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I'd guess it's an NPN transistor similar to a MMBT2222A. But if overheating destroyed it you have to ask yourself what caused it to pass excess current? Unless you can identify the cause a replacement transistor will probably give up the ghost too.
Thanks for your reply
I have just fitted BC17 (rs part number 807-5122) marking T1
This did not work.
In the past few weeks I have also tried
MMBT2369ALT1G Bipolar (BJT) Single Transistor, NPN (farnell part 1653624RL)
MMBT2369A Bipolar (BJT) Single Transistor, NPN (farnell part 9846719) marking 1S
BZX84B7v5 (rs part 800-9771) marking T15
BC807 -25LT3g (rs number 690 0079)
Thanks for your help do you have any other suggestions? I really need to get this part working. It was "dropped and hit tool box and cracked it"
I've not found the exact part yes, but I have found the marking layout - the centre "s" means it's manufactured by Siemens or now Infineon and the 56 is a date code, June 2005. (Or '95 or '15)
Other data I've found says "T1" could be a a BCX17 or BSS63 - (which I can't find listed for infineon).
But, no normal transistor would give the diode voltage drop readings you are getting on that supposedly good part, they make no sense at all.
There are 4 types of R3130N part, all very slightly different. but all do almost the same function.
The only part I could get my hands on was R3130N22EA and this sadly did not work. I have tried to purchasing from china, eBay allibarber the 44HA type with no joy. Fitting this the automotive part did not work, refitting the 2 original T1s sot's the unit works.
Note Pin 1 is connected directly to 0V/Ground on the board
With only two connections, it's not an R3130N or a normal transistor.
It's most likely a diode / zener diode / voltage reference, or just possibly something like a Dallas "one wire" memory device.
You should be able to tell by what the component below connects to - the red pad on your board photo.
If that's a resistor going to some external connection, it's a protection diode of some sort.
If it's a resistor to 5V, it's likely a zener or voltage reference. Either way, that would probably make the pad nearer the CPU a capacitor
Some of the "T1" devices I found earlier were diodes, so it could be one of those.
Edit - looking back to your earlier tests on a good device, try two series pairs of back-to-back schottky diodes, such as BAT42.
(eg. wire two side by side opposite directions, then same again in series).