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jurb6006@gmail.com: Nov 28 12:10AM -0800 All my sources have let me down.   It has some sort of microprocessor type problem, if I can't fix that I need to modify it for use as a separate [pert amp. The guy needs alor of power to keep up with live drums.

"pfjw@aol.com" <pfjw@aol.com>: Nov 28 04:18AM -0800 > All my sources have let me down.   > It has some sort of microprocessor type problem, if I can't fix that I need to modify it for use as a separate [pert amp. The guy needs alor of power to keep up with live drums.     https://ibzdckwfk.files.wordpress.com/2015/06/marantz-sr940-service-manual.pdf   If you trust the source.   Peter Wieck Melrose Park, PA

"pfjw@aol.com" <pfjw@aol.com>: Nov 27 09:27AM -0800 Some basics:   a) Isolation transformers are designed to protect users under some conditions, and *certain* types of equipment under *VERY* limited conditions. Those latter applications are primarily under hospital and research conditions where an isolated ground is not enough. Generally, RF-shielded rooms use isolation transformers in their power-supplies, for example. But, no equipment protects against deliberate stupidity or carelessness. If one inserts oneself into the circuit, one will be stung.   b) Voltage adjustment transformers tend to be as inexpensive as possible per-watt. A true isolation transformer would have very nearly twice as much conductor in it as a simple auto-transformer. Not t mention more core material as well - I am careful not to use 'copper' or 'iron', as very cheap devices will use neither.   c) Any unnecessary equipment adds a degree of unnecessary complexity - and with it an opportunity for error. I have a 110/220 step-up/down transformer purchased in Saudi Arabia with no markings at all. It came with a Euro/US adaptor that could plug into either side. So, I engraved "High Side" and "Low Side" on. Imagine me going the 'wrong way' in actual use. Not so bad going from 110 to 55 volts. But 220 - 440 V, not so good either.   If you need to step up/down, check the equipment. A surprising amount of vintage audio equipment has multi-tap primary transformers that might require only a simple change in wiring, and a surprising amount of modern consumer electronics have smart supplies that do it all automatically. Otherwise, a brand-name surge protector (with a downline equipment warranty) will be your best option to protect your equipment.   Peter Wieck Melrose Park, PA

gregz <zekor@comcast.net>: Nov 28 08:47AM >> Trevor Wilson >> www.rageaudio.com.au   > to protect my equipment, i picked up a new hobby.   Commercial isolation transformers get rid of common mode noise, and since one leg of output is tied to ground, forms a new local neutral. This prevents noise differentials between ground and output. There is always voltage sag, so a120 vol output is at full load. More perhaps too much with small load. Could be 10- 15% over 120 volts. This is not a test transformer with isolated output from ground referenced mains. Some have voltage regulation too.   Greg

vjp2.at@at.BioStrategist.dot.dot.com: Nov 27 09:42PM It's under another (KVM'd) computer and I don't really have the space to leave it open a week, so I'm trying to guess how/if to replace the power supply.   (how)   Amazon sells a cheap one as Apevia ATX-VS450W Venus 450W ATX It seems the specs are GATEWAY POW0016A01 145 WATT POWER SUPPLY P5-75 P5-120 ASTEC SA145-3435 and that (I guess) my main issue is the bus. The cheapest exact match I've found sells for five times the one on Amazon. Is there such a thing as a "universal" power supply?   (if)   Now, what seems to be wrong? I hadn't touche dth emachine all summer. THen it went on but couldn't find the hard drive. Evetually after about ten times it did. It worked daily for about ten days. I didn't use it for about a month, after which it refuses to turn on. So I'm GUESSING it's the power supply.     - = - Vasos Panagiotopoulos, Columbia'81+, Reagan, Mozart, Pindus blog: panix.com/~vjp2/ruminatn.htm - = - web: panix.com/~vjp2/vasos.htm facebook.com/vasjpan2 - linkedin.com/in/vasjpan02 - biostrategist.com ---{Nothing herein constitutes advice. Everything fully disclaimed.}---

tabbypurr@gmail.com: Nov 27 01:47PM -0800 > went on but couldn't find the hard drive. Evetually after about ten times it > did. It worked daily for about ten days. I didn't use it for about a month, > after which it refuses to turn on. So I'm GUESSING it's the power supply.   probably bad caps in either PSU or on the mobo. A component tester could probably tell you their ESR.     NT

jurb6006@gmail.com: Nov 28 12:18AM -0800 They are standardized but Gateway doesn't use a standard one usually.   I agree on the caps.   Companies like Gateway skimp on the power and make the power supply smaller. Nothing else will fit. They will usually work but they would have to be outside the case. And some of them use the power supply fan to cool the microprocessor. That really stickies up the wicket.   The only thing you can't get usually is the transformer. But be careful if you have to replace the main chopper. Generally it will be a MOSFET and the ratings not really all that critical, but you need at least like a 700 volt part because they use a line doubler for 110 volts and simply turn it into a regular rectifier for 220 volt operation.

