Help needed with Luxman L-230 integrated amp burning fuses

labusas · « **on:** 12 Oct 2004, 05:18 pm »

Could you please help me to troubleshout my Luxman L-230 amp?
I had an unfortunate accident with speaker wire short and now the fuse keeps blowing as soon as I plug the power on. It calls for 125v 5A fuse. I'm getting AC 120V before the fuse. The fuse stays OK when output wires are disconected from amp.
Could this be a damaged trasformer?
The transformer output has black ground and two positive red wires. The DC reading is all over the place at black/ground + any of the red wires. When I place my DMM to AC setting I'm getting 33V at each rail (ground with positive)and 66V on both red. I guess it's all right.
What else should I check?

Thanks
nariusb@cogeco.ca[/img]

JoshK · « **Reply #1 on:** 12 Oct 2004, 05:27 pm »

My guess is it is more likely blown caps. I don't know how you would blow a transformer. Do you have a multimeter? Can you take the lid off and check the caps for leakage?

Right now you are blowing fuses for a reason, something in the amp got damaged and the fuse is protecting you from hurting yourself. Take some pictures and post them for more help.

Wayne1 · « **Reply #2 on:** 12 Oct 2004, 05:45 pm »

The most likely culprit is the output transistors.

If the fuse is stable with no load on the outputs and then blows when outputs are connected, that kinda points to a shorted output device.

Pull all the outputs and check them. If any read bad, I would replace all the driver and output transistors in that channel. There may be some burnt resistors in there too.

labusas · « **Reply #3 on:** 12 Oct 2004, 07:35 pm »

Thanks very much for taking time to help me. First off all I should mention that the fuse is located before the transformer on one of the AC lines feeding it. The other AC wire goes to the switch. There are no other fuses in this amp. How can something damaged on the circuit board affect it? I guesss someting like shorting earth and positive lines.
All caps seem to be OK without testing them - I don't have capacitance tester. Again, this fuse blows only when the wires coming from transformer are soldered to the circuit board and OK when desouldered.
Thanks

Wayne1 · « **Reply #4 on:** 12 Oct 2004, 08:08 pm »

Do you have a schematic for this amp?

If not, I suggest you get one.

The transformer goes to the rectifiers and to the PS caps. This is what makes AC to DC. The output transistors are coupled to the + & - DC voltages. If the output transistors are shorted, a very good possibility if you shorted the speaker wires, they will directly connect either the + or - voltage rail to ground. This will then cause the power supply to try to draw a large amount of current from the wall causing the fuse in the AC line to blow.

Remove the output transistors and check continuity. If you read a short, you have found part of the problem. If you do not have a schematic it will be hard to progress beyond this stage.

labusas · « **Reply #5 on:** 13 Oct 2004, 12:05 am »

First off much appreciated, Wayne, for your help. I've got the schematics of a similar if not exact model at: http://www.hilberink.nl/amps/luxman/l215amp1.pdf
You were right about output transistors, both NPN and PNP of them for channel B are shorted out. Also R137b 390 ohm 1W resistor was burned out. I'm not sure if any of the other transistors are gone too. I'm not taking them all out to test at this stage - too many.
Do you think replacing those two output transistors and R137b will do the trick, if not what else should I pay attention to. Parts are on order.
Cheers

Wayne1 · « **Reply #6 on:** 13 Oct 2004, 12:17 am »

You might be lucky and just have those transistors and resistor gone.

When I worked as an audio amp bench tech, I always replaced the driver transistors as well. They are direct coupled to the output and may have been stressed when the output blew. They shouldn't cost too much and it is better safe than sorry.

labusas · « **Reply #7 on:** 18 Oct 2004, 11:32 pm »

Thanks to Wayne I've mooved forward. I replaced all drivers as well as output devices. Something else was still gone. After a good hour of my DMM work I found 2 out of four rectifier diodes were burned out too. I could not find the exact replacement for S3V45 and S3V44 rectifiers (D115-D118 on the schematics above). I did replace it with 3A similar rectifier. It worked perfectly for half an hour. Now I'm getting sound distortion on the same channel, but perfect on the other. Sound is kind of muffled, with almost no highs on that one side.

Question for you tech experts: is it because of mismatched rectifier I've replaced or is something else gone, like input transistor?

What replacement do I need for power rectifier/diode S3V44 / S3V45? There's nothing about it on the net, NTI crossreference...
Thanks in advance

labusas · « **Reply #8 on:** 19 Oct 2004, 05:16 pm »

It's not the diode rectifiers, I found the right replacement and it didn't make any difference - there's still sound distortion on the right, previously damaged side. I've resoldered all of the transistors i've replaced to no result. I used NTE replacements for those hard to find japanees transistors.
Is there any resistor that I'm possibly didn't look at properly? I know you cant check some of them while in circuit.
It's so strange - play for half an hour an then this!

Wayne1 · « **Reply #9 on:** 19 Oct 2004, 06:06 pm »

Part of the problem is using NTE. The circuit is designed to use specifc transistors. Try MCM Electronics. They should have stock on the OEM Japanese parts.

Check the .22 ohm emitter resistors. They are usually packaged in a three lead white ceramic square. Either one or both of these may be open.

You should check all of the resistors arounf the output section. You will either have to remove them completely or at least detach one leg to measure the resistance.

There are no quick fixes with a blown channel. You have to get in there and check everything. It does take time. That is why repairs cost so much. Parts costs may be small, but finding what part to replace costs money.

labusas · « **Reply #10 on:** 20 Oct 2004, 06:16 pm »

Hi John,
Thanks for your help, You're right one side of the emmiter resistor is open.
I can't locate this one though. Do you know where I couls look for it? The place you told me don't have it.
Its a white ceramic rectangular RGC55, 0.22OHM KX2, Noble E47.
Thanks again.

Wayne1 · « **Reply #11 on:** 20 Oct 2004, 06:32 pm »

http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=019-.22

The name is Wayne

labusas · « **Reply #12 on:** 22 Oct 2004, 12:26 am »

Thanks Wayne for the parts express link. The resistors are on the way. Keep you posted about the result when I replace them.
Cheers

labusas · « **Reply #13 on:** 25 Oct 2004, 11:16 pm »

Thanks to this community and Wayne I've got back to listening to music. I've replaced the emitter resistors for both channels, just in case. and it's rocking better than ether.
Thanks a lot Wayne