7D20 attenuators issues, calibration questions


Randy Newman
 

Hi all:
I’m restating my earlier topic “7k plug-in cleaning to be more descriptive of my current issue.
I recently purchased. 7D20 from that “e”-place. It arrived excellently packaged. I finally plugged it into my 7854 to see how it worked ( seller stated working, which it does mostly).
Self test reports error codes related to attenuators.
Before digging into the repair manual much (my bench is a very temporary setup, so only had so much time), I fed calibrator 400 mV into both ch 1&2. Ch 1 seems ok above 50 mV/div, but ch 2 seems inaccurate at any attenuators range. Btw, a bit of Old Home Week in this, in that I used one of these as a wee engineer.

I saw one post about substrate pad cleaning. I’ve not had time or space to start a disassembly….and am reticent to start, as I already have several repair projects in disassembly, and am hoping I really kept all the fasteners with them…(ADD and loose parts not a good mix).

Anyway, I’m a bit suspicious that some corrosion may be at fault since the front aluminum frame shows some oxidation. I also noted that the plastic trim around some of the gain/centering adjustments had either crumbled earlier, or in cases, crumbled when touched by my adjustment tool. Plugin is a bit on the geriatric side.

I’ve seen the early firmware post re: error codes (thanks!), but do not believe that is my issue.
I’d appreciate any cleanup/calibration advice anyone has.
ALSO, I noted the flex extender cables used for calibration. Not having these, I see that doing a cal with what I have on hand is not readily doable, except with repeated plug-in insert/extract cycles.

So, to summarize:
1) how best to clean attenuators?
2) extender cables options
3) and,,,would repeated self-test execution clean off relay contacts via wiping action?
( and yes, I saw Dennis’ discussion about vertically-sourced Tek design relays….too bad they did not have someone knowledgeable about relays, and things like materials science w/r/t contacts)

Am looking forward to getting this plugin fixed!


Zentronics42@...
 

Randy,
I might be able to help there. In terms of the attenuator there Is a prescribed cleaning method from Tek that most here adhere too. I am currently running an experiment with deoxit D100 non aerosol in the attenuator section of a 465B. This will most likely be responded with I am going to destroy the scope. To which my only response can be it was a last resort cleaning as I did not want to use sandpaper because the scope was stored in a barn before I got it so it was in desperate need of EXTENCIVE cleaning. Deodit was applied with a needle bottle and with as little as possible to do the job and a VERY small gauge needle. So far so good it has been a few months now and the attenuator is still working great. However I would NOT recommend this as a first pass.

If some relays end up being bad I had to replace some relays in a AA501A I designed some adaptor boards and used some coto relays in place of the failed reed relays. So there are many options available to get the plugin up and running again.

Zen

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Randy Newman
Sent: Saturday, September 18, 2021 5:32 PM
To: TekScopes@groups.io
Subject: [TekScopes] 7D20 attenuators issues, calibration questions

Hi all:
I’m restating my earlier topic “7k plug-in cleaning to be more descriptive of my current issue.
I recently purchased. 7D20 from that “e”-place. It arrived excellently packaged. I finally plugged it into my 7854 to see how it worked ( seller stated working, which it does mostly).
Self test reports error codes related to attenuators.
Before digging into the repair manual much (my bench is a very temporary setup, so only had so much time), I fed calibrator 400 mV into both ch 1&2. Ch 1 seems ok above 50 mV/div, but ch 2 seems inaccurate at any attenuators range. Btw, a bit of Old Home Week in this, in that I used one of these as a wee engineer.

I saw one post about substrate pad cleaning. I’ve not had time or space to start a disassembly….and am reticent to start, as I already have several repair projects in disassembly, and am hoping I really kept all the fasteners with them…(ADD and loose parts not a good mix).

Anyway, I’m a bit suspicious that some corrosion may be at fault since the front aluminum frame shows some oxidation. I also noted that the plastic trim around some of the gain/centering adjustments had either crumbled earlier, or in cases, crumbled when touched by my adjustment tool. Plugin is a bit on the geriatric side.

I’ve seen the early firmware post re: error codes (thanks!), but do not believe that is my issue.
I’d appreciate any cleanup/calibration advice anyone has.
ALSO, I noted the flex extender cables used for calibration. Not having these, I see that doing a cal with what I have on hand is not readily doable, except with repeated plug-in insert/extract cycles.

So, to summarize:
1) how best to clean attenuators?
2) extender cables options
3) and,,,would repeated self-test execution clean off relay contacts via wiping action?
( and yes, I saw Dennis’ discussion about vertically-sourced Tek design relays….too bad they did not have someone knowledgeable about relays, and things like materials science w/r/t contacts)

Am looking forward to getting this plugin fixed!