C70: Fuse Blew

[bberkom]

The C70 is a great preamp. Avionic is the man when it comes to restoring these Yamaha pieces and has helped me with a few issues on Audiokarma. I hope you can get it sorted out.

 

[Gary D Olson]

This photo shows a space on the C70 board that looks like something once occupied it but was ripped right off. I certainly didn't remove it, so then how is it that this unit has performed well over the past few years? Baffling.

C70 Missing Part

• Gary D Olson
• Apr 30, 2020
• 1

 

[avionic]

No.... Nothing is suppose to be there.

 

[Gary D Olson]

You mean as in "poof"? After you had me remove the 1st two caps...

View media item 21868

 

[avionic]

I just checked one of my C-70's .. There are no components residing in those positions.

 

[Gary D Olson]

Thanks. Previous owner's schmutz.

 

[avionic]

Check the integrity of that long jumper wire with the oxidized ends . Make sure the soldered ends show continuity. As well as that 18K Ω ( Brown/gray/orange/gold) resistor with the corroded lead. What did the bottom side of that small cap between the two larger caps look like.Scrape off all that dried glue.

 

[clinic-audio]

Hello

I pm'd avionic about sending my C70 off to him for rescue.

Remember what I said post #4

You will save time and money , no need to find possible banks to rob

 

[Gary D Olson]

Check the integrity of that long jumper wire with the oxidized ends . Make sure the soldered ends show continuity. As well as that 18K Ω ( Brown/gray/orange/gold) resistor with the corroded lead. What did the bottom side of that small cap between the two larger caps look like.Scrape off all that dried glue.

Continuity check of that jumper from the back of the board is 0.000v. I'm guessing that's not good?

The resistor is reading 6.7 ohms and going by your 18k reference, probably not good too?

 

[avionic]

Continuity check of that jumper from the back of the board is 0.000v. I'm guessing that's not good?

Continuity check with the ohms function.

The resistor is reading 6.7 ohms and going by your 18k reference, probably not good too?

Out of circuit...Ohms check..

 

[avionic]

Should be zero ohms from one solder pad to the other solder pad on that jumper wire.

 

[Gary D Olson]

Continuity check with the ohms function.

Out of circuit...Ohms check..

"Continuity check with the ohms function" 6.7 ohms

 

[Gary D Olson]

"Continuity check with the ohms function" 6.7 ohms

between 0 and 0.2

 

[Gary D Olson]

Should be zero ohms from one solder pad to the other solder pad on that jumper wire.

Post 92 was about the resistor

the jumper reads between 0 and 0.2 ohms

 

[avionic]

between 0 and 0.2

Thats good..Some times the corrosion seeps down into the solder connection and oxidizes all the lead (Pb) and leaves a tin(Sn) cold solder connection.The tin doesn't unsolder ..

 

[avionic]

Post 92 was about the resistor

Pull one end of the resistor loose and remeasure it. Its probably still around 18KΩ..+/- 5%
(gold band)

Out of circuit...Ohms check..

You can't really accurately check a lot of components" in circuit"..

 

[Gary D Olson]

Pull one end of the resistor loose and remeasure it. Its probably still around 18KΩ..+/- 5%
(gold band)


You can't really accurately check a lot of components" in circuit"..

17.75ohms

 

[avionic]

17.75ohms

Check your multiplier indication on your meter..17.75 K Ω ... Still within tolerance..

 

[Gary D Olson]

Check your multiplier indication on your meter..17.75 K Ω

17.6 k

 

[Gary D Olson]

Nobody's questioning my incompetency.