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Regarding your suggestion about Q1, I double checked and I can find no evidence of a short between the emitter and collector pins of Q1. I replaced the transistor once before trying to debug, but I will try it again in case somehow it turns out to be the culprit.Edit: I am an idiot. I located the short between the collector and emitter of Q1, as you said I would. The story of how I am only finding it now is too embarassing to publicly relate :) Anyway, problem solved! You are the man.
In response to your suggestions:
I discovered one other interesting thing using my multimeter: the positive pin of every LED in row 1 is in continuity with the emitter pin (right-most) of EVERY transistor. Does this mean I have a problem “downstream” of the transistor, or could the issue still be with the transistor? Thanks!
- The base pin of Q1 (left-most) is not connected to anything nearby (except RB1) that I can detect using the continuity function on my multimeter.
- The other end of RB1 is connected to pin 3 of U2, and only pin 3. Definitely not connected to pins 2 or 20.
- Forgive me, but I’m not sure I understand what “low-voltage position” means. I am not sure how to test this.
Almost done, and I have confirmed the above behavior–all LEDs work, the sketches run as they should, but Row 1 LEDs light when any LED from the same column is lit. Row 1 is very bright compared to the others. Checked transistor Q1, and I see nothing visibly wrong with it. Checked the soldering on U2 and it looks OK. Could I have a damaged transistor, or should I look elsewhere? Thanks!
Thanks Windell. I am in fact still working on soldering in all of the LEDS; I have about half in at the moment. I have narrowed down the issue more by running various sketches. The behavior seems to be that if ANY LED in a given column is lit, the Row 1 LED from that same column will also be lit.I will take your advice and continue to work on getting all the LEDs soldered, and see whether that makes anything more clear.Thanks again.
Thanks Windell. I am having some difficulty locating the short. Also, in looking at the circuit diagram, it’s actually row 1 (the second row of lights), not row 2 that has the issue. A few things I discovered in working on this:
- Using the continuity tester on my multimeter, when powered on, the + and – leads of the LEDS on Row 1 are continuous. This is not true of any other row.
- Row 1 is not ALWAYS all lit. When the device is powered on, an apparently random pattern of LEDS in Row 1 sometimes light (usually in blocks of three or four) with a few LEDS in between not lit
- My earlier statement that the LEDS show no response at all to the sketch may be incorrect. I can see them flickering slightly but they are so bright it’s hard to be sure.
I don’t know if this is possible to debug remotely, but if the above gives any indication as to where the short could be, could you please let me know? Thanks in advance.