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Posted: Sat May 17, 2003 7:21 pm
I bought a stereo equalizer from a garage sale, and plugged it in. It turns on, and sound only comes from it if the equalizer on/off switch is off. If I turn the switch on, no sound comes out, making it worthless. The model is a Sansui SE-500. I plugged the Preamp out into my reciever/tuner, and the sound source is hooked to source in. Is there some special 'trick' to getting it to work, or is the reason the people sold it because it doesn't work. Thanks in advance for your help.<p>-Mike
Posted: Sat May 17, 2003 10:03 pm
It dont work? My best guess. Its has a passive or active amp to the circuit, and that part, the heart of the unit, isnt working. The off, is simply a by pass circuit.
Posted: Sun May 18, 2003 12:40 am
Pop the case screws and tell us what you see?
Posted: Sun May 18, 2003 6:01 am
Are you sure? I should open the case, ignoring the huge lightning bolt and warning of high voltage on the back? And Chris, do you mean that there is a am in the equalizer that makes it work, butthe amp is dead? Thanks again.<p>-Mike
Posted: Sun May 18, 2003 11:06 am
YES, most equalizers have a amp, or a passive by pass circuit with all the chokes and filters. <p>Active, or passive.<p>Pushing the button is a divertor to one or the other, by pass, or filters/amp etc. <p>Opening it is ok, but you probably have some chips in there that are fried. Aside from that, the push buttons often freeze up or die, so push the buttons fast, wiggle them, and try to see if your lucky and its just a switch or two? <p>There are many things that go wrong, but the chips going bad are sometimes impossible to find and make it into a real "project"? But then the AMPs could also be blown, and make it simple to fix. Good luck, a good learning experience is at hand.
Posted: Sun May 18, 2003 3:26 pm
Inside equipment generally speaking there are parts that bite! (electrical shock)<p>Difficult to access from a forum however after unplugging the unit and opening the case the big electrolytic capacitors should be shorted with a resistor.<p>Does the switch work properly ?
Do the regulators function ? this requires the power on. A schematic is preferred.<p>So if you are patient and follow safety then eventually you will find the problem or you will become frustrated and use the spark method.<p>If it is worth while to you paying a qualified person may be the best alternative.
Posted: Mon May 19, 2003 4:45 pm
Hi Mike.<p>Assuming that when the switch is off, the switch bypasses the equalizer circuit and directly connects the inputs to the outputs. Here is another possibility: You may have the input and output wires reversed. This will also give you sound only when the switch is off<p>Bob
Posted: Mon May 19, 2003 11:58 pm
<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Are you sure? I should open the case, ignoring the huge lightning bolt and warning of high voltage on the back? <hr></blockquote>Heh heh --- it's never stopped me. They do that to avoid LEGAL stuff. (And in case you accuse me of inciting you to ignore warnings, my REAL name is SMITH...)<p>I'm virtually certain your equalizer runs off of a transformer supply. So there should be NO high-voltage-capacitors. Unplug it, remove the screws, and see where the power cord goes. Betchya it goes over to a TRANSFORMER, with either sealed connections or PCB contacts. If the contacts are OPEN, then yes touching them (whilst it's plugged in) will get you anything from a BITE to pushig up daisies. If _I_ was fixing it, I would plug it in, and see what voltage appears on the big electrolytic close to the transformer, next to the four diodes (the "bridge rectifier). I would expect up to 18 volts DC. There MIGHT be some regulators, usually something like a 7800 series (do you know the pinouts of these?) You don't hafta know which is IN and which is OUT, usually the CENTER is ground. Then just measure to ONE and then to the OTHER lead; you'll see the supply voltage (18 or whatever it was), and then the other will have the regulator voltage on it (12 volts, or 11.59 volts, whatever). Or 4.96 or 5.03 if it's a 7805. Could be either TO-220 (might even be on a heat sink) or could be TO-92 (looks just like a transistor). A schematic is definitely preferred, but if you can cross the amps you can connect an oscilloscope (doesn't everybody have one?) to the input, and then to the output. AND check its power supply.<p>I got some nifty Maxon walkie-talkies from a flea market on Maui; one worked, one didn't. Then the WORKING one died. RF signal but no audio modulation. Maxon very kindly sent me the schematic. I noticed that the input to the audio amp was sitting at ZERO VOLTS (driving the output to the rail); and the only way that was possible was if that TANTALUM COUPLING capacitor was leaking. Replaced that capacitor (in both units), with nice styrene epoxy nonpolarized caps, and both radios work just fine. You can lose the amp (but something CAUSES this), or capacitors just go bad (both electrolytics, and tatalum --- tantatlums are particularly bad about it). <p>You might wanna buy a can of "TV-TUNER-CLEANER", and spray on the switches; as Chris said they get dirty or oxydized or sticky. The chemical cleans and lubricates them --- some fast activating will fix them if bad. Cheap solution if it works.<p>And you know that CRACKLY volume control that always bothers you? Shoot some tuner-cleaner in it, and it's good as new...
Posted: Tue May 20, 2003 4:26 am
One of the first things to do is to examine its innards before plugging it into the mains. I doubt that the equalizer would use a switching supply, so the main capacitor in the power supply is unlikely to still be charged to any degree. <p>Note switching supplies as in computer style ones will have one or two large capacitors that must be discharged before touching the supply, unlikely to kill if you're healthy and not in humid conditions, but will certainly give a memorable zap.<p>Check to see if there are any obvious signs of corrosion or whether bold weevils have taken up residence - here in Oz cockroaches eating insulation and their droppings cause shorts as do Possums and paper wasps building nests in equipment. If any of the electrolytic caps are bulging at their tops where the little cross on the top of the can, or if there is a strong fishy smell and ooze, well you'll need to replace these caps.<p>If you are unhappy about fiddling near the mains supply, then before plugging in make sure that all the case earth is still attached (if a metal case), that the mains connections are insulated, insultaion tape while not the best protection will do in the short term wound over any exposed terminal lugs, track down the bridge rectifier, after this point you are looking at DC voltage and can probe around to your hearts content until the big bang, when you short the supply rails.<p>In fact once on the secondary of the mains transformer you are isolated from the power grid.<p>Mains isolation transformers are brilliant pieces of equipment to have for extra safety easy to make. <p>Note TV's and Monitors are often not isolation safe after the big transformer as they run on a live chassis and microwave ovens have a large cap near the magnetron that will give off a very hefty kick.