Fixing a faulty PSU
Added 2021-07-22 18:34:26 +0000 UTCYou don't really need to know a lot about switch mode power supplies to repair most faults.
The components most stressed in these power supplies are the output diode and capacitor, as they both deal with fairly high current at high frequency, and that results in much hotter running than old-skool power supplies that only had to deal with 100/120Hz ripple current.
https://www.youtube.com/watch?v=MZDX-1Arg7o
It's often the capacitor that fails and bulges ominously on top. That's caused by increasing resistance (impedance) causing an avalanche effect when electrolyte bubbles form.
The replacement capacitor has to be a low ESR (Low Equivalent Series Resistance) to deal with the high frequency without heating excessively. The diodes also have to be fast recovery types, and preferable Schottky, as their lower voltage drop results in much less heat dissipation.
Comments
Noise is becoming a big problem, especially our amateur radio. 73 de N2NLQ active
Michael Thompson
2021-08-03 07:01:25 +0000 UTCVery common. The two outer pads are often bridged together on the PCB.
Big Clive
2021-07-28 04:59:38 +0000 UTCDouble diode was in parallel? Is this always the case? Is this normally done like this? Thanks.
Tony Weavers
2021-07-24 09:39:49 +0000 UTCNot a dumb question at all. The passive circuit current will generally discharge it fairly quickly, but when the main circuitry has failed it may hold a charge a long time. The official technique is to use a discharging tool which is two probes with a resistor to limit the current to a sensible level. Some people just bridge the cap and make a pop and shower of sparks, but that's frowned on. Even just measuring the voltage across it will gradually discharge it through the meter's resistance, although that is generally slow.
Big Clive
2021-07-23 20:42:36 +0000 UTCProbably a very dumb question but how do you safely discharge a capacitor thatβs got such a significant charge stored up.
Rik Kershaw-Moore
2021-07-23 20:14:28 +0000 UTCThat was a good video indeed. I've come to learn about electronics because I want to learn how to repair stuff. As Clive explained on many occasions, it's often just a capacitor or a diode in the PSU which renders several hundred β¬ of hardware unusable. And I have fixed a lot using basic know-how and a cheap soldering iron over the past years. I've always thought if a "Clive Repairs" playlist (from existing videos on the channel) or even a new monthly instalment "Clive Repairs" would be something good. I think so. "Will it Carbonate" and "Yet another Ozone Generator" or "New Crap Made from Chinesium" videos are fine and funny. But I consider videos like this one, where Clive explains common faults in electronics, how to diagnose and fix them, are great. One video like this may save tons of electronics from being dumped onto a landfill...
Mario2020
2021-07-23 18:16:12 +0000 UTCIt's fairly common these days. They've gone even further in the chips for USB PSUs and LED drivers and got the component count down to rectifier, capacitor and a current sense resistor on the primary side.
Big Clive
2021-07-23 17:57:25 +0000 UTCThat's the first I've seen the switch mode power supply all done in the IC.
2021-07-23 05:45:54 +0000 UTCThe 2A fuse may be on the input? The higher voltage primary side operates at lower current. The charger may have detected an older high impedance battery?
Big Clive
2021-07-23 02:29:37 +0000 UTCI believe it was a Sony unit.
Big Clive
2021-07-23 02:28:07 +0000 UTCWhat make of blu-ray player did this power supply board come from?
Gadgetman
2021-07-22 22:09:44 +0000 UTCI like to use 105C caps instead of 85C ones, but they have much higher ESRs.
Frank
2021-07-22 20:30:43 +0000 UTCAh sorry, I didn't realise. Thank you for clearing it up :) also was charging My car battery the other day, the battery charger was connected worked went into standby. Tried on another vehicle and it worked. Thought maybe the fuse had gone in it. Why could noco put a 2A fuse into a 5A charger?
2021-07-22 19:49:18 +0000 UTCThe patreon streams are every second week.
Big Clive
2021-07-22 19:45:27 +0000 UTCFab looking forward to watching, has the patron stream url been announced yet?
2021-07-22 19:44:08 +0000 UTCBy the time you have it open you may as well "service" (replace) the output cap anyway. Sometime in the last decade Farnell stopped calling them "Low ESR" and started using "High Ripple Current". Cross-check the data and you should be fine.
Mike Page
2021-07-22 19:04:30 +0000 UTC
