I've been fixing a Tek 2336, the previous owner seems to have had a catastrophic ground lead vaporization event on Ch. 1
And I've slowly been tracing my way through the input circuitry.
So far I've replaced the attenuator assembly entirely, it was blown apart.
I've traced out a few more faulty components, by comparing to Ch. 2 (which works just fine). But so far they all seem to be very expensive or unobtainium...
Parts I need to replace:
Q4, dual "ultra matched" FET >>
>>
(
Red)
Q10, dual NPN BJT >>
>>
(
Green)
CR1 & CR2 Diodes,
>>
(
Blue) >>
PhotoThis is "ground zero" on Ch 1 that I'm trying to repair.CR3 is also dead, but it's actually a reasonable part#, 1N4152R. Which I presume can be replaced with anything roughly equivalent. Don't know what the R at the end means. But 1N4152's are available.
Variable cap C1 seems to be fine. But I'm not sure I trust it, since it was directly in the path of destruction. But I guess, I'll leave it as-is for now.
Q4 and Q10 can be found online, but they cost 11$ a pop, used but tested. Since these seem to be super duper special matched pairs, I guess I'm screwed when it comes to finding a modern / new replacement?
The CR1 & CR2 (same type) diodes appear to be unobtainium. I can't find any information at all, other than that they're out of stock in every spare parts store, and that the service manual refers to them being used as protection diodes. Can I just replace these with generic small signal silicon diodes? Since they're sitting in reverse straight across the input to Ground, I guess that the total series reverse voltage needs to exceed the max spec for the input?
Any help appreciated!
PS.
Oh, and I've always wondered about
these old Sprague capacitors... I see them everywhere in old gear. They don't seem to go bad. Are they not liquid electrolytic? Are they generally considered good unless proven otherwise?