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Siglent SPD3303D review
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FrankBuss:
Just a short update: I've discussed the remaining problems with the very helpful Siglent support and after the fix the power on/off spikes are completely gone and the short circuit problem is solved for me, too.

5V short circuit test after the repair:


2.5V short circuit test after the repair:


I'll publish the repair instructions with the CAD screenshots as soon as I get the permission from Siglent.
Hydrawerk:
Well, always buy a product that is in production for one year or so. Never buy a very new equipment with hardware bugs.
FrankBuss:
Siglent permitted to publish their CAD screenshots, this is what they sent me:



The instructions:

a: add a transistor, model 2N3904(Thru-hole) or MMB3904(SMD), connected as the circuit shows
b: add a 1000pF capacitor, connected between pin 2 and pin 3 of JC1
c: change the ZD703 to the 3.3V zener diode 1N4728A
d: replace CC13 with a 100nF capacitor, in series with a 20k resistor

Step d was a bit complicated, but I managed it by soldering both parts upright at one side of each pad, and then connecting the top sides with a wire. The old CC13 was 100nF, too, so could be used for this step, if it survives the desoldering. I used a new one, just to be sure. 0805 works fine, but looks like the original parts are 0603, but I had already all passive parts in 0805. This is how it looks like:



Instead of soldering at JC1, which seems to be soldered to the board, I measured it with an ohm meter and looks like pin 2 of JC1 is connected to junction of the big 0.04 ohm current measure resistor at the bottom and the diode DC5, and to pin 1 of UC5 (the middle pin, bad numbering in the CAD diagram), which made it easier to repair, because I could solder the transistor and the new capacitor at the bottom and use just a wire for the other side of the new capacitor.

This didn't really fix the overshooting, but after some more communication with the support, I got another instruction: Change RC5 to 200 ohm:



I used 220 ohm, and now it looks (nearly) perfect:

Just to show the effect of the changes, before the repair:



and after the repair:



And the power-on/power-off spike is gone, too.

 :-+ for Siglent, now I can recommend this power supply without reservations. The support told me that these changes are already included in a new revision of the PSU, maybe ask them which version you get if you don't want to open it and fix it yourself :)
Zbig:
I've fixed mine according to this description and I can confirm that CH3 problems are gone now. Great job, Frank!
FrankBuss:
Looks neat with the heat shrink tubing and hot glue.
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