Jon Elson <jmelson@wustl.edu>: Nov 27 02:31PM -0600 > So how do they get the good clean AC from these big generators? Those big power house alternators have more slots in the stator. The winding pattern is set up such that the middle of the magnetic pole has more turns, due to ovelapping sets of coils, than the ends of the pole. This creates the proper wave shape. Smaller alternators can't have as many slots, and thus separate coils, so the induced waveform has some "jumps" anf "flat spots" in it.     > at home just fine. The fridge, freezer, lights, phone and router. I > didn't try any computers. So maybe I don't need to even consider > filtering the generator output. Right, the inductance of typical motors smooths out the small imperfections in the voltage wavem and you pretty much get a sine-wave current. > output" from an inverter that is part of the generator electronics. So > maybe a pure sine wave is important for some electric or electronic > stuff. Clocks for example. Well, some inverter generators produce horrible square waves or stepped approximations of sine waves, that might cause problems for a variety of equipment.   Running clocks off the typical generator will be a waste of time, the frequency control will be awful.   Jon

etpm@whidbey.com: Nov 27 03:01PM -0800 On Mon, 27 Nov 2017 14:31:49 -0600, Jon Elson <jmelson@wustl.edu> wrote:     >Running clocks off the typical generator will be a waste of time, the >frequency control will be awful.   >Jon Thanks for the reply Jon. Do you think Tesla's generators at Niagara Falls were made the way you describe? I wouldn't be at all surprised. Eric

Jon Elson <jmelson@wustl.edu>: Nov 27 05:32PM -0600 > Thanks for the reply Jon. Do you think Tesla's generators at Niagara > Falls were made the way you describe? I wouldn't be at all surprised. > Eric Everything made since about 1890 had some scheme to control the harmonic problem. The first alternators had "salient poles" on the stator, which were just blocks of stacked steel laminations with coils wound on them. But, even with these, it was possible to shape the rotor flux field to minimize the harmonics. Later, they went to slotted stator lamination sections that made it possible to have coils that spanned several slots, and this made harmonics much smaller.   Also, in the early days, they ran the alternators off steam engines, and the AC had a definite pulsation with each stroke of the piston.   Jon

John-Del <ohger1s@gmail.com>: Nov 27 04:03PM -0800 On Monday, November 27, 2017 at 6:30:13 PM UTC-5, Jon Elson wrote:   > Also, in the early days, they ran the alternators off steam engines, and the > AC had a definite pulsation with each stroke of the piston.   > Jon     I would have thought they'd be using a nearly infinite mass flywheel to stave off power pulses.

vjp2.at@at.BioStrategist.dot.dot.com: Nov 27 09:45PM I got a switch that needs replacing but I'm afraid because the last time I replaced it the wires were old and the tips broke and i had almost no wire to use. An electrician chum told me about scothclock and I got two spools of wire (I didn't last time) but I'd like to see some videos to build up my confidence. BION last time I was so lost, it was late at night and I prayed for half an hour before I got it to work. Much obliged   - = - Vasos Panagiotopoulos, Columbia'81+, Reagan, Mozart, Pindus blog: panix.com/~vjp2/ruminatn.htm - = - web: panix.com/~vjp2/vasos.htm facebook.com/vasjpan2 - linkedin.com/in/vasjpan02 - biostrategist.com ---{Nothing herein constitutes advice. Everything fully disclaimed.}---

tabbypurr@gmail.com: Nov 27 01:53PM -0800 > wire (I didn't last time) but I'd like to see some videos to build up my > confidence. BION last time I was so lost, it was late at night and I prayed > for half an hour before I got it to work. Much obliged   If you tell us what you're talking about maybe we can help. Then what sort of wire etc.

Jon Elson <jmelson@wustl.edu>: Nov 27 03:13PM -0600 >> Serge   > Sounds like the ground end of the pot has come disconnected. Most likely > where it's soldered, or perhaps inside the pot. Yes, very frequent problem, especially if the pot is not bolted to the case, is that the resistance element has cracked. If that is the case, most likely the pot will have to be replaced.   Jon

tabbypurr@gmail.com: Nov 27 01:45PM -0800 On Monday, 27 November 2017 21:11:28 UTC, Jon Elson wrote: > is that the resistance element has cracked. If that is the case, most > likely the pot will have to be replaced.   > Jon   A basic multimeter should determine whether the pot is bad or disconnected.     NT

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