So today I am working on a JVC mini system which uses a SMPS and class D amplifier based on TDA7492 amp IC and a TDA7468 digital preamp bass/treble etc. The fault was the CD player not reading, I fixed what I though was a bad cable to the laser and tested it without the speakers connected.
I then disassembled the stereo again and touched up some solder joints around the focus/tracking for the CD player. I put it back together and get nothing at all. I measure voltages and see the SMPS is in hiccup mode so I inspect all my work and tried again but still nothing.
I thought I may have damaged one of the thin ribbon cables but as a hunch I removed the Vamp rail connector on the SMPS and the amp powered up instantly.
I still didn't know what was shorted as a few things run from this rail, so I connected the board to a variable power supply set to 2 volts at 3 amps to smoke out the component causing the SC.
It was the Class D amp IC getting hot, so in a blaze of fury I set the current to 10 Amps and let the damn IC desolder itself!
Is this common? Will I have to put a dummy load across outputs of class D amps while working on them? I didn't even go near the amp board and there was no music going to the amp as the CD player hadn't been repaired.
I then disassembled the stereo again and touched up some solder joints around the focus/tracking for the CD player. I put it back together and get nothing at all. I measure voltages and see the SMPS is in hiccup mode so I inspect all my work and tried again but still nothing.
I thought I may have damaged one of the thin ribbon cables but as a hunch I removed the Vamp rail connector on the SMPS and the amp powered up instantly.
I still didn't know what was shorted as a few things run from this rail, so I connected the board to a variable power supply set to 2 volts at 3 amps to smoke out the component causing the SC.
It was the Class D amp IC getting hot, so in a blaze of fury I set the current to 10 Amps and let the damn IC desolder itself!
Is this common? Will I have to put a dummy load across outputs of class D amps while working on them? I didn't even go near the amp board and there was no music going to the amp as the CD player hadn't been repaired.
Yes I actually wondered where the stress (there was no load) came from which actually caused the IC to fail. Is it just runaway oscillations? The IC is supposed to have over current (short circuit) and over temp. This is not the first time I have had class D amps fail, they seem very fragile.
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