1. Home
  2. Electronics Repair
  3. Tek2215a maximum intensity problem

Tek2215a maximum intensity problem

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

Reply to
belliv
Loading thread data ...

snipped-for-privacy@gmail.com wrote in news: snipped-for-privacy@z14g2000cwz.googlegroups.com:

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
Reply to
Jim Yanik

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

Reply to
belliv

snipped-for-privacy@gmail.com wrote in news: snipped-for-privacy@g47g2000cwa.googlegroups.com:

No,any small signal diode with similar Vr voltage and current ratings would work.

--
Jim Yanik
jyanik
at
kua.net
Reply to
Jim Yanik

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!"

Reply to
grg

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.