sci.electronics.repair@googlegroups.com

Google Groups

Cursitor Doom <curd@notformail.com>: Nov 15 02:34PM Hi all,   This subject continues to severely bug me. I've just read some audio amp servicing/repair book where the author states that customers often find it desirable to know an amp's actual output power, and to return an amp having measured its output power and noted it down for the customer's info. The trouble is, customers are familiar with "RMS power" - but there's no such thing! Irms X Vrms = AVERAGE power and that is all that matters. BUT - try telling that to a typical customer!   So it must all come down to perception. Customers have an idea in their minds what say 70WRMS sounds like through listening to dozens of various VRMS labelled amps over the years. So there ought to be some kind of notional, informal 'conversion factor' between Waverage and "WRMS" we could adopt to satisfy them without compromising on the accuracy of the correct measurement, n'est pas? What would that conversion factor be? Greater or less than unity for a start? Your thoughts invited.

jurb6006@gmail.com: Nov 15 08:20AM -0800 Well, we drive on parkways and park on driveways. the macula in your eye used to be called the fovea. Double density floppy disks had half the capacity or the high density disks.   Chalk it up to that.   Other than that "RMS power", no matter how nonexistant, is;   V * 0.707 ^ 2 / R   Might piss you off, but hey, what does a five pound can of coffee weigh these days ? And they say you can use less, bullshit. Do that and you'll be drinking dishwater. You are not supposed to see through coffee. And lowfat milk, no thanks, I got water. Go ahead "Oh they don't just add water", damn right, they are selling what they take out of it. Kinda like salt, they make more money from what they refine out of the salt than the salt itself.   This mythical RMS power is the result of the FTC trying to put a lid on ridiculous power claims back in the 1970s. It only has any real teeth when the power is stated in a certain way. Thye can rate a unit 2,000 watts on a 2 amp fuse, as long as they do not claim it as an actual, legal power rating. Note that the regulations do not apply to commercial or auto equipment, or to other than the front two main channels of a surround amp.   Now there are commercial amps lying their (_|_) off about power. Says 1,000 watts and I get into it and there is a little TO-220-15 package IC with a fan on it smaller than the one in my PC.   Same with cars. Do you really think they are 5,000 watts ? At 100 % efficiency it would have to pull over 400 amps. Even my 12 : 1 455 luxury racecar engine with a sloppy timing chain didn't pull that to start hot. For a car battery, 400 amps is a "cold cranking amps" rating. And alternators ? Change one lately ? They cannot handle anywhere near the current they used to, it is right on the box "DO NOT ATTEMPT TO CHARGE A DEAD BATTERY AS PERMANENT DAMAGE WILL OCCUR, CHARGE BATTERY BEFORE USING ALTERNATOR. What ? Know what that means ? That means if you leave your light on and need a jumpstart, it might wreck your "new and improved" alternator. And that suits "them" just fine. (I think I prefer the old and shitty ones that worked reliably)   Now some of these guys DO have a second battery and alternator just for the amps, but still. Does anyone even know the gauge of wire needed to conduct 400 amps ? They got fat wires in them cars but not that fat.   So there is a formula for it though it does not exist. Well, neither does the square root of -1.

Phreedom Karess <hapticz@sbcglobal.net>: Nov 15 01:40AM -0800 cheap thing bought at dollar store, at home used used a wallwart 12vdc with a cig lighter style attach, worked fine for year, then i accidentally managed to short the 5vdc output during a quick kludge on a project. now this cheap little thing started putting out 7.6 vdc rather than 5vdc, unbeknownst to me. long story short, i then used it to try charge one of those 'recharge your cell phone' portable batterys. and it toasted it, no more blue light showing charge or redlight showing it is charging. of course, it would, wrong input voltage! dumb eh? i figured there would be some sort of minimal input protection on the battery thing, boy was i wrong. take this little cheap thing apart, inside is a fuse to protect (whatever?) itself from over load, a resistor, a small millihenry inductor and a 6 pin chip that does 'all the work'. (oh and a red l.e.d. to show the output is on). nothing looks remotely cooked or smelled like usual toasted electronics, must be all internally fused or opened? amazing how cheap it was built, gotta give them chinese credit, they know how to slap these things out by the millions and never give a dang about failure modes or protecting dumb end users! ;-))   best way to 'repair' these cheap little things is to go to the dollar store and get another one.

