Looking for any tips on getting the distortion out of the amp. Nationals are a little different than the Panasonics. Service manual or amplifier section would be of interest for purchase.
Those are nice! Never seen one up close. The service manual is free on archive.org https://archive.org/details/manual_RXC300_SM_PANASONIC/page/n1/mode/2up In case your wondering, when I search I do "panasonic rx-c300 .pdf" on google and look at the images. I don't have a ton of service experience outside of basic repairs but whenever I hear distortion or static, I clean the function switches. This has a different set-up with multiple switches but cleaning the (membrane?) contacts might help.
They are pretty cool. Not very portable, more like some hybrid of a small home stereo and boombox. I paid dearly for the Panasonic and then proceeded to put another 400 dollars into it in modifications. I did download the Panasonic service manual and I have some concerns about it. The page for the amplifier shows outlines for many 14-pin DIPs. At least I think that was the pin count. Way more components on the schematics than there are on the board. I believe you may be right and possibly more cleaning is in order. I see that I was wrong in where the headphone jack taps into; it's actually the output of the power amp and not the pre-amp transistors as I'd believed. Possibly the contacts of that jack are corroded. I'm sure it's going to make me feel foolish when it's discovered. I really want to find the schematics for the National, as they are a little different. The way National/Panasonic does the amplifiers is new to me. They have the right and left being handled on the same stereo chip, with two chips in parallel. So, it would seem, you can have bad sound in both channels with only one bad IC. We have very sophisticated repair stations where I work so I may just take the thing in and check it out there. As you said, "lots of switches" all it would take is one dirty set of contacts.
I might be the exception but for most of my stuff it's the easy repairs but they might take forever to figure it out (cars, trucks and tractors also). One little corroded contact can reak havoc, just enough and no closed circuit. The National is most likely on some Japanese Website, maybe searching through yahoo.jp with the same input might work.
Good suggestion on the Japanese approach. I never heard of yahoo.jp. I just figured there was one internet and queries go everywhere. I will definitely share anything I learn with the group and try to spare the next person all this frustration.
If you really want to get into it, get a VPN which will signal your from Japan, sometimes you get even better search results.
Those are one pair of beautiful machines... thanks for sharing the picture! Do they work on batteries? I guess not...
