Dumont / Fairchild 401B Oscilloscope repair tips ?

[EE-digger]

I got this scope a few years ago from my neighborhood pizzeria.  The guy came from electronics and was cleaning his basement.  Funny thing is, this is the first scope I ever owned, back in 1970.

Summary:

brightness good
intensity works
focus works and decent
horizontal and vertical deflection both deflect only 5% of normal  <---
timebase works
y input - quiet when touch input with finger but then, deflection is way off
positionining - x position is centered about 1" from left edge of screen, only has about 1/4" adjustment range

Since both x and y deflection are broken, I'm thinking maybe a plate voltage?  Haven't worked on tubes in decades. 

Could be cap problems but with all systems sort of working except for deflection and positioning, maybe not.

Your thoughts are greatly appreciated!

[George Edmonds]

Hi

That should be good fun to work on, havent repaired such a scope for about fifty years.  Take care with 400VDC supply derived plate voltage.

G Edmonds

[EE-digger]

I found the manual with schematic at BAMA.  Nice, traditional schematic on two large pages.

They do have a rudimentary troubleshooting chart.  The X and Y amps are almost identical.  I see a +150V which they don't talk about but suspect that might be the culprit, common to both channel's symptoms.

Now for the reality check.  This is only for fun.  The bandwidth is spec'd at 30% down at 100kc, yes, kilocycles.   

I recall taking a direct hit from a color CRT anode on an early color TV about that many years ago also.  Most zaps today are self inflicted during ESD product testing.

[N2IXK]

Had one of those scopes decades ago.  Had lots of intermittent issues with the strange "surface mount" tube sockets they used on the circuit boards.  Solder joints would crack, or the contacts would loosen up.