Hi,

got a Tek 2215a to repair. At start, caps on +5V was dead, making a
direct link between +5 and ground.

now I can see lines or signals on crt but wit maximum intensity, which
is not good.

Z-Axis logic is ok, if I turn either A or B intensity channel I can see
signal amplitude changing.
So problem comes from DC restorer, but even with service manual, I
can't see what's going wrong.

At the DC restorer's output (control grid) I only have the DC
component (which is -2 kv ??!!) and AC component from Z-Axis logic is
not here anymore. So I thought somes diodes where out but I checked
caps resistors and diodes all components seems to be ok. Also I checked
connection between DC restorer and CRT wires are's ok too. What can be
the problem ???

thanks and sorry for english level


Laurent

wrote in
ps.com:

Hi,

got a Tek 2215a to repair. At start, caps on +5V was dead, making a
direct link between +5 and ground.

now I can see lines or signals on crt but wit maximum intensity, which
is not good.

Z-Axis logic is ok, if I turn either A or B intensity channel I can see
signal amplitude changing.
So problem comes from DC restorer, but even with service manual, I
can't see what's going wrong.

At the DC restorer's output (control grid) I only have the DC
component (which is -2 kv ??!!) and AC component from Z-Axis logic is
not here anymore. So I thought somes diodes where out but I checked
caps resistors and diodes all components seems to be ok. Also I checked
connection between DC restorer and CRT wires are's ok too. What can be
the problem ???

thanks and sorry for english level


Laurent



DC restorer diodes can break down under HV,and a normal DMM test will not
show that.If you do not have a curve tracer to test them to their rated
voltage,then swapping them out is the best method.

does adjusting the CRT bias pot (on main board)have any effect on beam
intensity?

--
Jim Yanik
jyanik
at
kua.net

thanks for your reply. CRT bias pot has no effect, I think diodes are
out. But where can I find FDH5004 diodes ?? seems to not exist anymore
? FDH5004 are 225V 200mA , but is there other thing to know about it ??


Laurent

Common problem especially if the scope has been stored upright is small
flakes of cathode material shorting out from cathode to grid. If the
control grid is at the same voltage as the cathode, that's a likely
cause. An ohmmeter may not show this problem as it may not short out
until there's a bit of applied voltage or heat.

These can almost always be fixed by applying a charged 400 volt, 10uF
capacitor across cathode to grid (with the scope power OFF!, CRT socket
unplugged!).

And put a note on the front panel: "DON'T put this scope on it's
back!"