MS2 v.3 Board MegaStim v2.21 No RPM

Building and using the Stimulator to test your Megasquirt

Moderators: jsmcortina, muythaibxr

MS2 v.3 Board MegaStim v2.21 No RPM

Postby gman » Sun Dec 14, 2014 2:23 pm

I just bought and built my MegaStim, and am in the process of building my MegaSquirt v3.0 MB. I am at step 55. I can get TPS, IAT, and CLT to work in TunerStudio. I get nothing for RPM, but do get a response for pot change on O2 if I disconnect power and reconnect. I'm setting up for Hall effect, have double checked polarity on all diodes, and jumpers XG1 to XG2, OPTOIN to TACHSELECT, TSEL to OPTOOUT. I have also replaced D1 with jumper, and D2 with 1K, 1/4W resistor. When that didn't work, I jumper the resistor. Still no joy. Searched board and did not find similar situation.

I'm open to any advice how to check Stim for proper RPM signal, so I can continue to the output section of the assembly.

Best regards,

Rob
gman
MS/Extra Newbie
 
Posts: 16
Joined: Sun Dec 14, 2014 2:14 pm

Re: MS2 v.3 Board MegaStim v2.21 No RPM

Postby gman » Mon Dec 15, 2014 7:43 am

As an update, I built the LED test probe per step 6 of the http://www.megamanual.com/ms2/V3trouble.htm, found that on the Megastim, the output of U1, Fout at pin 1, responds to the RPM pot (goes out when turned down CCW, lights when goes up turning CW). I traced the board and found that the driver output Q1 is not working. I also found that the v2.21 Megastim timing circuit does not match the v2.1 diagram http://www.megamanual.com/v2.1_timing.jpg. It appears that R5 is hooked up between the base of Q1 and Fout (pin 1 of U1), which will never work, because as we know, Battery voltage (VBAT, pin 28, 9V) is always higher than VREF (5V generated by the MS2 power supply), and so, Q1 will not pulse.

I believe the solution is to install a small resistor (1K or less) between VBAT and Q1 base, to act as a voltage divider network for the base of Q1, so that Q1 will turn off when Fout is high (9-5=4V, 4V*1K/11K < 0.4V, therefore not high enough voltage) but turn on when Fout is low (9V*1K/11K =0.9V, should be enough to turn on Q1). But I'm open to any other suggestions.

Best regards,

Rob
gman
MS/Extra Newbie
 
Posts: 16
Joined: Sun Dec 14, 2014 2:14 pm

Re: MS2 v.3 Board MegaStim v2.21 No RPM

Postby gman » Sat Jan 24, 2015 4:52 pm

Well, turns out the schematic is slightly different (see attached). I had to work with DIYAutoTune, but they diagnosed the problem to be a bad opto-isolator U3 on the main board. In the meantime, I posted a troubleshooting video to check the Stimulator here, without having to connect to the main board (or fry your transistor in the event of a bad opto-isolator).
gman
MS/Extra Newbie
 
Posts: 16
Joined: Sun Dec 14, 2014 2:14 pm

Re: MS2 v.3 Board MegaStim v2.21 No RPM

Postby Matt Cramer » Mon Jan 26, 2015 7:32 am

Can you post the MSQ you are testing? The V2.21 Stim only supports a few specific ignition modes (Basic Trigger, Fuel Only, and EDIS).
Matt Cramer
Super MS/Extra'er
 
Posts: 13740
Joined: Thu Apr 16, 2009 8:08 pm

Re: MS2 v.3 Board MegaStim v2.21 No RPM

Postby DaveEFI » Mon Jan 26, 2015 9:23 am

gman wrote:Well, turns out the schematic is slightly different (see attached). I had to work with DIYAutoTune, but they diagnosed the problem to be a bad opto-isolator U3 on the main board. In the meantime, I posted a troubleshooting video to check the Stimulator here, without having to connect to the main board (or fry your transistor in the event of a bad opto-isolator).


The LED in the opto has a current limiting resistor in series with it. I'd have thought that would also limit the current from the stim to safe limits - even if the opto had a dead short.
Rover SD1 3.5 EFI
MS2 V3
EDIS
Tech Edge O2
London UK.
DaveEFI
Super MS/Extra'er
 
Posts: 2777
Joined: Sun Apr 15, 2012 12:55 am


Return to MegaStim

Who is online

Users browsing this forum: No registered users and 1 guest