heathyoung
100 kW
OK - I'm sure there are a few of you who have meanwell 350W power supplies that have died (or you have killed)
I've just repaired 3 - all of them popped fuses violently on power up. Thanks to Hyena I had three dead ducks to fix.
Fortunatly, as far as SMPS's go, they are pretty simple beasts, with off-the-shelf components.
The first two units: Blew fuses, no crispy bits, the last one - ouch! But we will get to that later...
The most common fault is that they kill their high-side push-pull transistors (the big pair bolted to the end of the case) - they usually fail open or shorted. When they fail shorted, they also take out the bridge rectifier as well. Trust me on this one - it tests OK, but at high voltages they short out (they start to behave like Zener diodes - had one that was fine on the diode tester, but suddenly shorted at about 15V, and the other at 40V).
If the push-pull transistors are shorted, replace them - they are cheap and readily available from old PC power supplies if you want a $0 fix like I usually do. So are the bridge rectifiers. You also need to check R13 and R14 (0.47 Ohm resistors) as they become fuses as well
Now - the moment of truth. RULE number one in SMPS repair - don't just chuck a fuse in it and hope for the best! Put a 60W light bulb IN SERIES with the active (or HOT for those in the US of A) - If the light bulb flashes brightly for a second and decays (caps charging up) and the power LED lights up - you are in business. IF the light stays at full brightness, keep troubleshooting sunshine
Funny story the last power supply: It had burnt tracks around the common-mode filter choke, and the neutral line had no continuity - it appears that there was some bad soldering from the factory, but the lead let go and arc-ed badly - the resulting spikes killed the bridge rectifier, R13, R14 and high-side transistors - Replacing the parts (along with a salvaged common-mode choke from a computer PSU) and the supply was producing a voltage, but sounded VERY unhappy. Drat (or words to that effect). 25V was getting produced, albeit very noisily. Hmmm... This means there is a problem in the regulation section OR the push-pull driver section was only pushing (or pulling)
Some more poking and prodding rules out the transistors driving the pulse transformer - and revealed a dead 33V zener diode - ZD3. I didn't have a 33V one, but a 20V one did in a pinch (they are only to limit the flyback spikes to the transistors) and restored it to its full 48V output.
I've just repaired 3 - all of them popped fuses violently on power up. Thanks to Hyena I had three dead ducks to fix.
Fortunatly, as far as SMPS's go, they are pretty simple beasts, with off-the-shelf components.
The first two units: Blew fuses, no crispy bits, the last one - ouch! But we will get to that later...
The most common fault is that they kill their high-side push-pull transistors (the big pair bolted to the end of the case) - they usually fail open or shorted. When they fail shorted, they also take out the bridge rectifier as well. Trust me on this one - it tests OK, but at high voltages they short out (they start to behave like Zener diodes - had one that was fine on the diode tester, but suddenly shorted at about 15V, and the other at 40V).
If the push-pull transistors are shorted, replace them - they are cheap and readily available from old PC power supplies if you want a $0 fix like I usually do. So are the bridge rectifiers. You also need to check R13 and R14 (0.47 Ohm resistors) as they become fuses as well
Now - the moment of truth. RULE number one in SMPS repair - don't just chuck a fuse in it and hope for the best! Put a 60W light bulb IN SERIES with the active (or HOT for those in the US of A) - If the light bulb flashes brightly for a second and decays (caps charging up) and the power LED lights up - you are in business. IF the light stays at full brightness, keep troubleshooting sunshine
Funny story the last power supply: It had burnt tracks around the common-mode filter choke, and the neutral line had no continuity - it appears that there was some bad soldering from the factory, but the lead let go and arc-ed badly - the resulting spikes killed the bridge rectifier, R13, R14 and high-side transistors - Replacing the parts (along with a salvaged common-mode choke from a computer PSU) and the supply was producing a voltage, but sounded VERY unhappy. Drat (or words to that effect). 25V was getting produced, albeit very noisily. Hmmm... This means there is a problem in the regulation section OR the push-pull driver section was only pushing (or pulling)
Some more poking and prodding rules out the transistors driving the pulse transformer - and revealed a dead 33V zener diode - ZD3. I didn't have a 33V one, but a 20V one did in a pinch (they are only to limit the flyback spikes to the transistors) and restored it to its full 48V output.