Re: Lost Ch 1 on my 465 scope


Tom Lee
 

I have seen several scopes with blown inputs, although I acquired them in the dead state, with no knowledge of how they were killed.

That said, I'm sure it's not a big surprise that the input FETs do not fare well during big input overloads (the drain-gate diode tends to bite it, as it's used as a voltage clamp). Open up the 465, take a look around for obvious damage, and trace signals as they progress from the input forward. Don't be surprised if signal is lost pretty quickly. I've never seen wholesale destruction of a channel, so you may be lucky and find that the damage is confined to a small handful of components.

The 465 uses matched pairs in a can for the input source follower + bias. These were always somewhat rare, and they've only gotten rarer/more expensive over time. It's good that you have a parts queen. Hopefully that unit has good FETs, because I have a feeling that you'll be needing them.

Good luck!

--Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 10/12/2020 14:05, Ray, W4BYG wrote:
I accidentally touched the ground clip on my 465 Ch 1 probe to a "hot " AC-DC radio chassis. (I have an isolation transformer. Thought it was connected). It blew channel 1 out, but channel 2 and the rest of the scope's operations seem to be OK. I haven't yet started to trouble shoot the problem but tend to think it will be a major deal trying to fix channel one.

Has anyone gone thru this kind of an issue yet that they can offer any insight as to what gets damaged in a situation like this?

I bought this cope new in the seventies and have been the only user of it for all these years.

I have a spare 465 that is not working, which might serve for parts or modules as needed.

Your assistance and insight will be appreciated.
Ray, W4BYG

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