A bit more info... anything at all, could be a good starting point. You must have some ideas about things like manufacturer, or what product it was in, or wattage, voltage current, where the fuse is in the PSU (subcircuit), etc.
If all else fails, providing high resolution top-down and bottom-up pictures of the PCB might help. The other issue is whether the fuse just wore out (thermal fuses can do that eventually) or there was another problem causing excessive heat.
If the PSU is passively cooled it might run pretty hot but if actively cooled then you'd guesstimate what temperature would be considered excessive and pick based on that, and on peak current expected in that portion of the circuit if the PSU were working properly then add a little margin. For example you might seek about 70C active or 100C passively cooled, or a bit higher for active if it's 'sunk to another component's heatsink.
If all else fails, providing high resolution top-down and bottom-up pictures of the PCB might help. The other issue is whether the fuse just wore out (thermal fuses can do that eventually) or there was another problem causing excessive heat.
If the PSU is passively cooled it might run pretty hot but if actively cooled then you'd guesstimate what temperature would be considered excessive and pick based on that, and on peak current expected in that portion of the circuit if the PSU were working properly then add a little margin. For example you might seek about 70C active or 100C passively cooled, or a bit higher for active if it's 'sunk to another component's heatsink.
Hi guys. The PS comes from a frinds hot tub. I believe that this only powers the motor to raise and lower the TV screen.
I have assumed that it is a thermal fuse. The PS board shows "Fuse 1" although there is only one on the board. The fuse had self destructed and the only bits left were a fragment (which seemed to be glass) attached to one leg, and a heatshrink band. All that remained of the other leg was bare wire.
The board provides two 12v feeds.
Oddly the "fuse" was soldered at both ends, which seems to be a no-no when fixing thermal fuses. However the board has been modified at some stage from it's original state (perhaps to accomodate this application)
I can take pics if it helps (just need to get some batteries)
Rob.
I have assumed that it is a thermal fuse. The PS board shows "Fuse 1" although there is only one on the board. The fuse had self destructed and the only bits left were a fragment (which seemed to be glass) attached to one leg, and a heatshrink band. All that remained of the other leg was bare wire.
The board provides two 12v feeds.
Oddly the "fuse" was soldered at both ends, which seems to be a no-no when fixing thermal fuses. However the board has been modified at some stage from it's original state (perhaps to accomodate this application)
I can take pics if it helps (just need to get some batteries)
Rob.
Thermal fuses (usually, none I have ever seen) aren't glass. It is curious that it is so severely physically damaged, whether it were a thermal fuse or standard current-trip type, normally only the element inside would break.
I would inspect the slide and gearing for the TV screen, perhaps the mechanical portion was in a bind and this caused an excessive stall current on the motor. I'd also check to see whether the motor seems to spin freely if not attached to the gearing in case the bearings failed.
If the mechanism seems to operate well and the motor is ok (you could apply 12V from an alternate source and see if it spins ok with no load) then see if there are any markings on the motor to indicate the power requirements if the PSU has no indication on it and there is no other way to find the info.
Where is the fuse? Primary side before a transformer, or secondary side after one? This will determine the (ratio) average current it has to handle. However you wrote it provides two 12V feeds which is odd, to power a single motor, unless this is some kind of retrofit installation and the PSU was just some random power supply lying around for a one-off hacked installation since it is less expensive to use a PSU with only the outputs needed.
Some guesses about the current might be made if there is no other way to figure it out, based on PSU size, the switching transistor spec or transformer although motors aren't my forte, I vaguely recall they may need a significantly higher start up current compared to steady run current. If you have a few spare fuses lying around and the time you could split the difference and put roughly 6A in and see if it works without blowing.
I would inspect the slide and gearing for the TV screen, perhaps the mechanical portion was in a bind and this caused an excessive stall current on the motor. I'd also check to see whether the motor seems to spin freely if not attached to the gearing in case the bearings failed.
If the mechanism seems to operate well and the motor is ok (you could apply 12V from an alternate source and see if it spins ok with no load) then see if there are any markings on the motor to indicate the power requirements if the PSU has no indication on it and there is no other way to find the info.
