Re: A 2465 teaser...

Chuck Harris <cfharris@...>

U400 was high on my list. Its pins have all been given a drop
of deOxit, a second U400 was tried, and the suspect U400 was
tried in the working scope.

I checked the bias resistor, when the hybrid was out, and it measured
correctly, it had continuity to its supply. I checked the HF response
5K pot, it is good, and was adjusted to near full value... which means
the scope would have been a good candidate for the 1K -> 4.3K series
resistor change that happened at later serial numbers.

But, I agree, it would be worth looking at supply and bias connections
a little more carefully.. probably doing something like drawing current
from them to smoke out bad solder joints, etc... that might not be seen
with a low current ohmmeter.

-Chuck Harris [TekScopes] wrote:

A fault on Ch1, Ch2 but not Ch3, Ch4 or vice versa makes U400 the obvious culprit but you have checked most possibilities. It might be a long shot but incorrect bias current into U400 would probably change its switching speeds and it's worth checking the bias resistor. Also clean the contacts in U400's socket?


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