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| Thread ID: 121861 | 2011-11-18 04:17:00 | Weekend poll for Techie Types | Billy T (70) | PC World Chat |
| Post ID | Timestamp | Content | User | ||
| 1244167 | 2011-11-18 04:17:00 | A neighbour brought me over his JBL Platinum Series powered speaker system, he said he hadn't used it for a while because he lost the power pack. Apparently he found it again, but when he plugged it in all he got was a very loud hum. I tried it myself and he was right, uncontrollable hum. Checked the label 12 volts DC required, then I took a look at the power pack: 12 volts AC! So, the DC circuitry had been fed with raw AC at 18 volts peak to peak (nominally 13 volts RMS). I dug out a suitable 12 Volt DC Powerpack (ex Motorola analogue flip-phone, circa 1995), plugged it in and switched on. So, what do you think the outcome was? Cheers Billy 8-{) :) |
Billy T (70) | ||
| 1244168 | 2011-11-18 05:27:00 | The fact that it was still alive when you tried for a second time leads me to believe it was a fairly hardy unit. | Catweazle (2535) | ||
| 1244169 | 2011-11-18 05:31:00 | Yeah, I'll risk showing a near total ignorance of electronics by guessing that a diode on the input end of things saved it. End result being a bit like working with a stuffed smoothing cap until the DC was restored | Paul.Cov (425) | ||
| 1244170 | 2011-11-18 05:34:00 | Haha the exact same thing happened to me a few years ago, the exact same model of speakers even I plugged in the 12v AC adapter, then if I recall correctly a small while later 1 or 2 electrolytic caps blew up inside, producing lots of smoke and leaving electrolytic fluid over everything inside. I ended up stripping out the amp section and using the speakers themselves with a separate amp unit |
forrest44 (754) | ||
| 1244171 | 2011-11-18 08:38:00 | Haha the exact same thing happened to me a few years ago, the exact same model of speakers even I plugged in the 12v AC adapter, then if I recall correctly a small while later 1 or 2 electrolytic caps blew up inside, producing lots of smoke and leaving electrolytic fluid over everything inside. I ended up stripping out the amp section and using the speakers themselves with a separate amp unit Give it a good wash and dry, replace the capacitors and it probably would have been OK. |
Agent_24 (57) | ||
| 1244172 | 2011-11-19 22:18:00 | Sorry for hijacking this thread with unrelated subject: For Billy T The adaptor you discussed 2010 Toshiba mk2006gal drive I have an Iriver h320 that died the drive will be ok and I really do want the files from it Is the adaptor available in NZ If not How long did delivery take My apologies again but hoping you can help Regards T |
TrevorTheSparky (16629) | ||
| 1244173 | 2011-11-20 09:19:00 | Hi Trevor The adaptor does not appear to be available in NZ and I found it Here (www.dealextreme.com). I ended up buying two, because the drive connector on the first one was not properly secured to the PC board (bolts in the photo not fitted) and it broke free, destroying the connections. I bought a second one, still no bolts, so I araldited the ends of the connector before using and it was fine. Price is negligible and both were free delivery (you might not be so lucky), and the first took just three days from ordering to hit my PO Box. The second took several weeks for some unknown reason, so ensure you get airmail delivery. The drive fits either way, so make sure you insert it with the label at the top or the 3.3 volt regulator gets stinking hot (guess how I found out!). Cheers Billy 8-{) |
Billy T (70) | ||
| 1244174 | 2011-11-20 22:30:00 | So, what do you think the outcome was? Well, there was no diode on the input, in fact there was no protection of any kind, and by rights the reverse voltage should have fried the electronics and popped the main electros as various responders suggested. Unprotected solid-state electronics is particularly intolerant of reverse polarity because normally reverse-biased junctions become forward biased and the resultant current flow is limited only by the source impedance of the supply and the size of the smoke generator. This is usually accompanied by loud noises and frantic attempts to pull the plug, but smoke followed by sullen silence is the inevitable result. In over 40 years of electronics work, I've never seen an escape like this, however I will admit to causing a few premature deaths through meter probe slippage, certain solid state HiFi amps were of very delicate disposition. So, for unfathomable reasons (mostly luck) on this occasion the amp actually survived at least two fairly prolonged doses of ac without ill-effects. I'm buying a lotto ticket on this, and all those who reckoned 'she'll be right' ought to do the same. Cheers Billy 8-{) |
Billy T (70) | ||
| 1244175 | 2011-11-20 23:09:00 | Well, there was no diode on the input, in fact there was no protection of any kind, and by rights the reverse voltage should have fried the electronics and popped the main electros as various responders suggested. Unprotected solid-state electronics is particularly intolerant of reverse polarity because normally reverse-biased junctions become forward biased and the resultant current flow is limited only by the source impedance of the supply and the size of the smoke generator. But it wasn't completely reverse polarity though - half the AC wave would have been 'correct' for the circuit, and the reversed part was only there 50% of the time. Perhaps that was just enough that it could tolerate it. Perhaps the design of the ICs or protection diodes in them worked like rectifiers? (It's been done: dangerousprototypes.com) I still chose the option I did, because last time I experienced something like this, the device worked for about a week and then blew up anyway. |
Agent_24 (57) | ||
| 1244176 | 2011-11-21 09:50:00 | But it wasn't completely reverse polarity though - half the AC wave would have been 'correct' for the circuit, and the reversed part was only there 50% of the time. You could be right there, but the reverse voltage was close to 18 volts peak and that would usually be too much to bear. Got to give it credit though, it came through smiling and is still working. It is a pretty basic IC circuit and there were no external protection diodes. I've not heard of them being fitted to audio ICs either, but that doesn't mean they don't. I was pretty surprised I must say, because it had spent quite a while on AC while the owner looked elsewhere for the problem! Cheers Billy 8-{) :thumbs: |
Billy T (70) | ||
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