Oscilloscope repair

[dexters_lab]

i have an old Gould 1421 Analog/Digital (circa mid 80s) scope thats gone faulty on me and wondered if someone could suggest an area of it's internals that would be a good place to start looking. Thankfully i do have a schema.

The problem is on the display, on both channels the trace seems to fold back into a central point on the crt that never moves. Looking past the funny visual i can see a signal being displayed and the storage side all seem to work so i suspect it's something with the crt driver side.

I have a short video of the fault here: http://www.mr2.net/media/gould1421fault2.wmv

[qno]

It looks to me like some kind of power supply problem.

It looks like the x and y amp break down resulting in the beam ending up in the middle of the screen.

Because this is both x and y I would start in the power supply. Look for oscillating or constant switching on off.

The problem could be a capacitor that has lost all capacitance or something simple as a bad connector or a broken PCB track

[Neilm]

It is worth just reminding you that any CRT has some high voltages in it. So be careful when probing around and make sure that any caps are discharged.

[dexters_lab]

thanks guys, will check psu and see. It's certainly old enough for bad caps.

[qno]

Also check for broken power resistors.

[walterdelbono]

awesome video...

good luck...