Tek TDS 540 problem

[Dewey]

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...

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

Any idea what happened? Did I erase some critical firmware that is
required to boot or something? I flipped the switch back, but it
wasn't any help.


Any recommendations?

Thanks

Josh
Seattle, WA

 

[Dewey]

UPDATE to last post:

Okay! I pushed the mystery button on the top circuit board again
(labeled "S1"), with the memory switch flipped in the "unprotect"
position, hit power, and the unit fired up and stayed on again.

Same situation as when I first got it though...fan stays running,
front panel lights come on, but there is nothing on the screen.
(Indicentally, the front panel lights don't go off either). If I turn
it off and then back on again really quick, you do see the screen do
what an old B&W TV would do when turned off - there is a very
momentary squiggle of a line as the high voltage dies, but otherwise
no light.

Any ideas are greatly appreciated!

Thank you

-Josh

 

[mike]

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...

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

Any idea what happened? Did I erase some critical firmware that is
required to boot or something? I flipped the switch back, but it
wasn't any help.


Any recommendations?

Thanks

Josh
Seattle, WA

Change the caps and pray.
You haven't a chance in the hot place in fixing it after you mess around
and lose the calibration...unless you know someone with the magic...
google 'TDS540 "simple green" '
mike

 

[JW]

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.