Electronics > Repair
DSO-X 3024A Power Supply defect
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Spacemouse:

--- Quote from: jtmp on September 23, 2022, 04:29:38 am ---I have had the same blown power supply on a DSO-X 2012A, and replaced with a Mean Well RPS-400-12 following the advice above.

However now I am getting a ~120mVp-p ripple @~4kHz on the scope trace, even with the probe shorted to ground.

Have I done something wrong here, or are these power supplies much noisier than the original? I don't remember what I used to get but surely it wasn't this bad?!

Cheers

--- End quote ---
Hi! I had the same issue when I changed the power supply to one without sense inputs. The ripple was not that bad, but it was very disappointing as it would mean I could not use the oscilloscope. I remembered that in threads where people fixed the original PSU, the voltage was 12.7 or about that. Also, the PCB of the oscilloscope is marked with +13V, where the PSU output is fed into the oscilloscope. I turned the voltage to +13.0, and no ripple was seen.

Last, I checked with a lab supply with +12V. The ripple was not as bad as with the AC PSU, but it was still clearly visible. I guess the lab supply does not handle long wires well when the currents are about 5A.

Thanks, everyone, for your help. I was about to yield to Keysight and their 4200 EUR for the fix they offered.
charlyd:
Hi i have this question reading the posts here and tasting the replaced PSU doesn t bring that much fun when it comes to the power button for example not talking about the fitting.

why not repair the original PSU with components which will create not that high temps?  for example those 4x  22k Resistors on the bottemside can also be replaced by 1 watt resistor not? and the 420v /100uF Cap with an other model. and when those resistors don t get that hot the cap will last much longer.
Eclipze:

Another DSO with a power supply self destructing.  I'd previously replaced the resistors and added a small heatsink.  This time the MOSFET failed.  Likely capacitor issue.

I replaced with the EPP-300-12.  I liked the specs on it.  The datasheet has all the connector parts and pinouts shown clearly.  The power switch logic works the same.  Mounting holes align.  Although taller, it still squeezes in underneath the connector/wiring.  Adjusted to 12.7V.  Passed all self-tests and probe checks.  Voltage ripple on 10mV scale is low, as usual.  Back in service.  Attached pictures in case anyone wants to double check their wiring using this power supply.  I first powered up without the main connector fitted, to verify the 12V supply and no surprises.
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