Hope I have the right group here..

I have an 18" flat screen monitor which stopped working - I opened it
up and replaced the fuse inside. The fuse in there was a t3.15ah 250v
but the one I got from a local shop was a t3.15al 250v which i didnt
realise until after I had put it in and switched on. It blew the fuse
to bits. Can anyone tell me the difference between the ah and al and
if this would be why it blew instantly or should it still work.

Thanks

ICTUser

ICT User writes:

Hope I have the right group here..

I have an 18" flat screen monitor which stopped working - I opened it
up and replaced the fuse inside. The fuse in there was a t3.15ah 250v
but the one I got from a local shop was a t3.15al 250v which i didnt
realise until after I had put it in and switched on. It blew the fuse
to bits. Can anyone tell me the difference between the ah and al and
if this would be why it blew instantly or should it still work.

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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On Oct 24, 8:17 am, Sam Goldwasser wrote:

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.

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

wrote in message
oups.com...
On Oct 24, 8:17 am, Sam Goldwasser wrote:

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.

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.

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'.

wrote in message
oups.com...
On Oct 24, 8:17 am, Sam Goldwasser wrote:

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.

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


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




On 24 Oct, 17:07, "Arfa Daily" wrote:
wrote in message

oups.com...





On Oct 24, 8:17 am, Sam Goldwasser wrote:

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.

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

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- Hide quoted text -

- Show quoted text -

"ICT User" wrote in message
oups.com...
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.




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.

On Oct 24, 11:59 pm, ICT User wrote:
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.

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

"b" wrote in message
ups.com...
On Oct 24, 11:59 pm, ICT User wrote:
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.

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.

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:
On Oct 24, 11:59 pm, ICT User wrote:

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.


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