Smd resistor unbelievable

[bushtech]

I have got a burnt resistor that needs replacing. Schematic says 300Ω 5W. As far as I can tell this is an 0603 type smd. (0603 type 1.6x0.8mm) Can't find any resistors 300Ω 5W in a 0603 package.

Does such an animal exist? I have difficulty believing that something that small can handle 5W. (Maybe 0.5W typo?)

 

[bushtech]

Here is the circuit diagram showing the resistor R83

 

[(*steve*)]

I suggest you check again. R83 certainly looks like it will dissipate power.

0603 resistors are commonly rated at powers like 0.063W. maybe it's R63? R93? R88?

Check what the resistor is connected to.

 

[kellys_eye]

All the SM resistors are shown with small 'boxes' drawn around them - R83 isn't one of them....

 

[bushtech]

Well spotted kellys_eye. Thanks. This diagram might not then be exactly what I have. Investigation required

 

[Gandes]

Yes this is not 0603 for sure, this scheamatic needs to be updated

 

[73's de Edd]

Page 14 of supplied referencing . . . . .
You DO have a surface mounted 470 pf /1KV Ceramic capacitor that is shunting it.
The R83 will be a big ole boy . . . probably axial lead . . . possibly metal film or white cased block ceramic .

 

[bushtech]

Lol. It sure does not look like that!


There are similiarities, but my schematic does not talk to the pcb here

 

[73's de Edd]

Sir bushtech . . . . .

OH . . .BOYS! . . .a pickchoor . . I can SEE !

I think that if you check the other component side of the board that you are going to find the specified resistor as a metal film resistor of that previously mentioned value and is having, one lead folded back, and vertically mounted and is connected to my two circular YELLOW foil lands /pads.

Track down the lower fried resistors RED and BLUE paths that I have shown, for as far as I can see their views routings.

Then you see what components that they connect to, to relate to the schematic.
Also wasn't there at least one (a 2) or two numbers that still were legible on the burnt part ?

Re MARKUP . . . .



73's de Edd

 

[bushtech]

Thanks Edd
This might help:



When the infamous resistor went a leg on each of 2 transistors (see 2 red lines) got desoldered.

Edd, the resistor R83 sits close to cap C20 on the top view.
R83 looks like one side connected to one leg of Q21 and the other side to R82.
I cannot read anything on R83

 

[bushtech]

Oh, and it's a UPS

 

[73's de Edd]

I didn't knows that they had United Parcel Service over theres ?

Can you come in closer on the whole foil side of the board . . 2X . .3X . . .4X as nothing can be made out / worked with from the present pixel density of this photo.

https://www.electronicspoint.com/attachments/bottom-markup-jpg.36579/

You did find that resistor at suspected position . . . . .right ?

#1 problem with UPS's . . . . . time declined sulphated batteries . . . or failure to take charge, if gel cell related.
But you seem to have a bit of a different problem here.

73's de Edd

 

[bushtech]

Best i can do, don't know if it helps:

 

[73's de Edd]

Still not good enough resolution . . . at the example below . . .to make out the two relevant foil paths even at this mag level. . .needs mo' pixel content.
See if you can come in closer to encompass only the RED square, as I don't think that the paths will extend out of that area.

MAX MAGGED . . .



DAVENN . . . no need to waste hosting space of either of the last two . . .13 & 14 posts images. after der bushmeister sees it.

73's de Edd

 

[bushtech]

Let's try again
davenn is gonna roast me about the file size

 

[(*steve*)]

If you have a large image in terms of pixels, and in terms of space required to store it, you may be able to find a program to store the image at a lower quality. This can dramatically reduce the size without making the image itself smaller in dimensions.

 

[bushtech]

St Edd
"#1 problem with UPS's . . . . . time declined sulphated batteries . . . or failure to take charge, if gel cell related.
But you seem to have a bit of a different problem here."

This happened when I put a replacement lead acid battery in and switched on.

 

[73's de Edd]

Sir bushtech . . . . .

I am now reading the foil paths converging into that part in question, but it seems that they tie into transistors that are being different from the schematics given ones.
The schematic gives drive shunting / supression transistors Q19 and Q21 being related to having their collectors connected into gates of the Q20-24 paralleled power FETs and the Q23-Q25 paralleled power FETs.

Our bad part routes one path to the collector tab of Q18 which is being a non existant / assigned number.

Also you see some parts assigned SM resistor codes . . .which are probably high value resistors . . . 30C and 01A . . . check them out and see if they don't ohm out as being 100K or 49.9K units .

ALSO I frankly don't even see any resistors in this inverter circit on page 14, that are even being of a low enough resistance value that are EVEN "blowable outable", since we are only dealing with 12VDC supply power.

OR a possible 24VDC IF a mistimed or errant drive pulse lets the driven primary half of the inverter power transformer act as an autotransformer and thereby shoot 24 VDC over to circuitry on the other half of the winding..
Lastlty can you use an ohmmeter in low resistance mode to confirm that my Post 9's . . . RED line path . . . . actually does end up at the collector tab of " non existant" . . . on the schematic . . . Q18 transistor.
Also that the other BLUE path ends up at the 30C SM resistor .
Ohm it . . .30C . . . . out also.

73's de Edd

 

[bushtech]

Thanks St Edd
Some smd resistor values:
30C=20kΩ
01C=10kΩ
30D=100kΩ
224=49kΩ
01A=100Ω

On the red and blue paths: yes and yes. The red path ends up at the top left leg of Q18

Yes, some sort of surge happened when I plugged the new battery in

 

[bushtech]

If it helps the writing on Q18 says 1P with something like a j lying on it's side

Could it be this: http://www.s-manuals.com/pdf/datasheet/k/s/kst2222a_fairchild.pdf