Where is the fuse? Primary side before a transformer, or secondary side after one? This will determine the (ratio) average current it has to handle. However you wrote it provides two 12V feeds which is odd, to power a single motor, unless this is some kind of retrofit installation and the PSU was just some random power supply lying around for a one-off hacked installation since it is less expensive to use a PSU with only the outputs needed.
Some guesses about the current might be made if there is no other way to figure it out, based on PSU size, the switching transistor spec or transformer although motors aren't my forte, I vaguely recall they may need a significantly higher start up current compared to steady run current. If you have a few spare fuses lying around and the time you could split the difference and put roughly 6A in and see if it works without blowing.
Some pics.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
But did it stay lit? You'd have an initial inrush current to charge up the capacitors. Granted, I suspect that was an ordinary fuse, for one thing a thermal fuse isn't much good if not 'sunk against some part anticipated to overheat to a threshold level rather than air and empty PCB space.
I don't know what the story is with the modifications or repairs are on the bottom of the circuit board (assuming they are done correctly towards whatever end/reason they were done??), but "IF" the load itself wasn't drawing excessive current which could blow the fuse then I'd suspect a power surge or overheating took out the IC on the left side of the heatsink. I wouldn't expect overheating on an intermittent duty TV hoist motor application UNLESS the sensing for it to cut off at end of TV travel weren't working which caused the motor to get stuck with a high stall current . Wild guess perhaps, I'm just throwing ideas out there.
I don't know anything specifically about hot tub TV setups, but it seems odd to me that a motor beefy enough to use this PSU would be used instead of an AC motor unless it were a makeshift or DIY invention, or would it be an issue of keeping high voltage mains wiring away from a tub full of water?
I don't know what the story is with the modifications or repairs are on the bottom of the circuit board (assuming they are done correctly towards whatever end/reason they were done??), but "IF" the load itself wasn't drawing excessive current which could blow the fuse then I'd suspect a power surge or overheating took out the IC on the left side of the heatsink. I wouldn't expect overheating on an intermittent duty TV hoist motor application UNLESS the sensing for it to cut off at end of TV travel weren't working which caused the motor to get stuck with a high stall current . Wild guess perhaps, I'm just throwing ideas out there.
I don't know anything specifically about hot tub TV setups, but it seems odd to me that a motor beefy enough to use this PSU would be used instead of an AC motor unless it were a makeshift or DIY invention, or would it be an issue of keeping high voltage mains wiring away from a tub full of water?
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The supply apparently is fried, and that fuse was probably a standard glass cartridge fuse of indeterminate amperage. (Not a thermal fuse at all.) First things to check are the rectifier and filter cap, and then if those do not prove to be the culprit you'll need to dig deeper - probably better to get a new supply from the hot tub manufacturer as there are safety concerns.
A switcher was used probably because a significant amount of power was required and there was not space or budget for a high isolation linear supply.
A switcher was used probably because a significant amount of power was required and there was not space or budget for a high isolation linear supply.
Kevin, you must have read my thoughts! I am not sure that I can get the same board, but a switcher with two 12v taps should not be too difficult. I would have thought at least 5A capability.
Regards
Rob.
Unless the fuse had to deal with an enormous overload like shorting live and neutral of the mains together through it... (been there, done that, had to shake the glass splinters out of a multimeter that I accidentally hooked up to a mains outlet with the leads connected to the AMP busses
).I'm guessing component(s) on the primary side have shorted, that's where I'd start.
It's has occured to me that this must be the connection from a tranformer with much reduced AC rather than 240v. I may need to check the voltage from the cable to get the exact figure. Is this likely to be the case?
The LH chip on the sink is a TOP261Y if you are interested. The RH one is a 3pin diode.
EDIT:
The TOP datasheet suggests 240V input.
http://www.datasheetdir.com/TOP261YN+download
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Sounds like the rectifier or switching transistor have gone short.
Missed the second page of posts so the above already superceded.
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Thermal fuses do "wear out" as suggested, as do plain old fuses, but most of the time they fail for a very good reason. Best do some further checking of the supply. See if you can get the schematic or draw up the section around the fuse to see what it was protecting. Not being in airflow or on the heat sink, I doubt it was protecting against temp, but over current.
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