1. Home
  2. Electronics Repair
  3. Yamaha DSP Amp has hum and low sound on one channel

Yamaha DSP Amp has hum and low sound on one channel

I have a Yamaha amplifier that's about 5 years old. The right channel is normal, but the left channel has a low hum and significantly reduced sound volume/quality.

I've tried the following:

Switched speakers- Not a speaker problem. Switched from A to B speaker output- no change. Tried multiple audio sources and input jacks- Not a source or input jack problem. Tried headphones- Same results as speakers. Hum and low volume, low quality sound. Tried changing DSP program modes- hum stays the same in bad channel, sound changes as it should in working channel. Tried adjusting all knobs including balance- no effect other than as expected. Tried all switches off/on- also no effect other than as expected.

Notes: The hum exists even if no audio source is connected to the unit. The hum does not increase or decrease when I move the volume knob. The tone of the hum changes when I switch into the mode that lets you change the volume of five speaker output channels (front, rear, center) and when I switch from one channel to another. Adjusting the volume of channels otherwise has no effect.

I am a newbie to electronic repair but can read and follow directions and am willing to use this amp to learn on. I don't have any test equipment but would consider buying or borrowing it.

Any help would be appreciated!

Thanks-

Reply to
ElectroNovice
Loading thread data ...

Giving the model number would be useful.

I would suspect probably an edge connector problem or dry joint on a board.(after the volume control so follow the leads from that to the tone board or main board). Its unlikely to be the amp channel itself or the amp protection would have detected a problem and cut out.

AW

Reply to
JVC Dude

Other than a bad connecting cable or two, your chances of fixing this yourself are probably pretty remote. Yamaha's are nice pieces, but even many experienced tech get their comeuppance on these. Yamaha's are rather complicated and difficult even for the professional.

Mark Z.

Reply to
Mark D. Zacharias

Sounds like a leaky capacitor in the left channel of the amplifer. The capacitor may be a bypass filter component that would cause signal attenuaition by either 1/ dragging the supply voltage down if in power supply circuit, or 2/ causing loading of previous stage of amp by bypassing/shunting the signal to ground if found connected across input of each amplifer stage esp. the final power stage.

Reply to
Bobscar

Thanks for the tips. Sorry it took so long to reply...

The model is a Yamaha RX V795.

I will poke around a little (carefully) and see if I can find anything obvious. Thanks...

Reply to
ElectroNovice

I have some used Metcal gear including the Net Power Meter (NPM-50) and the MX-500P. When I connect the NPM in line with either of two handpieces, it shows power levels between 5 and 7 watts. I have not seen it go higher or lower.

Question: is the power supply output low or is the meter faulty ?

While it is possible to solder with a handpiece, I am not overwhelmed with the ability to deliver soldering heat. I would guess it higher than 10W but not 40W. This suggests that the NPM-50 is in error.

The MX-500 power supply draws 40-50 watts from the AC line (using an AC wattmeter between the power suply and the wall socket). The power consumption does not seem to be related to what the tip is doing. I.e. AC input power does not obviously go down when the iron is idling and up when it is heating the work. This suggests that the MX-500 is not up to snuff.

If the MX-500 could only put out, say 7W, then the iron would be getting some power but it would fit with most all the symptoms. What can I measure to know what's up ? Are there some common points of failure on either the MX-500 or the NPM-50 that I should look at ?

George

Reply to
George Pontis

Somewhere in the US Patent index their is a circuit for the Metcal iron.

Andrew

Reply to
Andrew Tweddle

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.