c4urs11 <c4urs11@domain.hidden>: Nov 15 02:35PM On Sun, 15 Nov 2015 01:40:36 -0800, Phreedom Karess wrote: > best way to 'repair' these cheap little things is to go to the dollar store > and get another one.   Dollar store got your money for the first one and now you are willing to give them money again for the same cheap thing? Nice way to slap dollar store for selling this in the first place.   "Them chinese" are perfectly able to produce a decent charger, but at a price dollar store wouldn't make the same profit on.   Cheers!

Jeroni Paul <JERONI.PAUL@terra.es>: Nov 14 02:34PM -0800 I'm looking at a DVD player with an odd problem in the tracking actuator servo. When a DVD is loaded, both original or recorded, it focuses, spins and positions the lens fine - up to this point the tracking actuator keeps the lens centered. Then suddently the lens moves to one end of the tracking actuator range, a click is heard as the actuator hits a plastic stop and the sled does not move. This situation lasts about two seconds until it retries by moving back and forth the sled, refocusing and reactivating the tracking servo - the same repeats. After two tries a disk spin down and spin up happens and the read is attempted two times more before a disk error message pops up.   This tracking failure happens almost always, but occasionally it will load and play the disk for a while but sooner or later the lens clicks again. I've seen it click, then recover and continue to play. It does not respond to mechanical stress to the board. I suspect this failure happens more often at higher spindle speeds, that may explain why original DVD are harder to get to load than DVD-R. I have double-ckecked the motor for shorts in windings or rotary contacts problems and could not find anything strange.   With CDs the behaviour is different, the tracking actuator does not click to one end but it has some difficulties keeping the tracking stable and the data readout error free, with occasional sled repositionings as if it had some trouble reading the data. These sympthoms happen more at the beginning and mid way tracks and never at the outmost tracks. I relate that again to the lower spindle speed in these tracks.   The player is a Supratech vision Artemis (DVD player with USB, card reader and DVB-T tuner) and has board SUNPLUS 8202A with SPHE8281A chip (256 pin version) and a Sanyo HD850 pickup. The SPHE8281A outputs the tracking actuator signal on pin 42 labeled DATEO and that is input to the CD5888CB (actuator and motor driver) through a 68K resistor. Monitoring this signal reveals a voltage of 1.5 to 1.7V during normal operation and jumps to 2.5 to 3.0V when the click occurs. There are three more pins on the SPHE8281A related to tracking, the names are referenced in the datasheet but no more details are provided: pin 34: TEO (Tracking error signal output) pin 35: TEOLP (TEO low pass?) pin 26: V165 (Reference DC BIAS voltage)   The datasheet refers to a servo datasheet for additional information that I could not find. Signals TEO and TEOLP follow the same behaviour as DATEO, and V165 is always 1.6V. TEO has a 330p capacitor to ground and TEOLP a 100nF one. I've checked all servo supplies and grounds and ruled out the power supply by powering it with a PC power supply. The board runs off a single 5V supply and has its own 3.3 and 1.8V regulators. I've checked all capacitors for ESR.   Thank you in advance for your replies.

makolber@yahoo.com: Nov 14 03:44PM -0800 Check for some mechanical issue re the holding of the disc. If it is loose and can wobble or if it can slip in rotation, that makes it more difficult for the tracking.

N_Cook <diverse@tcp.co.uk>: Nov 15 10:23AM > Check for some mechanical issue re the holding of the disc. If it > is loose and can wobble or if it can slip in rotation, that makes > it more difficult for the tracking.   And similarly. If a problem in the suspension , just at the usual neutral posistion. Try a piece of gummed paper or similar stuck to the platter, to shift the positioning a bit. If that is worse then, perhaps the platter has moved on the spindle. Usually just relies on friction fit so faced with a hard to remove disc and the platter gets out of position. Can you check the platter height against another with the same optical deck?

