[MTCB Hardware Development] Oldpapa49:
The can bus unit I have is for Ford Explorer and is being used in my 2005 Ford Freestyle with a Pumpkin 6.95" (7") Kit Kat DVD etc etc unit.

Bought around late Oct or November to replace a Cheap Walmart DUAL display that I bought for the car. I did add the can bus to that unit as well.

What has happen that this week, the radio would never shut down when key was removed and door opened. It would stay on with a display.

I have used Custom roms from all developers and updated the MCU to latest. So I thought yup, something bad with software, but that was proven to be wrong.

I contacted Pumpkin support and they said to test it by cutting the red wire (ACC) and connect to the car lighter. That is the understanding that the car lighter goes off. Mine does not, stays powered up.

But since I work as R&D and been in electronics for well over 55 years, I decided to look into the decoder.

1. It has a 16 pin plug with only 8 being used. Of the 8, take 2 out for power (constant and ground), 2 for can bus communication.

2. out of the 4, 1 is used for the ACC control (Red)., 1 for Illumination control (Orange), another had a cut Violet (purple) wire. A brown wire I did not trace at all.

The ACC wire connected to the cars ACC wire directly. This is the starting point to see why I had 12 volts when it was supposed to go away after so many seconds.

Internally of the can bus, 3 circuits that I found where controlled by P-Channel MOSFETS. These are transistor like on-off switches. A regular transistor controlled these MOSFETS to apply 12 Vs to the radio 3 wires.

1 was for the Illumination (Orange), the other in my case (Red) for ACC control. and the Purple one, well wire was cut. The MOSFET outputs (one side of the switch) had a large current diode that would apply

12 volts to the wires (Red, Orange and Violet). Well, the ACC one was a more hefty diode. The diodes are used to block the Cars 12V from directly connecting to the MOSFETs thus they are called Blocking Diodes.

I check the leads of the 3 MOSFETS with a digital ohm meter. The leads on the MOSFETs that I was concern are the S (source) and D (Drain). These are used like a switch contact. The G (Gate) is like the lever

which is controlled by the internal processor.

I had 1 MOSFET that was shorted S-D meaning it will have 12 V all the time on the lead which was the Red lead.

Since the Violet wire was cut and not used, I used that to replace the shorted one. These MOSFETs are 2.8 Amp components and are Surface Mount Devices (SMD).

Now the question is, how did this SMD short. The diode is still good, it most likely could short if the ACC circuit went to ground. The ACC wire of the car connects to the radio like the Can Bus. If thats the case, the control for that would also be bad, but with the Cheap DUAL radio, that works ok. So I think, it simply went bad, maybe because my trip just a week ago was in the Southwest of the states where the outside was 120 degrees F in the shade.

I have yet to put the radio back in the car to test it. Hopefully I get it back Saturday and see, but I'm sure it should be ok. I did inform Pumpkin of the results since part of my job (which is in the Medical Device Field) is to find why things fail and resolve it.

Now, how would on solve this on your own, .. Well, look at your radio and check which wire controls the function that seems to be working incorrectly. Mine was ACC Red wire. The Can Bus circuit Delays the shut down of the radio I think via the Can Bus. Cutting the wire that connects to the can bus that controls that signal (red) and see if the radio shuts down when you remove the key and open the door (Car ACC now controls the shutdown of the radio.

I wonder if a Diode should be put into the wiring between the ACC of the car end to the radio ACC input and tie the can bus ACC to the radio side ACC.

Kind of like Car ACC plug ------>| -----.--------Radio ACC in

|-------Can Bus Red wire

When the car ACC is 12 volts, it powers the Radio.

When car ACC goes away the can bus powers ACC to radio for time out.

Don't know..

I hope this helps.. I kind wonder off sometimes.. But I hope you understand

Wayne