Hi, I bought the 1.5A Stontronics linear PSU from Farnell/CPC and even managed to convince myself it sounded slightly better...
I bought it at Christmas and for various reasons I've hardly used the SB3 in that time and it's been unplugged from the wall mostly. I plugged it in yesterday and it was dead - or nearly. After a short while the SB3 came to life but the screen was flickering badly. Praying it wasn't the SB3, I hooked up the original PSU and all is working fine again. I see on other threads that these Stontronics PSUs are quite unreliable. I just took mine apart (don't worry, I have an EE background ;o). A standard configuration that you would expect to find would perhaps have a diode bridge to rectify the AC from the transformer, a large electrolytic 'reservoir' capacitor across the input of a 7805 regulator, bypassed with a small ceramic close to its input, and then a smaller electrolytic across the output of the regulator. Simple. I found most of that, but also: a) The large electrolytic was bulging and clearly distressed. It is a cheap no-name cap, 2200uF/25V. It does have a brand logo on it, but it's not easily discernable. Looks like it might be 'CIA' or something. Not something I recognise and I'm quite familiar with these things. b) There is a large heatsink running around the perimeter of the PCB, which has a regulator on each side. They are both L7805CV (ST brand). They are 1.5A parts but both are connected directly in parallel, with their outputs shorted together. This configuration is not ideal. You can get away with it but the regulators do not share the load equally and will have slightly different output voltages anyway. They will fight each other. There should at least be small-value resistors on the outputs of the regulators to isolate them from each other. c) The small ceramic bypass is on the output, not the input (small point). I'll replace the 2x7805 with one 2A version (L78S05CV = £0.89 from Maplin), at the side of the board where the cable exits, and replace the capacitors with something better. (I have lots of Elna, Panasonic and Nichicon lying around.) The transformer looks undamaged, the heatsink is large and sturdy, so it should be trivial to make this thing work solidly and reliably. I'll report back if I'm successful. Cheers, Glenn -- Glenn2 ------------------------------------------------------------------------ Glenn2's Profile: http://forums.slimdevices.com/member.php?userid=19286 View this thread: http://forums.slimdevices.com/showthread.php?t=61090
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