Yamaha C-85 - No Ouput

[beaminge36]

Hi,

I took an M-85/C-85 setup from my dad a while back because it stopped working. I plugged audio directly into the amp and it’s fine. I decided to open up the preamp and found two burnt resistors. Can someone tell me what these are and if the heat sinks are supposed to be moving like this? Video below. Also, are these larger caps supposed to be bulging like this?

TIA,
Nick

 

[avionic]

4.7KΩ 1/4 watt carbon film.There corroded from the glue around the heatsink usually..Seen it many times.. Replace with metal film..

 

[whoaru99]

And the caps are not bulging. It's just the top plastic covers have warped.

 

[avionic]

, are these larger caps supposed to be bulging like this?

It is usually just the warped plastic dust cap that pops up. Underneath the aluminum is usually flat as new.

 

[avionic]

Can someone tell me what these are and if the heat sinks are supposed to be moving like this?

No.. They were glued down.The glue no longer holds them down..Need to check and likely resolder those two transistors solder connections and then reglue them down.I use Ultra Black Permatex (sensor safe).. While your in there remove all that dried up glue.It promotes corrosion on anything metallic it comes in contact with. Including those anodized heatsinks.

 

[avionic]

decided to open up the preamp and found two burnt resistors.

You are refering to the two small resistors right next to the heatsinks ? Correct? The video just shows you wiggling the two heatsinked transistors.

 

[avionic]

I decided to open up the preamp and found two burnt resistors.

These two 1/4 watt resistors..? Slopped over glue usually corrodes the leads to the point of failure.

 

[beaminge36]

Thanks for the quick reply! Yes, the two resistors by the heat sink. I’ll hunt on mouser.

.

 

[avionic]

https://www.mouser.com/ProductDetai...=sGAEpiMZZMu61qfTUdNhG9FodMeJR7x9NX6bNwTFRx0=

 

[avionic]

Need to check and likely resolder those two transistors solder connections and then reglue them down

 

[avionic]

Get this at your local autozone or advanced auto store.. Low odor and sensor safe.To re-secure those heatsinks. Remove heatsinks and scrape off the glue and oxidation.Maybe give the transistors a fresh coat of thermal compound.( the messy white stuff) Glue them down in there correct places. When the adhesive has fully cured. ( about 12 hours)Then resolder the transistors. **** Just a little of the permatex per heatsink is all you need **** When this stuff fully cures the heatsinks won't be wiggling any more..

 

[beaminge36]

https://www.mouser.com/ProductDetail/Yageo/MFR-25FTE52-4K7?qs=sGAEpiMZZMu61qfTUdNhG9FodMeJR7x9NX6bNwTFRx0=

Thanks again, this is all super helpful!

While I have your knowledge flowing, what’s the best way to fix this? One of the rca inputs on the amp is missing the outer metal cap. Is this something I can just buy and pop in or do I need to replace the entire rca input piece?

 

[avionic]

Is this something I can just buy and pop in or do I need to replace the entire rca input piece?

Replace the entire piece with a parts unit donor or after market modification--> upgraded RCA jacks.

 

[avionic]

These two 1/4 watt resistors..? Slopped over glue usually corrodes the leads to the point of failure.

View attachment 1818047

Have a close look at the leads for those two film caps that are parallel with the two resistors. Sometimes they too are corroded by the damn glue.

Just in case....
https://www.mouser.com/ProductDetai...=sGAEpiMZZMv1cc3ydrPrF2CPLAojp4yW29gRXGnm4As=

 

[beaminge36]

Replace the entire piece with a parts unit donor or after market modification--> upgraded RCA jacks.

Thanks. Any idea where to find a replacement? Everything I find on mouser has only two pins. I found similar parts on eBay and amazon but it’s direct ship from Hong Kong with 1-2 month lead time.