Odd communication problem (ie not the normal ones)

[MKnight702]

I have Megajolt successfully installed on my car, I could communicate with it with the laptop, but not anymore. The laptop just won't talk to my Megajolt, I have tried unplugging the serial cable and swapping to a friends car who also has Megajolt and I can communicate with it with no problems, it just won't talk to mine.

Any ideas?

[NITROPIXIE]

Firstly lets start at the beginning. What unit do you have?? and does your friend have the same unit?? Did you buy the unit pre-built?? If all your cables are ok and it can talk to another mjlj unit then check.

1) are you getting power to mjlj ie green light on??

2) is the unit working correctly, ie not stuck at at limp home mode 10 degrees

3) then check you have 5v at Vref. If you can't get a multi meter then try a led and resistor.

These can be done without taking the unit apart and are quick checks.

If still no luck then we need to have a look at the max232 chip as this is the chip which talks to the computer. So take the unit apart and without power to the board check

4) all solder joints look good

5) for continuity between ground and pin 15 of the chip

6) then pin 16 and pin 3 of the voltage regulator (the pin nearest R9 and C2)

7) then apply power and check you get 5v between pin 15(gnd) and pin 16(+5v)

This should be a good starting point for fault diagnosis.

Ryan

[MKnight702]

Thanks for the reply,

Both Megajolts are V3 I believe, will confirm. Mine was prebuilt.

The Megajolt functions correctly in all instances, advance measured with a timing light changes in line with expectations (ie not stuck at 10 degrees). I have covered 3k miles with the Megajolt in place and have previously had no problems connecting the laptop to Megajolt to review/modify maps which is why my first point of call was a dropped pin in the serial connector. However, I have continuity between one end of the serial cable and the pin on the board leaving me scratching my head.

The unit is currently out of the car as the engine is being rebuilt but I will test those measurements when I can.

I have had the case apart and the joints all look good, no burnt tracks or components.

I will also see if I can connect to my Megajolt with another laptop to see if something weird is happening there.

[NITROPIXIE]

It maybe the max232chip. http://cpc.farnell.com/1/1/24308-ic-rs2 ... ersil.html for a replacement if needed

If you still have no luck and would like me to give it a once over for you then get in touch.

Ryan

[MKnight702]

Thanks, I've ordered the R232 and will give it a go.