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Hey guys, I bought another 2465 for parts, only 100 bucks. Have two 2465's already but couldn't stop myself from buying it. Channel Two 50 ohm DC Input is not working correctly. Can hear relay click, LED lights up, but input remains at 1Meg ohm. Can anyone save me some time and point me in the right direction? Where is the 50 ohm load located? I put new electrolytics in power supply, and new power switch. All voltage's good, scope is working fine except for the Channel Two 50 ohm dc input. If I use a 50 ohm termination on the bnc cable Time markers are correct.
David

Hey David,

The 50 ohm terminator is on the ceramic hybrid in the attenuator. It might
have been burned by applying too much power, but it's also possible that
you have an oxidized relay contact. There is overload protection for the
terminator, so it would have had to be a pretty gross overload to burn it.
These attenuators are fairly serviceable, I took some photos of mine from
my 2430: /g/TekScopes/album?id=12814. Here's the ceramic
substrate: /g/TekScopes/photo/12814/163755. I believe the
50Ohm resistor is the big black film on the top left - you can see that
it's been laser trimmed by the cuts on both sides of the film.

Siggi

On Sat, May 11, 2024 at 12:19?PM david via groups.io <davide_us=
[email protected]> wrote:

Hey guys, I bought another 2465 for parts, only 100 bucks. Have two 2465's
already but couldn't stop myself from buying it. Channel Two 50 ohm DC
Input is not working correctly. Can hear relay click, LED lights up, but
input remains at 1Meg ohm. Can anyone save me some time and point me in the
right direction? Where is the 50 ohm load located? I put new electrolytics
in power supply, and new power switch. All voltage's good, scope is working
fine except for the Channel Two 50 ohm dc input. If I use a 50 ohm
termination on the bnc cable Time markers are correct.
David

I got channel 2 to 50ohm by repeatedly switching between 1Meg and 50ohm, after several hundred times, but it is still intermittent. Believe the relay contacts are the issue. Where is that relay located?
David

So, the relay contacts are in the attenuator? I really don't want to remove the front panel if I can avoid it. Knobs are prone to breakage when removing them. But at least I'm sure that the relay contacts are the problem. If it continues to be an issue, I will have to open it up. I'm wondering if warming the knobs with a heat gun will allow me to remove them without breaking them. When I had to replace a BNC connector on my first 2465, I broke one Knob during removal. Previous owners probably never used 50ohm DC input enough to keep relay contacts clean.
David

Now that I think about removing the front panel, it comes off without removing the knobs. I had to remove the knobs to replace the BNC connector. Are the relay contacts hard to get at in the attenuator? I don't want to damage the attenuator.
David

?ann lau., 11. maí 2024 kl. 13:26 skrifa?i david via groups.io <davide_us=
[email protected]>:

Now that I think about removing the front panel, it comes off without
removing the knobs. I had to remove the knobs to replace the BNC connector.
Are the relay contacts hard to get at in the attenuator? I don't want to
damage the attenuator.

Once you get the attenuator out, it’s easy to get into it. You do need to
desolder the connection to the preeamp, though. Be careful with the lion
foot contacts, though.