sci.electronics.repair@googlegroups.com

Google Groups

N_Cook <diverse@tcp.co.uk>: Jul 28 10:52AM +0100 +/-15V on the "level" opamps, and 48V and 5V for digital. Looks as though I'll have to trace out the schematic around one of these pots and opamps to see what could be common to all the channels, requiring removing all the hardware to get to the other side of the pcb.

N_Cook <diverse@tcp.co.uk>: Jul 28 11:35AM +0100 I've just realised I've not seen a Level Set LED light on any channel with any input. No such LEDs on the 2800 schematic. Try and find the common voltage to the transistors or whatever buffer to those on each channel, before removing all the hardware.

N_Cook <diverse@tcp.co.uk>: Jul 28 12:41PM +0100 Getting somewhere now. To save desoldering a shielding plate I'd been probing the stereo channels. Problem is with 1 to 4 channels only, so removed shield. +/-15V ok on those opamps. LED supplies are off the -15V line, one zener per channel, giving nominal voltage of about -8.4V, varying a bit on each channel. Just pins 2 and 3 of each of the 4 off level double-opamp ICs show that same negative voltage on each channel, the B opamp of each is normal. Still a mystery what the problem in common is to cause that to each channel, but zeroing in.

N_Cook <diverse@tcp.co.uk>: Jul 28 03:13PM +0100 There are 2 simple -8.4V zener drop supplies per channel. One of those -8.4V is connected to pin 2input and the other to pin 3 output of the opamp, what is that about? Still no wiser what the interchannel coupling problem is either

Deane Williams <pyroartist.dw@gmail.com>: Jul 27 07:06PM -0700 I set up a thermostat in my garage that comes on at 80 degrees F. and sends a 6 VDC battery voltage to control a 120 VAC solid state relay which powers up the vent fan. The fans always quit within 2 months to a year with no obvious defects. These are inexpensive 20 inch box fans with induction motors. I have tried several brands and styles of fans. The latest was a Home Depot unit that only lasted 2 months. Does anyone know of a reason why I can't run an induction motor from a SS relay? What is killing the fans? I have taken two apart and there is no smoke smell, no visible damage and if there is a capacitor it tests OK. Thanks for any ideas. I am going to switch over to a mechanical relay.   Dean

John Robertson <spam@flippers.com>: Jul 27 11:32PM -0700 On 07/27/2015 7:06 PM, Deane Williams wrote: > Does anyone know of a reason why I can't run an induction motor from a SS relay? What is killing the fans? I have taken two apart and there is no smoke smell, no visible damage and if there is a capacitor it tests OK. > Thanks for any ideas. I am going to switch over to a mechanical relay.   > Dean   Have you had any other fans of the same make/model running on just 115VAC to see if they run any longer? They could be just cheap fans whose oil dries up.   Hard to see where a SS AC Relay could hurt an induction motor if the motor isn't overheating.   Does the fan still spin? Is there continuity in the winding?   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."

N_Cook <diverse@tcp.co.uk>: Jul 28 08:15AM +0100 On 28/07/2015 03:06, Deane Williams wrote: > Does anyone know of a reason why I can't run an induction motor from a SS relay? What is killing the fans? I have taken two apart and there is no smoke smell, no visible damage and if there is a capacitor it tests OK. > Thanks for any ideas. I am going to switch over to a mechanical relay.   > Dean   Do you do TIG/MIG welding in this garage?

avagadro7@gmail.com: Jul 28 04:47AM -0700 http://www.bcae1.com/relays.htm

Jeff Liebermann <jeffl@cruzio.com>: Jul 27 09:58AM -0700 On Mon, 27 Jul 2015 12:50:31 +0000 (UTC), Cursitor Doom >> which Newark and Digikey do not seem to carry.   >Is that inductiveness seriously likely to be a problem at audio >frequencies?   Disclaimer: I am not an audiophile or expert on audio equipment beyond a few occasional repairs and some long past work at a recording studio and several radio stations.   Well, that depends on what you're trying to accomplish with the dummy load. If it's performance tests for a data sheet with calibrated equipment, then yes, every divergence from exactly 8+j0 is important. However, if you're using the load to simulate a real loudspeaker to test for ringing, oscillations, crossover distortion, resonant peaks, and such, then there's no way a purely resistive load is even close to a real world loudspeaker impedance: <https://www.google.com/search?tbm=isch&q=loudspeaker+impedance>   Let's do some measuring and math. Digging through my junk box, I find a dummy load that I think was used to test power supplies: <http://www.11junk.com/jeffl/pics/drivel/slides/dummy-load-inductance.html> That's 2ea 2.5 ohm and 2ea 5.9 ohm inductive RH type resistors in series for a total of 16.8 ohms. Measured inductance of 16 uHy at 1KHz yields: Xl = 2*Pi*f*L = 2 * 3.14 * 1000 * 16*10^-6 = 0.1 ohms So, this load looks like: 16.8+j0.1 Good enough. However, if you were making measurements up to 100 KHz, where the load would look like: 16.8+j10 methinks a non-resistive load might be useful.   Considering that your original question was about testing a used amplifier to see "what it was capable of", y'er right. You can do that nicely without using overpriced non-inductive terminators. When you actually build your load, you might want to do the above measurement and calculations.   -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558

Trevor Wilson <trevor@SPAMBLOCKrageaudio.com.au>: Jul 28 07:32AM +1000 On 27/07/2015 10:50 PM, Cursitor Doom wrote: >> which Newark and Digikey do not seem to carry.   > Is that inductiveness seriously likely to be a problem at audio > frequencies?   **No.   -- Trevor Wilson www.rageaudio.com.au   --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus

Cursitor Doom <curd@notformail.com>: Jul 27 09:32PM Thank you, gentlemen.   So we're all agreed:   1. there's no problem using wire-wounds for a load provided the power output measurement is carried out with sine waves from a suitable external generator.   2. Even low rated power resistors can be used for the load provided their case temperatures are kept low by some effective means of external cooling (something more than mere heat sinks and fans, IOW).   Many thanks.

