This Roland JC120 is smokin'

[christarak]

I'm hoping you can help me identify a couple of components on the output section of one of the channels of a JC120. (I never realised how many variations of JC120 there are. )

As you can see in the photo R73 has been sending up smoke signals, and C35 is doing a Chernobyl. I found a JC120 problem on this forum from 10 years ago so I'll replace Q14 & Q15 with TIP41&42C's, and the power transistors with MJ(E)15023/24, the electrolytics around there, and R73, 74, and ...which leads me to my question:

What is R71 doing humping Q14? I assume its some sort of temperature dependent resistor.
The schematic shows 47R with an F in a circle, which I assume is a hieroglyphic for an ancient unit of temperature measurement. Can I reuse this thing? How do I specify it if I need to buy a replacement?
R75 and R76 are similar resistors. Is 10R its ambient Temperature resistance?
Does the resistance go up or down when it gets hot?
Looking at R71, I would assume that if too much current goes through it, then it would make sense that the resistance would drop, bypassing D2 and shutting off Q14. But then I look at R75 and I can't see what would be the benefit of R75 dropping in resistance.

[g1]

The Fu type is fusible, the F type is flameproof.
Someone has upgraded R71 from the original flameproof design, to a temperature dependent type. It may have been a factory improvement, or someone's upgrade mod.
It adjusts the bias to prevent thermal runaway and overheating.
It should be re-usable if it reads somewhere around 47 ohms. You can also heat it up with a hair dryer or something to see if it is changing with temperature.

[christarak]

The Fu type is fusible, the F type is flameproof.
Someone has upgraded R71 from the original flameproof design, to a temperature dependent type. It may have been a factory improvement, or someone's upgrade mod.
It adjusts the bias to prevent thermal runaway and overheating.
It should be re-usable if it reads somewhere around 47 ohms. You can also heat it up with a hair dryer or something to see if it is changing with temperature.

Thanks for that. I'll check that resistance.