unfusing

[ceramic]

What are dangers or problems you will encounter if you replace a fuse in an inverter board with a simple wire. Just wondering

[PlainBill]

Re: unfusing

It depends on why the fuse blew. On rare occasions a fuse will blow because it felt like it. Sometimes it can fail due to a power surge, a leaky transistor, or possibly a bad CCFL.

Let's say it was a shorted line to the CCFL and the protection circuit didn't shut down the inverter. You replace the fuse with a wire. The extra load on the transformer will cause it to overheat, the driver transistors will also overheat. Depending on design, you could burn a hole right through the circuit board, which will create a stink you wouldn't believe.

I've got a low current (1/4) A variable power supply. Before I jumper across a fuse even temporarily I will hook that up and slowly increase the voltage looking for something going wrong. I have also been known to use an ammeter across the fuse location to monitor the current. When a circuit that blew a 2 A fuse draws 1 A for an hour or so I'm pretty confident it was just a momentary glitch.

One example of just how bad this can get occurred at work about 30 years ago. The Boss (JW) went to use a piece of equipment. JW was a twiddler - he liked to take a pair of pliers and make sure everything was good and tight. On that day he did this on the power terminals to the test chamber. What he didn't know is the lug on the other side of the panel turned until it hit the chassis. When JW turned on the main power the short blew a 1A, 125V fuse. He couldn't find a 1A, so he replaced it with a 2A fuse. When that blew he tried a 20A 32V fuse. That blew too. But not before a pair of SCRs, the gate transformer, and the transformer driver transistors also blew.

To compound the folly, this equipment was 20 years old, it was a special build by the manufacturer, and the manufacturer had been out of business for more than 10 years. It took a couple of weeks to dig out the schematic and identify the specs for the bad parts. The transistors and SCRs were easy - I picked up replacements as a local surplus store for $5. But the transformer was only available through the distributor. It cost $5, but the distributor had a minimum $100 order plus something like a minimum $20 shipping charge. By the time I got it working over a month had passed. Oh, and I hid his pliers, too, which really pissed JW off.

PlainBill

[Toasty]

Re: unfusing

You may experience any or all of the following:
Total meltdown.
Fire.
A new odor in your room. i.e.- That "something electrical overheating" odor.
Your smoke detector going off repeatedly.

[jpdoe]

Re: unfusing

>> Oh, and I hid his pliers, too, which really pissed JW off.

LOL

Sticking it to the boss is always good

[PlainBill]

Re: unfusing

>> Oh, and I hid his pliers, too, which really pissed JW off.

LOL

Sticking it to the boss is always good

No!!! That's not where I put them (but I was tempted).

PlainBill

[Bobdee]

Re: unfusing

Would these NO NOs still apply, if say you had a 1Amp SMD fuse that you bridged across the top say, with genuine 1Amp fuse wire, hypertheticaly of course.

There is a thread somewhere on badcaps , that Lcdrepair sold a repaired inverter that the fuse was soldered blobbed

[willawake]

Re: unfusing

i like the new odor bit

[Toasty]

Re: unfusing

@Bobdee:
- "genuine 1Amp fuse wire" versus... counterfeit???

- Since fuse wire reacts to heat, how do you solder it?

- If it's an SMD and you can't get a replacement, try something such as Littlefuse's Picofuse line. They're about the size of a 1/8 watt resistor. IIRC Mouser & Digi-key carry them as well as the SMD's.

@willawake: TY

[Bobdee]

Re: unfusing

Hello Toasty
I seem to have some recollection in my head of seeing glass fuses that had blown, that were repaired outside with new fuse wire,soldered on end caps, many years ago mind you, but it might be my imagination, thanks for your info by the way.
bob

[Toasty]

Re: unfusing

Yes, you're correct. Years ago there were "Far East" ones that were done from the factory soldered too. I dug one from my parts drawer.

[EGuevarae]

Re: unfusing

Yes, you're correct. Years ago there were "Far East" ones that were done from the factory soldered too. I dug one from my parts drawer.

I've seen them too, years ago when my father repaired CRT monitors ....
It was a common practice in Mexico to do that back then. Never did that myself, but I know first hand that it was done.
I also have bridged fuses (SMD ones) temporarily to test boards (did that with the Westinghouse I'm using now), and then replaced the fuse (sometimes). But I recall seeing many PSU/Inverter boards (even one in a recent thread, but I don't remember right now what thread was the one ....) silk screened as Fxxx or PFxxx, and having a jumper instead. I guess that overrides any security the fuses intended to provide, from factory

[PlainBill]

Re: unfusing

Would these NO NOs still apply, if say you had a 1Amp SMD fuse that you bridged across the top say, with genuine 1Amp fuse wire, hypertheticaly of course.

