"bg" wrote in :


Jim Yanik wrote in message ...
"bg" wrote in :


Jim Yanik wrote in message ...
"bg" wrote in :

Both channels on the verticle front end are damaged. One dual FET
follower is a definite (Q1297). It is tek part number 151-1090-00.
I haven't seen one yet using google. Is there a replacement or two
discretes out there that will work?

They would have to be matched,else you get an offset.

check this out;
http://www.sphere.bc.ca/test/tek-parts/tekparts2.html
it appears they have some 151-1090's for sale.
they also cross ref to a "2N5911 family".



the 155-0078-xx is used in a lot of different scopes,several 7000
series plug-ins,too.

--
Jim Yanik
jyanik
at
kua.net
Thanks Jim. I had already been to that site and didn't see it the
first time, even with my glasses on!
Offset is the issue I am having.
bg



I've seen the input BNC connector cause DC offsets!
seems it absorbs contaminants and becomes a weak "battery".


--
Jim Yanik
jyanik
at
kua.net

I replaced the channel 1 connector, but plugged in one of the power
connectors backwards. So I blew one of the dual fets and the other one
seems to have a leakage problem. There is DC on the gate lead right
after the attenuator. The 1 meg resistor in the attenuator output
isn't low enough to pull the gate to 0 volts. Out of the circuit I
can't measure anything abnormal with the FET but in circuit the DC is
there. BTW , you are a great weath of info for these tek products.
bg


are there input protection diodes on that FET input? did you disconnect the
atten PCB and still have the DC?
(and then GND the gate and the offset goes away?)

--
Jim Yanik
jyanik
at
kua.net