"Ralph Mowery" <rmowery28146@earthlink.net>: Jul 27 06:09PM -0400 "Cursitor Doom" <curd@notformail.com> wrote in message news:mp681u$8ul$2@dont-email.me...   > 2. Even low rated power resistors can be used for the load provided their > case temperatures are kept low by some effective means of external > cooling (something more than mere heat sinks and fans, IOW).   That is the way I see it.   You can probably go at least 5 and maybe 10 times the power on the load resistor if you put it in some water or oil. Many times that if you have liquid nitrogen.

MJC <gravity@mjcoon.plus.com>: Jul 27 11:31PM +0100 In article <mp681u$8ul$2@dont-email.me>, curd@notformail.com says... > 2. Even low rated power resistors can be used for the load provided their > case temperatures are kept low by some effective means of external > cooling (something more than mere heat sinks and fans, IOW).   To an extent. Seems to me that the winding temperature will rise because the insulation between case and wire will not have infinite heat conduction. At some power level the lifetime must start to shorten...   Mike.

Phil Allison <pallison49@gmail.com>: Jul 27 08:08PM -0700 Cursitor Doom wrote:   > > which Newark and Digikey do not seem to carry.   > Is that inductiveness seriously likely to be a problem at audio > frequencies?     ** Not in the slightest.   Liebermann is blowing it out his arse, as usual.     .... Phil

Phil Allison <pallison49@gmail.com>: Jul 27 08:14PM -0700 Ralph Mowery wrote:     > Used a 100 MHz scope, function generator and Fluke 87 meter.   > From low audio up to 20,000 Hz and a sine wave with the 10 ohm WW there did > not appear to be any noticable difference.   ** And this is a sufficient test for the purpose.     > When I switched to a square wave   ** Which has harmonics into the medium and HF bands.     > I noticed a large spike on the leading and trailing edges, especially as I > went higher up in frequency.   ** All due to the harmonics way above audio range.     > From this rough test, I would say that if using sine waves you could get a > close to true test, but if music   ** Music signals stop at 20kHz.     > or other odd ball waveforms     ** An audio amplifier reproducing a square wave will not pass harmonics much above 50kHz top the load - so you are wrong again.     .... Phil

N_Cook <diverse@tcp.co.uk>: Jul 28 08:19AM +0100 On 27/07/2015 22:32, Cursitor Doom wrote: > case temperatures are kept low by some effective means of external > cooling (something more than mere heat sinks and fans, IOW).   > Many thanks.   2) only if you know the current carrying capacity of their winding wire

Phil Allison <pallison49@gmail.com>: Jul 28 02:19AM -0700 N_Cook wrote:     > 2) only if you know the current carrying capacity of their winding wire     ** Huh ??   Wot a classic Kookism.       .... Phil

Phil Allison <pallison49@gmail.com>: Jul 27 09:06PM -0700 N_Cook wrote:   > In my sort of electronics world, for torroidal transformers an NTC > thermistor would be included to avoid down-rating RCD or uprating MCB. > What would they do in the electrical world, anything like NTC thermistors?     ** MCBs come with various rating for the tripping time, known as B, C and D curve.   The C curve is the one usually chosen for motor start applications, it allows a current of up to 10 times the nominal rating to pass for about 5 seconds.   The problem is not the same as with large transformers ( ie core saturation due to DC component ) but simply that the motor is stalled when power is first applied and takes time to spin up.       ... Phil

avagadro7@gmail.com: Jul 27 03:14PM -0700 on the whole, computer video has a brain sorting the input to the output holding info on various standards rather than a group of bipods 'agreeing' on a 'standard'   TV has no brain. !!!! Eureka !   but the rig needs coupling and cable to start.   I assume the hookup and directions answers are found in brand forums as Dell Forums Inspirion.

"J.B. Wood" <arl_123234@hotmail.com>: Jul 27 02:17PM -0400 Hello, all. After 20+ years of home storage, I finally fired up the subject slide projector (Kodak's top-of-the-line in its day) which I purchased new way back when. The projector functioned but I have a cosmetic problem to solve. The rubber (?) retaining rings that secure the two wood-grained inserts to the side panels of the projector have broken in several spots due to dry rot. Anyone have any suggestions? The parts list for this projector shows only the side panels (which I presume includes the retainers and inserts). But then there's the problem of spare parts...Thanks for your time and comment. Sincerely, -- J. B. Wood e-mail: arl_123234@hotmail.com

Jeff Liebermann <jeffl@cruzio.com>: Jul 27 11:51AM -0700 On Mon, 27 Jul 2015 14:17:09 -0400, "J.B. Wood" >The parts list for this projector shows only the side panels (which I >presume includes the retainers and inserts). But then there's the >problem of spare parts...Thanks for your time and comment. Sincerely,   Don't toss the old parts. Glue or scotch tape the pieces together. Fill any gaps with some kind of putty. Using the old part as a pattern, make a two part mold using plaster of paris. Smear the contact surfaces with vaseline so that you can take it apart. Fill the mold with your favorite rubber compound (I used hard automotive RTV) to clone the part. Clean up the flashing with an Xacto knife.   -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558

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.