HEI setup

[BooBoo]

If I understand correctly:
V2.2 board, MSII, GM 4pin HEI running fuel only.

Correct

What was your setup for the MSD? Was it a VR sensor trigering an external MSD box or was it a " stand alone " distributor.

I had a MSD 6A and a stock distributer that I ran with a unmodified MS V2.2 - Later I added the MSII - I did no modifications to the MS at all except for adding the MSII.

[BooBoo]

if this is the case re-check the opto circuit, if diferent components were installed you may have burned out the opto.

Looks like this is the next step. How do I do this?

Could the fact that as soon as I turn on the ignition, I have 12V on the TACH terminal and all the way to the MS at pin 24. Is that supposed to happen? Could that have caused the failure of the input circut?

[Joethemechanic]

Could the fact that as soon as I turn on the ignition, I have 12V on the TACH terminal and all the way to the MS at pin 24. Is that supposed to happen? Could that have caused the failure of the input circut?

No, this is normal. you have 12v because the coil is litterally just a long piece of wire, so when you turn on the ignition you get 12 to the positive side and it runs clear through to the tach or negative side.

nothing happens until the HEI module sees a signal from the VR sensor, then it momentaraly ( like 4-6 millisecinds ) grounds the tach side, creating the magnetic feild that collapses when it un-grounds it. it is the ungrounding that creates the spark.

so... if you are seeing 12v on pin 24 the wiring to the MS is good. If you are getting spark chanses are verry likelly that you are getting a valid signal to pin 24 at the least.
As I said, A test light will verify this to pin 24, and on the board a logic tester ( LED with a resistor ) should be able to tell you if the opto circuit is working.

when firing direct from the coil, R10 can get hot, and both diodes should be active, if you had them jumpered you may have dammaged the opto, also it is a good idea when firing from the coil to remove XG1 and run a separate ground direct to the block.
The tach signal from the coil is extreamly noisy, that is why XG1 was put there.
Joe

[BooBoo]

when firing direct from the coil, R10 can get hot, and both diodes should be active, if you had them jumpered you may have dammaged the opto, also it is a good idea when firing from the coil to remove XG1 and run a separate ground direct to the block.
The tach signal from the coil is extreamly noisy, that is why XG1 was put there.

I have XG1 and XG2 jumpered together. Should I remove the jumper and run XG1 to X11 and then to a chassy ground. Should I assume that the opto (U4) is toast and replace it? If so, will changing the gorund keep it from happening again?

[Joethemechanic]

I have XG1 and XG2 jumpered together. Should I remove the jumper and run XG1 to X11 and then to a chassy ground. Should I assume that the opto (U4) is toast and replace it? If so, will changing the gorund keep it from happening again?

1, Yes, it is a ggod idea to isolate the opto ground when firing directly from the coil.

2, I hate to assume anything without testing it first, but, as chhep and readily available as optoisolator is, I dont think replaceing it is a bad idea.
Last time I was in radio-shack they had them, basically the same unit used on the MS. Unless you have it directly mounted to the board it is such an easy reair its worth trying.

I strongly encourage you to take 15 minutes at read the paragraph or two in the Mega manual
http://www.megamanual.com/v22manual/mass.htm#input
It covers just about everything.
Joe

[BooBoo]

it is such an easy reair its worth trying.

I agree for 35 cents and a little solder, I will give it a try while I am wating for my stimulator.

I strongly encourage you to take 15 minutes at read the paragraph or two in the Mega manual
http://www.megamanual.com/v22manual/mass.htm#input
It covers just about everything.

I found that last night and read it.