MS3 VCC goes to 0 after building TC4427 ign outputs

[eracerr]

I tested the MS3 using the Jim Stim and loaded the firmware prior to building the TC4427 outputs for the COP setup for a 4cyl (spark a,b,c,d). All was ok. Had transisors Q6,Q7,Q8 in place but not the LED's D14,D15,D16. After building the TC4427 circuits I now seem to have something drawing the voltage down. It's not a dead short. There is 697 ohms between the prototype board 5V and it's ground.

Should I have soldered the LED's in? Could this be a symptom of frying one of the TC4427 chips during soldering? I've looked at how I soldered the circuit and I can not see anything that is connected incorrectly.

Thanks in advance for the help.

[billr]

I don't think leaving the LEDs out is any problem. How about posting pictures of the TC4427 install? More eyes checking the connections can't hurt any.

[eracerr]

Thanks! Here are two pictures showing the connections to the TC4427. .pdf attached

[billr]

OK, I'll dig out the datasheet for that TC device and check things over tonight.

[billr]

I saw nothing obvious in the pictures. Did you measure resistance from the proto 5V to ground before the TC4427 addition? The load that 700 ohms represents, about 7mA, is quite reasonable considering the standard MS circuitry that is connected to the 5V. I would lift out the jumper connection to the proto 5V and see if the Vcc comes back to normal. That should be easy enough to do, let's be sure we are focused in the right area.

[eracerr]

I removed the +5VDC and ground jumpers from the TC4427 circuit and still have the same issue. I was using the JimStim with a 9VDC battery. Moved to a low current (2A) 12VDC wall wart and now see the voltage go up to 12VDC and then drop then come back up? I'm going to take a good look at all the diodes and capacitors.

Is there any general trouble shooting strategy to find something like this? I was thinking about removing the F1 polyfuse.

[billr]

Is that 12V supply from DIY or one of the other trusted MS vendors? Some 12V supplies may have enough AC ripple to send the 5V regulator into over-voltage shutdown. It's a long-shot, I don't know if that regulator even has such a feature, but I would try connecting to a 12V battery. An easy test.

Are you still using the Stim, no car harness connected right now? Is the MS daughter card off right now, you are working with just the mainboard?

[eracerr]

Still using the STIM. MS3 daughterboard is removed. I spent some time checking the diode polarity again. Looks ok. Looked at the tantalum capacitors near the voltage regulator. They were ok. Reheated the solder joints around the regulator and the D11, D12, D13 diodes. Seems to have helped.

I now have 5VDC, but only 6.8 VDC going into the voltage regulator on V12. Next up is to check if there is something wrong with the STIM to pin 28 on the DB37 connector. The wall wart is putting out 12 VDC even plugged into the STIM and the STIM plugged into the MS3. Weird.

** update **
Voltage going into STIM is 12.3 or so and 11.8 at JP8 on the STIM when unplugged from the MS3. If I plug it into the MS3 I get 12.3 ish at the 12V IN to GND on the STIM but only 6.8 volts at JP8 and to the MS3. Should I try a larger 12VDC power supply or is something else wrong?