Actually, I think I ought to clarify this. If the fuse had just gently parted companydue to an overload, after a quick visual check it was easiest to replace the fuse, switch on and look for smoke or possibly a valve anode starting to glow red as the set warmed up. If you were lucky, this might point you in exactly the right direction.
On the other hand, if the fuse had blown due to an obvious short, as here, it would be a waste of time to just replace it without carriying out an investigation first.
If you have the ability to do so, yes, and can spare the time..
I'd estimate that a driver would cover all those parts - and take less than half an hour to do.
Why bother testing?
When years ago I worked in a comany producing rather shoddy audio power amps, the girls who fixed them had zero theoretical knowledge. They were taught to replace all of the output transistors, the drivers, the fuses, and the power resistors if they looked burnt.
about 15 mninutes with almost completely unskilled labour...
The transistors were then tested later by an engineer on a transistor tester, and good ones put back as 'replacment parts' in the repair department.
I cant recall whether that tester was not in fact a simple home made device checking that they werent short circuit and exhibited some gain...
Agreed. But, given the OP's stated lack of electronics knowledge it might be helpful to explain that the bridge can be visualised as being one diode on each side of a square with the AC input to diagonally opposite corners. The other corners are the positive and negative outputs.
On the PCB, the square has been squashed into a thin rectangle with the AC input to the central connections to the pairs of diodes like this (must be viewed using a fixed width font):
True, but some older ones use power bipolar junction transistors for a chopper.
I should mention at this point that SMPS units are highly dangerous to work on live. Some have voltages close to 800V at more than enough amperage to kill. If you cannot avoid live testing then FFS use an isolation transformer and keep one hand behind your back all the time you're prodding around.
There's also an LC mains filter prior to the rectifier and that's highly prone to failure as well. When an SMPS fires up from cold, the initial surge current can be huge, 'cos it looks like a short circuit at switch- on.
1N5399 defines the ratings (not IN), so it's that simple. It just needs to go in the right way round, as per the original, line at the same end.
Other parts? We don't know is the only definitely correct answer. Anything else would result in no end of time wasting here. You might or might not need other parts.
When you power it up if you do so via a 100w light bulb it'll spare diode & fuse if anything else is faulty.
The NTC limits the switch on surge. The filter would be more to stop hash getting out from the PSU than anything coming the other way.
It isn't prone to failiure either. The coil has very few turns of comparitively thick wire, so in the extremely unlikely event of a shorted turn or two, you would never know the difference.
Assuming your neigbours don't listen to long wave on their wireless that is.
The input capacitors are x or y rated and are not prone to the failiures that the old polyester devices were subject to.
I personally have never ever replaced a coil or cap on the mains input of an SMPS,
Now a transorb is a different matter, I have replace a good number, but the similarity to a capacitor tends to end after body shape.
Unfortunately, that's likely to lead to even more component failure if you've failed to identify and replace *all* of the faulty components since the rapid destruction of the safety fuse will have limited the damage in the original failure event by timely suppression of the destructive transients before they could do any further damage.
A typical SMPSU is effectively made up from a selection of components arranged as a fleet of "Accidents waiting to happen". Almost every component in an SMPSU can lead to a catastrophic cascade of faults with very few of them resulting in a non-catastrophic failure depending on whether they'd obligingly failed open or short circuit as required to allow such a non-destructive failure event.
Considering the workings of a SMPSU gives me the heebee jeebies every time[1]. It's rather like an electronic form of Jenga or Russian Roulette where 5 bullets have been loaded into the "Six Shooter Revolver" where the victim is that obligatory safety fuse whose primary role is to "Put out fires before they get a chance to take hold and destroy the whole forest.".
SMPSUs *can* be repaired but unless it's one integrated into the main PCB of an expensive piece of kit, it's usually far cheaper to simply replace what has now become a commodity item with a new replacement unit.
