I'm wondering if anyone knows the minimum loading that a Hypex SMPS400 may need on both the +/- main outputs as well as the +/- aux outputs for doing some basic go/no-go functional checks. I didn't see it on the Hypex data sheet but I could have just read right past it. The context for my question is the local high school has a commercially sold powered loudspeaker that the music department uses. It is based on the SMPS400 for the power supply, a custom pre-amp board and then 3 hypex amplifier modules (1 for the tweeter, 2 in bridge config for the bass/mid). There is a logo that is supposed to light up on the front of the unit but instead it flashes with a quick flash ever few seconds and there is no audio. I'd like to break the problem in half and decide if it is or is not the power supply which is what lead to my question about minimum load. Or can this unit handle running with no load? When the unit is fully connected (i.e. power supply, pre-amp, amp boards all connected normally), the supply main outputs are definitely not right (+ very low, - even closer to ground).
Regarding lab capability, I have access to various DMM, decent soldering equipment that is sufficient for the SMT stuff on the hypex boards, scope, microscope, and the usual sort of electronics bench hand tools. Regarding my experience, I'm an IC designer by trade but mostly not related to power electronics. That said, I've serviced tube amps as a hobby and in a previous life designed an offline flyback converter so I'm not totally without experience keeping my fingers and tools away from mains. For anything beyond a really light load I'll have to obtain something that can handle a bit more power.
FWIW, last year I fixed the other one of these units that the school has but in that case it was a linear regulator on the pre-amp board made out of discretes. That was a bit easier to track down even if the manufacturer did put a lot of goop on the components.
Anyone have a decent schematic for these supplies?
Thanks so much in advance.
-Dan
Regarding lab capability, I have access to various DMM, decent soldering equipment that is sufficient for the SMT stuff on the hypex boards, scope, microscope, and the usual sort of electronics bench hand tools. Regarding my experience, I'm an IC designer by trade but mostly not related to power electronics. That said, I've serviced tube amps as a hobby and in a previous life designed an offline flyback converter so I'm not totally without experience keeping my fingers and tools away from mains. For anything beyond a really light load I'll have to obtain something that can handle a bit more power.
FWIW, last year I fixed the other one of these units that the school has but in that case it was a linear regulator on the pre-amp board made out of discretes. That was a bit easier to track down even if the manufacturer did put a lot of goop on the components.
Anyone have a decent schematic for these supplies?
Thanks so much in advance.
-Dan
It shouldn't require a minimum load as it is likely a simple forward converter (i.e. it is not a regulated supply using a closed loop).
Thanks. It appears that this unit uses 2 power FETs on the primary side and then a pair of FETs for each of the 2 main outputs on the secondary side as synchronous rectifiers. The aux supplies look like they just use diode rectifiers. So far I'm just poking around a little doing some sanity checks on transistors with the DMM in diode drop setting. This seems to have a fair amount of symmetry in a number of circuits so I've also been doing some "one of these sides is not like the other" checks. Nothing has come up yet. I did go ahead and power it up and verified with the meter that the supply is not working correctly unless I've misunderstood the control connections from the pre-amp and power amp modules. It tries to come up but fails. None of the electrolytics appear to have a short, at least not anything wrong with ~0V bias. I came across a partial schematic online but it is missing everything on the output side of the transformer and at least some on the mains side 🙁