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?
I noticed that the pinouts for the chip following the dual FET (U1290), are
incorrect. Doing a diode test on the chip, there are several pins
mislabeled. The external circuitry seems to go to the pins as shown on the
schematic, but the internal circuitry ohms out to different pins. This would
only be an issue if you ohm out the chip like I did to see if the chip was
bad. If anyone is interested, I can post what seems to be the correct
internal circuitry.
bg

"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".

I noticed that the pinouts for the chip following the dual FET
(U1290), are
incorrect. Doing a diode test on the chip, there are several pins
mislabeled. The external circuitry seems to go to the pins as shown on
the schematic, but the internal circuitry ohms out to different pins.
This would only be an issue if you ohm out the chip like I did to see
if the chip was bad. If anyone is interested, I can post what seems to
be the correct internal circuitry.
bg



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

--
Jim Yanik
jyanik
at
kua.net

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".

I noticed that the pinouts for the chip following the dual FET
(U1290), are
incorrect. Doing a diode test on the chip, there are several pins
mislabeled. The external circuitry seems to go to the pins as shown on
the schematic, but the internal circuitry ohms out to different pins.
This would only be an issue if you ohm out the chip like I did to see
if the chip was bad. If anyone is interested, I can post what seems to
be the correct internal circuitry.
bg



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

"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

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

"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

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 ch1 connector, but connected a power connector backwards. It
blew one of the dual FETS and the other seems to have a leakage problem.
There is DC on the gate where the attenuator output connects. The one meg
resistor in the attenuator output is not low enough to pull the gate to
zero. Out of the circuit, I don't see anything wrong with the fet.
BTW , you are a great resource for these tek products, thanks.

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




Now that's certainly not something I'd have expected. I'll keep it in mind
should my 465 ever misbehave in that way.

"James Sweet" wrote in
news:A_PYi.24184$Cb.6275@trnddc08:



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




Now that's certainly not something I'd have expected. I'll keep it in
mind should my 465 ever misbehave in that way.




definitely a weird one. only had a couple of those,as I recall.


--
Jim Yanik
jyanik
at
kua.net