Luxman L3 problem

[Amapola]

Hi there,

Suddenly on a L3 220v version (with p-2251 power transformer) i had a blown fuse (f001) 1a.

I just changed this fuse 1 time ; and the same...

I checked on the power board ; all transistors are ok expect q407a and q470b. All diodes and bridge are ok.

I decided to put out the q407a and q408a ; and same for "b".

I placed a new fuse of 1a ...and for now no sign of life...

Anyway , after putting light in my brain... if this fuse has blown, the problem comes from before the fuse...so the power transformer

In fact, i've on primary 11ohm

secondary : 1.2 ohm for red wires which supply the rectifier bridge
2.5 ohm for blue wires

I've also measured the resistance of the primary through the mains plug with switch off "nothing" (there it's normal) and on; I have 11.3 ohm.
But if 11.3 ohms are found in the "on" position, the on switch is ok; true?
So the mistake dont come from the on/off switch...

I desoldered the secondary from the power board ; but for now no sign of life with this power transformer ! When i push "on" , nothing...

In normal work, a power transformer make always a little noise (about 50hz) ; and there 's nothing.

What do you think about ?
Anybody can confirm whom power transformer is out ?

Thanks in advance for light

[Helmholtz]

It is not possible to tell if the PT is defective from your DCR readings. Most probably the PT is ok, if/as the mains fuse no longer blows with secondaries disconnected.
With both red secondary wires disconnected from the board, what are AC voltages between each red wire and ground/black wire?

[Amapola]

The mains fuse no longer blows even with i push last time with the secondary wires connected .

In that case, i couldnt take values of voltage ...

For info, am in 240v area , and i just saw this amp was a 220v version...!!?? All my vintage amps have multi voltage selector expect the luxman... with time i think it's a good way to destroy a PT ; no ?

[Helmholtz]

In that case, i couldnt take values of voltage ...

Sorry, I don't understand why. If the mains fuse doesn't blow with secondaries connected, measure AC and DC voltages.

i think it's a good way to destroy a PT ; no ?

Very unlikely. But in rare cases higher mains voltage might cause the mains fuse to blow.

Disconnect speakers while troubleshooting.

[Amapola]

Sorry, I don't understand why. If the mains fuse doesn't blow with secondaries connected, measure AC and DC voltages.



Very unlikely. But in rare cases higher mains voltage might cause the mains fuse to blow.

Disconnect speakers while troubleshooting.

Since, i pulled out the 2 q407 and 2 q408... at this step, the amp is ok when it's turn "on"...the fuse still ok. I'll check the differents voltages ...