Luxman rx-101 blown channel repair

[Merzie]

So I was a little surprised to find that my ebay find of a suckface had no right channel working. I opened it up, and, surely enough, both fuses for the right channel were blown.

Next, I took a fuse from the left channel and put it on the right channel, hooked up a speaker, tuned to a radio station.. and very quickly the speaker went up in smoke. Squeals. Very low volume. Ruined the speaker.

Does anyone have a suggestion for which area to look at on my machine? do these fuses work in parallel and I need to have both in for both channels (A and B and left and right)?

Are you suspicious of the fact that both fuses were blown?

[singa]

Originally posted by Merzie-
Are you suspicious of the fact that both fuses were blown?

Hi, That should already alert you of a blown channel and that you should not connect a speaker to test ,just putting a fuse to test is sufficient but chances are that there's a problem and you should do a diode test of the
power transistors in the first place.

[Merzie]

Yeah. I'm a newbie with this sort of thing. Luckily, I used a cheap speaker... So how should I proceed? I have a basic multimeter. I'm reading that I need to check for continuity... but I'm unsure of the most efficient means of doing so

Actually, there are 9 total fuses. the two that were blown were next to a big cap and are rated for 3A

[singa]

Hi, A multimeter is all you need.So just do a diode test including reverse
probes and use continuity buzzer for shorts on power devices and drivers
and pcb continuity.Good luck.

Actually, there are 9 total fuses. the two that were blown were next to a big cap and are rated for 3A

Is this the power supply circuit?

[Merzie]

bottom of unit... front is to the left.. 4 fuses are fine here.



top of unit. front is to the right. two fuse bays on top of capacitors were the ones found to be blown. There are two below which I assume are for A/B of the left working channel.

[Merzie]

Is it the psu?

[Merzie]

Which transistors should I start with? are they all a certain type.. do I need to test them in different ways?

[Merzie]

HOorah! I found the dead transistor. It was confirmed by a local audio guru...$12 replaced the the pair and the suckface is up an running again. The technician believed that it was caused by running the receiver with only one speaker (computer forced mono)... Not all receivers have a safety mechanism built in for this function.

Thanks for your guidance!

[singa]

Originally Posted by Merzie

The technician believed that it was caused by running the receiver with only one speaker (computer forced mono)... Not all receivers have a safety mechanism built in for this function.

This is not true,an amp can run on one channel.I believe the one pair of output transistors could be running close to it's safety limits as most japanese amps are designed to minimise costs.Then the angle bar heatsink does not help.It should have more cooling fins like a proper heatsink.Anyway congratulations.

[amptech]

Glad you sorted your and all is ok...the normal thing to do here is to test the out put transistors.. Merzie welcome to the show..we here to help were we can...just ask!

you say your a newbie, reading up on electronics will help you get a better understanding on how things work and there's plenty of on line web pages to guide you..

Many of us have been in the trade for countless years and seen all manor of fault's that will drive us nut's...just like your amp fault..never just replace a fuse and power up as you found out pop went your speaker..if you have a working side use this to carry out voltage test's and take note's of all voltages. be careful of the mains voltage!! make sure you have plenty of work space to place your item on plus a good meter to carry out your work. never run a amp with all the speakers to one side that's a no no..uneven loading there I seen this so many time's... Also a working amp channel will have very low dc volts on the o/p say in the mv volt reading hight dc say 10 volt's will burn your speaker...
all way's test the out put of you amp to ensure there's low dc.set your meter on 200vdc range and take it down to 20v dc if all is well, also when testing a repaired unit use load resistors this will save you cooking your speaker..dummy load's can be 10 ohm 10 watts or 4..8..ohms at 50w to 1000w.. test gear such as scopes signal's gens..or just use a cd player for hifi amps and see if you out put music is the same no break up in sound..

A helpful tip is to try an get the circuit diagram to aid repair but some time's it's down to good old voltage testing...

good luck with your repairs..

kind regards.