There is a thread somewhere on badcaps , that Lcdrepair sold a repaired inverter that the fuse was soldered blobbed

As a temporary measure I've used a pigtail fuse, a fuse holder, or similar. If I have determined there doesn't appear to be an excessive current drain I have been known to use a single strand from stranded wire (for example, from a lamp cord). This allows me to do a burn-in for a few hours (hopefully one without smoke).

In any case, the goal is to wind up with something that an expert would look at and say 'neat repair', not 'what kind of a moron worked on this?'

PlainBill

[EGuevarae]

Re: unfusing

As a temporary measure I've used a pigtail fuse, a fuse holder, or similar. If I have determined there doesn't appear to be an excessive current drain I have been known to use a single strand from stranded wire (for example, from a lamp cord). This allows me to do a burn-in for a few hours (hopefully one without smoke).

In any case, the goal is to wind up with something that an expert would look at and say 'neat repair', not 'what kind of a moron worked on this?'

PlainBill

Yep. I use a fuse holder when possible, but with the SMD little ones I have bridged three or four.Now that I remember, I didn't remove the bridge on this very LCD...

[Toasty]

Re: unfusing

I prefer car jumper cables myself.

[kc8adu]

Re: unfusing

I prefer car jumper cables myself.

reminds me of the 1956 chevy sedan delivery i got free as a teenager.some moron sawed the heads off some 1/4" bolts and snapped them into the fuse block.luckyly nothing happened.
truck had a bad ignition switch.1 switch and a handfull of REAL fuses later and i had a nice truck.regret selling it.

[ceramic]

Re: unfusing

thanks a lot guys. I've had to thrash a couple of lcd monitors because I couldn't find a replacement fuse. i was was tempted to just use a jumper but thought the fuse was there for a reason.

[PlainBill]

Re: unfusing

thanks a lot guys. I've had to thrash a couple of lcd monitors because I couldn't find a replacement fuse. i was was tempted to just use a jumper but thought the fuse was there for a reason.

OK, a couple of things here. First of all, NEVER trash an LCD monitor just because you can't find the proper fuse. PM me, If it's one I think I can fix I'll gladly pay shipping from anywhere in the USA.

Next, for testing purposes you don't need an exact match on the fuse. There is nothing wrong with replacing a pico fuse with a pigtail fuse, or soldering in a fuse holder while you are testing.

Last, if you are in the USA you can match just about any fuse made by looking in the Digi-Key and Mouser sites. I'm sure other countries have equivalent suppliers. (OK, if you're at McMurdo Station in June delivery might take more than three days.)

PlainBill

[EGuevarae]

Re: unfusing

OK, a couple of things here. First of all, NEVER trash an LCD monitor just because you can't find the proper fuse. PM me, If it's one I think I can fix I'll gladly pay shipping from anywhere in the USA.

Next, for testing purposes you don't need an exact match on the fuse. There is nothing wrong with replacing a pico fuse with a pigtail fuse, or soldering in a fuse holder while you are testing.

Last, if you are in the USA you can match just about any fuse made by looking in the Digi-Key and Mouser sites. I'm sure other countries have equivalent suppliers. (OK, if you're at McMurdo Station in June delivery might take more than three days.)

PlainBill

I can take them too. Just don't trash them. They can be fixed, used for parts or even the shell can be used.

[ceramic]

Re: unfusing

OK, a couple of things here. First of all, NEVER trash an LCD monitor just because you can't find the proper fuse. PM me, If it's one I think I can fix I'll gladly pay shipping from anywhere in the USA.

Next, for testing purposes you don't need an exact match on the fuse. There is nothing wrong with replacing a pico fuse with a pigtail fuse, or soldering in a fuse holder while you are testing.

Last, if you are in the USA you can match just about any fuse made by looking in the Digi-Key and Mouser sites. I'm sure other countries have equivalent suppliers. (OK, if you're at McMurdo Station in June delivery might take more than three days.)

PlainBill

well, these are actually work lcd monitors and we usually send them to a recycling company when they aren't working. but i took the initiative to fix those that i can from my little experience and electrical engineering background.

thanks for the info PlainBill. I tried soldering one of those SMT fuses, and it was a nightmare it was virtually impossible for me to solder without overheating or damaging it somehow. maybe i wasn't using the right equipments

[PlainBill]

Re: unfusing

SMT fuses are a little more tricky than snapping a new fuse into a fuse holder. It's pretty easy with a little practice.

Remove the bad fuse, clean as much of the solder off the lands as possible. Drop the fuse in place and have something handy to hold it down. I suggest using a 25 watt iron with a small tip. Put a small drop of solder on the tip, hold the fuse in place, and apply the tip of the iron to the land until the solder flows onto the end of the fuse. Let the solder cool and repeat on the other end.

As an alternative, use solder paste. Again, heat the land, not the fuse.

PlainBill