"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!

--
HAM AND EGGS -- A day's work for a chicken, a lifetime commitment for a pig.

Dave M