Tek 2430 (non-A) Overheating Somewhere(?) - Stinks!

[wb0ldj]

A few days ago, I got a Tek 2430 from my friend at the local electronics emporium.  He said it came up, but smelled bad, so he shut it down.  When I got it home, I pulled off the case, turned a fan on the CCDs and fired it up to check the voltage rail test points on the side board.  Every one measured exactly where it was supposed to be.  There was a little bit of a scorched PCB smell, but it wasn't that bad (no magic smoke!), so I let it go.  The Self-Test screen came up for several seconds and then the screen went immediately into a display of the A and B sweep lines.  I was able to move them all around, and when I hooked the probe to the calibrator, I got a nice square wave.

Since I wasn't familiar with the 2430 screen navigation, I went to the other side of the shack to pull up the user guide on the computer.  A few minutes later, I went back to the scope.  The 3 GPIB status LEDs were still lit, but there was nothing on the screen at all.  The fan was also throwing out a LOT of "scorched PCB" smell (hot phenolic).  I shut the scope down and waited a couple of hours, then tried powering it up again.  Absolutely nothing on the screen.  The longer I had it powered up the stronger the scorched smell got, so I shut it down.

I spent most of the night removing the boards from the scope and carefully inspecting them for any signs of overheating.  Nothing.  No scorched spots on the boards, no visibly overheated components, no discoloration anywhere.  This morning, I put everything back together and fired it back up (out of the case with a fan on the CCDs).  Nothing on the CRT!  Every single voltage test point on the side board showed exactly on spec.  By the time the scope was on long enough to make the measurements, it was really starting to stink again, so I shut it down.

At this point, I am stumped!  I have the complete (original) 070-4917-00 (1-1/2") manual and I'm reasonably experienced at trouble shooting, but I'm sort of at an impasse.  I would have thought that anything that caused that much of a stink (like a shorted component) ought to show some physical signs of overheating somewhere or at least dragging one of the rails down, but to this point, I haven't been able to find any.

Anyone out there who has experience with a 2430?  Do these symptoms sound familiar to anyone? 

I know the smell was there before I fooled with the scope, because the guy at the store mentioned it, but the scope did work the first time I had it powered up (for a few minutes anyway), so I'm guessing that it's a power supply issue, but I can't find any indications that something in there is getting hot, and of course, there's no way to get into the P/S while the scope is powered up.

Thanks for any help or ideas!!!
Mike Harmon, WB0LDJ
mharmon at att dot net

[george.b]

Have you checked the infamous RIFA capacitor on the PSU input? On my 2430A it self-combusted. Or, well, anything on the PSU, really - it's under a metal shield IIRC, if you haven't removed it, you might have missed something.