Panasonic RS-820S

nabeelsayegh

AK Subscriber
Subscriber
Hello AK...

Hoping to get some help with a problem I am having with this guy. When you power the unit on (after a few seconds) there is a white noise/hiss the comes through both channels evenly. You can hear is with the volume all the way down and gets very loud when you turn the volume up (with Aux input selected. You also hear it on Phone, tape and in the background when AM or FM is selected.) If you put the balance all the way to the right, you no longer heard anything in the left speaker. Opposite is true if I have the balance all the way to the left; the right channel goes quite.

As a result of the balance making the output go quiet, can I assume the amplifier and power supply sections are not the cause of this? If I am correct, any pointers on where to look?
 
It's normal to have left and right w/balance knob maxed either way for the opp channel to be silent. As for the hiss could be any number of things.
 
Appreciate the response. I expect it to be a possible number of things. I also expect it to be a leaky/noisy transistor, but the fact that it is happening on both channels has be a bit concerned. This thing is loaded with a number of 2SB346 and 348's. I replaced one (the pre-amp) with an NTE102A and the ramp time for the white noise in that channel seemed to slow. I also replaced coupling caps, main filter caps and nothing seems to be making any real change. What I am afraid of is that ALL of these transistors may need to be replaced. My scope is showing the white noise in varying locations and amplitudes on the amplifier board.
 
I studied Ge transistors today; more the sale cost and availability? (your schema is very small when enlarged, at least you have one.)

Try this guys test and 'treatment' for 'hissy' Ge's. just down page a little but explains the cause of the hiss. worth a shot against cost of shot gunning.
http://www.markhennessy.co.uk/articles/vintage_transistors.htm

Save any old ones that don't pan out... they can be used in guitar 'hot rod' apps like foot pedal fuzz boxes (no shi* the noisier the better apparently.)
bink
 
That is an outstanding article and did provide some insight. My original thought was that it should be an upstream transistor because the white noise can get very loud when you turn the volume up. but I guess the reality is, it could be any of these prior to the main outputs.
 
Does this unit have any carbon comp.resistors in it? They can also contribute to the problem with hiss as well as noisey transistors.....
 
I wonder if OP tried the fix in my link. Seems a plausible fix as author swears by it.

Where abouts are you located in NC?
 
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