Confirm resistor type

[Bluejets]

Have an RAC fan coil control board with a couple of components burnt up and need to confirm what I think are a type of ceramic resistor used in and around the damage.

I have shown the resistor in question (possibly 2w ?) alongside a standard 1/4w carbon resistor for comparison.

Resistors are RO2 and RO3.

Resistors have taken a bit of a beating but are still the same body colour so perhaps that may help.

Also included a quick sketch of the section of the circuit which may help.

Input voltage to the motor is 240V AC.

Thanks...Jeff (lecky)

 

[davenn]

hi Jeff

that circuit and those resistor values .. are they from the manufacturer ?

or did you draw out the cct and measure the resistor values ?

Dave

 

[Bluejets]

Hi Dave,
Drew the circuit out myself, followed traces on the board, found part numbers for the thyristor and trigger and applied that to the drawing.

The resistor values as far as I could read them were (R03) 990R (white white brown gold)...it read 770R on the meter with part removed.
This is the one shown, the first band of white has flaked off after I removed it from the board.

The other (R02) 100R (brown black brown gold) and read 107R on the meter.

The first value seems like an odd value but the colours match...??

 

[Bluejets]

Components for the fan motor drive received quite a touch-up but the rest looks quite ok and other parts of the system are working ok also.

The one resistor in question may well be a higher multiplier as it has been cooked a bit.

RAC is an LG... LS-J0962HL

 

[davenn]

Drew the circuit out myself, followed traces on the board, found part numbers for the thyristor and trigger and applied that to the drawing.

OK no probs ... the reason I asked was that you/whoever appeared to have mislabelled the 2 semiconductors
in relation to the LED. The M1L43 is a plain triac that 3 terminal TO92 case that looks like a BC546 transistor
to the left of the burn hole

Where as the TLP726 for as much as I could get info on is an opto coupled triac with which the LED is in internal part of and is that 5 pin black device labelled IC01J

The resistor values as far as I could read them were (R03) 990R (white white brown gold)...it read 770R on the meter with part removed.
This is the one shown, the first band of white has flaked off after I removed it from the board.

The other (R02) 100R (brown black brown gold) and read 107R on the meter.

The first value seems like an odd value but the colours match...??

experience tells me and something you will learn too, resistors rarely show their correct colours when subjected to that much heat... the colours you see are likely to be pale cooked renditions of the originals

your resistance measurements are better to go off

990 Ohms ... not a standard value, but falls within the 10% tolerance of a 1k (1000 Ohm) resistor
770 Ohms is also not a standard value but it could be an 820 Ohm
They are probably both OK ( changing them wouldn't hurt)

As for the cooked board yeah!! haha

OK Options ....
clean the board thoroughly around the burnt area, removing as much of the burnt board as possible
this is essential as all that carbonised board will make a great conductor with 240V
you also have to consider why the burn up happened ... possibly a dry joint that started arcing at the termination solder pads of the missing resistor and that became a cascade effect with nearby solder pads as they heated up. Maybe that 3 pin triac and or the other one has also failed.

cheers
Dave

 

[Bluejets]

Ok ..thanks
Yes, had the component numbers a-about.

After a bit of thought might be better to tap into the opto and refit another that could drive a standard relay.
Couple of wires tapped in and mount new bits away from the charcoal......

Thanks again...Jeff

 

[shrtrnd]

The two resistor picture: The one on top looks like a metal film resistor.
I don't think the one on the bottom that fried is ceramic. I think it was the 'flame-proof' variety.
Just 2 cents worth from an outside observer.