Trying to fix a Luxman R 1040....

So my parents bought this Luxman R 1040 when it was new. They haven't used it for years now because one side of the speaker channel doesn't play. They sent it in for repairs, the guy replaced some fuses, charged a lot of money, and sent it home. Of course the fuses blew again because he didn't fix anything. That was over 5 years ago. Since my parents love this receiver so much, I thought I'd try to repair it for Christmas. When I opened it up, I found more than just some blown fuses. One of the amplifier circuits is pretty much toasted (specifically, circuit PB-1009 in the service manual). Two questions for you all: 1) What could have caused such heat damage, simple over-use or something more sinister? 2) Any idea at all where I might be able to find a replacement, short of buying a whole other receiver for parts?


PS- if anyone is looking for the service manual for the Luxman R 1040, I have it in a .pdf file.


Thanks

Do you have pics of the damage?

It may not have been the tech's fault. If the speaker wires were shorted, that would blow the output stage, and if the problem with the wires wasn't remedied, the amp would have immediately blown up when you switched it on. Many people have the speaker wires stripped so that over 1 inch of bare wire is sticking out of the speaker terminals on the receiver and the speakers. Someone moves something to dust, then the wires touch and short out. The wires should only have 1/2" of bare wire exposed at the end. Then you neatly twist the strands together and insert them into the speaker terminals. If wires are spliced, they must be properly insulated with electrical tape or heat shrinkable tubing. If they run under a rug, they should be checked for frayed insulation.
Luxman equipment is well designed and very seldom blows up because of internal failure of a part.

dr*audio -

That is a fair point about the tech and the speakers. In fact, when my parents got the receiver back from the technician, he said he had plugged his speakers up to it and everything worked fine, so that implies our speakers are faulty. On the other hand, my parents switched the speakers right to left and left to right, and the same side was bad regardless. But I will check the speakers/speaker wire. (btw the speakers are model JR 149)


ryuuoh -

You should find pics of the damage attached. There are two Hitachi 2SC1030 and Hitachi 2SA756 transistors attached to the back of the ciruit. You can see a little damage to the board where their posts are soldered in. All other damage is pretty visible.


If there is any other information I can provide, please let me know. Also, any idea where I could find a replacement board?

I'd say just reflow the solder on the output transistor socket connections.Then have a closer look at the two transistors in the picture below .I see oxidation on the TO-220,check the TO-92 right next to it as well.May have blown out quite a while back.

It looks like both parts are readily available, but you need to find out what took them out. The board looks salvageable, so I'd try to fix it.
Good Luck!

Both of those transistors are fried. They have a matching pair on the other side of the board that are the same way. They more or less melted together and then I just yesterday popped them apart. The receiver hasn't been powered up for over 5 years, so the oxidation isn't much of a surprise, but I suppose it does make it easy to spot damage lol.

So the consensus is to salvage? That's good to hear, because finding that board was turning into a difficult search. My only concern is that in the couple of circuits classes I've taken, we were always told that when the board got over-heated like that, it was generally better to replace the whole thing. But then again, I suppose that when a replacement is not available, work with what you've got. There are some components near the transistors in question, namely the R210a resistor and the C205 capacitor, that look like they may be damaged. I'm guessing those will have to go as well, but I haven't taken any testing equipment to the board yet to find out.

Thanks guys for all your help!

The board is salvageable. Be careful when you desolder the components, since the board has been heated, the pads on the board may not be bonded to the board anymore, at the components, or the bond may be weakened. Use solder wick, a heat controlled iron, and very light pressure on the pads. Place the solder wick on the pad and the iron on top of the wick. When the solder has wicked up into the solder wick, remove the iron, do not leave it on the joint any longer than necessary. If the leads of the parts are bent over, be very gentle when you pry them up, and don't use the iron to do it. You can gently apply some heat to the pad as you gently wiggle the lead loose. It is better to remove all the solder you can first, then try to straighten the lead. Often the lead will come free, once the solder is removed. You just don't want to tear the pad off when you lift the lead.

Thanks so much for all your instruction thus far, could I be so bold as to beg some more guidance?

I found it near impossible to work on the board in the stereo, so I decided to remove it. I very neatly numbered all the wires I cut so i would know which ones go to which when I put everything back together. My mistake was not thinking this through before I started snipping. I cut a wire that seems to be some kind of coax, with a current runing through the center and then the ground running though the outer part. I've never run across something like this before, and have no idea how I'd splice that back together. Any suggestions? The first two pics below show the wire in question.

My next problem is that the Hitachi transistors connect the heatsink to the board. This is a problem because the heatsink is blocking the side of the board that I need to get to. Is there anything wrong with just taking the screws out of the transistors, popping the cap off, and removing the heatsink? Or is there a better way to go about that? Also, if you peer down real closely, you can see that the solder around those transistors on THIS side of the board looks pretty good. Should I still reflow those connections?

As you can tell this is my first time fiddling around inside of a stereo. I really don't want to bungle this up, so the more help the better. Thanks in advance!

Verify that the transistors are indeed soldered to the PC board.Most amps I've seen have transistor sockets soldered to the PCboards. Unscrew the two screws and gently pry up to remove transistor from the socket.Try not to damage the mica insulator. Once the transistor are removed, the circuit board will be seperated from the heatsink. Make a note as to which transistor was removed from which socket.
I would have unsoldered those wire connections rather than snipping them.Alot of those audio components were not very generous with wire length. When you go to reassemble you may come up a little to short.

