Value Of Resistor??? Help

[Bobdee]

Hello guys
need help with this 5 band resistor, colour coded
ORANGE
ORANGE
SILVER
GOLD
BLACK
fairly new at this, but i do know it cant start with black or end in black,also it cant have a colour of silver as third colour am i reading this wrong, if so can you explain where i am going wrong.
its a pinky colour about 12mm long and 3mm wide, from a dell monitor 18000fp, off the power board,
hope someone will help please
many thanks
bobdee

[gg1978]

Orange, orange silver, (the first three bands) are 0.33 Ohms, 5% tolerance (gold band), with the black being the quality band..

some Inductors use the color code also, but that kind of size of device is most likely a resistor.. Probably an inrush current limiter or voltage sense, if i had to guess..

[Bobdee]

Thanks gg1978
that was swift with reply,
the resistor in question comes off the large 450v 100uf cap on power supply, and ajoins a cool MOS power transistor that is mounted on a large heatsink.

I take it that i should have read it as a 4 band resistor ???
and ignored the black or is this black important when tracking down a replacement ???

bobdee

[gg1978]

Nah, that's a standard three band resistor, just the last black band is a "quality" thing that can indicate resistor tempco, or some other thing.. Look up "resistor color code" on wikipedia, you'll see what i mean..

As long as you replace it with another 0.33 Ohm resistor, of appropriate wattage, you should be fine. Thats a decent size resistor, going by your physical description, so probably a 1 or 2 watt device, perhaps more..

Was the old one burnt up?? If it was, there might be another fault in the PSU somewhere..

[Bobdee]

Thanks again gg1978
When i said a 4 band resistor, i meant 3 value bands plus 1tollerance band equalling 4bands, and i wll certainly look at wikipedia for that black code bar and more about tempco, i will have to look into wattage also.

The old resistor on close inspection has cracks along it, something inside has expanded, and its bursting open.

there have been issues 1st a cap that had .14 esr that i replaced it looked good from outside, 2nd small cracked joints on transformer that i dont think they were causing any problem yet but resoldered them all anyway, 3rd the big one there was two dual diode barrier rectifiers mounted on large h/sink, joints to board were cooked badly,must have been arcing badly, removed and they checked out ok so resoldered back in plus other cracked joints around that area as well as 3.15 t fuse blown at power connection

bobdee

[Gianni]

Hi Bobdee

I think the resistor is for current sense, if it is connected between Mosfet Source and ground.
If it is open, probably something very serious happens to the Monitor PS.
probably also the PS IC controller is broken because the voltage across sense resistor could have exceeded the IC maximum voltage.
Check also the Power Mosfet, probably it is shorted.
If you replace the resistor, mount a 3W film resistor type.
Usually there is also a small resistor (value can be few Ohms up to 1KOhm) between sense resistor and IC controller, and small ceramic cap between IC controller and ground, this is a filter to smooth current signal and avoid false trigger caused by spike. Check also these components if they are in the circuit.

Ciao
Gianni

[Bobdee]

Hello Ciao

very grateful for your great input, ...but, a big but at that, is that i am a retired carpenter doing this as a hobby, started electronics about 7 mnths ago so you have given me a lot to take in,
the resistor does go to Mos source and other end goes to large filter capacitor, neg lead and also, neg lead of bridge rectifier plus a leg on the transformer, but i get no earth as you mentioned
have pulled Mosfet and it is shorted, for me to move on with your info,
??? can you tell me what one is ic contoller out of these???

3 leg 1a volt regulator mounted on h/sink

8l leg power supply module ICe 2as01

4 leg pci unidentified as yet

wait on your reply many thanks.

bob

[Bobdee]

hello gg1978
looked up coulor codes in wikipedia found the tempco band ratings but no rating for black,cant understand why band is there at all if theres no rating for it,why put it there, any help anyone
bob

[Gianni]

Hi bob,

the controller I think is ICE2AS01, here attached you can find the modified datasheet, I have removed some pages to reduce the size, the original one is here .

In my previous post when I wrote "ground" I meant the primary negative, I use to call it ground, it is the negative pole connected to the input bridge rectifier, bulk input electrolytic capacitor...
In the attached datasheet you can see they call GND the negative pin of ICE2AS01.

From the datasheet I see the limit for current sense is 3V (page 15) and on page 10 they explained this IC has a "leading edge blanking" so the current sense resistor is connected to the controller without any filter to smooth spikes. During this short period (220nS) the IC ignores the signal from current sense so it does not trigger on spikes at Mosfet turn on.
You have found the sensing resistor cracked

Originally Posted by Bobdee

The old resistor on close inspection has cracks along it, something inside has expanded, and its bursting open.

so I think the voltage on it went very high, enough to kill the controller, but I can't make any hypothesis, I have never used this IC.
If there were bad joints on rectifier, trafos, ecc... everything is possible, I have seen some PS with sense resistor completely destroyed due to transformer saturation.
For current sense resistor you have to avoid "Wirewound" type because they are "inductive" and since the current frequency is high (KHz) they can create problem. You can use "Carbon film" or "Metal film" , I attach here a datasheet as example.

