ta2020 in fault mode - help for beginner - diyAudio
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Old 7th February 2010, 04:11 PM   #1
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Default ta2020 in fault mode - help for beginner

got stuck on my first diy-audio project, an amp-6 by 41Hz. following situation:

kit completed, everything in place, soldering inspected and ok, pcb clean. with a 7w/12v test bulb in series the amp draws estimated 200-300mA in sleep mode. when waking up the amp, it goes into fault mode.

following things measured at the chip:

voltage regulator of the chip is ok - on pin 2, 8 and 30 i have the 5 volts required. high voltage supply ok - on the pins for the high voltage supply i have the 14,6 volts needed.

the inputs seem to be ok, no short at the cable connections and the expected 22k at the pins of the chip.

the output seem to be ok too, i got a resistance of 2k between + and - of each channel, which seems reasonable. when powered up i have 6,0 mV at channel 1 and 6,5 mV at channel 2. i don't know if that means anything.

when it comes to the power supply for the both channels it gets a bit strange: looking at the layout of the chip on the data sheet, the supplies for each channel should behave identically. unfortunately they don't. on the chip i measure from pin 25 to pin 28 a resistance of about 200R, rising to about 255R. after powering up the board there was a short, then the resistance rised again to about 200R. for channel 2 things are different. i measure first an infinite resistance, then it drops and stabilizes at about 850R. what's also weird is the fact, that i have a resistance of about 200R between pin 27 and 28, means between power ground and supply voltage.

unsoldered the capacitor between pin 25 and pin 28 and double checked if there's anything wrong with the soldering (using a magnifying glass) - unfortunately not. everything clean, no solder bridges or anything like that.

so - should i worry about the chip?

and if the chip is defecitve - what could have damaged it? no, i don't have an esd working place, but i grounded myself when handling the chip, didn't wear any clothing that produces static electricity, so what else are possible "killers" ... ?? is the chip sensitive to drops? unfortunately it fell down twice before mounting it - shame on me if so!

thanks for any helpful advice!
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Old 10th February 2010, 02:49 AM   #2
BWRX is offline BWRX  United States
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You shouldn't be using your multimeter to measure resistance the way you are. The resistance setting should be used to measure resistances in an unpowered circuit.

Anyway, you could have problems on the input side of the circuit. On pins 10 and 13 you should see about 2.5VDC. If you don't see 2.5V check all of the components on the input for bad solder joints and/or shorts.
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