D17 overheating
Posted: Mon Mar 20, 2017 6:12 pm
I am building a MS-II/v3 board. I have assembled the board to the point where I am ready to do some testing. I have a Jimstim that I will be using for testing. The Jimstim has been fully tested and passes all the criteria. The first time I plugged the Jimstim to the MS-II and powered everything up with the 12VDC/1A wall wart power supply I am using, the polyfuse in the Jimstim heated up almost immediately, it got extremely hot in a matter of seconds. Given that the Jimstim tested out fine using this power supply (and still does test fine after the heating of the polyfuse), I surmised that my problem was somewhere in the MS-II.
Applying power to the MS-II directly (+12V to pin 28, Gnd to pin 19), I was able determine that D17 is getting very hot (to the same degree as the Jimstim polyfuse in the same amount of time). I have scoured the MS-II board for solder bridges and found nothing. I have cleaned the board multiple times with alcohol. As I understand it, D17 is part of the Injector 1 circuit. I have checked D18 of the Injector 2 circuit and I do not detect any heating at all. As best as I can tell no other components on the board are getting hot, though I am only applying power for a few seconds at a time.
I am pretty limited in my electronics knowledge when it comes to transistors so I am not sure how to troubleshoot this problem... there are 5 transistors in this circuit as best as I can tell. Could it be that I just have a bad diode (D17) or a bad transistor ? ...and if it is a transistor, how can I tell ? I have done some simple comparing of the voltages of the various component pins in the two injector circuits and I am not detecting any voltage differences from one circuit to the other.
I am reluctant to just proceed with replacing parts on the hope that I will get lucky and fix the problem. I am afraid of damaging the circuit board with all that soldering/desoldering.
Anyone have any ideas as a direction I should take ?
Thanks for your time...
Applying power to the MS-II directly (+12V to pin 28, Gnd to pin 19), I was able determine that D17 is getting very hot (to the same degree as the Jimstim polyfuse in the same amount of time). I have scoured the MS-II board for solder bridges and found nothing. I have cleaned the board multiple times with alcohol. As I understand it, D17 is part of the Injector 1 circuit. I have checked D18 of the Injector 2 circuit and I do not detect any heating at all. As best as I can tell no other components on the board are getting hot, though I am only applying power for a few seconds at a time.
I am pretty limited in my electronics knowledge when it comes to transistors so I am not sure how to troubleshoot this problem... there are 5 transistors in this circuit as best as I can tell. Could it be that I just have a bad diode (D17) or a bad transistor ? ...and if it is a transistor, how can I tell ? I have done some simple comparing of the voltages of the various component pins in the two injector circuits and I am not detecting any voltage differences from one circuit to the other.
I am reluctant to just proceed with replacing parts on the hope that I will get lucky and fix the problem. I am afraid of damaging the circuit board with all that soldering/desoldering.
Anyone have any ideas as a direction I should take ?
Thanks for your time...