My one and only AT PSU went pop the other day. No smoke or smell. I opened it up and it looks... fine? Can't see anything that has obviously exploded, still no smells or burn marks. Can you guys see anything bad?
bigger https://i.imgur.com/aSdCK8l.jpg
Did you try turning it on again ?
that's what I'm going to do, with only the minimum connected up, as I can't see anything that sticks out as being bad!
nothing:(
I doubt the fuse blew up, it looks intact (you could double check it just to be sure). Have a closer look at the primary and secondary MOSFETs. Sometimes, if they pop, a bulge will develop on top of their package.
If that is the case, you can't fix it.
And as everyone would say, let those BIG filter caps discharge for 15 mins (if you plan to get the PCB out). They are a serious hazard when charged.
Check the underside of the pcb.
Out of curiosity, what is the function of those metal fences I see in these old PSUs? It doesn’t seem to be a heat sink for anything. EM shield?
Swiego wrote on 2020-05-09, 21:56:Out of curiosity, what is the function of those metal fences I see in these old PSUs? It doesn’t seem to be a heat sink for anything. EM shield?
What fences are you talking about?
In the very first photo in the OP's post, the vertical metal stand (looked kind of like a fence to me) to the left of the two capacitors.
To the left of the two primary bulk caps is the desk. To the right is the heat sink mounting the main switchers.
All hail the Great Capacitor Brand Finder
Swiego wrote on 2020-05-09, 23:00:In the very first photo in the OP's post, the vertical metal stand (looked kind of like a fence to me) to the left of the two capacitors.
They *are* heatsinks and have MOSFETs attached. You just can't see them from the picture.
Guys, this psu uses BJTs and not FETs . These are too very different transistor types.
Almoststew1990, it is possible that the high voltage primary side is good and something has gone bad on the secondary output side. Does the fan twitch or does the psu give out some high frequency noise when you power it up? Or stays completely still and silent?
Almoststew1990 wrote on 2020-05-09, 09:22:https://i.imgur.com/doMjjuCh.jpg Bigger https://i.imgur.com/doMjjuC.jpg […]
Is it just me or is that mosfet closer to the AC power cable port kinds of off colored? Like its blown? Or is it just dust.
DAVE86 wrote on 2020-05-10, 21:29:Guys, this psu uses BJTs and not FETs . These are too very different transistor types.
Nobody could see the package ink to know that, nor does it make a difference when it comes to understanding the topology of the PSU. Detailed engineering and component testing is different, of course, but I usually consult the datasheet to confirm pinout anyway.
DAVE86 wrote on 2020-05-10, 21:29:Almoststew1990, it is possible that the high voltage primary side is good and something has gone bad on the secondary output side. Does the fan twitch or does the psu give out some high frequency noise when you power it up? Or stays completely still and silent?
Don't guess. Meter it.
All hail the Great Capacitor Brand Finder
gdjacobs wrote on 2020-05-11, 05:35:Nobody could see the package ink to know that, nor does it make a difference when it comes to understanding the topology of the PSU. Detailed engineering and component testing is different, of course, but I usually consult the datasheet to confirm pinout anyway.
Well yeah, it's the curse of the profession. I could see that this is a half bridge with bjt-s. Small driver and current sensing transformers in the middle and that Ka7500 on the secondary. The overal layout is a dead giveaway.
Almoststew1990, you should get a multimeter if you can use one. Otherwise it stays a guessing-troubleshooting game 🙁
DAVE86 wrote on 2020-05-10, 21:29:Guys, this psu uses BJTs and not FETs . These are too very different transistor types.
Almoststew1990, it is possible that the high voltage primary side is good and something has gone bad on the secondary output side. Does the fan twitch or does the psu give out some high frequency noise when you power it up? Or stays completely still and silent?
Does it really matter if they are BJTs or MOSFETs? If any of them are blown, it isn't worth the risk of trying to replace them.
Maybe OP will get lucky with a burn mark on the other side of the PCB.
I usually wouldn't bother fixing any SMPS, especially if it's a cheap and common AT unit.
The PSU doesn't make any noise and the fan doesn't spin at all 🙁 I don't have a multimeter to test it out unfortunately
computerguy08 wrote on 2020-05-11, 07:19:Does it really matter if they are BJTs or MOSFETs? If any of them are blown, it isn't worth the risk of trying to replace them. […]
DAVE86 wrote on 2020-05-10, 21:29:Guys, this psu uses BJTs and not FETs . These are too very different transistor types.
Almoststew1990, it is possible that the high voltage primary side is good and something has gone bad on the secondary output side. Does the fan twitch or does the psu give out some high frequency noise when you power it up? Or stays completely still and silent?Does it really matter if they are BJTs or MOSFETs? If any of them are blown, it isn't worth the risk of trying to replace them.
Maybe OP will get lucky with a burn mark on the other side of the PCB.
I usually wouldn't bother fixing any SMPS, especially if it's a cheap and common AT unit.
what risk? the risk of wasting 10 minutes replacing them?
Don't touch it without knowing what you are doing. The fact that you don't have a $10 multimeter is a dead giveaway.
Almoststew1990 wrote on 2020-05-11, 11:05:The PSU doesn't make any noise and the fan doesn't spin at all 🙁 I don't have a multimeter to test it out unfortunately
Most likeIy something failed on the high voltage primary side. There might be something on the solder side of the circuit that shorted traces or leads of component. At this point I wouldn't encourage you doing more then observation since there is the chance of getting shocked.
