My PT is dead but reads fine. WTF?

[Baguette]

So I have this 90' Fender Super 60 PT ar home.
The thing does not yield any voltage at the secondaries (actually, it yields around 50mV at the HV tap).
When I measure the resistance of the windings, they all read fine : around 7 ohm at the primary, around 100 at the HV sec (of course I can't read the 6.3V since this wire is so big it doesn't have much resistance). This makes my think all the windings inside are fine as nothing is open. Still, the big black thing does not work.

How could you explain?
Can a PT blow without any wire opening?

Thanks!

[sluckey]

How are you applying voltage to the PT?

[Baguette]

I feed it with my 230V wall voltage.

[jojokeo]

Trannies fail in two ways, open or shorted. Is it possible it could be shorted giving you a reading in that way w/ your ohm-meter? If left plugged in what happens? Does it get hot w/out a load on it? Are you getting voltage readings on other taps/windings? Sometimes certain trannies have a fuse wired into them under the wrappings too. People will throw them away w/out really checking or disecting them.

[phsyconoodler]

Does it have an MOV to protect the PT in cases like this? It may be you just have a blown MOV or it may be inside the windings of the PT itself.Depends on the amp.I'll take a look at a super 60 schematic and see.

Took a look.It has some fused protection for the export models.Where this is in your amp is where you may find the issue.Or not.It may still be a bad PT,but there are a couple of 'fuse like' devices on the schematic.

[sluckey]

Just to be clear, do you have only a PT, or do you have a PT that's connected to a chassis or circuit? I had assumed you only had a PT.

[sluckey]

I've looked at the schematic and drawn a simplified hookup diagram. (I'm also assuming you have the export PT since you are connecting 230V to the primary.) This diagram should help. BE SURE TO JUMPER THE BLK/BRN AND BLK/YEL WIRES!

[Baguette]

Yes, that's the PT I have (Super 60 export). and that's the way I tested it (no load, just the 230 feeding the primary (black / red and black / yellow jumpered).
None of the primaries give a reading (a few mV for the HV).
The internal fuses are all ok. Some ass replaced the main fuse with a 5 amp unit (VS. 1.5A recommended). I guess it killed it.


What is a MOV?


(those red knobs Fenders are a PITA to diagnose and repair BTW).

[sluckey]

just the 230 feeding the primary (black / red and black / yellow jumpered

You had it jumpered wrong and the two primaries just cancelled each other since they were 180° out of phase. Try again, but jumper the black/yellow and black/brown wires. Connect one line to the black/red and connect the other line to the blue (or white) wire.

[Baguette]

Thanks for the answer mr Luckey. The damn thing seems to deliver good voltage now.
The thing is I just don't know how comes the amp was not working (No light, no sound, no voltage at the secondaries, no nothing) and all the fuses were ok.
That's a real headscratcher.

Thanks all for your help.