Onkyo P306RS Preamp Left Channel of Phono stage Popping and Hissing.

[Territup]

Hello I have a problem with an Onkyo P306RS Preamplifier Everything works perfect on it accept when the input is set to phono the Left channel pops and hisses and blows the over protection on my Amp which is an Onkyo M-5030. It is only there when you turn up the volume and when nothing at all is connected to the phono Inputs its still there I connected my turntable and the right channel is fine but the left is just the Distortion seems to not be getting any signal input from the left input.Its got me stumped because it is only when it is on phono I haven't had it long i just didn't have a turntable so I never tried the Phono stage on it . Anyone have an idea where i would check for distortion on just he phono section it sounds like a leaking cap but this Preamp is pretty complex it shows in the service manual the phono section has 2 of the super servo circuits in it which are all in there own orange plastic cases under the Huge Metal Plate which is to just block out external distortion from outside devices etc. The plate weighs about 20 lbs and has a screw securing it to each or the Super Servo Amps like its a heat sink but it isnt the part it screws to are plastic. If anyone has any experience with these preamps it would be greatly appreciated if you could tell me where to start etc. And also i was wondering if an old 5mhz Scope would be good enough to possibly help in troubleshooting the older amps and preamps . All i have at the moment are two 5meg scopes ones a Ilco Model 460 and the other is a Heathkit IO-5205 lol, I'm Showing my age here lol. Any help would be appreciated.

Thank You!

[redwire]

Re: Onkyo P306RS Preamp Left Channel of Phono stage Popping and Hissing.

I could not find a schematic for Onkyo P306RS. I did find Onkyo P3060R and assume it is similar.

It could be dirty switches or a failed semiconductor, probably not caps.

It's a DC-coupled preamp and any imbalance would go through to the outputs. If the power amp is also DC coupled, it will trip its protection circuit as the DC offset just propagates through.

The phono preamplifier left channel needs work, I would measure voltages on the transistors. You can compare to the right channel. Also measure the phono input RCA jacks to see if there is DC offset there. If so, do not damage your phono cartridge if it got say >10V. ESD can damage the input JFET 2SK148 but rare and hard to find that part.

There is one DC null trimpot and a servo-amp trimpot just for the phono preamp; same for the preamp output amp. If they were out of adjustment, I wouldn't expect popping noise.

The diyaudio site might have people there who know more.

[Territup]

Re: Onkyo P306RS Preamp Left Channel of Phono stage Popping and Hissing.

Thank you Redwire the schematic i found is for the p-3060 too. It has the discharging hissing popping sound from the left channel even without any input on it so it does it without the turntable even connected. You don't hear it unless you start turning up the volume then it will blow the amp protection and the Amp is a Onkyo M-5030. I cant see where the phono section is on the schematic is it the section right under the equalizer section on the schematic? it shows 2 servo amps in it but there are like 6 inside of it all mounted under a huge metal plate each servo amp is in a orange plastic box that the cover is removable. The metal plate screws into each of the plastic covers, it isn't a heatsink it is a shield for external interference is what I have read. Where do you suggest I measure voltage at on it ? Thanks for your help.

[redwire]

Re: Onkyo P306RS Preamp Left Channel of Phono stage Popping and Hissing.

The phono-preamp is called "equalizer amplifier" on the schematic. Higher level signals like Tape, Aux, Tuner etc. go right past it as they don't need an extra amplification stage.

It looks like the amplifier sections are in black shielded boxes? Around them looks like servo circuitry, in this picture I found.

I'd take the covers off, to access the phono sections. Parts nearby matching the schematic would tell you if you are in the right section. i.e. twin capacitors C301, C303 are left servo caps. I think the phono modules are nearest the center chassis bar. Or post pictures, that would help.

The main risks here are static electricity- touch earth ground somewhere before touching the insides.
And making sure the filter capacitors have discharged for a while before poking around.

[Territup]

Re: Onkyo P306RS Preamp Left Channel of Phono stage Popping and Hissing.

Thank You Redwire, The boxes are orange and say servo amp on them. I will take pictures tomorrow and post them mine is a little diff than the photo you posted.

So I think the whole left circuit board is for the phono section like you said. I thought it was just a part of it not the whole thing lol .It makes more sense now I will post the pics tomorrow. It might just be the switches need cleaning I have to get some deoxit and clean them but when i hook the turntable up I didnt hear any music just the leaking noise and popping. I got to order the cleaner online im in Alaska and no where has any here lol. The switch connects to a ribbon cable like a mechanical ribbon cable that goes to a switch on the main EQ board. Should i clean that also or just the switch contacts I have never seen a setup like it before.

Thanks for your help again it is really appreciated.!