Fusible resistor selection

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Russ_Verdon 20 years ago

Hi, I just fixed a 19" monitor rescued from the kerb (LICOM N9054LP), and I got there before the annoying man who goes aroung cutting off all the cables from appliance did!

Horizontal but no vertical. The Vertical chip was TDA 0472 (couldn't get any data).

The obvious fault was an overheated R501 fusible resistor probably a 1W size. If feeds the chip with 15V as per the diagram. Its value changed quite dramatically when you flexed the leads from about 60R to hundreds of ohms. My problem is that the heat had caused the colour bands to change colour and were undecipherable. My question is what is the method for calculating a value for these protection resistors? I assume we want to minimise Voltage drop and have the resistor run within its rating. What base load would you run through the resistor? I ended up with a .68ohm with .6volts dropped across it. This seemed to restore vertical. The resistor thus dissipates .5W. IS this ok?

15V supply ______| __| / | \e--------^^^^^^------ pin2 /TDA0472 NPN _|_ R501 _|_ __ _ _ |__________ | GND

Regards

Russell

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electricitym 20 years ago

Russel, your calculations seem close enough and your final selection of a .68 ohm 1 Watt resistor seem to be quite plausible. Run the television for a couple days and make frequent checks to make certain than nothing overheats. Nice rescue from the curb. electricitym . .

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Chance 20 years ago

I'd find that guy and beat him. "Kerb" side shopping is the best, even I can afford the prices!!!

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David Nebenzahl 20 years ago

Russ_Verdon spake thus:

I'm curious about this part of the story: who is this guy, and why does he go around cutting off cords from potentially good appliances? Is this some kind of official function? or is he just an asshole? What municipality is this?

Pierre, mon ami. Jetez vous une plus de Scientologiste dans le vat de l'acide. - from a posting in alt.religion.scientology titled "France recommends dissolving Scientologists"

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3T39 20 years ago

Hello, David! You wrote on Sat, 15 Apr 2006 11:12:37 -0700:

DN> Russ_Verdon spake thus:

DN> I'm curious about this part of the story: who is this guy, and why DN> does DN> he go around cutting off cords from potentially good appliances? Is DN> this DN> some kind of official function? or is he just an asshole? What DN> municipality is this?

The same thing happens at the recycle centre where I salvage a lot of my stuff, (A different man though I think, just the same job) The basic reason is the connector wire is recycled seperately and also it makes stacking easier ( when your dealing with dozens of TV's , VCR's etc the dozens of wires become entangled)

With best regards, 3T39. E-mail: snipped-for-privacy@hotmail.com

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Russ_Verdon 20 years ago

Hi, I think this guy collects the wire for selling as scrap copper. It is all he takes. I saw him once, he just uses a knife to hack through the cables, be it power cords, signal cables from monitors or anythimg else. I have lost count of how many cords I have had to attach to scavanged equipment to test .

Regards Russell

PS I got a 21 inch monitor off the kerb today, thankfully it had an IEC socket and separate signal cable. It even goes( just a tweak of the screen control and focus required.)

and I

cables

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Tom MacIntyre 20 years ago

It's amazing how people (even supposed technicians) have been brainwashed into thinking that most electronics isn't worth repairing, or cannot be repaired. It's sad, actually...

Tom

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Fusible resistor selection

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