bigbuzuki

The PCM 2.0 unit in my 2003 Cayenne has been intermittently playing up recently, powering up on some occasions and not on others.
The model of the unit is BE 6635.

I have experience in the electronics industry and my curiosity got the better of me and so I pulled the unit forward from the dash and opened the lid for a visual inspection. I reasoned that maybe I have a suspect dry solder joint etc.

As fate would have it the unit worked perfectly when it was naked in front of me.
There was an orange led on the main board which was illuminated when the unit was on and I could see the red fiber optic light flashing on and off at the back of the fiber plug. The display was working along with all the other functions.

On another occasion when the unit was not working, I noticed that the orange led was not illuminated on the main board.
Power was still available as the nav cd would spin up for about 30 secs and then stop.

When the unit would recover from its non working state, the OBC info such as the average fuel used, distance traveled, time since reset info, would all be reset to zero.

I suspect the orange led not illuminating is a clue as to what is wrong with the PCM 2 unit.

I tried getting circuit diagrams and service literature from Porsche and Harman/Becker with no luck as the item is "proprietary" blah,blah,blah.
They will however sell me a new unit for a lot of money since I am out of warranty.

I have attached a picture with the orange led location (yellow arrow) for reference.

Does anyone have any info they can share on this?

Thanks.

99firehawk

I cant really offer to much help.................but if your info is reseting the ecu is losing its term 30 power (constant 12v) you would need to trace the wire from the back of the radio into the unit, I would assume it runs to a power supply of some sort.

bigbuzuki

The main board is double sided and a little complex to visually trace back the power circuit. This is where the circuit diagrams would be handy.

I don't believe the unit is losing all its power because with the fault present, the cd spins up ok, the fibre optic led flashes on the back of the unit and the display illuminates with the backlight although no picture or letters are present.

I have had the unit on a bench with a power supply connected and with the fault present it still draws about 500mA of current.

99firehawk

your sol on the diagram from becker or porsche, the only way you could ever get that is if you got a job with becker and snuck it out. Just because you have power to some components doesnt mean that they all do, there could be a splice/union somewhere down stream of the power supply that is loose

Robin 993DX

Without a schematic you are SOL.

Slow Guy

I wonder if LTC squirreled anything away during one of his previous employment ventures?

ltc

Don't have to...photographic memory.
Just looking at that picture made me sick...

Slow Guy

What he needs is schematic memory....

bigbuzuki

Had some luck with rectifying the fault on the PCM.

With the defect active I began taking some DC voltage measurements from the test port connector on the board.
I noticed that the DC voltages were not stable and kept fluctuating.

I began flexing the PC board gently and noticed that the voltages became stable when the board was pressed around the ST10F269-T6 chip.

I reheated the solder on all the power pins of the same chip and WELLA, the orange LED illuminated and all is well.

The ST10F269-T6 chip is marked with a red A and the power pins are marked in yellow. The test port connector is at position B.

Unit has been reinstalled in the vehicle and has operated perfectly since the repair.

Slow Guy

Outstanding! Wish I had that kind of solder skills.

ltc

Reflowing the pins on a 0.5mm pitch TQFP is best done with a hot air nozzle.
You can do it with a Metcal soldering iron and a special tip.
I used to be able to, but now I'm legally blind, so those days are long gone.

bigbuzuki

Correct. The reflow was indeed done with a hot air nozzle.

ltc

Nicely done.

gogobg

I am not sure how the two forums relate, but I think this is the missing picture here (got it from rentech)

gogobg

Is there a way to source the entire board to replace? I have a "patient" that I can cannibalize to figure out serial numbers and other identifiers, but I have no idea where to start and where to go source that from.