Re: 2465A channel 2 problems


To diagnose the attenuator relays you can simply measure the DC resistance
while you run up and down the scale. It should be 1MOhm within fairly close
tolerance throughout. If you have bad contacts you'll see non-trivial
deviations from that.

On Thu, Oct 17, 2019 at 12:18 PM machineguy59 via Groups.Io <machineguy59=> wrote:

You should be able to hear the relays switch as you change scales. That
will indicate the logic is operating. It is more likely the attenuator is
dirty and the fingers don't make good contact on the ceramic substrate.
Cleaning is a delicate process to not break the ceramic or bend the contact
fingers. Sometimes you can clear the problem by spraying a contact cleaner
into the attenuator. But the best, long term solution is to open the
attenuator and clean it, OR replace the attenuator. Both are involved
On Wednesday, October 16, 2019, 06:58:23 PM CDT, GerryR <
totalautomation1@...> wrote:

That's the problem, in the normal mode, the 1, 2 and 5 volt ranges are
off, for example, a 1V signal on the 1V per division scale, displays as if
on the 100 mV scale, etc., so I am assuming the attenuator is not
for those ranges, but don't know if the relays in the attenuator, or the
logic telling which tells them to switch that is bad. The digital readout
shows 1V on the 1V scale but the display of the wave is as if it is on the
100 mV scale.
Is there a list of digital words for the different scales or a way to tell
if the logic is bad?


----- Original Message -----
From: "machineguy59 via Groups.Io" <>
To: <>
Sent: Wednesday, October 16, 2019 6:48 PM
Subject: Re: [TekScopes] 2465A channel 2 problems

How does Channel 2 work when using the scope in the "normal" mode? If it
seems about right (just not precisely calibrated) when measuring known
voltages then the attenuator is switching.
On Wednesday, October 16, 2019, 03:31:47 PM CDT, GerryR
<totalautomation1@...> wrote:

A little history first: Acquired the 'scope recently and everything was
working fine. Old battery dated 07-87. Decided to change battery and took
all known precautions, but somehow screwed up and requires re-cal. I have
attempted re-cal, and went from a "Test 04 Failed 04" to a "Test 04 failed
02" which is a limit failure. Channel 2 "calibrates" up to the 10V input
(cal 02), and I get a Limit 130 error, no matter what I try, so I assume
that is my problem. In the non-calibrate run mode, the channel 2 input
works up to the 500 mV range (Hi-Impedance input with co-ax) and with the
10X probe, up to 5V. The display range readout works, but in the 1V, 2V
5V ranges, it appears to stay in the 100 mV, 200 mV and 500 mV ranges, so
appears the attenuator isn't switching properly.

Is there a way to tell whether it is the attenuator, or if the proper
outputs are not getting to the drivers for the attenuator relays, or is
still a calibration problem? I have no way to monitor a "word" from the
processor at this point. I did try monitoring channel 1 at the drivers and
comparing them to channel 2, but found it difficult to get any meaningful
data. Any help will be appreciated.

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