Jason Roehl
04-07-2007, 1:28 PM
Okay, I've now been fighting my P-C drill, charger and batteries for the better part of a year--I'm sure much of this is my fault, but I am trying to remedy the situation. First, there has been water involved. That cost me the variable speed in the trigger of my original 14.4V drill, now replaced with a new 14.4V hammer drill. There is a circuit board in the trigger, and one of the connections had corroded through. A new trigger assembly was $50 (I dismantled the original getting it apart enough to see the corrosion, and there were a few miniscule pieces that fell out--no way they were going back in without me needing lots of therapy).
Last spring, I discovered my charger was no longer working (no light when plugged in or anything--it had gotten wet in the past), so I took it apart. I discovered 2.5 things: one, a capacitor had burst, two, the fuse was blown, and 2.5, a transistor appeared to have gotten too hot (there is a heat sink attached to it that is about 50x the size of the transistor, and there was a brownish spot on the other side of the circuit board from the transistor, about the size of the transistor). So, I replaced all three things. I was back in business, but...
A couple months later, my batteries (pushing 5-6 years old at the time) were not holding much charge, so I had them both rebuilt at Batteries Plus locally. All was good again until last week. I hadn't used my drill much recently, and I had a dead battery, so I put it on the charger, which told me after about two minutes of charging that the battery was defective. Now it's telling me both batteries are defective. Right before it flashes this code, I can hear what sounds like a rhythmic arc in the area of the transistor that I previously replaced, with a buzzing background noise. No caps are blown, the fuse is fine, and, like I said it appears to charge normally for about two minutes. A few weeks ago, I got one of the batteries to charge overnight normally, and it measured about 17.5V, now, to get one usable, I have to keep resetting the charger every two minutes, and I can get one up to about 15.9V. All the cells in the battery measure the exact same voltage, about 1.320-1.321V (I figure my multimeter isn't any more accurate than that, maybe not even).
Here are my questions:
1. Can I test the capacitors on-board? I've tried probing them on the back of the board with my multimeter set to "CAP", but I'm getting readings all over the place, and nowhere near their supposed ratings. I'm guessing I would have to de-solder them from the board to test them as the rest of the circuit is throwing off my readings.
2. How would I test the transistor? My multimeter has a place to do so, but the transistor has 3 leads, and the multimeter's test port has 8 holes arranged in 2 rows x 4 columns. Row 1 is "NPN", row 2 is "PNP", and the columns are labelled at the bottom "E B C E". At least, I assume this area of the MM is for testing transistors, as that click on the dial is "hFE". I don't remember much of my EE days, I dropped out of that discipline at Purdue about 12 years ago, never really getting beyond the very basic function of a transistor.
3. There are 3 terminals to the batteries. The two outside terminals are the ends of the cell chain, and the middle one is hooked to one of the outside terminals by some small thingie. It looks like a small, clear cylinder with a reddish/copperish band around the inside near each end. Small inductor, diode or resistor, maybe? (It doesn't look like the standard tan resistor with the color-coded bands). I don't get continuity on it, it doesn't register as a diode on my MM, and the resistance started at 12.1K-ohms when I first probed it, but was slowly dropping as I held it on there (took about 2 minutes to get down to 11.6K-ohms. Obviously it has something to do with the diagnostic function or over-charge prevention function of the charger. Okay...I just held that component between my fingers: before was 12.25K-ohms, after was 9.5K-ohms, so it has something to do with temperature, I'm guessing, as the charger does tell me when the battery is too hot or cold (but that's not the problem). So scratch this last question--I guess that's an NTC thermistor (I didn't get that far in EE).
Somebody help me before I build something hooked to a lamp timer that crams 20V into my batteries. No Hindenburg comments, please.
More:
When I probed the battery terminals while charging just now, the battery charged from about 16.1V to 16.6V before the buzzing sound started, took about another 0.05V before the "defective" code started flashing, then dropped back to 16.1V rapidly.
Last spring, I discovered my charger was no longer working (no light when plugged in or anything--it had gotten wet in the past), so I took it apart. I discovered 2.5 things: one, a capacitor had burst, two, the fuse was blown, and 2.5, a transistor appeared to have gotten too hot (there is a heat sink attached to it that is about 50x the size of the transistor, and there was a brownish spot on the other side of the circuit board from the transistor, about the size of the transistor). So, I replaced all three things. I was back in business, but...
A couple months later, my batteries (pushing 5-6 years old at the time) were not holding much charge, so I had them both rebuilt at Batteries Plus locally. All was good again until last week. I hadn't used my drill much recently, and I had a dead battery, so I put it on the charger, which told me after about two minutes of charging that the battery was defective. Now it's telling me both batteries are defective. Right before it flashes this code, I can hear what sounds like a rhythmic arc in the area of the transistor that I previously replaced, with a buzzing background noise. No caps are blown, the fuse is fine, and, like I said it appears to charge normally for about two minutes. A few weeks ago, I got one of the batteries to charge overnight normally, and it measured about 17.5V, now, to get one usable, I have to keep resetting the charger every two minutes, and I can get one up to about 15.9V. All the cells in the battery measure the exact same voltage, about 1.320-1.321V (I figure my multimeter isn't any more accurate than that, maybe not even).
Here are my questions:
1. Can I test the capacitors on-board? I've tried probing them on the back of the board with my multimeter set to "CAP", but I'm getting readings all over the place, and nowhere near their supposed ratings. I'm guessing I would have to de-solder them from the board to test them as the rest of the circuit is throwing off my readings.
2. How would I test the transistor? My multimeter has a place to do so, but the transistor has 3 leads, and the multimeter's test port has 8 holes arranged in 2 rows x 4 columns. Row 1 is "NPN", row 2 is "PNP", and the columns are labelled at the bottom "E B C E". At least, I assume this area of the MM is for testing transistors, as that click on the dial is "hFE". I don't remember much of my EE days, I dropped out of that discipline at Purdue about 12 years ago, never really getting beyond the very basic function of a transistor.
3. There are 3 terminals to the batteries. The two outside terminals are the ends of the cell chain, and the middle one is hooked to one of the outside terminals by some small thingie. It looks like a small, clear cylinder with a reddish/copperish band around the inside near each end. Small inductor, diode or resistor, maybe? (It doesn't look like the standard tan resistor with the color-coded bands). I don't get continuity on it, it doesn't register as a diode on my MM, and the resistance started at 12.1K-ohms when I first probed it, but was slowly dropping as I held it on there (took about 2 minutes to get down to 11.6K-ohms. Obviously it has something to do with the diagnostic function or over-charge prevention function of the charger. Okay...I just held that component between my fingers: before was 12.25K-ohms, after was 9.5K-ohms, so it has something to do with temperature, I'm guessing, as the charger does tell me when the battery is too hot or cold (but that's not the problem). So scratch this last question--I guess that's an NTC thermistor (I didn't get that far in EE).
Somebody help me before I build something hooked to a lamp timer that crams 20V into my batteries. No Hindenburg comments, please.
More:
When I probed the battery terminals while charging just now, the battery charged from about 16.1V to 16.6V before the buzzing sound started, took about another 0.05V before the "defective" code started flashing, then dropped back to 16.1V rapidly.