I believe that regulator output has touched the heat sink which is directly connected to the collector of the big transistor which caused that Cap to blow

That regulator for the fan made contact with the copper from the cooler and got shorted because you didn't isolated the board under!  🤣🤣🤣

I built that kit in 2019 - building it into a housing and added 10 turn pots and a Volt/amp meter.  And it works great !!  Best thing ...... unlike many of the constant current power modules  you can buy - this one actually does a great job with current limiting !!  It actually limits current down to 2.5 mA.  Great for power injection and testing diodes !!

For 37 years, I have been involved with electronics.
You just taught me something.
"Toothpick" <----- Sir... Thank you! Sometimes that is so frustrating trying to move solder away from a hole.

It's not only you, when I try to build something to show someone, sometimes I have such "luck" as well.

The best way  to learn electronics is this building something from zero. Nice one

It's funny... you went from "Electronics Repair School" into "ElectroBoom" in this video... loved it Sorin... :)

Gotta love the fact that your videos are so "organic". You also include fails along so we can learn from that, coming to a conclusion in the end and learning a new fix or a new way to blow up electronics, haha. Keep it up, Sorin! Looking forward to the next upload. Have a nice evening :_Lovee:

i built two of the power supplies powered up and op amps burned up  so i change op-amp to lm741 because higher voltage rail and use dip sockets. i also also use 2n3055 as output transistor. used if for five years now

Thank you, your videos make electronics fun again.

beware!!! :D
that kit is wellknown, and have some flawless, too.
the most easier flaw to fix is using for AO's a local power supply, like a Zenner and a resistor, calculated for no more than 30V over AO's, negative power included!
it's a -5V on negative, so, 30-5=25, but there are no 25 V Zenners, not 3 terminal stabs, so, 24 volts.
most easier is to use the already present 24V, for cooler.
some small adjustment for resistors, and is perfect.
of course, you need a nicely strong mains trafo, 24V or a bit more. or a bit less, if you accept a bit smaller voltage on full load... :)
(written immediately after i seen the kit... is a wellknown for me! :D now, play to the finish... i'm really curious what you will find about... as a side note, is a really antique schematic, older than 60 years, in some variants. one of them use 3/4 AO's in a 324, and the last one is used as overload indicator, doubled as relay activator... :P )

later: min 13: to much current on a diode in the bridge! it's what happens most of time, without dealing with small smps's :D
also, looks like you don't set the 0 volts, that blue multiturn is used to set the 0 volts, because this is a "virtual ground" power supply. for same reason you fried it first time with a 19 v laptop brick! :)
lemme see... you just repeated the very same mistakes me and a lot of people does for the first time they meet this schematic, and, later, this kit... chinese started to manufacture and sell those kits some 15-18 years ago! :)
i patiently seen the video to the final... Sorin, that blue led is NOT "power on" led, but "overload led", it need to be on only when you load the PS with more than your current limit! :)
why is all the time on? some of these kits are correct, some not... some have a slight different schematic than the original in that part, and led is on the opposite directions, and is on all the time. other kits have wrong orientation printed on pcb.

looks like electronics-diy point com shunned out that power supply, even this was their top-grade reason to check their website, a lot of years...
you can find a lot with a google search, but i have trust in "radioscamateurs" sites, so... check  the link down. i have not patience to search exactly about setting-up procedure, i had done it for some kits, and leaved it alone...
also, with a bit of more searching, you can find a giga-talk about that schematic on a romanian forum, in power supplies section. a forum i leaved it for some years, even if i was one of the only posters there, for a lot of years, too... :)

să fii iubit. :)

https://www.qsl.net/z33t/dc_0-30v_0-3A_eng.html

I originally posted something like this in response to someone's question, but it seems a lot of people miss the issue, so I'm posting again with some elaboration.

This is intended for use as a bench power supply. With a bench supply you really need to be able to deliver full rated current into a short circuit or close to a short. You may not need to do this often, but the need does arise. Your power supply needs to be able to survive it.

