Tektronix 2235 Dead CRT?

[kontour]

Picked up a nice Tek 2235 for cheap the other day. Get it home and find CRT works but trace is all messed up. Following tek troublshooting guide points to an issue with horizontal deflection. Get to the end of the chain just before the CRT with everything checking out ok.

I’m probing the last testpoint when the probe ground lead slips off the test point. I hear a bzzt and the scope loses power. Check fuse and it’s blown. Scope will now blow the main fuse everytime it’s powered on. I can bring it up on the variac to about 60v and the indicator lights come on and I can hear transformer whine but then the fuse pops. Swear at myself a lot before packing it in for the evening.

Return the next day to find the culprit for the mucked up horizontal was simply that the lead had come off the pin on the CRT aka I’m an idiot and should have checked the most simple solution first.

So now I’ve spent the last two nights attempting to troubleshoot the power issues. Appears the SCR mosfet is dead but can’t find any other definitive issues. $80 worth of parts from digikey later and all it needed was a new SCR.

Scope now powers up fine but I’ve got a lot of distortion in the CRT, both at the edges and in the middle as per the photos below.

I have very limited experience with CRT’s so I’m wondering if the CRT is dead or I’m looking at another issue to diagnose….

[kontour]

Having played with it a bit more, I’m leaning towards this CRT being damaged by impact before I purchased it, see picture below.

[EggertEnjoyer123]

Does the horizontal output still look good?

You could have killed other components when you shorted the supply out,

[David Hess]

Having played with it a bit more, I’m leaning towards this CRT being damaged by impact before I purchased it, see picture below.

That is what it looks like to me.  What often happens is some glass supports inside the CRT fracture due to external impact, and the pieces dent the scan expansion mesh causing the CRT geometry to become weird and non-linear, like a crumpled mirror.

You might gently shake the CRT or roll it and see if you hear any rattling inside.  Visual inspection toward the back of the neck might show lose pieces.