Dave M wrote:
"vic" wrote in message
...
Hi,

I recently bought an oscilloscope on eBay, and I don't know if the seller
lied in the description or if it was damaged during the transport, but the
trace is completely distorted and shows strange grid-like patterns. I made
a few pictures and a little video :

http://img222.imageshack.us/img222/1984/focused.jpg
http://img212.imageshack.us/img212/6566/unfocused.jpg
http://www.youtube.com/watch?v=c5RTaTM0tJk

The shape of the trace changes when I change the y-position dial. This
makes me think the problem is in the tube and not in the electronics.

I'm wondering if this could be caused by a bent grid somewhere in the tube
? Could it have been damaged if the oscilloscope received a shock for
example ?

I think the tube is pretty much toast, as well as the scope since there is
no way I could find a replacement tube (Tektronix 2225), but I wouldn't
mind to be proven wrong :-) Thanks.

I strongly suspect power supply problems. Check for bad power supply filter
capacitors. These are typical causes of distorted and fuzzy traces on a
scope.
As I remember, this model scope isn't particularly easy to disassemble and
repair, so get ready for some bench time. If you have or can borrow another
scope, that will make your troubleshooting a LOT easier. If you don't have
a service manual, you really should get one. You can buy a digital copy
from http://artekmed.startlogic.com/page2.html for $10.00. Artek sells high
quality scanned copies; I can recommend them from personal experience.
Cheers!

Tubes busted internally, if it was signal distortion the shape would be
the same top, bottom or middle of the screen.

You will most likely here glass tinkling inside the tube if you tip the
scope, also remove the blue implosion filter and check for tiny marks on
the phosphor from debris.
JC