When the output current is set to maximum and the output is shorted, the power dissipation in the transistors will actually be more than 100% of the full rated output power of the supply. If the supply is rated for 5 A and 30 V, that means the transistors would dissipate 150 watts, minimum. If fact the dissipation will be even greater because the voltage across the transistors will be equal to the full unregulated voltage from the bridge rectifier and filter capacitor. For the 30 volt supply that might be 35 volts (or more). At 35 volts the transistors would dissipate 175 watts at 5 A. That is a lot of heat to get rid of!

If you use the regulator for some specific application where the output voltage is not very low, the situation is different.

With high powers it is important to be careful that the transistors used have adequate safe operating area. "Second breakdown" can limit the allowable steady-state power dissipation to something well below the nominal rating of the device. With low voltage this often isn't a problem, but it very definitely becomes a problem when you get up into tens of volts.

13:35 - Strange thing you didnt stop video recording and check what sparked. Its power supply for fan, little capacitor. 12:39 spark.
I believe that green pcb touched heatsink, and heatsink is soldered to the back of that big transistor. 18:29 you placed isolation tape on back :D

The little buck converter board was sitting right on top of the copper heat sink. Wild!:face-blue-wide-eyes:

the big transistor collector (probably 20V) touch the "ground" from your 5V regulator and blow up the track and the tiny regulator

I noticed that your current limit led is constantly on, it should only come on when the current limiting kicks in. On my board the silkscreen had a error and the transistor that controls the led needs to be rotated 180 degrees that will make the led work correctly.

12:40 if you go frame by frame first you see big spark that looks like it comes from transistor and then smoke + red glow from the capacitor on voltage regulator for the fan. I think that regulator touched fan pipe and capacitor on fan regulator shorted over the transistor 😎.

FYI when you pause the video you can move forward and backwards frame by frame by comma and dot keys on the keyboard 🙂.

Learning by doing is the best way to lean and to achieve experience and not be afraid of the unknown or new. Smoke is good, smoking lessons from Sorin are funny, familiar friendly and very infesting always. All the best “moșu!”. Big hug!Cosmin from Switzerland 🇨🇭!

This guy is great, I love this guy, he brings electronics into fun and fascination with his awesome videos👍

If you want to use it as a lab ps you should test it at low voltages at high current - like 5A, 3Vout, 24Vin - you will have to dissipate more than 100Watt. And the 3300mF filter cap is by far to low even at 2A, there will be huge ripple you shoot in your device. A ps at 12V, 5A MUST have a minimum 8600mF cap for low ripple, and yes your bridge/diodes must be adeguade. When you test ps the voltage should remain constant - on the bench when you repair something, like audio devices (a car radio, preamps, power amplifier, bt speaker etc) you mainly use 3.7 (lion battery voltage), 5 (standard logic), 12V (standard and car component), 15/18 (op amp) and you want something that gives a decent power with low ripple and low noise, not possible with cheap switching. Personally I would prefere different upgrades for this linear ps: good and big filter caps (if you handle with low voltage, a parallel of two 6800, minimum or one 10000), adeguate big heatsink and a good transformer (no matter if toroidal or classic) with a center tap, multiturn for voltage setting and I won't go over the 2 A - the pcb has no adeguate tracks for 5A after the bridge for continuos work. This kit consists of china component, better stay far under the limits, better "feed" them with a good filtered DC, the tl081 and final tr will thank you. My old lab ps, the one I use more, is 0-30V, 2A has a 100VA trasformer, two 10000 mF caps, big heatsink, it can stay on for days at 3V, 2A and that is the main reason to have a linear ps: simple circuit that can be easily repaired, a clean and stable current, better without noise of a fan. The best upgrade would be to have a trasformer with central tap (15+15V) double the circuit so you can double the current in parallel use or as a dual in series at low voltages when you work with opamps