Re: Tek TDS 540 problem

On Fri, 25 Apr 2008 16:52:46 -0700 (PDT) Dewey <josh.dewinter@xxxxxxxxx>
wrote in Message id:
<f04d34f9-a4bb-48d6-8a2e-d7b3a96fc05c@xxxxxxxxxxxxxxxxxxxxxxxxxxx>:

Hi
I just got a used Tektronix TDS 540 o'scope. I was advised that
these had a huge problem with leaky caps. Before I had it, it was
explained to me that the panel lights lit up, but the screen didn't
show anything. In asking the owner of a repair shop what he'd
recommend I do when I got it, he said to make sure the memory protect
switch wasn't in the unprotect position.

So, today I got the scope. Sure enough, there were panel lights on
power-on, but no screen. I tried to find the switch through the holes
on the side of the case, but couldn't seem to get it. I opened the
case, found it, and flipped it. I then powered up the unit, thinking
I had put it in the "protect" mode. As it turns out, I didn't. It
had been in the protect mode when it arrived.

When I power it up now, the front panel lights come on and the fan
starts to whirl, but only for about half a second before they go dark
and the cycle repeats, click-click-click...

Could be that electrolytic caps on the power supply have high ESR. BUT,
try disconnecting the ribbon cable that goes to the deflection board. If
it powers up with this disconnected, the problem may lie there. I had a
TDS784D that had this problem, turned out to be a shorted MRF544
transistor on the CRT neck board.

Stupidly, I also remember pushing a little tiny button mounted on
the top circuit card momentarily.

That switch has the same function as the front panel power switch. Not to
worry.
.