Marantz model 26 receiver: Almost done

[Alex_Baker]

Here I will try to compile a list of things I know, and from there we can try to narrow down the options for the noise source.

-The background hiss is independent of volume setting(with inputs grounded, there is extra noise otherwise)
-The balance control will cut out the hiss by turning it all one way or the other.
-Both the treble tone knob and the high filter switch has an effect on the hiss, though the tone knob not as much.
-Grounding J414 with a 0.1uF ceramic cap removes 90% of the hiss(what I would consider to be normal with vol control at min)
-Grounding J412, J410, J406 or J404 has no effect(again with the 0.1uF cap)
-Grounding J408 cuts the hiss down by about half(with the 0.1uF cap)

I am not sure what to make of this, how would grounding J408 have an effect on the hiss but not J412, which should be further down the line?

The other annoying noise besides the hiss is a 120Hz hum, which mostly goes away if I touch the chassis, could it be related to the 2.2M resistor R011 on the mains side of the transformer?

[strawberry]

noise is amplified

[El Rubio]

I don’t want to point out the obvious, but have you inspected the solder side of the boards? Specifically for lifted traces? I would look closely at all of your solder joints as well as confirm polarity on electrolytics ( not trusting the silk screened labels) .  I had recapped a receiver several years ago. It was completed and I was finishing up the alignment process. At the time, I had a shelf above my workspace made from that vinyl coated wire shelf that you can get at home depot. I would hang small wire cutters and pliers on the front edge. I had a particularly long needle nose that was top heavy. I bumped it, it fell into the receiver. Sparks flew and it was dead. It blew out a fused resistor and a zener in the PS. Got the power restored, but had low output and a hum. I stumbled upon a switch housing that was not grounded ( but should have been). Tracing that, I found the ground for the entire input board with the RCA jacks was broken. It was a trace on the board that was very thin and not easily noticed that it was broken. Jumpered that and all was well.
So, never store things that can fall above your workspace, and closely inspect your previous work. If you get frustrated, walk away for a few days. Don’t get discouraged and keep at it. Good luck.

[Alex_Baker]

Thanks for the tips.

Every thing is fine on the other side of the board, and I double checked the caps after I replaced them. Funnily enough thee was a mistake on the silkscreen from the factory, three 407uF caps on the power supply board were labeled wrong and I did not check them, two minutes later I got a face full of capacitor steam. Needless to say I did not pay attention to the silkscreen after that.

Honestly though, as a whole I am not impressed with the circuit design and fit and finish of this Marantz, I though they were supposed to be top of the line but the more I work on it the more it feels like a Marantz badged Panasonic, they both came from japan after all.

[strawberry]

schematic C407

[Alex_Baker]

I just realized today that I had some signal wires crossed that go to the amplifier board, so I fixed that. Grounding the different pins with a cap still nets the same result though.

[El Rubio]

I always take photos before I work on something just to be sure. Some guys will take a sharpie and put a dot on the board near either the pos or neg side of each cap. There are lots of silk screen errors. If I’m not sure, I find it on the schematic and trace out the position on the board. Do it enough and you will not forget to take the pics, lol.

[rsjsouza]

I don’t want to point out the obvious, but have you inspected the solder side of the boards? Specifically for lifted traces? I would look closely at all of your solder joints as well as confirm polarity on electrolytics ( not trusting the silk screened labels) .  I had recapped a receiver several years ago. It was completed and I was finishing up the alignment process. At the time, I had a shelf above my workspace made from that vinyl coated wire shelf that you can get at home depot. I would hang small wire cutters and pliers on the front edge. I had a particularly long needle nose that was top heavy. I bumped it, it fell into the receiver. Sparks flew and it was dead. It blew out a fused resistor and a zener in the PS. Got the power restored, but had low output and a hum. I stumbled upon a switch housing that was not grounded ( but should have been). Tracing that, I found the ground for the entire input board with the RCA jacks was broken. It was a trace on the board that was very thin and not easily noticed that it was broken. Jumpered that and all was well.
So, never store things that can fall above your workspace, and closely inspect your previous work. If you get frustrated, walk away for a few days. Don’t get discouraged and keep at it. Good luck.

These are indeed excellent tips for repair, in particular the last one. Frustration and tiredness are the biggest enemies of any meticulous work. 

For capacitor polarity, I usually scribble on paper a map of the board and the polarity of capacitors as I was also burned by bad silk screens - things blew up on my face due to that.

[Alex_Baker]

Does anybody have any idea as to why grounding J408 with the 0.1uF cap would reduce the hiss but not J412?

If I ground J412 without the cap in series all the noise goes away, likewise grounding J408 also without the cap still cuts the hiss in half. Does this suggest that both the tone control pots and the second preamp stage is the source of most of the hiss?