"c4urs11" wrote in message
...
On Sat, 11 Jul 2015 17:25:35 +0000, Cursitor Doom wrote:

Hi all,

Forgive me for not having very much useful detail on this, but a friend
has a scope that's unfocusable and produces a thick trace. My immediate
reaction was maybe noise getting into the signal path from a faulty mains
filter or maybe an internal component in the smps section failed, but he
reckons he's ruled out the latter as apparently it's a linear supply. He
doesn't have another scope to check the rails for noise with so he's kind
of limited. Anyway, that was only my hunch, I don't know the precise
model of scope this is; I just wondered if anyone would like to toss in
their 2c worth if they've encountered this issue themselves and what
might be the cause of it?
thanks,
cd.

Anything Tek one address:
https://groups.yahoo.com/group/TekScopes

Cheers!



Well, there's no real substitute for actual troubleshooting - but having
said that, I understand some Tek's have had bad focus potentiometers, and
there's always the possibility of a bad high-value resistor in such a
circuit. A bad 2.2 meg resistor caused a B&K 'scope of mine to not quite
focus. The focus pot ran out of range first. Replacing the resistor fixed
it.

If you do attempt to troubleshoot, be aware there are some rather high
voltages in such circuits.


Mark Z.