Last output test - fail

[Mark Atterbury]

Good morning all,

Sometimes it is best to take a new run at the issue after setting it aside for a little bit.

I got to the end of the build (DIY kit, firmware code 2.891, using Jim Stim to validate). Everything tested fine until the last test of the output circuit.

The issue I would like to resolve is that the three LEDs on the MS are constantly illuminated when power is supplied through the stim. (actually I see a mild flicker on the injector LED in sync with those on the stim, but very hard to see). The Accel Enrichment and Warm Up Enrichment LEDs are constantly illuminated. However, I can see the MS output is working correctly through Mega Tune (the indicators at the bottom of the interface turn on and off correctly)

The LEDs stay on if I remove the daughter card.

The MS itself looks well assembled and I used the good iron. I checked all the transistors for proper orientation and solder bridges - no issue. ( especially Q6, 7 and 8 )

Any ideas where to look to resolve this? Except for these three lights being lit, the MS looks like it is functioning correctly through Mega Tune.

Thanks,
Mark

[Matt Cramer]

Check the transistors that control the LEDs - any chance they're in backwards, damaged, stray flux, etc?

[Mark Atterbury]

Check the transistors that control the LEDs - any chance they're in backwards, damaged, stray flux, etc?

Matt,

There is nothing obvious, they are in matching the silk screen. I checked with a multi meter and there are no solder bridges. Is there any way to check if they are damaged before I pull them off?

Anything besides the transistors that could cause this? I agree that it makes sense for the issue to be close to the LEDs since it appears to work correctly in Mega Tune.

Thanks,
Mark

[Matt Cramer]

The LEDs have somehow become grounded, and about the only thing that could do this is a very odd board fault or the transistors. Is there any chance you may have the wrong transistors in there? I know, kind of a long shot.

[trakkies]

Check the transistors that control the LEDs - any chance they're in backwards, damaged, stray flux, etc?

Matt,

There is nothing obvious, they are in matching the silk screen. I checked with a multi meter and there are no solder bridges. Is there any way to check if they are damaged before I pull them off?

Anything besides the transistors that could cause this? I agree that it makes sense for the issue to be close to the LEDs since it appears to work correctly in Mega Tune.

Thanks,
Mark

Check the voltage on the base of each transistor. And check the type number of the transistors as fitted against the schematic.

[Mark Atterbury]

Dave,

You mentioned checking the voltage at the transistors. I understand that they are essentially a switch. What voltages should I be looking for on which pins?

I'm thinking of changing the transistors - can't hurt - although I don't see anything obviously wrong. Replacing components w/o understanding always maks me nervous (or broke)

I'll let you know if a transistor replacement works.

Thanks
Mark

[Mark Atterbury]

OK - changed out the transistors. Let me see if I can get this right:

Removed them all and all the LEDs went out - good

Put in the transistor for the Acell Enrich (AE) - worked fine - very good

Put in the transistor for the Warm Up Enrich (WUE) - LED constantly on - bummer, but the AE still worked properly

Slid in the transistor for the Fuel Injectors (FI) - The LED for the FI worked fine, but now both WUE and AE LEDs are constantly on. - yuck.

OK - lets pull all the transistors and start over -

Now, with no transistors, the AE and WUE LEDs are still lit. ???

Tried slipping in individual transistors - only the FI worked correctly.

OK - soldered that in (at lease one will work). But no! Now the FI LED is illuminated constantly too.

So here is what I have on the board:

Transistor in the FI position (correct orientationa nd type with no solder bridge). No transistor in the WUE or AE position.

All three LEDs are lit constantly.

Thank God it is only a display issue and everything else appears to work fine.

I am thinking that it must be a board issue - what else could cause this?

Mark

[Matt Cramer]

Ok, if all the LEDs were out when you first removed the transistors, that would indicate they are grounding through the area of the board where the transistors are installed. This could be damage from too much heat, but is more likely to be stray flux or the like.

[Mark Atterbury]

all LEDs were out the first time all the transistors were removed

The second time all the transistors were removed the AE and WUE LEDs stayed lit.

Hope you can understand my confusion.

I'll try cleaning the board in that area again (I used flux cleaner and a toothbrush the first time through, but I like flux and it has been a while)

If that doesn't work I'm thinking of building the circuit outside of the board, since this area is pretty simple. (of course it is that much more furstrating that it does not work - being simple)

since the tansistors are NPN, don't they close the switch when the transistor sees a positive potential? This would let the LED go to ground and illuminate. If there is a failure in the board (or flux) that is letting the LED get to ground, wouldn't they be illuminated? (well I guess that they are). I just want to understand your reply.

Thanks
mark

[Matt Cramer]

Correct, the transistors pull the LED to ground. If the LEDs did turn off the first time you removed the transistors, but came back on once you soldered the transistors back in and took them out again, it appears whatever problem you have is in the area of the transistors.