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Old 12th Mar 2020, 9:35 pm   #1
Deric nichols
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Question Luxman LV-105U.

Hello, would anyone be willing to help me troubleshoot my Luxman amp, it worked until I zapped it.

What I need to know is where to begin. I had a stereo mixer hooked up to tape in and wasn't paying attention when I changed the rec out selector and the output of the mixer was extremely high. I have power, all the fuses are good but no sound output.

I really appreciate the sound of this amp and it has sentimental value, so I have to fix my mistake. Really would appreciate your help.

Thanks.
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Old 13th Mar 2020, 9:49 am   #2
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Default Re: Luxman LV-105U.

Hello and welcome to the forums.

I suggest that as a first step you obtain the service manual which can be downloaded here:-

https://elektrotanya.com/luxman_lv-1.../download.html

What is your skill level and what tools and test gear do you have?
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Old 18th Mar 2020, 8:02 pm   #3
Deric nichols
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Default Re: Luxman LV-105U.

I have the service manual, I can read a schematic I have an oscilloscope, voltmeter i have study the schematic and I'm just not sure where to begin my level of skill is above average . it has been a while since I worked on a stereo so im a little rusty
thank you for your reply...
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Old 18th Mar 2020, 11:38 pm   #4
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Default Re: Luxman LV-105U.

Hi Derec,

This is going to take some doing.
The schematic is cr.p as you can see.
I believe the original papers were in colour clearly emphasizing the signal paths but now you're stuck with a so-so quality scan and a somewhat complicated circuit that's been made even more complicated with the addition of a couple of valves.
Anyway, there's more than one way to skin a cat, and an amplifier is an amplifier also when over-engineered.
Turn volumecontrol down, disconnect any speakers and turn-on the power.
Start from the rear-end or what they call the "Main P.C. Board"
You can easily spot the speaker-protection relay RL5101.
Has it been pulled-in/engaged to allow the output signal to reach the speaker-terminals ? Check voltage across diode D5102. Zero Volt = disengaged.
If not engaged, the protection-circuit may do just what it's suppose to: Protect.
Check DC-voltages at either end of coils L7301 / L7302.
Both coils should be easy to spot on the PCB, most likely wound over resistors R7323 / R7324.
DC-voltage must be Zero Volt.
If not, the protection-circuit has disconnected the speaker-terminals to avoid damage to the speakers.
So, here zero is good and non-zero is trouble.

Please report.

rdgs,

/Torben
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Old 20th Mar 2020, 3:19 am   #5
Deric nichols
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Default Re: Luxman LV-105U.

I can do this, I will let you know what I find, thank you.
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Old 21st Mar 2020, 1:36 am   #6
Deric nichols
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Default Re: Luxman LV-105U.

I took your advice and if I did it correctly all my readings were 0 volts...
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Old 23rd Mar 2020, 7:02 am   #7
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Default Re: Luxman LV-105U.

Quote:
Originally Posted by Deric nichols View Post
I took your advice and if I did it correctly all my readings were 0 volts...
Zero Volts across D5102 or Zero Volts measured from either coil towards ground ?
The idea is to discover if the protection-relay is engaging or not.
Remember it HAS to engage to connect the amplifier-output with the speaker-terminals.
You should actually be able to hear a >>Click<< from the relay a few seconds after turning-on the amp.
No click and no voltage across D5102 indicates it doesn't engage.
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Old 26th Mar 2020, 5:29 am   #8
Deric nichols
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Default Re: Luxman LV-105U.

I had zero volts from coil to ground on both coils, I do not hear the relay click on, thanks.
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Old 26th Mar 2020, 10:56 pm   #9
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Default Re: Luxman LV-105U.

Assuming you are right, both power-amplifiers seems to be OK and the problem is in the protection-circuit not engaging the speaker-relay.
Locate the diode D5102 connected across the speaker-relay coil.
Turn the amp on and wait for a moment.
Now do a voltage measurement between the cathode and ground.
You should observe the supply voltage for the relay, possibly 12V DC.
See what's written on the side of the relay; the specification for the relay should be shown.
Measuring from D5102 anode to ground confirms the relay is not engaged if it has the same voltage as the cathode. If you measure 0 Volt towards ground the relay-coil is open and the relay should be replaced. This rarely happens.
If you have no relay supply voltage the source of the voltage should be traced down on the diagram and checked. As this is an extremely cr.ppy diagram I wish you good luck with that.
If the voltage is there and the relay is deemed OK (no voltage across D5102) you should check the supply voltage for the protection circuit itself.
The voltage can be measured from transistor Q5104/Emitter towards ground.
This voltage is actually the positive full supply voltage to both output amplifiers.
Now, before we continue, check the above.
And.... obviously you have already checked the amp for any blown fuses besides checking the supply voltages for the output-amplifiers, havent you?
If not, this is the time to do so. Actually it's not; it's what should be done as step A-1, but I just assumed you'd already checked the obvious.

rgds,

/Torben
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Old 3rd Apr 2020, 4:34 am   #10
Deric nichols
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Default Re: Luxman LV-105U.

All fuses are good, haven't checked voltages to output amps, will do that first and follow your advice on the rest, I really do appreciate your time Thank You!!!
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