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hello everyone, i removed the board from a pioneer pd 7700 cdp and unsoldered three wires coming from headphone jack board. when i soldered them back, there was a very tiny bridge between two of the pins that i did not see. when i turned it on, i had no sound and there were two regulators L7806 AND L7906 THAT GOT VERY HOT. i replaced them with lm317 and lm337 the 337 came close to the 6 volts at 5.94v dc but the 317 gets 9.12 input and puts out about 9v. dc. using same resistors and its not shorted. the unit works but, i have 5.94v- dc on pin 4 of my ad 826 but i have almost 9v+ dc. on pin 8. any ideas would be appreaciated. thanks, alley-kat ps. regulators do not run hot now the bridge is removed.
Follow Ups:
The 317 and 337 pinouts are different. Also if I understand you correctly you are trying to regulate +/- 6 VDC from a +/- 9VDC input which is close to the worst case dropout voltage of the 317. Should work but is a little close. Check the pins and make sure they are connected right on the 317 because that sounds like your problem.
Don't worry, those voltages are well inside the ballpark. You rarely ever get the exact voltages specified for regs, unless you use adjustables and install a pot with it to trim to the exact voltage. Voltages given can be geneerally regarded as approximate and can vary by a couple of 10ths of a volt without problem.If you're going to continue mod'ing and tweaking, and I hope you do, invest in a jeweler's binocular loupe and a couple of dental picks. After soldering put on the loupe and closely inspect for bridges, voids, etc. as you remove the solder flux; saves a lot of grief. You might also want to build a 'Fuse Saver'. Take a junction box and mount a duplex outlet with the outlets electrically separated. Install a spdt switch that allows you to either connect the two outlets in series or bypass the top outlet and mark the switch positions "series/bypass" or "Test/Run".. Buy a light socket that plugs into an outlet and install a line cord and plug to the outlets thru the switch. After mod'ing a unit insert a lightbulb in the top outlet that draws about the same current as the DUT (device Under Test) and plug the DUT into the bottom outlet. Set the switch to "series/Test). Turn on the DUT. If the bulb glows dimly or not at all you can safely bypass the bulb. If the bulb lights brightly you have a short in the DUT but no damage will result as the bulb acts as a current limiting resistor.
Happy Listening !
hi pkell44, thanks for your response. well i found the problem, the pin out specs for the L7806 i got on the net, were wrong. i now have 5.94v. dc which is plenty close enough to my 6 volts i needed. thanks for that light bulb trick, that's very interesting i will have to try that. i have a lighted magnifier but got lazy one time and thats all it took. thanks again alley-kat
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