Tektronix TDS1002 w/ Ault SW424RA0000F03

[Behemot]

Re: Tektronix TDS1002 w/ Ault SW424RA0000F03

If there is some load on the supply I think the cap charge will be discharged quickly. Especially if it has some stand-by rail which remains active! Which I would say it has - there is likely some constantly-powered switch which turns the main PSU on. My Rigol has it that way…

[budm]

Re: Tektronix TDS1002 w/ Ault SW424RA0000F03

So C6 (+ is connected to pin 6 of SMPS IC 1 which should be the VCC pin of IC 1) start up/running cap is only 2.2uF (not 22uF?)? It is good for sure?
IC 1 is ?????
D2 is the rectifier diode that rectifies the AC through R10 (24 Ohms) from AUX winding of the transformer to provide running VCC once the SMPS is running. D5 is Zener connected to pin 6 and GND for protection.
Q2, Q3, Red cap are the Royer Oscillator that drive the Inverter transformer T2 for the backlights.

[rnjacobs]

Re: Tektronix TDS1002 w/ Ault SW424RA0000F03

Ok.
Swapped out IEC cable for one that felt "tighter". (Actually did this yesterday)
Reflowed solder on C14 socket, switch, fuse, and thermistor(??—green thing silkscreened TH)

The solder on the C14 socket looked good before hand, but the socket was kinda floppy, and it's definitely tighter now.

Tested, had one more power failure. Removed power supply from mounting posts so that I could get a voltmeter onto the solder side and ... haven't been able to reproduce since.

I guess it's in "burn-in" stage now to see if I can coax out a failure again. If I can't, how annoying that my problems seem to have been due to the lack of strain relief on the power socket.

Especially if it has some stand-by rail which remains active! Which I would say it has - there is likely some constantly-powered switch which turns the main PSU on. My Rigol has it that way…

Not in this supply. Mains—both hot and neutral—is completely isolated from all other components when the switch is off.

So C6 (+ is connected to pin 6 of SMPS IC 1 which should be the VCC pin of IC 1) start up/running cap is only 2.2uF (not 22uF?)? It is good for sure?

I apparently don't have a useful capacitance meter—just an ordinary DMM that goes up to 99uF, and no ESR measurement. C6 is nominally 82uF 35V. R3 and R15 are both 15kΩ 2(?)W.

IC 1 is ?????

KA7552.

D2 is the rectifier diode that rectifies the AC through R10 (24 Ohms) from AUX winding of the transformer to provide running VCC once the SMPS is running.

:enthusiastic learning:

Does anything keep power from being dissipated in the shunt regulator of R3+R15+D5 after it bootstraps?

Q2, Q3, Red cap are the Royer Oscillator that drive the Inverter transformer T2 for the backlights.

Ooh! Thanks for the correct term to look up!

[CapLeaker]

Re: Tektronix TDS1002 w/ Ault SW424RA0000F03

"I guess it's in "burn-in" stage now to see if I can coax out a failure again. If I can't, how annoying that my problems seem to have been due to the lack of strain relief on the power socket."

Well, that wouldn't be the first time.

[budm]

Re: Tektronix TDS1002 w/ Ault SW424RA0000F03

That is an odd number for C6, 82uF?

[rnjacobs]

Re: Tektronix TDS1002 w/ Ault SW424RA0000F03

how annoying that my problems seem to have been due to the lack of strain relief on the power socket.

Well, that wouldn't be the first time.

Indeed! Even after having encountered it on low voltage barrel connectors many times before it just didn't occur to me.

That is an odd number for C6, 82uF?

Just maybe the time constant of 30kΩ and 82uF and D5's zener voltage works out to something?? But that doesn't seem likely.


8 hours of running the power supply on its own (logging the 3.3V and 6V rails with a logic analyzer), and 12 hours of powering the 'scope later ... it seems to be just fine. Success!

Anyway, I'd like to thank all of you for walking me through the debugging process, even if it had nothing to do with bad capacitors

[CapLeaker]

Re: Tektronix TDS1002 w/ Ault SW424RA0000F03

glad to hear you got it fixed!

[luizbitencourt]

Re: Tektronix TDS1002 w/ Ault SW424RA0000F03

I know this is a very old topic, but I need to share!

I came here looking for a solution to this power supply fault; however, I've discovered that C6 caused the fault in my case. This 56 uF bad cap caused the failure.

I have the same oscilloscope model with the same power supply brand but a different part number (PN: SW424KA0000F02). Upon connecting the power cord and switching it on, nothing occurred. After removing the power supply board and measuring the J9 voltage outputs, they're all 0V.

The solution came from changing the C6 to a new one. Now, it works! All the outputs are good!

If someone in the future needs it, it can be a path to the solution!