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!


Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070

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

Join to automatically receive all group messages.