On 21 Feb 2008 14:11:35 GMT Jim Yanik wrote in Message
id: :

JW wrote in
:

On 20 Feb 2008 16:01:59 GMT Jim Yanik wrote in
Message id: :

JW wrote in
:

Hello all,

I have a Tek 475A whose CH1 bandwidth falls off as the input
frequency increases. At 200MHz, the vertical amplitude is about half
of what it should be. CH2 is working fine. The fault seems to exist
no matter what the vertical sensitivity is so I don't think that
it's the extenuator, and the 100 and 20MHz bandwidth limiter also
appear to be working. Does this fault suggest anything in particular
to the experts out there?

Thanks!

If the problem is just on Ch1,then you have a problem in Channel 1.
Ch 1 and 2 don't combine until the delay line driver/channel
switch,IIRC.

the tiny HF trimmer caps in the 400 series had a habit of developing a
black oxide underneath them that effectively insulates the rotor from
the solder pin,making the cap -open-.(and no effect when adjusted)
They also would freeze so they could not be turned without breaking
the screwhead loose from the rotor disc .

essentially,you have to replace the bad trimcaps.
Then recal per the cal procedure.

Thanks, Jim. Given the age of this scope and lack of a
schematic/service manual, I think I'll just scrap it.


doesn't the BAMA site have any 475 manuals?

Yeah, but only operators...

475's were good scopes;I doubt you'll find any new scopes as good.

I'm sure that I can use parts from this one to fix the next one to come
across my bench. I work as a tech for a test equipment salvage company,
and I'd have to be able to justify my time and cost of calibration for
this to be worthwhile. Not having the service manual (or having to pay for
one) on a scope of this vintage just isn't worth it.