MR16 Channel 6 not working

[theavguy99]

All channels but 6 work correctly.

I've retouched all solder pads on the ic's and on the mosfet.  The voltage on the Driver IC for channel 6, with channel 6 at 100%, is around 12 volts- which is an 'off' state votlage, as the other channels at 100% are right around 7 volts.

I erased, blank checked, programmed, verified & read the pic and it has the correct checksum (90d4), substituted another pic and led driver chip, both with same result- nothing on channel 6.

Any ideas?

[theavguy99]

Anybody have any idea what may be happening here?  I've tried everything I know to get channel 6 to work, but still can't.  It appears to me that the driver chip is not firing on the pin driving channel 6, which to me would mean that either the driver chip or PIC is defective, both of which I've substituted, with no change.  I'm new to programming PIC's, so I'm not certain that I got it programed correctly, but all other channels appear to work properly.  Thanks!

[RJ]

The resistor and cap on that channel the same as the rest or could you have a part mixup? Just a thought.

RJ

[Ampfan]

Have you checked that the pin for that channel is not bent up under the socket and so is not driving the FET? I've had that happen before, and it was a PITA to find because it 'looked' fine.
With no power applied check for continuity from the top of the TLC chip to the FET gate.
You may also have a hairline crack in the PCB which the soldermask is hiding.

And do let us know what you discover so that others will learn from your experience.
Bob

[ponddude]

Can't it be a bad FET?  If it isn't opening but the driver is putting out the voltage, it probably is a stuck FET.  I have more from the COOP if you need one.

[theavguy99]

I'm actually metering directly on the leg straight off the driver IC- it's as if the channel 6 output is not sinking when it should be.  I'm out of town till the end of the week so I can't test further.  But I know that both chips are inserted properly since I inspected them under bright light and magnification- carefully looking at the gap between the underside of the chip and the dip socket.

I programmed the pic several different times, until I finally think I figured out the proper procedure- the final time I got the correct checksum, so I'm reasonably sure that it is programmed correctly.  From memory- I loaded the hex file, setup the pickit3 programmer, voltage is at 5 volts, it read the chip properly, I erased it, then did a blank check, which reported the chip was empty, then I programmed, verified and read it- after each step the checksum reported as 90d4.

Could there be a problem in that I had tried to program it several times (incorrectly) prior to finally figuring out the correct (at least I think correct) steps?

Just saw the post about the stuck FET- I suppose it could be this, but wouldn't I still see the voltage change at the driver ic pin, as the driver sinks 5 volts trying to fire the FET?