# Faulty PIR

#### scudo

Jun 25, 2021
7
The images are from an PIR that went faulty, wouldn’t turn off my security light.

On opening it I realise the damaged part would not be within my capabilies to repair (too small)

Anyhow can anyone identify the part and possible reason for failing.

#### pharaon

Oct 28, 2014
415
as what i can see it's a SMD resistor . you can get it's value by the number on it if you can read it
also check the SMD transistor beside it as well

#### 73's de Edd

Aug 21, 2015
3,463
Sir Scudo . . . . .

Initially can you take some solvent and an acid / paste / horse hair bristle brush and clean all of that white particulate matter
that is all around and in the vicinity of the 560 ohm and 1500 ohm resistors and the mini surface mount transistor . . . . . also get its number if being more than ? CP.

Give us a good close up photo of the then cleaned up area. Since . . . . .to date . . . . . I have no idea of what type of component transpired there. . . . . .excepting that it left a WHOLE lot of white powder and white particulate matter, in the surrounds..

Also get the number of that . . .probably dead shorted MT1 to MT2 . . . . POWER TRIAC
Confirm if I have the foil path correct in my drawing foil interconnects between pin 2 of the controller I.C. to the 10K resistor to the base of the transistor.
For your part, take ohmmeter in hand and confirm / draw up all of the the foil interconnecting paths between the C and E of the transistor and the 560 ohm and the 1500 ohm resistors and the final connection into the Gate of the TRIAC

In a NO POWER APPLIED . . . or even plugged into AC power . . . .Take DVM and put in OHMS test function, lowest range
SHORT the test leads together to see what is displayed for a dead short, and then move over and probe the MT1 and MT2 terminals of the big TRIAC and see what it is reading in ohms, if not being the same shorted reading.. We also need that TRIACs number.

MY LOOKIE HEAR SHEET . . . . . . ( I dun did it all by myselfses-es )

The schematic above differs from your unit in the YELLOW outlined power supply and the use of a power relay for switching, yours uses the POWER TRIAC.

Specifically, on yours, AC power cones into the R1 confusible resistor and then goes out and up to the Orange Drop poly cap to then use the caps value and its capacitive reactance to drop AC voltage down to 12 'ish volts AC and then D1 converts to DC and probably C1 is the first filter cap encountered and then Zener Diode 1 regulates on down to 12 ? or 5 VDC.

I can easily make out of the ground lead sides of all of the E-caps except the RED circled C5. Seems like I can make out
a 25VDC rating and a 2'ish or 20'ish capacitance value . . . . what is your REAL reading ?
I still couldn't confirm its ground lead . . . . . but it could be a, special non polarized unit.
The E-caps negative lead sides are being marked using BLACK rectangles.

Why not now take ohmmeter and see if all of the ground leads of those E-caps are being connected together . . . .possibly excepting that C5 if you can not see its marking.
The majority of these caps will be power supply filters with a few being used with some companion resistance to establish time constants .
You can see the 3 related trim pots at the front, related to sensitivity , time delay before turn on, and time delay before turn off.
PLUS there is being the additional photocell that de activates the unit during daylight time.

Your CONSTANT ON is probably related to a shorted MT1 to MT2 in the triac.
OR you might have taken a LIGHTNING STRIKE, and all sorts of damage might have been inflicted.

When we get down to initial testing . . . . . . . out of pin 2 . . . of the controller I.C. . . . . .we can then see if the "front end " of the unit is or has been damaged. . . . . . . abandon ship !

Thaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaasssssit . . . . . .

73's de Edd . . . . .

As long as the answer is right, who cares if the question is wrong?

.

#### scudo

Jun 25, 2021
7
73,s de Edd, Thanks for taking the time and detail you have given me. Being more mechanical than electronically minded it will take me a couple of days to decipher your reply (Thats a compliment not a complaint). I will attempt to get some more detailed images tomorrow during daylight hours.

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