shitty chinese psu kit

[m3vuv]

base of q1 is 0v,emitter is-11.93v

[m3vuv]

ive tested d5 thats ok,does the output of u1a feed q1 via c3?,i see 7.7v on one side of c3,and zero on the other leg,could it be open?,but cant see how that can turn on q1 unless its a sort of pulsed dc signal,ie pwm?

[xavier60]

base of q1 is 0v,emitter is-11.93v

The Base of Q1 should be much higher based on the previous reading at the anode of D17.
And I have no idea yet as to how there can be -11.9V at the Emitter of Q1, the TIP41.
But for what ever reason you are reading those voltages, Q1's B-E junction must be open circuited.

[m3vuv]

it looks like the led is wired in reverse,would that cause the issues?

[xavier60]

it looks like the led is wired in reverse,would that cause the issues?

Yes, that would explain a lot of the problems.

[xavier60]

When the LED was removed earlier, there should have been normal voltage regulation if there were no other problems.

[m3vuv]

could the regulators that i fitted wrong killed q1?,i now get volts on the base that tracks with the volts pot but no amps out.

[m3vuv]

would the fact,i amm trying to drive 6x pass transistors be the issue?

[xavier60]

would the fact,i amm trying to drive 6x pass transistors be the issue?

That would be just guessing. The recent readings dont make much sense at all.
With the LED removed and a small load, take voltage readings starting at the anode of D17 and at each point along the drive path ending at the output.

[m3vuv]

Well i have just ordered some new opamps,so this can go on the back burner untill they arrive,thanks for the help so far.

[xavier60]

Those voltage readings would have helped me to make sense of it.

[xavier60]

There is a test for the output stage that can be done while the opamp is removed.
The output should go up to the  full unregulated voltage, then test to see how it holds up with a load.
But of coarse, dont short the output.

[m3vuv]

Well this is on the tuit pile,I have a new kit the same that i am just building,i have a few mrb  5200 diodes,would i be better using one of these in place of D5,that is a 1N5408 ? ,its a  sschotty diode so .3v drop the original is  about .6v TIA

[daisizhou]

Generally we do not use this power supply.Sellers only sell open source solutions.Many electronic components are cheap.There are important parts such as imitation or inferior mos tubes.
Most items sold on AliExpress are imperfect, or come from informal manufacturers. If there is a need for quality, it is recommended not to buy.

[m3vuv]

Generally we do not use this power supply.Sellers only sell open source solutions.Many electronic components are cheap.There are important parts such as imitation or inferior mos tubes.
Most items sold on AliExpress are imperfect, or come from informal manufacturers. If there is a need for quality, it is recommended not to buy.

and what has that got to do what diode to select what i asked?,maybe there is a hidden answer in there somewhere,do i need a crytstal ball to view it??.

[MK14]

Generally we do not use this power supply.Sellers only sell open source solutions.Many electronic components are cheap.There are important parts such as imitation or inferior mos tubes.
Most items sold on AliExpress are imperfect, or come from informal manufacturers. If there is a need for quality, it is recommended not to buy.

That makes a lot of sense. The thing is, some people see something that looks shiny and cheap, and they just can't resist going for it, time and time again (it seems). Despite good advice from people like you.

I suspect there are a number of proper/decent power supply schematics, which would be considerably better. But it is not necessarily obvious, which those are. As there are plenty of bad/problematic ones, available on the internet.

Anyway, your advise has helped me, be even more sure, that these cheap Chinese (not so cheap these days) kits, are not as wonderful, as they might first appear.

[m3vuv]

So for the 3rd time do change the silicon diode for a Schottky Diode ?

[m3vuv]

with most aliexpress kits i normaly replace the components with what i have in my junkbox and use the pcb ,knobs etc

[xavier60]

There is no advantage in changing D5 from an ordinary silicon type.

[magic]

It's specified as 1N4007, not 1N5408, and there is no need for a high current diode there. And the substitute part number that you posted doesn't exist.

