MJLJ-to-USB cable as originally supplied

minimower · Post by **minimower** » Sun Sep 09, 2018 10:21 am

I run a 6-7 yr old MJLJ
I suspected the cable to be faulty as MJ and laptop not talking to each other.
The cable used those days was a strange lash up with a serial cable thing but it works !( cant add a photo, 'too big')
I opened up the connector to find a small pcb within
My question is, can I trace the wires through and do away with the in-line plugs , just run the (3) wires straight from MJ plug, to the USB plug having joined the individual wires instead of the 2 make-shift original plugs?
Thank you

Post by **brentp** » Wed Sep 12, 2018 6:00 pm

Hi,

Yes, you can totally create an RS232 cable that can plug into your computer's RS232 port (if it has one) or into a USB to serial adapter.

We have wiring instructions here for making your own cable:
https://wiki.autosportlabs.com/MJLJ_V4_ ... rial_Cable

Hope this helps!

minimower · Post by **minimower** » Mon Sep 17, 2018 8:22 am

brentp wrote:Hi,

Yes, you can totally create an RS232 cable that can plug into your computer's RS232 port (if it has one) or into a USB to serial adapter.

We have wiring instructions here for making your own cable:
https://wiki.autosportlabs.com/MJLJ_V4_ ... rial_Cable

Hope this helps!

THANK you so much for replying, that helps a little but can you show me the complete run, that is where wires end up in the USB plug,1-to-4 pins ?
I've reached my wits' end with this all. I borrowed a friend's fully working cable, did a full destructive recovery on laptop, re installed ports to get PORT 3,all good, just can't connect PC to MJ
Is there ANY way you can give me some sort of expected readings for my multimeter so I can test at the USB plug for connectivity with the MJLJ, that would be SO helpful

Post by **brentp** » Mon Sep 17, 2018 5:55 pm

Right.

So, all you need to do is create the cable as specified - with the DB9 on one end, and the RJ11 at the other.

Then, you purchase a common USB to serial adapter. The USB to serial adapter plugs into your computer, and the other end connects to the DB9 on your custom cable.

This two cable combination creates the complete cable that will work with your Megajolt.

If you're not comfortable with the wiring for creating this cable, we recommend finding your local friendly computer/electronics tech friend, school or college tech group to help you out.

minimower · Post by **minimower** » Mon Sep 17, 2018 6:58 pm

Ok, that will get me a cable again, having destroyed the original but I already know the fault isn't the cable as I borrowed a working one. But I still can't tune my car ! AARRGH
I have the dreaded "Could Not Open Port"
What I was hoping for is some expected readings at the USB plug when it's connected to the MJ either with or without engine running. That would help enormously by telling me if the fault is within the PC or the MJ

Post by **brentp** » Thu Sep 27, 2018 5:25 pm

When it says "cannot open port" it's due to a couple of things:

1) the drivers for the USB to serial adapter are not installed correctly. Check the manufacturer's instructions for the USB to serial adapter you are using. It should show up as a COM port under device manager.

2) Or, the port is not configured correctly in the megajolt software. Once you verified the COM port for the USB to serial adapter shows up under device manager, you can go into the megajolt software to switch the COM port to the port that matches what you see in device manager.

This part of the wiki will step you through the process as well:
https://wiki.autosportlabs.com/MJLJ_V4_Operation_Guide

Thanks,

minimower · Post by **minimower** » Fri Sep 28, 2018 8:04 am

I think,as with most things I get involved in, I am a phenomenon !!
Computer tells me the driver etc for the usb -to-MJ lead is correctly installed and working properly
Port is set correctly, happens to be 3
I should add that I've been using this set up for 6 years with only the occasional refusal and also that it stopped working in the time that it was not in use. i.e. working one time and a few weeks later went to use it and no luck
This is why I was hoping that you could give me some expected readings at the usb plug to simply tell me if the MJ is sending info to the lap top. This would help enormously with fault finding

minimower · Post by **minimower** » Sat Sep 29, 2018 7:09 pm

Ok now, I've got it sorted thanks

Edwardatherton · Post by **Edwardatherton** » Thu Oct 25, 2018 9:50 am

Any idea what the solution was?

minimower · Post by **minimower** » Fri May 03, 2019 1:56 pm

Edwardatherton wrote:Any idea what the solution was?

Hello, sorry, I've only just seen this !!
It was to do with the Com Port number but I can't exactly remember in what way