In SX Microcontrollers, SX/B Compiler and SX-Key Tool, tdg8934 wrote: Roy, I received your board today and have troubleshooted it. I have attached datasheets for the 5x7 display and a suitable datasheet for the 74HC245. When applying power (batteries) when the PIC chip is socketed or not, the COLUMN 1 (pin 3) of the LTP1257 display (4th) is always on. SW2 can switch it between red and green columns. Since it was the entire row, it first led me to believe it may be a bad transistor. I took it out and tested and resoldered in a new one with the same effect. I then looked closer at the 2N3904 NPN transistors around them and compared voltages on the Collector, Base and Emitter. On the surrounding transistors the Bases had ~300 mV or roughly 0 vdc. However, on the Q4 Base (which the Emitter went to pin 3 {COLUMN 1} of the 4th LTP1257 display) it was reading about 3.8 volts and NOT about 0 volts like the other Emitters. Hmm. After bringing up your PCB (PDF file you previously attached) and looking at Q4, on the bottom solder side you will see a trace from the Base going straight down which is then picked up on the component side and run sort of underneath R1 (140-150 ohms) and connected on 1 side of R1. This R1 connection is also run down and connected to pin 6 of the PIC chip. This may not be a problem because other adjacent transistor Bases had traces going directly into subsequent PIC pins. However, if we get back to the "other" side of R1, we see that it is connected to the Collector of Q6 which is also connected to all of the other transistor Collectors AND roughly 5 vdc as you might expect to see. Here is where the problem lies. What is the purpose of R1? By connecting 1 side to the Collector of Q6 (as well as the other Collectors and 5vdc) it is dropping that 5 vdc across R1 and placing that 3.8 vdc on the PIC pin 6 as well as the Base of Q4 which then causes the Emitter to go positive to about 2.8 vdc across pin 3 {COLUMN 1} of the 4th LTP1257 display. So If I un solder the R1 leg going to the Collector of Q6 it will take the 3.8 vdc off of the Base of Q4 thus not allowing it's Emitter to get to 2.8vdc and turning on Column 1. However, if this R1 resistor is removed as such then I see nothing on the display (whether the PIC is inserted or not). Perhaps this is how it is supposed to be as an I2C signal from JP2 maybe what excites this display. Who knows without more information and schematic. What puzzles me is why R1 is needed if the adjacent transistor Bases don't have a drop resistor going back to the PIC pins. At this point, without more data to work with it will probably never be workable because we don't know enough about what the PIC is going to do. However, it may be possible to remove the PIC from it's ZIF socket and access the LTP1257 via the transistor Bases and conect an SX28 AND possible driving hardware to have a workable display. The 74HC245s have 2 functions. They act as buffers as well as also driver the Cathode rows on the LTP1257 displays. SW2 controls the /OE pin which switches the displays from green to red. I uses a similar technique using 74HC573's before to control red and green leds on a smiley face 16x16 bicolor clock (got published in Jan 2009 of Nuts and Volts magazine). Summary - Unless you can provide me more data on what this display does (especially the purpose of R1), I recommend it be scrapped as a PIC project and possibly look into interfacing it to an SX28 through the PIC zif socket (to test) and later direct solder to the underside of the PIC once working. It may need additional drive components besides the sx28 but maybe not. I would need to look at all of the annode and cathode lines from the transistor bases and 74HC245 chips and see if they are all accessible from the PIC socket. If so, and there are no other problem resistor, capacitor, crystal, etc. interferences, then we should be good to go. I will also mail you a couple of 0832 displays and make a solderless breadboard IDC connector for you if you wish. This may be the easiest approach (although it is only 1 color - in my case green LEDs) - but the work is already done by me. Let me know how you would like me to proceed. Tim ---------- End of Message ---------- You can view the post on-line at: http://forums.parallax.com/forums/default.aspx?f=7&p=1&m=381840#m384125 Need assistance? Send an email to the Forum Administrator at forumadmin@parallax.com The Parallax Forums are powered by dotNetBB Forums, copyright 2002-2009 (http://www.dotNetBB.com)