I hope it is not too tech for you but if you need any clarification I will try to help you more.

Can you post some pics about you problem?

Ciao
Gianni

[Bobdee]

Hello again Ciao
thanks for putting yourself out, i am grateful,
Phew sounds like i have a bit of a problem on my hands,
have had to read your post several times, and i think i follow most of it, if not all,
forgot to mention in last post "resistor open"
did follow you on the ground passage and understood i think,
so it is probable controller gone,i can get one at bluestar i think, bridge rectifier solder joints in perfect condition, i did have a couple of very hard to see slight cracked joints on transformer, resoldered all joints on transformer,
2 x schottky rectifiers TO220ab in bad way at joints, pulled them and they tested ok
joints of transformer 6 to 10 have suffered a bit of heat, slight melting of yellow insulation tape low down to bottom, looks minor, coil wires that are visable are clean and bright.
so i definetly need 3w .33 carbon resistor and the mosfet, and possibly new controller,i dont know how to test controller,its new to me, and the original resistor is less than .5" long, i thought this would be half or 1w,
you say 3w , can you confirm please that 3w will be ok ??? and do i search for current sense carbon resistor or just carbon resistor???
if transformers shot, i wont be worried its been a good learning curve that i have been enjoying, learned alot from it, and from you.
many thanks
bob

[Bobdee]

hello again Ciao
sorry left out about pictures,
i have a camera samsung s760, i dont know how to use it for this type of picture, or even if its good enough for close up work,also i havent learned how to send pictures either, will make every effort to look into this,even comps are fairly new to me , especially typing, i am so slow, never mind hey, i get there in the end.
thank again
bob

[Gianni]

Hi bob,

for the resistor, considering the dimensions you have indicated in first post it should be a 1W. You can use a 2W, 3W is waste of space/money. I have written 3W in first post before checking dimensions, anyway I have never found resistor, used for current sense, bigger than 2W in most PS.
You can use just carbon resistor.

Originally Posted by Bobdee

slight melting of yellow insulation tape low down to bottom

If the transformer insulation has melted down I think some turns has overheated and probably shorted, this could explain the shorted POWER Mosfet, open current sense resistor...

So I don't know if it is enough to change the components (MOSFET, Resistor, IC controller), if the transformer is damaged you have to find a new one.

To troubleshoot PS I use oscilloscope and 2 lab power supply, both have voltage regulation and current limitation.
You can read here how I proceed when I have to repair a PSU.
I don't know if you have such equipment.

Don't worry if you can't post pictures, proceed step by step and even if you can't repair your Monitor, you can learn something or at least you can start to understand how things work.

Ciao
Gianni

[Bobdee]

Hello Gianni
Apologise for my Italian bloomer, my wife set me right when i ask for a pronounciation.
Read your link on psu transformer testing, and must say your English is Perfecto, better than mine.

As for testing transformer, not possible, dont have access to scope ect, and would not know how to use them if i did, will buy new one if need be, if resistor, mosfet and controller is not the fix, as for going on with this, lots of this is over my head, but im game with your help if thats no trouble to you, and if the outcome is still a dead monitor, no problem, this is a new learning project for me.

Have found out where to buy mosfet, controller, and transformer but resistor is eludeing me, will keep on searching.

When i googled transformer, i found it plus a monitor manual that i hope i can send a link to you, because i am of the understanding that this monitor uses the same psb, i read this on a forum a couple of weeks ago that i had come across, its very comphrehensive, schematics, troubleshoot,part list ect.
Havent had time to look at it yet, but i will understand a bit of it when i have read it a couple of times.
hope i can make the link work, here goes

http://www.curto-circuito.com/esquem...B886F_FULL.pdf

Soon as i get somewhere to buy resistor i will send for all parts.
Is it worth trying resistor, mos, and controller before buying transformer???

Chow
BOB

[Gianni]

Hi Bob,

in these days I have some problem so I won't be here frequently.

You have found a nice service manual, thanks for the link, and if you see (page 32) the resistor you need is

R923 0.33 OHM 2 W 5% TA62 (if I'm not wrong)

It is hard to find this kind of resistor, at least I tried now on Digikey, Farnell, Vishay without luck.
I found this one from RS, you can buy 3 and mount them in parallel if you don't find anything else. I hope you can use RS.

Originally Posted by Bobdee

Is it worth trying resistor, mos, and controller before buying transformer???

I don't know. If the transformer is damaged with some turns shorted, when you turn the monitor on you can break again Mosfet, IC etc...
I always prefer to check at low voltage the controller and only when I'm sure everything is OK I proceed with power.

Pay attention to solder joints when you replace components, be careful not to short pads/tracks.

About scope: I have a TDS210 60MHz at home but I use it twice/year; if you are a newbie with it or you are planning to play a lot with circuits/electronics and buying one it is worth, otherwise I suggest you don't waste money.
After you buying a scope you need also power supplies for testing, cables, a variac .. so on.
I have spent some money because 12 years ago I did some work at home but today I don't use this stuff very much.
Very soon I will post some pics about what I have in my cellar... if I'm not wrong I have some big... big transistor