Paralleled caps and occasional voltage drops in smps output. Should I be worried ?

Thread Starter

p699

Joined Oct 8, 2021
18
Hello everybody :)
I bought a used/old network switch from another person for a nice bargain price, and had a look inside. The monkey in me thought if I can replace these old spent cheap TAICON caps with my spare nichicon VZ(M) high ripple current caps maybe I can make this device last longer and get a bang for the bucks I spent. So I started replacing them.

At the input (from left in the attached pic) I replaced the two large 680uF caps. I operated the device for sometime. No bang or smoke, so I continued. Now I replaced the 330uF 6.3v (see the red arrow in the attached pic). I didnt have the correct value capacitance at hand, so I paralleled four 100uF 50v caps. I attached extra probe wires at the base to monitor the output voltage. Started the device, Operated it for 30 minutes, fortunately no loud bang or smoke :)

The probe wires I had soldered showed a "steady 3.39v". Occasionally it dropped to 2.99v or 2.75v for a split second and went back up. This happened only once in maybe 3 minutes randomly. I was browsing the internet all these 30 minutes and there was no restart or cut in ethernet connection. Maybe this output isnt used to power the processor.

So my question is : Is my paralleling of caps (hence low esr,esl) has caused instability or its just a voltage sag induced by sudden power demand from the processor hence I need not worry ?

Sometime back , I had tried to build switching regulated power supply from scratch and know what oscillations look like. But here 99% of the times the voltage held steady at 3.39v. I have monitored the voltages with just a DMM and I dont have an oscilloscope to observe in detail. Have you experts observed such occasional sags in your switching PSUs ?

Thanks for your time.
IMG_20220313_194208.jpg
 
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Thread Starter

p699

Joined Oct 8, 2021
18
Note IC beside the 100 inductor is RT 8293AH, FREQUENCY CONVERTER 340KHZ.
https://agelectronica.lat/pdfs/textos/R/RT8293AH.PDF
I noticed the Vout also overshoots sometimes upto 3.47v. Will such occasional fluctuations affect lifespan of the device/components ?
 

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Thread Starter

p699

Joined Oct 8, 2021
18
Today morning I took another identical network switch, in unmodified and original form, soldered probe wires and observed. It too behaves the same, occasional drops in voltage below 3v. This behaviour if labeled as instability exists even in original circuit and the device has worked for few years under this condition. I am beginning to feel like this modification wont hurt the device.
 

Thread Starter

p699

Joined Oct 8, 2021
18
I "recapped" the entire board. The fluctuations I complained about have become rare. I caught it happening again but the voltages are far more steady than with the older capacitors. If any other person reading this is sitting on the fence regarding recapping I definitely will give my recommendation to try it out. I believe better quality power will make the device last longer.
I now conclude this project. Thanks all :)
Bye
 
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