"Mark Zacharias" <mark_zacharias@sbcglobal.net>: Nov 15 07:37AM -0600 "N_Cook" <diverse@tcp.co.uk> wrote in message news:n29mbc$goa$1@dont-email.me... > friction fit so faced with a hard to remove disc and the platter gets out > of position. Can you check the platter height against another with the > same optical deck?   It is not uncommon for there to be an increasing distance between the objective lens and the disc as the sled moves further along it's track. This means an increasing focus error. If the laser is aged, the servo can no longer account for this as reliably.   (I assume you have cleaned the lens.)   In any case - these things are usually repaired by replacing the entire traverse unit, if they are repaired at all.   Most players are so cheap anymore, they simply aren't worth it.     Mark Z.

Rick Casey <caseyrick@gmail.com>: Nov 14 10:48AM -0800 > Look for internal fuses. Generally what you did will not damage most amps.... But it may well pop internal fuses or links. But not always. Next would be the output devices.   Thanks for the tip! Will see if I can find that...

Phil Allison <pallison49@gmail.com>: Nov 14 10:05PM -0800 Rick Casey wrote: > the right solution to fix my amp.   > I have a Roland Cube, which I basically use as an amplifier > to play music through, or my guitar.     ** The first Roland cube was the "Cube 40" released in 1978, then followed Cubes 20 and 60 and then too many new models to count. Roland claim to have sold over 1,000,000 Cubes of all the various sorts.   Which one have you got?     > Pulling the plug immediately, when I later tried to play music through the amp again at proper volume, nothing comes out but a steady hum.   ** Was that the power plug ?   > So my question is: what damage did I likely do? > Can it be fixed? Is there any other testing I can > do to determine what was damaged?   ** Answer the first question and maybe we can make an educated guess.   One possibility is the input jack ( or the PCB it is mounted on) has broken. All depends on which model Cube you have.     ... Phil

John Robertson <spam@flippers.com>: Nov 14 11:53PM -0800 On 11/13/2015 2:35 PM, M Philbrook wrote:   > Maybe when yuo yanked the cord you could of broke a wire in the cord > or a solder joint where the plug is inside the unit.   > Jamie   I'm with Jamie here. Have you powered up the amp with ONLY the speakers hooked up? No other cables going to the inputs.   If still hums, does the hum volume go up/down with the volume control? This could indicate a problem in the pre-amp section.   If the hum level is steady, then the problem could be a blown fuse on one of the power amp rails (B+ or B-).   John :-#)# -- (Please post followups or tech inquiries to the USENET newsgroup) John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9 (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games) www.flippers.com "Old pinballers never die, they just flip out."

"Ian Field" <gangprobing.alien@ntlworld.com>: Nov 14 06:11PM <Paintedcow@unlisted.moc> wrote in message news:nbuc4b12bvjo4u534st66447ksgetm03of@4ax.com... > fails. I did have one burn the transformer out, after it got rained on. > I learned that the hard way! I always cover them now if they are in use > outdoors.   Somewhere I've got an ancient charger that the Halfords store used to sell - the metal case is the only original part.   The rectifier was replaced with one from a motorcycle and the transformer with one from a Philips black & white portable. The cheap & nasty plastic moving iron current meter was replaced by an Admiralty bulkhead mounting instrument.   A resistor was added before the rectifier to limit the current because a TV PSU transformer doesn't have a charger transformer impedance characteristic. A couple of big film capacitors were added to make the rectifier voltage doubling (for some strange reason it actually gets up to about 42V with no load!). Which works rather well for saving sulphated batteries. Later I added a big fat electrolytic for zapping whiskered nickel cells.

You received this digest because you're subscribed to updates for this group. You can change your settings on the group membership page. To unsubscribe from this group and stop receiving emails from it send an email to sci.electronics.repair+unsubscribe@googlegroups.com.