Hi there to anyone who reads this post I hope you may be able to help I have a laney powered mixer and on power up there is a loud buzz coming from the output and low volume with distortion to the input signal.I have done a few tests and have found no -15v d.c. on the output leg of the lm7915 so replaced it but to no avail if you've seen this type of fault or something similar and may be able to give me some pointers please get in touch.
Many Thanks Big Zab.
Many Thanks Big Zab.
If it is over five years old you could check the electrolytic filter capacitors in the power supply circuit. They are between the rectifiers and the 7915 regulator. If you don't have a $150 high value capacitance meter with ESR measuring function (I don't) you could just replace them. Shorted filter caps often also take out the rectifier, so check it for forward drop (~600 on silicon or less on schottky) and backward impedance (1000000 or up). All my consumer quality devices, I just replace all the electrolytic caps at 15-20 years, but some devices come with them low value producing ripple right from the store.(Like my Apex DTV converter from W*** M*** with diagonal lines the first 5 minutes). At 15 years or so the rubber seals age crack and the water leaks out, which is the insulator. There are good caps available with better sealant than rubber, but consumer devices don't have them.
If it has a switcher power supply (little toroids instead of and E frame transformer) the caps usually take out more stuff than the rectifier. I can't fix those yet, myself. Never any schematics on this consumer ****.
If it has a switcher power supply (little toroids instead of and E frame transformer) the caps usually take out more stuff than the rectifier. I can't fix those yet, myself. Never any schematics on this consumer ****.
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You found no 15v on the output of the regulator, but did you check the input pin of the regulator? If there is no voltage there, it can;t put any on the output.
Hi thanks for the replys there is -29v appearing at the input pin of the regulator but zilch at the output pin maybe 0.6v not sure if my dvm is just picking that up from elsewhere all help greatfully recieved .By the way this P.A. is just out of it's warranty ("always the way") and it's for a local jam night which i help to run on a shoestring budget so hence that's why I'm attempting to have a go before we have to send it back to Laney.
Regards Big Zab.
Regards Big Zab.
-29 volts on the input side of the voltage regulator is quite high - so the 7915 regulator will run HOT, unless attached to a very big heat sink.
I would suspect that it might have failed - but do ensure that there isn't a short circuit on the output side before replacing the regulator.
If you can disconnect the output load - this will help prove the fault.
Don't forget that the pin configuration of the 7815 and 7915 are different.
I would suspect that it might have failed - but do ensure that there isn't a short circuit on the output side before replacing the regulator.
If you can disconnect the output load - this will help prove the fault.
Don't forget that the pin configuration of the 7815 and 7915 are different.
They run hot if the output is loaded, but they run cold if they have failed open inside.
How far out of warranty is "just"? I run a pro audio shop and do warranty work for many brands. None of them are looking to anger their customers. If the warranty expired a very short time ago, contact the company and ask for special consideration. I usually do this for my customers, but sometimes they show up with a letter from the factory offering special "one time" warranty service past the coverage date.
How far out of warranty is "just"? I run a pro audio shop and do warranty work for many brands. None of them are looking to anger their customers. If the warranty expired a very short time ago, contact the company and ask for special consideration. I usually do this for my customers, but sometimes they show up with a letter from the factory offering special "one time" warranty service past the coverage date.
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