Bought this scope from the local electronics shop as not working, on power up she smelled a bit funny. Opened it up and it looks like something let the magic smoke out on the power supply pcb. I'm assuming it's a cap (tantalum?), however the manual has no overlay of the psu board. Anyone ever had one of these scopes and know of a psu overlay? Also, what could have cause this little guy to blow?

Thanks,
M.

 

Too much voltage, reverse voltage, or sometimes tantalum caps do this 'cos they feel like it.
Can you trace out what it is connected to to decide the polarity?
Otherwise, you could remove it and (quickly) switch on and check the polarity.

 

The, "why" of it: Because parts fail.
It might be that the capacitor failed all by itself or something else failed first and killed the capacitor. After you're finished finding all the faults, you might figure it out. Until then, it's all guessing.
I think the stupidest question I ever heard was, "Why did it choose today to fail?"
"Why did it fail" isn't anywhere near as stupid because finding the cause is often a very important question. It's just that you can't figure that out until you find all the failures, and sometimes, you still are left with nothing except, "Parts fail".

 

Too much voltage, reverse voltage, or sometimes tantalum caps do this 'cos they feel like it.
Can you trace out what it is connected to to decide the polarity?
Otherwise, you could remove it and (quickly) switch on and check the polarity.

Thanks, I'll trace out around it to get an idea of what's going on and the polarity. I just don't know what value to replace it with! Once I know I'll put in a new one and test all of the supply voltages (using the conveniently located near by with lovely marked test points - thanks Tek). I also inspected all the of other boards and plug-ins and there are no other physically damaged/leaking or blown components.

 

Do you have this manual? You do now.

It has the Electrical Parts List and the Part Loaction Grid tables and drawings.

 

Do you have this manual? You do now.

It has the Electrical Parts List and the Part Loaction Grid tables and drawings.

Thanks! However, I've already been through the manual several times, it has all the location grids and schematic for every board (including the HV PSU) but not the main power supply board.

 

Do you have this manual? You do now.

It has the Electrical Parts List and the Part Loaction Grid tables and drawings.

This is the closest I've found in another copy of the manual.

 

Thanks! However, I've already been through the manual several times, it has all the location grids and schematic for every board (including the HV PSU) but not the main power supply board.

Oh. I see what you mean. I did not look closely at the manual I uploaded. I just assumed that it was complete.

This is the closest I've found in another copy of the manual.

Where did you get the drawing you posted? Did it come another Tek model that shares the power supply board?

 

Oh. I see what you mean. I did not look closely at the manual I uploaded. I just assumed that it was complete.


Where did you get the drawing you posted? Did it come another Tek model that shares the power supply board?

I found another version of the manual that says "Complete, OCR." Got it from this site, http://w140.com/tekwiki/wiki/5441

 

Update: After desoldering the cap, I noticed that Tek was nice enough to put polarity identifying pads, and following the polarity of the diodes (cathode to square pad) answers the polarity question!

 

Do you have a capacitor 22uF - 100uF and at least 63V? You could connect that and then measure the voltage across it.

 

Do you have a capacitor 22uF - 100uF and at least 63V? You could connect that and then measure the voltage across it.

Thanks for all the replies! Called up a friend and he said try 10uF @ 25v. So to double check the polarity I powered her up and took measured across the pads(15vDC) and look at the the face and it was working! Everything seems to be working fine now, just need to pop in a cap!

 

When you have fitted a capacitor, do check the supply voltages just to be sure.
It looks like the capacitor just decided that its time had come.

 

When you have fitted a capacitor, do check the supply voltages just to be sure.
It looks like the capacitor just decided that its time had come.

Thanks, popped in the cap and powered her on and she works like new, still well within spec too!

Here are the voltages:

+5v is 4.95v
+15v is 15.00v
-15v is -15.04v
+30v is 29.98v
-30v is -30.00v
+200v is 202.6v

Everything seems to be in order, thanks for your help!

 

Here's a pic of the beast!

 

Check page 4-16 of your manual. You will find that your plus 30V is out of specification. Of course I'm assuming you considered your meter error when doing the tests.

 

Check page 4-16 of your manual. You will find that your plus 30V is out of specification. Of course I'm assuming you considered your meter error when doing the tests.

View attachment 110231

Manual says 29.925v and I recorded it at 29.98v, the meter I used is a calibrated Fluke 27/FM with a +/-0.1% +1 accuracy(at ambient temperature between 20 and 30 degrees C). I feel confident in that measurement, and I took it more than once to be sure. I've also been running the scope for several hours now, doing various tests and feeding it various signals with a signal generator (1kHz shows up as 1kHz), and everything seems to be working nicely! Readout is working, nice bright display, storage mode works, all the controls are responsive.

Thanks for the suggestion though, I will keep that in mind if I get around to going through the calibration procedure sometime in the future.

 

I misread what you wrote. I got dyslexic