Tektronix T935 oscilloscope P.S problem

[Faz]

Hi all. need help to fix an old analog oscilloscope, which keeps blowing fuse.

 

[JimB]

You have not given much information there Faz.

Do you have the manual/Schematic for the scope?
Which fuse keeps blowing?
Open the case and examine the PSU for any obvious faults.

Not much else that I can suggest.

JimB

 

[Faz]

Hi JimB,
Thanks for your reply, and sorry for not answering earlier.
I have a T935-35Mhz oscilloscope which was working fine before I put it aside for more than 10 years now.
I turned it on that day, the ON led flashed once and that was all.
I have very basic knowledge in electronics, but have no choice other than try to fix it by myself.
The fuse which was blown is F722 on the power supply diagram , it's a delayed fuse I guess, of ( 0.062A/250V/20SEC )
on the unregulated 100V line.I replaced it with a fast 300mA/250V for testing, but when turned on, some smoke came up.
After inspection, F722 was fine, but R458 on the CRT board was burned and F700 on the PSU was dead.
I concluded that 300mA was too much as a replacement for F722 and assumed that a shorted component was on the right side of it,
and since C458 seemed to be a perfect suspect, I tested it and found its value unstable.
I replaced F700, F288, R458 and C458, and everything is in order now, except that I'm not sure whether
C458 is the only cause of this problem.

Any idea about who caused what in all this would be appreciable, and thanks anyway.