Another Logitech Z5500 done today.
This is the 3rd Logitech Z5500 i've repaired so far, and each one has had a different issue.
Behavior of this unit was as follows: Plug it in, turn it on, red light on console comes on. Push the power button on the console, light briefly turns blue, display turns on, falls back to red light and display turns back off.
Voltages on the main board inside the subwoofer checked out okay, so i turned my attention to the console. After about an hour of troubleshooting, the problem was found. An intermittent diode.
The console has 3 main regulators, all three are LM317 in D2PAK. One makes 5v, one makes 3.3v and one makes 2.5v. There is a 8v rail coming in from the subwoofer, which these 3 regs feed on.
For whatever reason, Logitech decided to feed the 3.3v and 2.5v regulators thru 2 diodes first, to drop some voltage and share the load. These diodes are in MELF capsule and physically located next to the 2.5v regulator, which seems like it gets the hottest of the bunch (PCB slightly discolored around it). It turns out that due to overheating, one of those diodes went intermittent and the regulators would drop out when turning the console on. Both diodes checked out fine on the meter, but they had discolored significantly.
Replaced both diodes and the console stayed on, and everything worked fine. This is yet another design flaw of this system - the other two that i'd fixed exposed two other design issues. None of them had the power amplifiers blown, which is usually what you would see with such things.
Behavior of this unit was as follows: Plug it in, turn it on, red light on console comes on. Push the power button on the console, light briefly turns blue, display turns on, falls back to red light and display turns back off.
Voltages on the main board inside the subwoofer checked out okay, so i turned my attention to the console. After about an hour of troubleshooting, the problem was found. An intermittent diode.
The console has 3 main regulators, all three are LM317 in D2PAK. One makes 5v, one makes 3.3v and one makes 2.5v. There is a 8v rail coming in from the subwoofer, which these 3 regs feed on.
For whatever reason, Logitech decided to feed the 3.3v and 2.5v regulators thru 2 diodes first, to drop some voltage and share the load. These diodes are in MELF capsule and physically located next to the 2.5v regulator, which seems like it gets the hottest of the bunch (PCB slightly discolored around it). It turns out that due to overheating, one of those diodes went intermittent and the regulators would drop out when turning the console on. Both diodes checked out fine on the meter, but they had discolored significantly.
Replaced both diodes and the console stayed on, and everything worked fine. This is yet another design flaw of this system - the other two that i'd fixed exposed two other design issues. None of them had the power amplifiers blown, which is usually what you would see with such things.
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