When you have the transistors removed.Check them with a multimeter for shorts.If the amp was blowing fuses , there is a possibility one or more output transistors is shorted.Especially if a speaker /or speaker wire was involved.

If you have enough length of the coaxial cable, you can carefully strip the jacket using an exacto knife. Bend the coax, and press the knife on the bend, working around the cable. This will expose the braided shield. Using a pick, spread the braid near the jacket to reveal the inner conductor. Pull the inner conductor through the hole in the braided shield. Twist the braid into a wire shape. Use appropriate sized heat shrink tubing to rebuild the cable.

Due to the Holidays and other distractions, I've just gotten back to work on this board. I've gotten the Hitachi transistors out just fine (they were in sockets) and they seem to be in working order. dr*audio, is it really necessary I use a temperature controlled soldering iron? or could I use just a standard Rshack special soldering iron (if I'm really careful)? It's just I don't really have the money to get another soldering iron right now (as cheap as that may sound).

In other news, I believe speaker wires were the culprit in this case.

In yet other news, I was able to bring a Pioneer SX-780 (that I ordered for my bother off *bay, but showed up damaged) back to life successfully. Much simpler fix than this Luxman....

You can use your iron but use very light pressure on the pads on the circuit board and remove the iron as soon as the solder flows.
Check all the transistors with your meter. Something has to be blowing the fuses. Do you know how to test the transistors?

watts8041 said:

Both of those transistors are fried. They have a matching pair on the other side of the board that are the same way. They more or less melted together and then I just yesterday popped them apart. .....

Click to expand...

Same problem here on my R-1070. Looks very wierd, melted together like that. :tears:

And it looks like there are 4 small caps that blew their tops too. And the durn thing still plays... how weird is that? (No I don't use it in that state) ... the previous owner left it on for years because he said you had to turn it on/off 5 or 6 times to bring it on. Protection circuit light is on. They really built robust gear back then to take this form of idiotic abuse... same people who ignore warning overheating and brake failure lights on car dashboards ugh. :bat:

Previous problems fixed... baffled by new one

After several months' distraction, I'm back on this project. I was able to find replacements for the questionable transistors. Replacing those and putting in new fuses has brought this receiver to back up to 95%. As mentioned before, the crossed speaker wires were identified as the source of the blown fuses.

I've found a new problem that has me completely confused. I hooked the receiver up to my parents' brand new Audio-Technica TT and discovered it played mainly out of only one speaker! The TT has been tested with other amps/receivers and is not at fault. The Luxman plays out of both sides when using all other inputs. But when the TT is played through the Luxman, the right channel plays normally and the left barely produces any sound at all.

What I've done to identify/fix the problem:

1) Cleaned the phono connections on the back of the stereo
2) Cleaned the input selection knob contacts on the front of the stereo
3) Because the phono input uses the receiver's preamp, I thought perhaps that circuit was shot. However, the AM/FM tuner uses the same preamp, and the stereo plays normally when listening to the radio.
4) Switched speakers L to R just to be sure
5) Cleaned the input selection knob contacts again

None of the above had any effect


As mentioned, the stereo plays normally when using the Aux and Tuner inputs.

Any ideas/suggestions??

Are you able to locate the phono section inside? Also, does the receiver have a mono switch? Try it in mono if possible.

Look on the schematic (by the way, I would like to get a copy of that manual, shoot me a PM.) Follow the circuit from the Phono inputs and you will find the Phono preamp, which is used only for phono. You can troubleshoot this with no test equipment! You will use a small screwdriver or dental pick to inject body hum from your body into the circuit, while monitoring the output with speakers or headphones (turn the volume down!) Insulate the probe with electrical tape so that only the tip is exposed, to help guard against shorting anything out. Follow through the circuit from the input towards the output, and touch the probe to each point. For example, the phono jacks will connect to a capacitor on the input of the board, probably. Probe at the input side of the cap. No sound there, probably. Probe the output side of the cap, do you get sound? If so, the cap is bad. And so on through the circuit until you get a point where you get sound on the dead channel. You can compare the bad channel with the good one.

ryuuoh: I located the phono section inside the receiver. When the mono button is pressed, sound does come out of both L and R channels.

dr*audio: I followed your advice, using a small wire I started probing around the circuit board that the phono inputs connect to. Some other members may find this annoying, but since you have the schematic now I can tell you exactly what I was looking at. The circuit is labeled PB-1064 in the service manual, and if you scroll down to the second to last page you can see it there next to the inputs on the left-hand side of the page. The strange thing is that when I started at the inputs, I got hum out of both sides. Working my way through, though, I found a capacitor (C408) in the left channel that seems to be dead. When I touch C408 in the right channel with my wire I get hum, but not when I touch C408 in the left channel. Does that makes sense to have hum when I touch the wire "upstream" from the capacitors at the input, but not when I touch the positive side of the capacitor itself? I've had several circuits classes, but I'm not an electrical engineer or a trained technician, so I'm having a little trouble figuring out c408's purpose in the equalizer. If it does what I think it does and acts as part of some filter, then I guess it would make sense.

Looks like you have isolated the problem board. I'll let people with more experience follow up. Good job though, you're learning stuff! And so am I.