Fuse blown in 18" flat screen..

I'm not sure of the difference, but the current rating is the same. If it was blown to bits, doubt your problem was simply a bad fuse. It sounds like there is a short in the power supply.

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Well, the *ah* fuse is a time-delay and the *al* fuse is an instant. This means that the *al* fuse will very most likely blow at start very most likely every time.

However "blew ... to bits" is indicative of something more serious than the wrong fuse. So: find the correct Time Delay fuse and try it ONCE (1-Time). If it holds, move on with caution. If it blows again, seek professional help.

Peter Wieck Wyncote, PA

If the previous fuse blew to bits I would *definitely not* try just one more! This could be more likely a S/C bridge rectifier or any suppression capacitors associated with it as the chopper circuit usually has current sensing resistors that tend to 'protect the fuse'.

I don't think that is right. It's the "T" at the start which determines whether or not a fuse has a "T" ime delayed action, and the "H" or "L" at the end specify whether it has a "H" igh or "L" ow breaking capacity - that is the maximum current that it can safely interupt. The fuse in the front end of a SMPS is usually a "T" rated HRC type, often with a ceramic body to prevent potential shattering. The "A" preceding either of these letters is merely for "A" mps. So the OP's original fuse of T3.15AH, is a high breaking capacity time delayed 3.15 amp fuse, which is exactly what I would expect in that position.

As far as I am aware, low breaking capacity fuses are typically rated 35A and high breaking capacity ones at 1500A. I think all combinations are also available, so you can get a "T" rated fuse in an "L" or "H" version, and likewise for an "F" rated type.

FWIW, an "L" specified fuse should still work ok and should not vapourise under normal circumstances. The fact that it does, would indicate an additional problem which is causing a current draw which exceeds the fuse's

*rating*, which is the only important factor as far as the fuse failing is concerned. As long as they are both "T" rated types, the A or H is of no consequence, except with regard to safety from the glass shattering. As others have said, the problem is likely to be a bridge diode, line-side filter cap, or possibly the switching element itself, depending on design. When the problem is sorted, the fuse should be replaced with one of correct specification, to maintain the monitor's safety approvals.

Arfa

Thanks for your replies. I guessed that it would be more than the fuse, wanted to check before I tried again - it did scare me when it blew and it also knocked out the trip switch. When it originally blew it didnt seem to make any noise, i was using the monitor at the time and it just went off, which is why i just replaced the fuse inside. As im not an expert in electronics I may just bin it or try and find a local electronic shop that might be able to fix it as its/ was a great monitor.

Thanks again.

ICTUser

Thankfully you didn't do as some, and keep putting a bigger fuse in until the monitor is completely destroyed.

It'll likely be a simple and inexpensive repair at this point.

sometimes fuses open up, in that case trying a replacement is often all thats needed. BUT fuses which go blackened or blow apart indicate a dead short very near the point where the mains enters the device . measure the rectifier diodes out of circuit. Then proceed towards the chopper. if it is a CRT then remove the degauss posistor.

in future, to avoid surprises like that, connect the mains in series with a 100watt light bulb to protect the device. if the bulb shines then the short is still present.

-b

Suggesting a current limiting lamp requires a little more explanation. Charging of the mains reservoir cap will cause the lamp to light for a short period, which should not be confused with a fault. In the case of a CRT display the degauss posistor can take a couple of minutes to heat up with most of the supply dropped across the lamp, the slow risetime of the supply can seriously confuse the PSU - possibly tripping the UVLO shutdown, its best to remove the posistor for this test. In the event that the PSU starts, this will draw more current through the lamp and increasing the 'lost' voltage - this can also trip the UVLO so the PSU will probably pulse or "breathe" a few times and then shut down.

A sigificant number of LCD monitors can be revived by replacing all the cap's on the power supply board.

Use low ESR high temp rated caps from a reputable manufacture

Hugh

b wrote: