PIC based Multicolor LED Equipment HELP - Page 1
Forum section: electronics / repair

author: zayance
author_rank: Contributor
timestamp: September 23, 2014, 07:16:50 pm
content: Hi There,I'm facing some issues with a unit called "Moduled 318C", wich are Multicolor LED Lights that can be controlled via DMX via 3x differential bus transceiver "SN75176BD".I'm not a pro in terms of Microcontroller and DMX and all, don't know how to program neither (will do hopefully in the future if time permits),but i'm trying to figure out what can cause the behaviour i'll explain, and maybe someone could shade some light on this, given that i don't have full infoson these, and no Schematic etc.... (i could have sketched some block diagram or even Reverse Engineer the thing with some prcise values and all but i was too lazy), so please apologize.This equipment has a 24VDC Switching Power supply, and a circuit feeded with +5VDC, with two 18F242 (28 SOIC) (i guess for having more I/O), that seem to drive 3x LMH6644MA, and these seem to drive 9x N channel Power Mosfet "STP55NF06FP" (1 Mosfet per Color per Matrix etc...)Ther is a Temp sensor too on the device.Now the problem i have on 95% of these (beside some PSU that has blown), is all the Red LED's on the Centre MAtrix (Aluminium Base Round PCB with Luxeon I type LED's i think) , are blinking, not in a random way when they do, but periodically but can happen in random moments.That could be on power up and DMX command pushed up for that RED Color, or it takes a little bit of time before it happens, like playing around with the STROB options, fade in in and out etc... and suddenly starts blinking a little.The remaining two LED Matrix are working good no prob.After trying to find the weak spot on the circuit, it seems like Pin 21 of the PIC (RB1/INT1) that seem to be the control of this RED LED Matrix is dropping from 4.8VDC to about 3.6V when those blinking happens.Now most of all the ports are used to control LED's, via PWM i imagine if using a DMX, and having the ablity to fade things etc... (TTL would not allow that fonction right?)The other parts are doing fine, and the LED Matrix also, Molex/cables as well etc..., Not sure about the DMX circuit based on the SN75176BD, but the controls are working no prob, and there is no individual control of the 3 Matrix in the mode they are at. You push up Red light Fader, and all RED leds are ON etc....Maybe one of the Differiental Bus Tranceiver's, since there are Three, one might just started acting weird, bu that could still affect Green and Blue colors etc... ( don't know much about how the DMX language is really feeded into a PIC via those Bus Tranceivers etc...)Could it be the PIC that has been going kookoo after many years of use? (or Programmed to go kookoo?) Or some bad voltage at one time that could have caused the RB1/INT1 Pin to act this way???I mean why does all the other colors and Matrix work ok and only one command is failing on 95% of these, and there are maybe 40pieces of these having same prob, that would be one hell of a coincidence no???Anyway, just wanted to have some light by one of you guys that knows better on Microcrontrollers than me.Thanks a lot for any infos, help, ideas.T.

author: zayance
author_rank: Contributor
timestamp: September 24, 2014, 08:10:44 am
content: Anyone would have an idea? Maybe i'm actually asking for too much with only an explanation on this,sorry if it's the case, and please let me know, it's pretty vague for me too anyway haha.T.