

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