Hi! I have an Sony WM-DC2 which i repaired a year ago, i replaced the center gear and capstan ring. I sold it and now the owner is reporting that is it's completly dead after 1 year. He says he hasn't been using it in the mean time. My bench power supply is configured at 3V at 500mA. When i press play (or FWD/RWD), the currect direclty jumps to 500mA, so it looks like there is a short somewhere. And after 1 or 2 seconds, the current drops to 0mA. FG Coil is fine, i measure arond 700 Ohms at the two wires. The motor is fine, it works with a direct 3V and draws around 10mA I also replaced the servo board with the CX20084 from another DC2, same issue. So it seems that there is an issue with the circuit board. I'm guessing that the owner has used a non supported power supply, although he says he did not. And then i would expect that it blew up the CX20084. What options are there more? Caps looks fine, and i don't see any broken traces, or blown up components. Any help would be useful. Thanks! Roland
Update! Just randomly, i thought, let's check the capacitor which is closest to the power connecter. In case of the DC2, this is C312, a 220uF 4V capacitor. I unsoldered the capacitor and according to my tester, it was showing as a 0,7 ohm resistor. I replaced the cap with a new 220uF and boom, it started working!
Electrolytic capacitors can fail short-circuit, although it's very rare. Remember seeing it on a Sanyo MGP-33. Also saw it in some of 12voltvids YouTube videos. Unit worked fine and was in storage for a couple of months. When I took it out, the power LED would get intermittenly dim and power would cut out completely. Same behaviour when powering it with lab supply, it would go into current limitation becoming obvious there's a short somewhere. Touching the board, something was getting hot. And sure enough it was the capacitor connected to main voltage rail. Given it was that particular capacitor that failed, I can suspect unit was powered with reversed polarity or higher voltage at some point. But fact there were no other failures (servo usually fails when reverse polarity is applied) would suggest cap simply failed. Another aspect in regard to the DC2 is the AC adapter. Unregulated adapters will usually output higher voltage than the spec (even when loaded) and that cap is only rated 4V, while 3V is the operating voltage. So if an adapter which outputs 3.8V for example was used, it would be no surprise the cap failed. But it is equally possibile the cap simply failed out of its own.
Thanks Valentin, I spoke to the owner a few days ago when he was at my place to receive the repaired unit. He told me that he never used an external AC adapter, but that he might reversed the batteries once. He said that is worked for a few seconds and then it stopped. I found it very hard to beleive his story, so i still suspect either reverse polarity with an AC adapter, or indeed used to much voltage with an AC adapter. Anyway, owner is happy now!
