Sorry my mistake I thought you wanted to ID what the board's function was.
What does that board do, though?...
Agent24
I see dead caps
Last Activity: Today, 10:40 AM
Joined: 10-04-2007
Location: Hiding inside a plated-through hole
-
This - it's quite possible the diode failed short and prevented the voltage from damaging the rest of the circuit, hopefully anyway.
If that is the case you should replace the diode for continued protection......Leave a comment:
-
What are the numbers on the ICs on it?Leave a comment:
-
Not necessarily, it could be just for a sound-activated switch or something.
I'm wildly guessing some kind of home automation controller, it has 3 relays for switching things, and inputs that could be connected to various other systems....Leave a comment:
-
Is that a QFN that only has pads on 3 of the 4 sides?
I wonder if you can find the piece that blew off, it may still have the part number on it...Leave a comment:
-
The only case I can see this happening is as mon2 suggests, the Raspberry Pi official power supply for example has a deliberately higher voltage - perhaps one of those would cause problems.
Otherwise, you have the QC and USB PD chargers that should only output voltages higher than 5v when negotiated with the device, but will otherwise only output 5v, unless there's a fault, I suppose.Leave a comment:
-
I don't know a lot about IGBTs but my brain immediately jumps to something wrong with the gate/base drive circuit - poor switching waveform, wrong voltage, low voltage, slow rise/fall time, etc etc...Leave a comment:
-
Unfortunately troubleshooting further likely needs equipment like an oscilloscope and such. But hey at least it works at all! You solved some interesting problems and I'm sure learned a lot.
The only other thing that springs to mind is a leaky diode or such that's causing problems under load. Basic Vdrop measurements on a multimeter won't typically tell you if a diode is leaky, only if it's shorted or open.Leave a comment:
-
Okay, that's good, but they can still fail with high ESR from drying out, while keeping the capacitance, and looking physically okay.
That's why an ESR meter is so useful here.
Startup problems can be caused by failed capacitors, and if one of the ones you left in has high ESR, this could cause such problems.
I also wonder if the series lightbulb is causing a problem with startup. If it is too small and limiting the current too much the supply may be shutting down because it's getting too low line voltage.
You can try a larger bulb or just none at all....Leave a comment:
-
So you have 120V AC at the input to the bridge rectifier?
You should have about 170V DC coming out - do you get that?
No sense worrying about the 5vSB startup circuit until you know it's actually getting power....Leave a comment:
-
Well, you can make as many guesses as you like but you won't know for sure until you actually get the thing out and start doing some tests.
Do you need help on how to do that?
You said earlier you didn't know where the fuse was - that doesn't matter straight away.
If the PSU has a power switch, make sure that's in the ON position, then check continuity from the live and neutral pins of the AC input to the AC pins on the bridge rectifier.
You should get continuity on each side. If one is open, you likely have a blown fuse.
As stj says -...Last edited by Agent24; 11-05-2025, 03:25 PM.Leave a comment:
-
Great to hear that, always nice to see a finished repair.Leave a comment:
-
Okay, so definitely no 5v standby and it looks like nothing on the primary capacitors either.
So now you have to find out why they have no voltage getting to them.
So you need to start checking the primary side input circuit and tracing through from the AC inlet to the primary capacitors.
Quite possibly you have a blown fuse but a blown open bridge rectifier could also cause this problem.
If you do have a blown fuse, then check all the primary side components (including capacitors) for shorts.
Post some more photos please, and we can find...Leave a comment:
-
Are you saying you didn't replace the bulging ones that still measured OK?
Because if they are bulging, they are bad 100% and it doesn't matter what they measure in terms of capacitance.
It's more likely the ESR goes bad in these situations, and is most likely the case.
Replace ALL bulging capacitors, even if they test OK for capacity....Leave a comment:
-
Those aren't axial though...Leave a comment:
-
You're going to have to check the 5vSB rail while it's plugged in, measuring it after you unplug it isn't going to tell you much of anything useful.
We need to know for sure if the 5vSB is running or not, because that determines the next stage of troubleshooting.Leave a comment:
-
Vishay seems to be the brand with the largest range, Cornell Dubilier also has a decent amount, and Kemet and Epcos have half each of that again.
Which one is the best quality brand from those four? No idea, but I'd trust them over the average Chinese junk.Leave a comment:
-
Why does this sound like it was written by chatGPT?Leave a comment:
-
What do you expect it to do?
If you limit current, the voltage has to decrease to keep the current limited.
If you have a load that is trying to draw more than that set current, anyway.Leave a comment:
No activity results to display
Leave a comment: