No VCC when MS3 daughterboard installed

Ask questions about DIY board assembly issues, fault finding and testing. (Covers all Megasquirt versions and board.)

Moderators: jsmcortina, muythaibxr

Post Reply
pit_celica
Master MS/Extra'er
Posts: 682
Joined: Tue Jul 18, 2006 3:12 pm

No VCC when MS3 daughterboard installed

Post by pit_celica »

Hi,

I was testing a fully assembled v3.57+MS3+MS3X board on my bench today and I think I fried something. I was trying to adjust the VR pots using a press drill and a distributor. While adjusting the R52 VR pot, I accidentally dropped my metallic screwdriver in the SD card/U3/U4 area of the MS3 when everything was still powered on. Right after, I wasn't able to communicate with the laptop anymore.

After some basic power/ground testing, I found that the 5V at VCC was going from 5V to 0.5V really fast after a power ON with the external power supply. The output of U5 is a clean 5V, but VCC is 0.5V in steady state.

I then removed the expansion board and the MS3 daughter board and the VCC is now back at 5V. As soon as I reinstall the MS3 daughter board, the VCC drops at 0.5V.

I'm pretty sure I screwed up something, I just want to make sure what it is before ordering some costly parts.

Let me know if you have any ideas.

Thanks!

Sam
billr
Super MS/Extra'er
Posts: 6828
Joined: Sun May 15, 2011 11:41 am
Location: Walnut Creek, Calif. USA

Re: No VCC when MS3 daughterboard installed

Post by billr »

Have you peeked into that SD card socket, made sure there aren't just some contacts that got bent and are shorting?
pit_celica
Master MS/Extra'er
Posts: 682
Joined: Tue Jul 18, 2006 3:12 pm

Re: No VCC when MS3 daughterboard installed

Post by pit_celica »

Some new info on this :

- On the main board, without the MS3 daugtherboard connected, I have 12V at pin#3 of U5 (should be 5V isn't it??). So, I also have 5V at pin #20 of the 40 pins daughterboard connector and also at the pin #26 of the DB37 connector of the main board. I suppose that U5 is bad. What other components might be faulty?

- With the MS3 daughterboard unconnected and sitting as is on it's own, there is continuity between pin #31 and pin #32 of the 34pins JP2. This means that there is a short between 5V and GND on the MS3 daugtherboard itself.

Now, what to do with this? I'm ready to send it to someone to have it diagnosed/repaired. Who should I contact in Quebec, Canada?

Thanks in advance!

Sam
pit_celica
Master MS/Extra'er
Posts: 682
Joined: Tue Jul 18, 2006 3:12 pm

Re: No VCC when MS3 daughterboard installed

Post by pit_celica »

Again, some update.

Please ignore the first point in my last post above. My ground lead from my power supply wasn't correctly connected and this lead to +12V on both left and right pins of U5. With the ground correctly connected, I now have 5V on all required places. I swapped the MS3 daughtercard with a known to be working one and all is fine now.

So, I have a MS3 daugthercard that is faulty because it has continuity between +5V and ground on itself. How do I deal with this. Please let me know what you think.

Have a good day!

Sam
Matt Cramer
Super MS/Extra'er
Posts: 17499
Joined: Thu Apr 16, 2009 8:08 pm

Re: No VCC when MS3 daughterboard installed

Post by Matt Cramer »

If the daughter card is less than a year old, contact the vendor you bought it from directly; they're covered by a one year warranty.

For out of warranty daughter cards, Peter Florance is probably the best one to call.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
Post Reply