A 2W resistor in a pc ps, o/c with no sign of heating at all,so clearly marked bands of red,yellow,yellow,gold, silver. Before I remove it and make an axial scrape along the coating would anyone know what that value should be ? 3 band accuracy in a pc or is there some other convention not ordinary 5 band coding ?
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
on
PCs are no different than any other device, resistors are resistors. Red yellow yellow would be 240k according to my calculations.
anyone
some
on
But the point is its 5 bands so 24.4 ohms but the third yellow band implies accuracy between 2.43 and 2.45 ohms but the silver band implies a value between 22 and 26 ohms or so - illogical as Mr Spock would say
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
correction - between 24.3 and 24.5 ohms
Read your post. red, yellow,yellow,gold, silver. What third yellow band? If you're talking about the gold, that'd be the multiplier on a 5-band resistor, or 10E-1. Silver is tolerance.
I read it as 24.4 at 10% tolerance, so 21.96-26.84.
Dave S.
alright correction , putting in an apostrophe or two for the third yellow band read the third, yellow band,
it still does not explain the tolerance illogicality Why and how would anyone stock a 3/5 band range of resistors which are only
10 percent tolerance?-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
on
NO. That colour code chart is not complete.
The gold is the multiplier and silver is the tolerance. Odd to have 3 bands for the digits though, that's normally only on close tolerance parts.
It looks like 24.4 ohms to me.
This is cute ! Check it out.
Graham
band?
only
But why a 2W 240K resistor in something that is unlikely ever to have more than 350V across it. I've not taken apart yet so it may well never see any high voltages.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
Why do you expect it to make sense ?
I'm sure I've seen 5 band 5% resistors.
Graham
clearly
anyone
some
on
bands for the digits though, that's normally
a fun app. Interesting the significance of the wide space between band 1 and 2. In 4 band useage you would normally read the other way around as the space would be between the multiplyer and the tolerance band
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
We do in the UK too actually.
Graham
How much experience do you actually have in repair ?
From its location in the circuitry you must have SOME idea of its likely value from context ! A fusible is normally a lowish value for example.
Graham
Are you sure it's not the startup resistor, and not a fusible type at all ?
240k at a couple of watts is not unreasonable for a resistor in that location, and they do go open for no apparent reason, but probably due to voltage stress, as they do have about 350v across them in normal (UK) operation. I've always assumed that they tend to use these 'bigger' rated resistors, as they have a better working voltage rating, although sometimes, you find two more conservatively rated resistors of 120k each, in series, to double the voltage rating. You can easily tell if it is the startup resistor, because one end of it will be connected directly to the "+" terminal of the main filter cap, or the most "+" terminal if it uses two stacked caps. Beware if it is an open startup resistor, as the main filter cap(s) will remain fully charged ...Arfa
yellow
5-bandare
sometimes
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I've not removed the security screws yet, just the top cover so don't know what its functional area is yet.
I looked around all the 5 band resistors that I have laying about , all 1/2 or 1/3W , not 2W, but they are all brown , 1percent, tolerance band which is logical but silver 10 percent makes no sense at all.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
a 1/2
is
and all those 5 band 1/2 and 1/3W resistors , perhaps 20 different values and from different sources have the wide gap between bands 4 and 5 , not between 1 and 2
Could that last band be a gray instead of silver? That would give you a .05% precision resistor
On Fri, 28 Sep 2007 15:30:13 +0100, "N Cook" put finger to keyboard and composed:
The only places I can think of that would require a precision resistor (but not fusible) would be the voltage sensing inputs of the PWM controller IC on the secondary side, or maybe the +5VSB supply. In these cases precision resistors are usually preferred to trimpots.
If you could describe the circuitry in the immediate vicinity, or provide a photo, perhaps someone may be able to make sense of it.
- Franc Zabkar
anyone
Now taken apart and no longer viewing this R skew on. It is 5 bands as stated but is only 1W. Doing an axial scrape it was obviously 240K and goes between the rectified mains + to pin 3 of a 4 pin , TO220 device marked
1HO165B and italic f logo so maybe Fairchild power switch KA1H0165R so plenty of datasheets, pin 1 of that device goes to mains rectified -veSo still a mystery of the gold and silver bands 4 and 5
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
So it is the startup resistor, as I suggested it would be. I would replace it with two 120k 1 watters in series to double the voltage rating. Watch that cap "+" terminal when you take your soldering iron to the resistor, for in that cap lurks lightning ...
Arfa
The startup resistor as Arfa suggested IIRC.
Now that info would have made establishing its value so much easier.
Graham
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