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465B strange ripple


Stephen
 

Hi all,

I was starting to check and calibrate my 465B which I haven’t used in a very long time, when I noticed that channel 1 behaved very oddly on some settings (mainly but not only .1 and .2 V/DIV). It actually more than doubles the amplitude I’m supposed to see.

Also, on both channels, I often see a noticeable ripple on the “flat trace” even when absolutely nothing is connected to them. And the trace on this scope is definitely not as sharp as on my other scopes.

Have any of you ever encountered this behavior before?
Any clues as to where I need to start looking first?

PS: Oddly enough, when the shield covering the channel 1 attenuation parts, there is no trace amplitude doubling...
It’s very disconcerting.


satbeginner
 

Dirty attenuator switches.
Remove both aluminium covers, use alcohol and put a small piece of paper in between an open contact, turn the V/Div selector till it closes, and carefully pull the paper from the closed contact.

Mind you, there are contacts above and below the grey cylinder.....

Good luck,

Leo


Stephen
 

On Sat, Jan 30, 2021 at 09:16 AM, satbeginner wrote:


Dirty attenuator switches.
Remove both aluminium covers, use alcohol and put a small piece of paper in
between an open contact, turn the V/Div selector till it closes, and carefully
pull the paper from the closed contact.

Mind you, there are contacts above and below the grey cylinder.....

Good luck,

Leo
Thanks Leo,
How do you deal with the bottom ones?

Could that also be the cause of the « ripple » I see when nothing is connected ?

This is what it looks like:

https://groups.io/g/TekScopes/photo/260052/0?p=Created,,,50,2,0,0


satbeginner
 

Hi,

I just cut narrow pieces of paper, about 8mm (1/4") wide, and I was able to slide them under an open contact.

Leo


Stephen
 

On Sat, Jan 30, 2021 at 09:51 AM, satbeginner wrote:


Hi,

I just cut narrow pieces of paper, about 8mm (1/4") wide, and I was able to
slide them under an open contact.

Leo
I’ll try that. Thank you Leo.


Stephen
 

I cleaned everything the best I could, but the problem is still the same....
The ripple is still there, and the amplitude flickers up and down quite often, at random, on several VOLTS/DIV settings.
Sometimes I have the impression that some capacitors, C30 to C37 are not seated properly. Because when I press on them down a tiny bit, most of the time all comes back to normal. At least for a while.
It’s very weird....


Stephen
 

However, the “ripple” is still present even when the amplitude is not jumping up and down...


Stephen
 

Here’s a little follow up on my issues with this 465B.
The attenuators (C30 to C37) are definitely not always seated properly. It seems the contacts are not optimal, and sometimes they lose them. I have to press them down a little. Not good.
Also, it seems that the trace gets much sharper when I touch the chassis ground. It’s otherwise unusually blurry.
Also, I notice that same trace ripple when I try to compensate a probe. It’s not steady at all. The trace is bouncing up and down almost like a 50-cycle hum. That is noticeable at low frequencies. At higher ones, it’s probably there too, but it’s less visually noticeable. Sometimes I see this waves within the trace itself... You can see that on the pictures I posted above.

I’ve checked all the voltages, and they are all within specs, but I think the ripple is very high.
It’s actually very hard to clearly see it, as I can’t even get a clear trace of it on the 466 I used to check it.
Unless I didn’t measure it correctly, it does seem high except on the 110V TP.

Any help you can provide will be appreciated.

Thanks in advance.


Stephen
 

Here are more pictures of the ripple I’m seeing.
Legends are below the images.

https://groups.io/g/TekScopes/album?id=260052


Jean-Paul
 

Stephen bonjour

Set the sweep hor 5 or 10 mS/ div, set trigger LINE

you will see if the symptoms are at a 100 Hz mains frequency

Then check every power supply DC voltage and rippling vs manual specifications

Most likely due to dried powered supply electrolytic caps, needs recapping.

It also sounds like you have a ground issue, perhaps faulty mains earth.

Bon Chance

Jon


Stephen
 

On Tue, Feb 9, 2021 at 01:30 PM, Jean-Paul wrote:


Stephen bonjour

Set the sweep hor 5 or 10 mS/ div, set trigger LINE

you will see if the symptoms are at a 100 Hz mains frequency

Then check every power supply DC voltage and rippling vs manual specifications


Most likely due to dried powered supply electrolytic caps, needs recapping.

It also sounds like you have a ground issue, perhaps faulty mains earth.

Bon Chance

Jon

Hi Jon,

First of all, thank you.
Now, all the voltages are ok within specs as per the manual.

This is what I see on the 110V TP at 5mV/Div - 5ms/Div - SOURCE LINE:

https://groups.io/g/TekScopes/photo/260052/1?p=Created,,,50,2,0,0

This is what I see on the same 110V TP at 10mV/Div - 20µs/Div - SOURCE. AC:

https://groups.io/g/TekScopes/photo/260052/0?p=Created,,,50,2,0,0


Stephen
 

On Tue, Feb 9, 2021 at 01:30 PM, Jean-Paul wrote:

It also sounds like you have a ground issue, perhaps faulty mains earth.
How to I check/fix that??