One normally wouldn't even bother *attempting* to repair a ten quid commodity PC ATX PSU these days. The only time I broke this rule of thumb (don't get sucked into wasting precious time on a folly) was when a customer returned their PC after a completely successful repair after blowing the safety fuse in its ATX PSU by accidentally nudging the dual voltage switch into the 110v setting when they'd been setting it up on returning home.
This particular failure mode gave me pause to reconsider the benefit of opening it up to do some basic testing of the HT module with a view to simply try a replacement fuse. Said tests suggested there was a possibility that the fuse had blown in time to prevent damage so it was duly replaced and the offending and redundant voltage selector switch was disconnected. Contrary to my expectations, the repair proved successful.
Prior to that, I've repaired a custom AT PSU (NEC Powermate II) that had become so reluctant to restart that I needed to utilise a hair-dryer to persuade it to spring back into life (it was a Novell Netware 3.11 fileserver box). This involved replacing a small 100mF 16v capacitor that had dried out from the heat of an adjacent plastic power transistor.
Much earlier than that, I'd managed a successful repair of a 1970s Gould
5v 10A SMPSU which had blown one of its 1N4000 series bridge rectifier diodes along with its user serviceable glass fuse. I can't remember the exact number of the diode, only that it was a 700PIV rated 1N4000 series diode. I remember the PIV rating rather than the precise part number only because it struck me as rather odd that Gould should have chosen a diode with a barely sufficient PIV rating for the job.
A bridge rectifier needs to have a PIV rating equal to or greater than double the peak voltage of the maximum permitted mains supply (2 times root 2 of 265 = 2 x 375v = 750v) to avoid the need to provide current spike limiting resistors when used with a smoothing capacitor. The 700v rating was barely enough to cover mains voltage excursions up to 247v which aren't uncommon events where I live (urban underground supply).
Gould could so easily have used 1N4000 series diodes with 800 and even
1000 volt PIV ratings which begged the question, "Why not?" which then led me to conclude that this may have been a deliberate choice based on the concept of "Better to have a ten cent diode sacrificially fail to protect a more difficult to replace ten dollar HT switching transistor".
This was reinforced by the fact that the diodes were far more accessible than the HT switching transistors and the fact that the SMPSU would have cost far more than a typical Hi-Fi set up of the day, maybe even as much as a small capacity motorbike!
Today, thanks to consumer demand driven mass production, the once cheap 'n' cheerful 50Hz mains transformer bridge rectifier capacitively smoothed low voltage DC supply is now both inefficient and heavy and the most expensive in the cost of its raw materials that the new "Cheap 'n'Cheerful" has become the ubiquitous SMPSU. Only the most canny of futurists with his wits at full stretch would have foreseen this dramatic turn around in the time of just a single generation (Thanks to the PC revolution, commoditised SMPSUs became a fact of life in the late 8os to early nineties).
[1] The only other example of a PSU circuit diagram (a DC to DC converter actually) giving me the heebee jeebies was seeing the use of thyristors in place of switching transistors relying on secondary thyristors to discharge a capacitor across the primary switching thyristors in order to turn them back off. Predictably, fuse blowing events were a fairly common failure mode with this novel use of thyristors on DC supplies. :-)
Assuming you're discovering and replacing one faulty component at a time, a pack of 4 fuses will allow you to replace as many as sigma 4 (10) components in total before you run out of fuses. If you carry on the procedure using another pack of fuses, you could land up replacing components a total of 36 times (8+7+6+5+4+3+2+1).
I think your good fortune is that they *only* come in packs of four. I can't see you investing in yet another pack to continue your "Suck it and see" approach to repair by component substitution unless you really do have nothing better to do with your spare time.
If you've seen any of my previous follow ups, you'll know exactly where I'm coming from on this. :-)
I agree with you but I have to work within my limitations so the fuse and diodes are about the extent of it then it will head to the bin. It is too late in life to start learning the `trade` so I have to follow as best I can the advice given. Mechanical is my thing mostly, like just started watch repairing which wont be a problem for me as I can physically see whats wrong, unlike electronics. DIY I will always give something a go before binning.(with safety in mind)
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