Help needed identifying failed components

[Wolfi]

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

 

[Eeyore]

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?

HER303 is a rectifier.
http://www.google.com/search?&q=her303

Graham

 

[Wolfi]

Am 05.07.07 23.30 schrieb Eeyore:

HER303 is a rectifier.
http://www.google.com/search?&q=her303

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 :-\

 

[Lostgallifreyan]

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 :-\

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.

 

[Wolfi]

Am 06.07.07 17.40 schrieb Lostgallifreyan:

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.

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?

 

[Wolfi]

Am 07.07.07 20.33 schrieb Wolfi:

OR Blk = 1% tolerance and the final Red = dunno.

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.

 

[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?

Agreed, 1 ohm is likely.

http://xtronics.com/kits/rcode.htm 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.

 

[Randy Robinson]

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.

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

Randy

 

[Wolfi]

Am 08.07.07 18.26 schrieb Randy Robinson:

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

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

 

[[email protected]]

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

Does it look like an old carbon comp?

 

[Wolfi]

Am 16.07.07 23.08 schrieb [email protected]:

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

Does it look like an old carbon comp?

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

 

[Eeyore]

Am 16.07.07 23.08 schrieb [email protected]:

Sorry, but I don't understand what you mean by "comp".

Composition.
http://www.google.co.uk/search?&q=carbon+composition+resistor

Graham