Tek 2236 Scope: Counter/Timer/Multimeter (CTM) Problem

[Michael J. Linden, N9BDF]

I've got a problem with the Counter/Timer/Multimeter (CTM) function
of a Tektronix 2236 oscilloscope. The CTM is not operating correctly
when I try to measure the voltage on channel 1. When I try to measure
the DC voltage of channel 1 (DC Coupling), the fluorescent display
reads "DC OUCH" indicating an overvoltage EVEN when NO voltage is
being applied. When I try to measure the AC voltage of channel 1 (AC
Coupling) the fluorescent display reads "AC 0.0013" (or somewhere
around there) regardless of what voltage is applied to channel 1.

The CTM measures voltage correctly when I use the multimeter
connector inputs on the right side of the oscilloscope. Therefore, it
appears that CTM is basically functioning, but there is some sort of
problem in the coupling of the channel 1 signal into the CTM.

Anybody familiar with this problem?

Thanks, Michael

 

[tekman]

Are you shure it is not a problem of setting up and using the scope?
May be a look in the operating manual might help to set things right.

You can download one for free from www.teknetelectronics.com


hth,
Andreas

 

[Marcelo David]

Not connecting anything to channel 1, doesn't mean voltage = 0V, it is
"in the air" so, any voltage may be there. Try shortcircuiting the
channel, and see if the same problem appears...

 

[Michael J. Linden, N9BDF]

Yes, I have the manual and I'm sure the scope is configured correctly
to read voltage off of channel 1.

Thanks, Michael

 

[Michael J. Linden, N9BDF]

I've tried doing this with a 1 KHz 3vpp signal (AC coupling), a 1.5v
alkaline battery (DC coupling), and an open circuit (AC and DC
couplines). The behavior is the same in all three cases. I will try
short-circuiting the probe to see if the behavior changes.

Thanks, Michael

 

[Jim Yanik]

Yes, I have the manual and I'm sure the scope is configured correctly
to read voltage off of channel 1.

The proper way to proceed is to look at the schematics and circuit
description in your service manual,and check the voltage/signal that's
picked off from the Ch.1 vertical and applied to the DMM input.

 

[Michael J. Linden, N9BDF]

OK, guys, I found the problem. The cable that routes the channel 1 signal
from the "attenuator box" had disconnected itself. It looks like the weight
of the attached toroid was probably responsible.

Thanks, Michael