Thank you


Mike Merigliano
 

There may be a loose grounding screw. There is a document on cleaning the switches in 4xx scopes, and within it is this:

"One OTHER thing to check: (I'm not sure, at the moment, if this is only for the 465 model, or if it also applies to the 475:) JUST behind the metal attenuator/switch shield "boxes", there may be a screw that connects a metal piece of the box/shield to the circuit board. If that screw is loose (which I have seen on about a third of the 465 scopes I've worked on!), or if it doesn't make good contact, you may see very noticeable effects in the trace(s), such as fuzziness or distortion, and may see trace-distortion effects when adjusting the trigger-level control (possibly especially-so at the highest frequencies), and possibly other triggering problems."



Sorry, I don't remember where I found this, but imagine someone in the group would know, or even wrote it.


satbeginner
 

I recently cleaned up my 475A that I got a while back, and found something similar.

On one of the channels the aluminium cover was not there causing a fussy trace.

I too had the dirty contacts on the plug-in capacitor/divider units.

Just unplug them, clean the contacts, and plug them back in.

I made a replacement cover using thick aluminium foil and a self adhesive plastic foil.

Do you have the covers on the attenuators?

Leo


Stephen
 

Hi Mike, and Satbeginner,

I see the box shield, but I’m not sure which screw/metal piece you’re talking about...
This happens whether the shield is on or off...

You guys did understand that there are apparently 3 separate issues here.
The first one is that I have to press down on some divider units to get a normal undistorted trace, the second one being that the trace gets a bit sharper when I touch the chassis ground, and finally the last bu not least, the ripple on the trace (even when no signal is being fed. I actually see a moving wave like the one you can see in the album shared in a previous post. That wave is actually present and very visible when the time base is at about 2ms/division. It’s less noticeable, if at all when it’s faster. But this is not normal. I changed 2 of the filter caps today, C4419 and C4439; respectively for the -8 and +110V, but nothing has changed so far.

If that wasn’t enough, the trace itself is rather thick compared to my other scopes, and seems to look literally like a “rope”, as if it was made from twisted pairs... It’s very weird...

I have take the attenuators off and cleaned the contacts. No luck there. Some for now I have to leave the shields off. When the are on, especially on channel 1, the traces are erratic on some V/Div settings...

I’ve been trying to do my best to explain what I see, so I hope I’ve been making sense...


satbeginner
 

In my 475A I was able to find what divider had the " worst" contacts, by swapping one at the time between Ch1 and Ch2.

I also soaked them one at the time in IPA and turned both the C set screws, to find the problematic one.

In the end, after cleaning, they were all ok, but had all dirty contacts.

As a test you could ground the output of the attenuator, just before the input of the amplifier.

Again, one channel at the time to see what happens.

Leo


Stephen
 

On Wed, Feb 10, 2021 at 10:22 AM, satbeginner wrote:


In my 475A I was able to find what divider had the " worst" contacts, by
swapping one at the time between Ch1 and Ch2.

I also soaked them one at the time in IPA and turned both the C set screws, to
find the problematic one.

In the end, after cleaning, they were all ok, but had all dirty contacts.

As a test you could ground the output of the attenuator, just before the input
of the amplifier.

Again, one channel at the time to see what happens.

Leo
I will try that tomorrow and report back. Hopefully that’ll do the trick as far as the attenuator problem goes.
I did soak therm in IPA, but I didn’t work the set screws while in it. Maybe that’s why the results were disappointing...

I’ll try to find appropriate caps for the remaining power supply as well.

Thanks Leo.

PS: My 475A and my 465 have been need some repair for a while now. I’ll get to that someday... Hopefully soon. There’s only 24h in a day unfortunately... 😶


Stephen
 

I soaked all the attenuators, one channel at a time, and this time I worked the set screws quite a bit, both directions. I hadn’t done that before. I had to do that procedure 3 times, but at the end all is fine on that front.
They must’ve been extremely dirty inside!! That also to away the grounding issue, for some reason. Now the trace is quite sharp again.
However, the ripple I see on the trace at lower speeds (about 1ms/div and lower) is still significantly there.
It could be the filter caps...
Unless someone has a better idea, I will hopefully replace them tomorrow and see what that does...

BTW, I checked the two I already replaced for leakage (C4419 and C4439), and there were ok...


n4buq
 

Stephen,

I don't know if this has already been considered, but do you see that ripple with the input switch set to GND for the channel you've selected?

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Stephen" <stephen.nabet@gmail.com>
To: TekScopes@groups.io
Sent: Thursday, February 11, 2021 11:40:28 AM
Subject: Re: [TekScopes] 465B strange ripple

I soaked all the attenuators, one channel at a time, and this time I worked
the set screws quite a bit, both directions. I hadn’t done that before. I
had to do that procedure 3 times, but at the end all is fine on that front.
They must’ve been extremely dirty inside!! That also to away the grounding
issue, for some reason. Now the trace is quite sharp again.
However, the ripple I see on the trace at lower speeds (about 1ms/div and
lower) is still significantly there.
It could be the filter caps...
Unless someone has a better idea, I will hopefully replace them tomorrow and
see what that does...

BTW, I checked the two I already replaced for leakage (C4419 and C4439), and
there were ok...






Stephen
 

On Thu, Feb 11, 2021 at 07:01 AM, n4buq wrote:


Stephen,

I don't know if this has already been considered, but do you see that ripple
with the input switch set to GND for the channel you've selected?

Thanks,
Barry - N4BUQ
Hi Barry,

I’m not in front of it at the moment, but as far as I can remember, no.