Power Issues MS2v3.0

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

Moderators: jsmcortina, muythaibxr

Post Reply
WM111
MS/Extra Newbie
Posts: 2
Joined: Sat Aug 19, 2017 1:07 am

Power Issues MS2v3.0

Post by WM111 »

I just finished assembling my MS2v3.0 but am having power issues. It seemed as though my U5 reg was faulty as it had 12V on the input but 0.2V on the output rather than 5V. I couldn't see any solder bridges or burnt traces on the board, nothing let the smoke out as far as I could tell and I have checked all my diodes and caps polarity about 10 times over. It wasn't getting hot either, just not working properly. I desoldered it and tested on a breadboard and with no load it shows 7.65V and with an LED+220R load it shows 5.4V. I have a new LM7805 which tests 5V load or no load, will this solve my problem if I put it on the MS or is there likely something else wrong with the board. Daughterboard was never put in place, didnt get through the testing section in the manual.
DaveEFI
Super MS/Extra'er
Posts: 4175
Joined: Sun Apr 15, 2012 12:55 am
Location: SW London, UK

Re: Power Issues MS2v3.0

Post by DaveEFI »

My guess is you have a short somewhere on the 5v rail causing the reg. to shut down. If it is still removed, measure the resistance between the 5v rail and ground. My first suspect if there is a short would be C17 which is a tantalum cap and can go short circuit (although usually only after some use, rather than new) - if no obvious solder bridges, etc.

Best to use the correct reg. General purpose ones may not cope with the odd spike you get on car electrics.
Rover SD1 3.5 EFI
MS2 V3
EDIS
Tech Edge O2
London UK.
prof315
Super MS/Extra'er
Posts: 3760
Joined: Sun Jan 18, 2009 3:13 am
Location: Melbourne, FL

Re: Power Issues MS2v3.0

Post by prof315 »

Check D19, the 5V Zener diode. It can short even easier than C17 and will pull the 5V straight to ground causing U5 to get warm/hot to the touch
Linfert Performance/321 Motorsports
SCCA 2019 SM National Champion Crew Chief
SCCA 2023 FP National Champion Tuner/electrical engineer
100s of MS systems built installed and tuned
Support the developers!
racingmini_mtl
Super MS/Extra'er
Posts: 9128
Joined: Sun May 02, 2004 6:51 am
Location: Quebec, Canada
Contact:

Re: Power Issues MS2v3.0

Post by racingmini_mtl »

I agree with the 2 replies above but if you find out you need to replace the voltage regulator, do not use an LM7805. It has a voltage dropout that is too high for this application. Use an LDO regulator such as the one provided with the kit (LM2940 or similar).

Jean
jbperf.com Main site . . . . . . . . . . . . . . . . . . . . . . jbperf.com Forum
Image
WM111
MS/Extra Newbie
Posts: 2
Joined: Sat Aug 19, 2017 1:07 am

Re: Power Issues MS2v3.0

Post by WM111 »

Sorted! I checked C17 and D19 and they both appeared shorted at first, but after removing D19 the cap seemed ok. Removed it anyway and soldered on new parts including a LM2940. 5V rail working nicely now. Thanks very much for the help!
Post Reply