R34 Skyline climate control unit transistor

[sinn3r]

Hi all,

 

long time listener, first time caller

 

i was wondering if anyone can help me identify a transistor on the climate control unit board that decided to fry itself

 

I've circled it in the attached photo

 

any help would be appreciated

[GTSBoy]

It's almost certainly the same as the one next to it.

Have a fish around amongst these hits

https://www.google.com/search?q=surface+mount+transistor+m33&sca_esv=9cb49794e0b2005d&source=hp&ei=2vJ5aNjTB7Kw0PEPldnS8QM&iflsig=AOw8s4IAAAAAaHoA6qkfmF6XcygtrZ4Vu9f92NXF_RFd&ved=0ahUKEwjYqIPP7MWOAxUyGDQIHZWsND4Q4dUDCA8&uact=5&oq=surface+mount+transistor+m33&gs_lp=Egdnd3Mtd2l6IhxzdXJmYWNlIG1vdW50IHRyYW5zaXN0b3IgbTMzMgUQIRigATIFECEYoAEyBRAhGKABMgUQIRigAUjKCFAAWABwAHgAkAEAmAHfAaAB3wGqAQMyLTG4AQPIAQD4AQL4AQGYAgGgAuYBmAMAkgcDMi0xoAfMBLIHAzItMbgH5gHCBwMyLTHIBwU&sclient=gws-wiz

[dbm7]

That's not a transistor --- it's marked ZD1 which makes it a zener diode. As to what the breakdown voltage is, not enough there to divine.

[GTSBoy]

24 minutes ago, dbm7 said:

That's not a transistor --- it's marked ZD1 which makes it a zener diode. As to what the breakdown voltage is, not enough there to divine.

Yes it is. ZD1 is on the other side of the board. Where ZD1 is marked is clearly opposite a 2 pin device. Our 3 pin device here is not a ZD.

[dbm7]

Need to see other side of PCB in that area...ie; I don't see any thru-hole mounting, just soldered vias (smd zeners in SOT23 have 3 legs but only 2 are used, as reflected by PCB tracks)

[GTSBoy]

58 minutes ago, dbm7 said:

Need to see other side of PCB in that area...ie; I don't see any thru-hole mounting, just soldered vias (smd zeners in SOT23 have 3 legs but only 2 are used, as reflected by PCB tracks)

Hmm. You might be right. @sinn3r, please post up more photos. Xtreme closeup of this side and the other side.

[sinn3r]

You can’t see much on the other side as the lcd is there

I don’t think it’s the same as the m33 beside it as the markings on top is not the same

was hoping someone had a good quality photo or if they just happened to have the unit in hand, quickly take the cover off and take a photo to clearly show the marking on top to identify the diode

 

the unit is currently with an electronics repair shop so I can’t take another photo at the moment

hopefully they are smart enough to know if it’s a zener diode or not

[MBS206]

20 hours ago, dbm7 said:

That's not a transistor --- it's marked ZD1 which makes it a zener diode. As to what the breakdown voltage is, not enough there to divine.

I came here to note that is a zener diode too base on the info there.

Based on that, I'd also be suspicious that replacing it, and it's likely to do the same. A lot of use cases will see it used as either voltage protection, or to create a cheap but relatively stable fixed voltage supply. That would mean it has seen more voltage than it should, and has gone into voltage melt down.
If there is something else in the circuit dumping out higher than it should voltages, that needs to be found too.

It's quite likely they're trying to use the Zener to limit the voltage that is hitting through to the transistor beside it, so what ever goes to the zener is likely a signal, and they're using the transistor in that circuit to amplify it. Especially as it seems they've also got a capacitor across the zener. Looks like there is meant to be something "noisy" to that zener, and what ever it was, had a melt down.

Looking at that picture, it also looks like there's some solder joints that really need redoing, and it might be worth having the whole board properly inspected. 

Unfortunately, without being able to stick a multimeter on it, and start tracing it all out, I'm pretty much at a loss now to help. I don't even believe I have a climate control board from an R33 around here to pull apart and see if any of the circuit appears similar to give some ideas.

[sinn3r]

1 hour ago, MBS206 said:

I came here to note that is a zener diode too base on the info there.

Based on that, I'd also be suspicious that replacing it, and it's likely to do the same. A lot of use cases will see it used as either voltage protection, or to create a cheap but relatively stable fixed voltage supply. That would mean it has seen more voltage than it should, and has gone into voltage melt down.
If there is something else in the circuit dumping out higher than it should voltages, that needs to be found too.

It's quite likely they're trying to use the Zener to limit the voltage that is hitting through to the transistor beside it, so what ever goes to the zener is likely a signal, and they're using the transistor in that circuit to amplify it. Especially as it seems they've also got a capacitor across the zener. Looks like there is meant to be something "noisy" to that zener, and what ever it was, had a melt down.

Looking at that picture, it also looks like there's some solder joints that really need redoing, and it might be worth having the whole board properly inspected. 

Unfortunately, without being able to stick a multimeter on it, and start tracing it all out, I'm pretty much at a loss now to help. I don't even believe I have a climate control board from an R33 around here to pull apart and see if any of the circuit appears similar to give some ideas.

