Ibanez TSA15H Blowing fuse when B+ is connected

[Saransk93]

I have an Ibanez TSA15H coming in that apparently is blowing a fuse when the B+ is connected, even with the tubes removed.
It may be a bit premature since I don't have the amp apart on the bench, but even without knowing if it is either the primary or B+ fuse, with the tubes removed I'm a bit stumped as to what could cause either fuse to blow when there is no real load on the B+ line.
The amp is just about a year old so I don't think it has been abused.

I've seen a couple of threads elsewhere that the B+ fuse was originally undervalued at 500 mA and there was a tech notice to increase the value - it would great if that was the issue.
I'm hoping that the output transformer isn't toasted although a 6V6 output isn't that expensive.

Any ideas or "history" on fuse issues

thanks
Mike

[alexradium]

I have an Ibanez TSA15H coming in that apparently is blowing a fuse when the B+ is connected, even with the tubes removed.
It may be a bit premature since I don't have the amp apart on the bench, but even without knowing if it is either the primary or B+ fuse, with the tubes removed I'm a bit stumped as to what could cause either fuse to blow when there is no real load on the B+ line.
The amp is just about a year old so I don't think it has been abused.

I've seen a couple of threads elsewhere that the B+ fuse was originally undervalued at 500 mA and there was a tech notice to increase the value - it would great if that was the issue.
I'm hoping that the output transformer isn't toasted although a 6V6 output isn't that expensive.

Any ideas or "history" on fuse issues

thanks
Mike

old fuse blows sometime,but when you replace it its sorted out,then it can be a shorted rectifier,faulty main capacitor,defective HV secondary.

just use a bulb limiter in series with mains voltage.

[vintagekiki]

F2 (0.5A) fuse must be slow (T) not fast (F).
If F2 (0.5A) fuse blows when STANDBY (SW2) is OFF check / replace D5-D9 (1N4007), C27 (47u/450V), and eventually C42 (.1/1000V).

https://music-electronics-forum.com/showthread.php?t=36807&p=408014&viewfull=1#post408014
http://el34world.com/Forum/index.php?topic=25027.0
TSA15 Schematic

[The Dude]

The B+ is fused pre-rectifier on the transformer secondary, so you could have a shorted rectifier diode or diodes.

[Saransk93]

The fuse that blows is the Primary - F1
I have to go out and find replacements because the fuses are the smaller metric size
There is no apparent failure, blown component, etc.
Since the fuse blows without the tubes, doesn't blow if the B+ from the transformer are disconnected, it most likely has to be in the rectification circuit.
I want to see what happens when I put in a known "slow-blow" fuse and put it on a "lamp limiter."
I also want to look underneath and see if there is a visible clue - or even something like a pinched wire.ne "weirdness" is that, while shown on the schematic, the 470 ohm Screen Resistors are not installed.
While I haven't found a definitive photo, I don't see them installed in any "gut shot" and I wonder where they would be.
There are a couple of other errors on the schematic that don't match the boards - such as the connection numbers for the heater circuit - so this might be the case.

I think it is a simple error, just figuring out what it is without a real visual failure will take time.
Thanks Mike