My first posting here, I'm hoping it can help others with this problem. This is how I repaired a Squeezebox 3 that was damaged by lightning.
My SB3 went dark during a violent lightning storm (despite the "protection" of a surge arrester at the power outlet). Various other electronic devices in my house were also damaged; it was not a good day. I first checked the output of the 5V 2A power adapter with a voltmeter and confirmed that it was completely dead: zero volts. I replaced it with another known-good power adapter, but my SB3 stayed dark. I opened up the SB3 and could not see any damage. But with the new 5V adapter plugged in, I measured the voltage inside the SB3 and could see that it had fallen to only about 3 volts, strongly suggesting that a short circuit in the SB3 was dragging down the supply. I could not locate a schematic for the SB3, but I found a thread in this forum titled "SB3 almost dead.." which contained crucial information. forums.slimdevices.com/showthread.php?80209-SB3-almost-dead I confirmed that the 5V, 1.2V, 3V, 14V and 56V test points described in that thread were all way off-spec and/or noticeably unstable. I still could not see any physical damage internally, but my finger noticed that U17 (the switching regulator chip, type NJU763) was hot. This chip provides the 1.2V supply voltage to the microprocessor. A quick search suggested that finding a replacement chip would be impossible. And even if I assumed that this chip had failed, it wasn't evident if it was the only fault, or if there were other failures lurking elsewhere. Deciding I had nothing to lose, I desoldered U17. Tip: I used a low-melting-point solder aid called ChipQuick -- only the second time I've used it. I do find it helps a lot to prevent making a mess when removing tiny surface-mount parts, and I recommend it. Removing U17 restored some of the test voltages, a hopeful sign. But of course there was no 1.2V supply for the microprocessor. So, again relying on Adam_F's advice in the thread cited, I bridged in a new, physically separate 1.2V regulator. This was intended to functionally replace the U17 chip that I had removed. Concerned about heat dissipation, I did not use the LM317 linear regulator proposed in the thread. Instead I installed a small DC-DC Buck Converter module (eBay from China). This circuit board is a switch-mode supply based on a LM2596 chip, and runs cooler than a linear regulator. The module is much bigger than the chip it replaces, but is still small, measuring just a few cm long. It accepts a wide range of DC input voltage (between 4 and 30V) and steps it down to a regulated output that can be set as low as 1.2V, which is perfect. The output voltage is adjustable using an on-board variable resistor. Obviously you must set it to 1.2V BEFORE you install it in the Squeezebox! I soldered three short thin wires to connect the module to the SB3's circuit board. One wire runs from +5V at the power socket to the module's +V input. A second wire goes from Ground at the power socket to the module's -V input (this also connects internally to the modules's -V output terminal). Finally, I connected the module's 1.2V output to the solder pad at the right-hand end of L4 on the SB3 circuit board, beside D14. (You'll find these components near the SB3's power socket.) The last connection requires very careful soldering so as not to dislodge L4 or any of the other tiny parts nearby. Make sure you set the output to 1.2V BEFORE you connect the last wire. With this voltage regulator installed, my SB3 sprang back to life! It has been running for the last three days without problems. I found that there is enough space inside the SB3 to accommodate the additional regulator module without doing anything fancy. The module was small enough to rest gently on top of the SB3 circuit board, positioned between L4 and the top edge of the circuit board. I carefully applied thick insulating tape to the module's underside to electrically isolate it from other components on the circuit board. I found that the SB3 case fit back together without problems but close enough to keep the extra board from shifting position, without needing any glue or attachments to hold the little module in place. One additional tip: ensure that your replacement 5V power adapter can really supply adequate current to the Squeezebox. My original blown-out SB3 adapter was marked 5V 2A. I found that one replacement adapter I tried sagged a couple of volts when plugged into the SB3, despite also being labelled "2A". It couldn't supply adequate current, and it simply didn't work. If in doubt, it can't hurt to choose a replacement power adapter with a higher rated current capacity, like 3A. Many thanks to Adam_F and other contributors for invaluable information that enabled this solution. ------------------------------------------------------------------------ arlenm's Profile: http://forums.slimdevices.com/member.php?userid=62744 View this thread: http://forums.slimdevices.com/showthread.php?t=101236 _______________________________________________ diy mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/diy
