TDS1002B PSU repair

[Slh]

Having successfully fixed my TDS1002B yesterday (for the third time) I thought I'd put a post out in case anyone finds the same problem.

My scope came to me with a fault where it wouldn't start up. The back light and LEDs would flash every second or so but it wouldn't get any further. I guessed that it was a power supply issue and investigated more. I believe it's got a flyback producing around 12V and then several other supplies off that one. The power rail would go too high, hit some sort of over-voltage threshold and then turn off. And repeat.

I spent a while desoldering, testing and replacing a load of components in the feedback circuit without finding any iffy parts. As you do, I plugged it back in and it worked! Aha, iffy solder joint!

It's failed twice more since then. The second failure was exactly the same but now I knew what I was looking for so I just hit a load of joints in the feedback circuit with the soldering iron until it worked again (I know - scientific right?).

The third failure, I was really struggling. Hitting all the solder joints in the feedback circuit with the iron did nothing. Eventually I found a tinned wire link that clearly had a bit of extra oxygen etc. No solder was sticking to it. I replaced the wire and problem solved.

When the scope came to me it had clearly had a rough life (some impressive laser burns). It's possible that the solder just cracked from physical abuse. Since then, it's had a fairly gentle life on the shelf as I tend to favour my Rigol so I don't know why it's kept failing.

[Vovk_Z]

I can add my experience too:
If it doesn't start or starts and goes off immediately (tries to start) and has some years then the reason is typically one or two aged electrolyte capacitors on a power supply board.
I guess your scope has some years.
I had similar problem several days ago with an old GDS-806. Two small electrolytes and one larger needed replacement. I have in-circuit ESR meter so it is quite  easy to find bad electrolyte cap with it. If you don't have one (I guess you don't) you may start with replacing all small electrolytes first. There is a stand by power supply (with small caps) and main one (with larger caps like 330 uF 25V).  Or just recap all electrolytic caps on a power supply board. You need caps of a Low-ESR type.
But be carefull with polarity - it's easy to put it wrong.
Check large semiconductors too just for a case.

[Paulo Peres]

I had PS issues with a TDS, too. These artesyn boards are designed with  caps too close of hot areas.
These are the first suspects.