It's prob. well known, people usually damage the front end of a SA, by applying too much D.C. (Statistically, that results in opens or shorts [There is a low prob. of other modes of failure])
That said, over the years, I have had a chance to buy Tek SA plugins, for 7000 frames; but, never bought one. The ones I looked at were cooking away, in the frames, producing a lot of heat.
I don't know (And, I would like to know.) whether that is a common failing? of the Tek SA plugin designs (producing too much heat?)
If there is a lot of heat, and supposing one is talking about a Schottky diode ring mixer (for example)...there are papers that suggest "heat", over long term causes the diode's parameters to change.
So, if in fact Tek SA plugins operate normally producing lots of heat, and a particular SA plugin has been in service a long time...I would think that the mixer could degrade.
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Pjotr Tolstiakov <ilmuerte@...>
Sent: December 20, 2017 12:25:54 PM
Subject: Re: [TekScopes] 7L14 Bad first mixer?
The greater sign by the -30 ( < -30) means that the variable gain isturned out of the cal position
to some increase of gain. and the noise floor is to high, should be 20dB lower than shown.
You're welcome and yes, you're right. I tried now the same settings on my
7L18, may not be fully comparable but noise level is indeed much better.
The reason I think the first mixer is bad is it has the same displayconditions as my old 7L14 with bad mixer.
I don't have much experience with SA mixers, always thought these are
simple devices that either work or not. Is it really possible to "singe" it,
so that it still works, but with lower sensitivity? I mean is it common to
get only partial damage?
The price on the auction is already stellar so I'll pass for sure as well.
Best Regards, Nenad