Megastim I2 does not light up

[r3dplanet]

Hi there.

An another recent topic, I couldn't get my IDL light to work. Thanks to Mr. Cramer, we got it to work and I understood a little better how I make my own problems. All of the details can be hard to juggle at once.

The last bit of help I need with an otherwise operational Megastim 2.21 board is that the second injector light (I2) does not flash. Searching the forum, I see from a similar post that another user could not get I1 to work. Following that troubleshooting, I got as far as pulling the CPU board and connecting Pin 22 of U1 to ground to see if I2 would work directly. It doesn't light up. But when I connect Pin 21 (I1) I get that light to work. So I'm not sure where to go from here.

Thanks!

[SymTech Laboratories]

When you ground pin 22 of the processor socket, what voltage do you measure at pin 5 of U4?

[r3dplanet]

Thanks for helping me.

I get 2.53 volts.

[SymTech Laboratories]

This sounds like a U4 failure. You should measure close to 12V on that pin. Are you using low impedance fuel injectors?

[r3dplanet]

I see. It's easy enough to swap. I'm using a Holley 502-6 (GM TBI replacement) on a Chrysler 360ci engine. From what I've found, these are low impedance injectors.

[r3dplanet]

I might also point out that I'm using an MSD-6al ignition system and coil, and to my knowledge I've followed the supplemental instructions for modifying that circuit. I know that I'm not using the VR outputs from the MSD if that makes any difference. I see that the U7 is an VR circuit OpAmp.

[SymTech Laboratories]

I might also point out that I'm using an MSD-6al ignition system and coil, and to my knowledge I've followed the supplemental instructions for modifying that circuit. I know that I'm not using the VR outputs from the MSD if that makes any difference. I see that the U7 is an VR circuit OpAmp.

We thought you were using a v2.2 board. If you're using a v3.0 board, the failed part is U4. Whatever modifications you made to the VR circuit shouldn't affect the injector driver.

[r3dplanet]

My apologies. I don't know why I didn't post that information. What I have assembled is an MS2-v3.0 board and flashed it with v3.2.4 firmware, along with instructions for modifications for IAC stepper valve and inputs from an MSD-6AL ignition unit. I'll track down a U4 replacement and see what happens.

[r3dplanet]

No success so far. The new MOSFET driver (U4) arrived today, but I2 still doesn't seem to work. I1 works as always. I thought perhaps the 8-pin IC socket may not be perfectly soldered, so I pulled it and replaced it. Still no luck.

[SymTech Laboratories]

Do you still measure ~2.5V at the gate of the MOSFET? If so, since you have a v3.0 board, look closely for solder bridges on Q15. A short on this component could shut down INJ2.

[r3dplanet]

Yes, I'm still getting 2.53 volts on pin 5 of U7. I re-flowed the connections on Q15 and I'm quite sure that the pins are not shorting.

[SymTech Laboratories]

Yes, I'm still getting 2.53 volts on pin 5 of U7. I re-flowed the connections on Q15 and I'm quite sure that the pins are not shorting.

What are you measuring at U4? U7 is the part on a v2.2 board, U4 is the part on a v3.0 board.

[r3dplanet]

Ack. Sorry. Pin 5 of U4 is getting 14.8 volts.

[SymTech Laboratories]

Ack. Sorry. Pin 5 of U4 is getting 14.8 volts.

And you're measuring this with the processor removed and pin 22 of U1 grounded, correct? If so, the MOSFET, Q5, might have failed.

Did you build the stim yourself? Did I2 ever work? If not, you might want to inspect the stim too. Is the LED for I2 inserted correctly? If it's backward, it won't light up.

[r3dplanet]

Oh d***. Now I'm embarrassed. I never thought to check the Megastim board because it was so simple to assemble. The LED was correctly oriented, but apparently broken. I swapped it out for another one and *poof* I2 is lighting right up and pulsing correctly.

I feel as though I've wasted your time. But hey, it's working! Hoo!

[SymTech Laboratories]

Oh d***. Now I'm embarrassed. I never thought to check the Megastim board because it was so simple to assemble. The LED was correctly oriented, but apparently broken. I swapped it out for another one and *poof* I2 is lighting right up and pulsing correctly.

I feel as though I've wasted your time. But hey, it's working! Hoo!

Not at all, that's what we're here for! We're glad the problem is solved, and thanks for reporting back with the solution.