CSA Thermal protector in Fender PT

[Groover]

the Fender Musicmaster Bass schematic shows a CSA thermal protector which I understand is inside the power transformer, and doesn't appear to be anywhere else so I guess that's where it is. I see this also on the schematic of some SFTR amps.

Can this be accessed and replaced by opening up the transformer end cap or or does it render the transformer "disposable" if it blows?

[Jazz P Bass]

Thermal Fuse

The fuse cannot be replaced.
If you solder on a new one you will destroy it.
I have seen these thermal fuses go for no apparent reason.
Personally, I think the ones that do open (again, for no apparent reason) are not rated properly.
Chinese crap.
If you can manage to peal back the tape on the transformer, you will see the critter.

[Enzo]

CHinese, Schminese. Thermal fuses have been inside power transfomers for decades, CHinese ones, US made ones, ones made most anywhere. They are required by law in some places. I don;t see any more Chinese ones open than US one in the old days.

They blow for a reason, they blow from metal fatigue, they open from mechanical shock.

You can buy thermal fuses - usually called thermal cutoffs - from places like Mouser or MCM. They are rated by temperature, not current.

I have replaced numerous thermal fuses. SOme people maintain that if the transformer got hot enough to open that fuse, then the insulation in the transformer is compromised. I don;t know that I agree with that. I have never had one come back at me after such replacement.

The thermal fuse looks like a silvery diode most times. it is tucked down within the windings, and may or may not be readily accessible. it won;t be out and visible, you find it by its shiny leads coming out of the innards and soldering to the little terminals for the winding wires. If you can fish it out, you can fish a new one in.

I solder to them, use an alligator clip as a heat sink right by the body of it on its lead.

Often to get at them, you have to cut through the fish paper and tape. You then must repair that.

[Gtr_tech]

Just for reference, I saw therm cutoffs at rat shack when I was in there yesterday. I didn't look at the temp tho...they may be intended for coffee makers and the like so they'd be useless for xfmr replacements.

[Dave Curtis, dB AudioTech]

Just for reference, I saw therm cutoffs at rat shack when I was in there yesterday. I didn't look at the temp tho...they may be intended for coffee makers and the like so they'd be useless for xfmr replacements.

You might be talking about a Klixon; a thermal switch that opens at a preset temp. They also look similar to a diode.

[Enzo]

The thermal cutouts inside transformers do not reset themselves when cool.

[Dave Curtis, dB AudioTech]

The thermal cutouts inside transformers do not reset themselves when cool.

Correct, I didn't mean to imply that. There are, however, some that do. Maybe not used in MI gear; fluorescent ballast transformers come to mind. The Behringer bass amp I just worked on had a thermal (113C) in the tranny, but I would guess it's a one time "fuse".

[jrfrond]

Yes, thermal links have been in transformers for years. Even though you can often access them, occasionally having to peel back insulation tape, what everyone must know is that replacing them is illegal. If you are doing it for yourself, that is one thing. However, if you are a working tech, or own a shop, you should know that if anything happens as a result of replacement, you can get royally screwed.

This is one of those repairs I just will not do, because it violates the Standards codes. Another on is 120/220 transformer conversion. Unless a unit was designed to be switched and passed Standards tests, whether they are UL, CSA or CE, voltage conversion can also be a legal issue.