Luxman L-30 power supply transformer problem!

[cademan]

I'm thinking of 20 other possible suspects but first check to see if you get any music out of it. If you say its humming but your speakers are not smoking or blown due to excessive DC then you should be ok to try a cd or something. Try that first. Will just have to plan on doing a process of elimination over the internet.

 

[glen65]

no hum before the 'pop', just right after it!

Did you pop both channels or just one?

 

[johannesnic]

I still think it is not getting clean DC, that is why I hear a hum on the headphones steady as soon you turn the amp on unchanged on all channels, but I also think it just could be only in the pre-amp and therefor feeds the main amp with just that signal, I am not an expert but want to know what is really going on here and thank you all for you input, because that brings me on new possibilities.

 

[johannesnic]

I think both channels popped and when I decided to remove the amp from the speakers, I replaced it temporary with a pioneer SX880 for now but shortly after using this other receiver the left loudspeaker tweeter stopped working and had to replace a blown tweeter so I don't trust it at all.

 

[glen65]

I still think it is not getting clean DC, that is why I hear a hum on the headphones steady as soon you turn the amp on unchanged on all channels, but I also think it just could be only in the pre-amp and therefor feeds the main amp with just that signal, I am not an expert but want to know what is really going on here and thank you all for you input, because that brings me on new possibilities.

That could be, or you could have a bad grounding or connection point someplace. If both channels are being affected in the same way, you would need to look at things which would have that effect on both at the same time. The power supply would be one of those areas.

 

[johannesnic]

exactly!

 

[johannesnic]

Tomorrow I am going to check a few things we have discussed today here and I will get back , but for now I am going to bed.
Thank you for all your comments so far, any input is much appreciated..

Johannes....

 

[mbz]

Suggest check the power supply, amp powered off and unplugged.
- Diode test D204, both directions, in circuit ok
- Diode test Q209, best to remove from circuit, looking for a c-e short
- have C218,9,220 (all 220uf/50V) been replaced?

 

[johannesnic]

Hi good morning all, D204 in diode check measures 577 in one direction and nothing in the other.
Q 209 is a brand new transistor C 560 Philips and checked before I put it in.
C218/9,220 all have been replaced and checked before they were installed with better voltage ones from Nichicon Gold.

 

[johannesnic]

F205 measures 10.6 ohms for that 0.1 amp fuse, looks high to me as it is just a fuse. I did check that fuse before but because it is not really faulty , I did not bother replacing it.
I just measured a brand new 0.25 amp fuse and it is 3 ohms, I don't happen to have a new 0.1 amp fuse here right now to replace it with.
Could I try testing with the 0.250 amp fuse to see if the hum disappears or would that be too much of the good here?
Further I have installed the main power supply caps in place, to try testing the voltages again.

 

[glen65]

F205 measures 10.6 ohms for that 0.1 amp fuse, looks high to me as it is just a fuse. I did check that fuse before but because it is not really faulty , I did not bother replacing it.
I just measured a brand new 0.25 amp fuse and it is 3 ohms, I don't happen to have a new 0.1 amp fuse here right now to replace it with.
Could I try testing with the 0.250 amp fuse to see if the hum disappears or would that be too much of the good here?
Further I have installed the main power supply caps in place, to try testing the voltages again.

Looks like it's not making good connection creating some resistance. Make sure the meter probes are clean. Check the reading with the probes shorted.

 

[johannesnic]

Just checked, it reads 0.7 ohms if I short the probes.
I maybe need a new battery in my meter, it is asking me to replace it already for awhile.
The reading stays the same on the fuses

 

[glen65]

Just checked, it reads 0.7 ohms if I short the probes.
I maybe need a new battery in my meter, it is asking me to replace it already for awhile.
The reading stays the same on the fuses

Unless they are gold plated, clean the probe tips as well using something like a fine steel wool pad.

 

[johannesnic]

I have just turned the amp 'on' with all the fuses removed and I measure 35.6 volts on F201,202,203 and 204.
That is with the fuse removed at F205 as well and the Main caps 3300mf installed in the circuit again.
I do not hear a hum on the headphones and everything is quiet.
I am going to do this again with a new fuse installed on F205 and check if the hum is back, wish me luck.....

 

[johannesnic]

O and F205 is measuring without the fuse installed at the moment 35 volt AC.

 

[johannesnic]

Ok I just did it!!!!!
I have installed the new fuse on F205 and turned the amp back 'on' with the headphones on and it is quiet now without the hum.
Now I will measure the voltages again on the fuses 201 to 204.

 

[llwhtt]

With all of the fuses removed I would imagine it would be very quiet as the amp has no voltages to work.

Craig

 

[johannesnic]

I installed F201 and F202 back in place and the hum is back on my headphones on both channels just like before...
Voltages were good on Fuses F201 to F204 and is 35.8 volts DC before I installed F201 and F202 back in place

 

[johannesnic]

So nothing was wrong with F205 after all..

 

[llwhtt]

F201 and F203 are for the left channel power amplifier, F202 and F204 are for the right channel power amplifier, F205 is for the preamp for both channels. You need to use some logic in your fuse pulling. Install F201 and F203 only, what do you hear?

Craig