I know why it happened and I’m embarrassed to say but I was testing the polarity of one of the led bulb to see which side was positive with a 12v battery and that’s when it decided to fry

hoping I didn’t damage anything else

[Duncan]

1 hour ago, sinn3r said:

I know why it happened and I’m embarrassed to say but I was testing the polarity of one of the led bulb to see which side was positive with a 12v battery and that’s when it decided to fry

hoping I didn’t damage anything else

Good on you for mentioning, that helps as far as other things you might need to check

[MBS206]

2 hours ago, sinn3r said:

I know why it happened and I’m embarrassed to say but I was testing the polarity of one of the led bulb to see which side was positive with a 12v battery and that’s when it decided to fry

hoping I didn’t damage anything else

Ahhhh... If you were putting 12V to the led in there, that's likely made it very unhappy.

Chances are how you put power, was 12V across an LED that's meant to only have about 20mA through it at peak, and a forward voltage of about 1.8 to 2.4 volts. That circuit is likely only a 3V3 circuit, and will have a resistor in series with the led too.

That's my guesstimate on that light, without having touched one.

[dbm7]

Bit of a pity we don't have good images of the back/front of the PCB ~ that said, I found a YT vid of a teardown to replace dicky clock switches, and got enough of a glimpse to realize this PCB is the front-end to a connected to what I'll call PCBA, and as such this is all digital on this PCB..ergo, battery voltage probably doesn't make an appearance here ; that is, I'd expect them to do something on PCBA wrt power conditioning for the adjustment/display/switch PCB....

....given what's transpired..ie; some permutation of 12vdc on a 5vdc with or without correct polarity...would explain why the zener said "no" and exploded. The transistor Q5 (M33) is likely to be a digital switching transistor...that is, package has builtin bias resistors to ensure it saturates as soon as base threshold voltage is reached (minimal rise/fall time)....and wrt the question 'what else could've fried?' ....well, I know there's an MCU on this board (display, I/O at a guess), and you hope they isolated it from this scenario...I got my crayons out, it looks a bit like this...

 

...not a lot to see, or rather, everything you'd like to see disappears down a via to the other side...base drive for the transistor comes from somewhere else, what this transistor is switching is somewhere else...but the zener circuit is exclusive to all this ~ it's providing a set voltage (current limited by the 1K3 resistor R19)...and disappears somewhere else down the via I marked V out ; if the errant voltage 'jumped' the diode in the millisecond before it exploded, whatever that V out via feeds may have seen a spike...

....I'll just imagine that Q5 was switched off at the time, thus no damage should've been done....but whatever that zener feeds has to be checked...

HTH

[sinn3r]

perhaps i should have mentioned, I plugged the unit in before i handed over to the electronics repair shop to see what damaged had been caused and the unit worked (ac controls, rear demister etc) bar the lights behind the lcd. i would assume that the diode was only to control lighting and didnt harm anything else

i got the unit back from the electronics repair shop and all is well (to a point). The lights are back on and ac controls are working. im still paranoid as i beleive the repairer just put in any zener diode he could find and admitted asking chatgpt if its compatible

 

i do however have another issue... sometimes when i turn the ignition on, the climate control unit now goes through a diagnostics procedure which normally occurs when you disconnect and reconnect but this may be due to the below

 

to top everything off, and feel free to shoot me as im just about to do it myself anyway, while i was checking the newly repaired board by plugging in the climate control unit bare without the housing, i believe i may have shorted it on the headunit surround.

Climate control unit still works but now the keyless entry doesnt work along with the dome light not turning on when you open the door. to add to this tricky situation, when you start the car and remove the key ( i have a turbo timer so car remains on) the keyless entry works. the dome light also works when you switch to the on position. fuses were checked and all ok

ive deduced that the short somehow has messed with the smart entry control module as that is what controls the keyless entry and dome light on door opening

 

you guys wouldnt happen to have any experience with that topic lmao... im only laughing as its all i can do right now

my self diagnosed adhd always gets me in a situation as i have no patience and want to get everything done in shortest amount of time as possible often ignoring crucial steps such as disconnecting battery when stuffing around with electronics or even placing a simple rag over the metallic headunit surround when placing a live pcb board on top of it

 

FML

[Duncan]

some days eh?

The keyless entry and interior light on/off with the key will be controlled by the Body Control Module, but I'm not certain where that is or what it looks like (you might get lucky with a search to get a part#, which could be printed on it). I'd start at the A pillar/ Under dash/kick panel on the driver's side

[sinn3r]

Update all

 

thanks to the workshop manual, it lead me back to checking fuses

as mentioned central locking and door open lights worked when acc was switched on.

diagram attached shows two points of power 1. ACC and 2.  Batt with the later being fused (#28)

I did check the fuses using a multimeter but I must have stuffed that up also. Went back and checked the batt fuse in interior fuse box and you wouldn’t believe it… a blown fuse.

replaced fuse and everything is now working as it should including the climate control

 

thank you all with your positive insight and knowledge.