Quote:
Originally Posted by JasonACT
Oooh, that black dot wasn't there before. You will be up for a new mosfet then (I'm glad you identified what it was too - I hadn't mentioned it before because it's not a regulator, and it didn't change values for me when the screen was on or off - so whatever it's switching isn't the screen directly).
I'll do some more tracing tomorrow after work, to find where the +20v is generated from. That would seem to be the "thing" for the screen to light up (at least).
I'm not quite sure what you mean by "mv all round"?
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Quoting myself.. because I did later say it is switching the screen on and possibly controls the brightness.. I'm almost sure this isn't actually true as I've done more tests this afternoon. My original comments stand I think...
It doesn't matter if the screen is on or off for me, if the 12v is applied to the large external connector for the car loom, the screen remains off and I get 21.45v on the gate pin (enabling the MOSFET). When I switch the screen on, that drops to 20.3v (still enabling the MOSFET). 12v power is going through the MOSFET and powering the large regulator, the 8v small regulator and the small unknown device - and is also sent into pin 5 of the board joining connector. The original 12v is coming in from pin 1. I'd say there's a timer that eventually switches the MOSFET off in a deep sleep mode to save power, but it doesn't happen in the first few minutes. Since you are getting dodgy voltage readings, the MOSFET still needs to be replaced before we can continue.
Pin 5 must power something else on the large board related to the screen, and I've found two components of interest (one is very close to the red and black wires).
That one is a TSSOP 16 device, I hate this one, the entire bottom is a ground which gets soldered to the circuit board as a heat sink - making it impossible to remove without damage. I just rip the legs off them and leave them there. You need to get a TSSOP 16 breakout board to use them - but I don't see any with the ground/heatsink and a heat gun might be needed to get the base soldered properly anyway. It's an LT3517 (Linear Technology) LED Driver with 1.5A switch current. It'll be doing the brightness control. They are available on ebay from China.
The less likely chip (further away and closer to the audio components on the large board) is a MSOP 10 device, I hate all of these, you guessed it, bottom is a ground/heatsink. You need a MSOP 10 breakout board..blah..blah.. Those do have a heatsink. It's got LTDXS written on it (Linear Technologies) which is their code for LT3972 - 3 Amp power regulator. Also available on ebay from China.
Would I try any of this? (Well, I have before, so that answers that.) At $700 for an exchange, I would again. $365 is sounding like an OK deal though, as I did buy a backup at around that price (which I didn't know had SAT NAV). That was also to do bench testing though, as I knew my ultimate project of getting the FGX Sync 2 unit working would require all the
CAN BUS codes I could get from a MK2 unit first.
(Side note, I still don't have all the codes - I keep finding things I don't use - but at least I wouldn't miss them.)
I really hope it's just the MOSFET on the small board.