Help needed identifying failed components

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Wolfi 19 years ago

I got one of those small, 1/3W, maybe even 1/2W, fusible metal film resistors, which burnt through, due a failing diode in a computer monitor's SMPS.

Now I'm having some trouble to identify the value of this R. There a 5 colour rings on it, distributed symmetrically. In the center: BlK - Gld - Blk and, a hair thinner, Red and what appears to be Brn, one on each side on the thicker contact caps.

Now, how is this one to be read, starting with Red or with Brn? And what is the meaning of the 2 rings following the gold one? Which one is tolerance and what is the other one for?

The blown diode has the following on it: B119 HER303 (1,3mm wires, body

9.2mm × 5.2mm diameter).

Could anybody please provide some specs on it and possibly one or more suitable replacement types?

Wolfi

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Eeyore 19 years ago

HER303 is a rectifier.

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Graham

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Wolfi 19 years ago

Am 05.07.07 23.30 schrieb Eeyore:

Thanks. Yesterday I only had access to a Mail/News client, so I couldn't use a search engine. I now found a few possible replacement types.

But I'm still stuck with the colour code puzzle of this fusible resistor :-\

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Lostgallifreyan 19 years ago

Wolfi wrote in news:iHwji.4419$ snipped-for-privacy@newsfe19.lga:

Probably Red, Black, Gold, Black, Brown. (Assuming the gold really IS gold and not some weird metallic shade caused by burnt pigment). The value likely begins with Red for 2, that would be a very unusual tolerance band.

So, maybe 2 ohms with unusual markings, 3 colours for 1,0,/10, unused, and brown for 1% tolerance at the end. The fourth band might have been printed by a machine ready for the 4-colour scheme for value, but set to put the unused black band for the old three colour scheme after the multiplier instead of before it as is usual on metal film types in readiness of an extra significant digit.

If the gold colour is a result of burning (I have seen bands look silver as a result of this, and the centre band is the first to burn), it might just be standard 1% tolerance 5 band 200 ohms, Red, Black, Black, Black, Brown.

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Wolfi 19 years ago

Am 06.07.07 17.40 schrieb Lostgallifreyan:

Judging from the surrounding circuitry, which I further re-engineered by now, I have to assume, that its value is most likely 1 Ohm at most, perhaps even

0.1 Ohm, (even though 2 other people also looking at it and both came up with gold being the center ring). From a tap of the SMPS transformer, a HER303 diode, which shorted out is connected via a wire bridge with a ferrite core around it to this little 7mm × 2mm fusible resistor, and from there feeding the CRT cathode heaters with a negative 6.3V voltage. The heaters have a cold resistance of some 5 Ohm and assuming that when hot, the resistance increases by at least 50% to about 8 Ohms, then it still would mean some 0.6W dissipation in the little R (with an assumed value of 1 Ohm). My guess is, that it isn't rated for more than 0.5 W, so it would be already a bit tight. But on the other hand, it is no DC, it still is a pulsing current, so it might be just fine and the above rule of thumb calculation resulting to high anyway. But I think it also quite surely eliminates the possibility for a 2 Ohm reading, so it has to be something like Brn-Blk_Gld => 1 0 ×0.1, next Blk = dunno, and finally Red = 2% tolerance OR Blk = 1% tolerance and the final Red = dunno.

Any other thoughts?

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Wolfi 19 years ago

Am 07.07.07 20.33 schrieb Wolfi:

Well, sorry. This part of course doesn't make sense, since Blk doesn't represent 1 at all :-[

So it has to be 2% tolerance and 1 0 × 0.1 = 1 Ohm with a Blk = dunno filler ring.

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Lostgallifreyan 19 years ago

Wolfi wrote in news:J9Xji.2783$ snipped-for-privacy@newsfe13.lga:

Agreed, 1 ohm is likely.

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indicates a 'quality' band in place of the other possibility for 5th band, temperature coefficient. In this case it might mean 2% likely failure risk every 1000 hours for those resistors.

That page says 1% tolerance resistors have three value bands before the multiplier. I think that's true even if the third is unused (black). As yours has a multiplier as third band, it presumably can't be 1% tolerance, but that doesn't explain why the tolerance band is black. :)

Maybe it's a thermistor with its own coding type? It might be designed to limit the inrush current to a cold heater.

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Randy Robinson 19 years ago

resistors,

What is the make, model and serial number of the monitor?

Randy

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Wolfi 19 years ago

Am 08.07.07 18.26 schrieb Randy Robinson:

KDS 17"CRT, Model: XF-7P, Mfr Code: DFT, Rev No: 00, Chassis No: C718, Mfr Date: July 2001.

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JasonDMX22 19 years ago

Sounds like a choke to me - that's not standard resistor color coding.

Does it look like an old carbon comp?

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Wolfi 19 years ago

Am 16.07.07 23.08 schrieb snipped-for-privacy@hotmail.com:

Sorry, but I don't understand what you mean by "comp". To me it looks lioke a metal film resistor (blueish-grey body colour)

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Eeyore 19 years ago

Composition.

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Graham

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Help needed identifying failed components

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