The circuit doesn't look too bad. I like the floating power supply to the regulator - it makes the regulator operate at constant (unity) gain, breaks any cap on output voltage due to opamp supply limits and renders some types of faults completely impossible as there is no DC connection between the two power supplies. The few missing protection elements could be hacked into it.

[ledtester]

fwiw, Steve has a new video on his PSU build...

This one focuses on the internal placement of components within the enclosure he's using.

https://youtu.be/nkn7lQgIrfM

[m3vuv]

It's specified as 1N4007, not 1N5408, and there is no need for a high current diode there. And the substitute part number that you posted doesn't exist.

The circuit doesn't look too bad. I like the floating power supply to the regulator - it makes the regulator operate at constant (unity) gain, breaks any cap on output voltage due to opamp supply limits and renders some types of faults completely impossible as there is no DC connection between the two power supplies. The few missing protection elements could be hacked into it.

you dont seem to know what i am talking about,i have the pcb and parts infront of me,you are 100% WRONG!!!!
what are these i brought then? https://www.ebay.co.uk/itm/134027369085?_trkparms=ispr%3D1&hash=item1f34a75a7d:g:hv8AAOSwPzhaITBU&amdata=enc%3AAQAGAAACkPYe5NmHp%252B2JMhMi7yxGiTJkPrKr5t53CooMSQt2orsSHYXPhGXR5uguexJBeHwfgdfqzbAWa0SaMMAeG5vPfVxF5kfWaZs%252FgMGAq%252Fw94q8f0M1f0UBg%252B0ytSjPJWOEgbfo66W05WVyF7M0W50luZiVXNH4bmoXr8m97sYs0HKWcPLwm5lzevw6GOG8FoidqaO3iBFI7dxa3LaOIcGmfgbsPZgMPXk7Qy4cDhTqYds92%252Bz60PptwjDfTsReTVQzaWe9LvjLLtGM78LX2plySdU%252BbWpitX8t7dqjlnYk459WGJf0DR3z6ZeiPdn8T1xrm6AIyxbZW5ra7YxxzE%252BILU5pHPeJHeBfGOWFRDXIuHwG4TduY64UGM1vBm9N57HONvQe4MyaiqboUXn%252B5n9BonJqbQmIxeNRkZMkx%252F%252BDri2IcdcNh1dZaRt1wolglYVSsgkP%252BqKhzPoW4mpkgmLZyL8PkBtCZojWBi6J7CMScIck8MnSU7bs8WEJpwO%252FbQlgoMecHr270hU24Qk2y3R48rD4AnsE2IDCNaXkKXKYxF1%252F2nRES9GG6lxfesY0HHl0ROAmYsvZB7dsVNnUcWcubOX%252FCE5fv%252FcxOfm%252BSiK8QVy8cLRUP7n40kpB9wmrEEDYLD8c4Hahplju9AmP9mjSOS3rS0P%252B83qlsHz%252FmnEWNNax6EK8O%252BNbUoyGryFdpVF6zhLK%252BihvJ2tMN9iJrBJCv68dggWvvd%252BeTNGbjOP1NY%252FZYzuJFkuA1J3q09ODiQUGx5e2YyOhEc87x%252FQGMBDLUruBBzlkNO7w7YSBXVhQn6QN5cDKnYx88urwlVH60YRHke8HcATOb7nWur0nF8WBoVrlXkJJ9qABcKF6xKd2Wv%252Fh2%7Cclp%3A2334524%7Ctkp%3ABFBM2oyZ2PFf

[magic]

Then nobody here knows what D5 is because we don't have the same PCB in front of us and you have used component numbers from at least two different schematics so far.

The diodes you linked are of course either SR5200, SB5200 or MBR5200 and maybe it's all the same, but they aren't MRB5200. I supose that was a typo, fair enough.

[m3vuv]

sorry it was d6 i made a typo.

[m3vuv]

Those diodes were ordered a few months ago to repair an smps in a 22" phillips flat screen monitor.