C-2a DIY hack job?

[jdsalinger]

My newly-acquired C-2a has had a loud hum/buzz on the phono, tuner, aux inputs (not on the tape, so I can at least use those inputs)

I found that all of the phono input pins are shorted together and it appears that there was some DIY work done. But there is also some of the factory glue, so that's confusing me.

Can anyone confirm if the pic below looks factory or were the jumper and film caps added afterward? (maybe it's obvious) The solder globs don't look "factory" and I wouldn't think that Yamaha would add a jumper wire or caps on the bottom of the board.

The other thing that is confusing is why the tuner and aux also have a grounding buzz problem. Maybe all the grounds for these inputs are shorted together somehow.

 

[jdsalinger]

OK, looks like the jumper may be original. The pic below is from a Japanese website.
It shows the jumper but no film caps or glue.

 

[avionic]

Factory... I've see those caps before. Some units had them , some didn't. Possible SB mod.

 

[avionic]

The solder globs don't look "factory"

Yes they do look OEM unfortunately.

 

[avionic]

The other thing that is confusing is why the tuner and aux also have a grounding buzz problem. Maybe all the grounds for these inputs are shorted together somehow.

Do you know how to read a schematic ? Most likely the grounds are all tied together.

 

[avionic]

Have a real close examination of the rear RCA jack printed circuit board. I've see burnt ground traces in a couple units in this area before.

 

[avionic]

I use acetone and a cheap 1" paint brush to clean all that reddish excess solder flux from the circuit board.

 

[jdsalinger]

Do you know how to read a schematic ? Most likely the grounds are all tied together.

Yes, I can, and yes, the schematic shows all grounds as chassis ground.
However, measuring shows that the phono inputs share grounds and the tuner and aux share a ground, but phono ground is separated from tuner and aux.

 

[jdsalinger]

Have a real close examination of the rear RCA jack printed circuit board. I've see burnt ground traces in a couple units in this area before.

Yeah, that's the ticket.
I'll just have to reference the pcb trace print and decipher which traces should be tied together and which not. (the one from HiFi engine and the AK database are low res scans).
I'll have to print it out and somehow invert it or invert it in my head.

 

[avionic]

Yes, I can, and yes, the schematic shows all grounds as chassis ground.
However, measuring shows that the phono inputs share grounds and the tuner and aux share a ground, but phono ground is separated from tuner and aux.

Yes it appears to be so.. Look at the RCA jack board..

 

[avionic]

Yeah, that's the ticket.
I'll just have to reference the pcb trace print and decipher which traces should be tied together and which not. (the one from HiFi engine and the AK database are low res scans).
I'll have to print it out and somehow invert it or invert it in my head.

All the free down loaded scans suck..

 

[avionic]

E-mail Norman at https://www.analogalley.com/osccart...id=55&osCsid=d972f3525bc11d49e77cb487bacd489f

Tell him what you need..C-2a SM
These are kick ass color HiQ pdf files. $12-14 is a good deal.

 

[jdsalinger]

well, I discovered that the aux input earth is not connected to common earths. Not sure exactly where the break is. I suppose I could jump it to a good ground. But decided to let it be for now until I have the urge to bring the turntables back into my system. Right now I mainly stream Pandora and Spotify due to convenience.