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No output from an HK Audio Lucas Nano 300
No output from an HK Audio Lucas Nano 300
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Old 22nd December 2019, 08:51 PM   #1
Yambo is offline Yambo  Maldives
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Join Date: Aug 2019
Location: Maldives
Default No output from an HK Audio Lucas Nano 300

I have got a HK audio lucas nano 300 in for repair. The issue was the unit not powering up, no indicator lights. Opening up the unit I found that something was shorting out +15V and -15V power rails. The culprit was 2 tantalum capacitors on the preamp board. There were actually 4 capacitors and it seems to be that 2 capacitors are in parallel with the 15V and -15V rail.
After removing the two shorted out capacitors I powered on the unit. This time the unit sprung to life but the amp is on mute mode. The indicator light is red and the LED on the main board labeled 'mute' is also lit. I measured the power rails and everything was ok and stable.
During troubleshooting one of the remaining tantalum capacitor on the preamp board shorted. So I have replaced all the capacitors now, there are no shorts now but the amp remains in mute mode. I tried playing back audio thinking that amp was in idle mode or something. No change, no sound but I heard very faint audio from the small satellite speakers.
I couldn't find any service manuals online, which makes the troubleshooting that much harder. I emailed the manufacturer but they are not willing to hand out the service notes unless its their authorized re-sellers, even for their legacy products. Any help on getting the service manual would be really appreciated.
The amplifier chip is LM4780. Nothing seemed to be shorted there. One thing I would remark is that the -VEE pin is tied to ground. I thought it would be connected to the -15V.
I traced the mute pin track to a SOT26 package transistor, the markings on it is '1Ft'. I couldn't find the pinout, knowing this would also help to figure out why the amplifier chip is mute.
Any help on this would be really appreciated.
Thanks in advance.
Attached Images
File Type: jpg Main Board.jpg (152.8 KB, 125 views)
File Type: jpg Preamp Board.jpg (171.3 KB, 122 views)
File Type: jpg Transistor.jpg (147.7 KB, 121 views)
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Old 22nd December 2019, 11:05 PM   #2
MAAC0 is offline MAAC0  Portugal
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Join Date: May 2010
According to SMD cookbook 1Ft =BC847B. Worth checking.
-VEE to ground. LM4780 can work with single or dual supplies.
The SMD Code Book
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Old 23rd December 2019, 09:05 PM   #3
Yambo is offline Yambo  Maldives
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Join Date: Aug 2019
Location: Maldives
I have figured out why the amp is muted. The output of this 555 timer needs to be pulled low in order for the amp to un-mute. I manually pulled it low and the amp was working fine as long as I had pulled it low.
Can you please help me figure out how this 555 timer is used (which configuration) and what might be the possible reason for the output to not going low. I suspect R25 and C20 to be the culprit. The marking on R25 is '30E' what would the resistance be? I am guessing the 555 timer is used as a delay to start up the amp.

Thanks in advance for the help.
Attached Images
File Type: jpg 555 timer.jpg (103.2 KB, 113 views)
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Old 24th December 2019, 07:48 PM   #4
MAAC0 is offline MAAC0  Portugal
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Join Date: May 2010
According to this tables it's 2 MOhm, but I'm not very familiar with SMD markings. Perhaps someone can shed a light on this. As what the 555 concerns, We need a schematic to understand the circuit. Google 555 start delay circuits.

SMD resistor examples (EIA-96 code)
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Old 3rd January 2020, 06:10 PM   #5
kevinaston1 is offline kevinaston1  United Kingdom
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Join Date: Oct 2010
Default Lucas NANO

I have a service manual, but at 7MB it exceeds the limit. PM me


Kevin
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Old 4th January 2020, 01:04 PM   #6
Yambo is offline Yambo  Maldives
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Join Date: Aug 2019
Location: Maldives
Quote:
Originally Posted by kevinaston1 View Post
I have a service manual, but at 7MB it exceeds the limit. PM me


Kevin
PMed
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Old 12th March 2021, 12:22 PM   #7
mijoub is offline mijoub  France
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Join Date: Feb 2021
Location: France
Default lucas nano 300 testing the tripleamp 200

Hi everybody,
I plugged a line output (mixer) to the input 2 of my lucas nano 300, but leaving the switch in the instrument position. Thenů no more sound, no more light to the status indicator, speaker out leds still lighting red.
I have completely dismantled the subwoofer. I tested the + 15V and -15V pins on the tripleamp 200 board with a multimeter by turning it on.
1 when the preamp cable is connected, the -15V pin drops to -1.5V, the + 15V remains stable.
2 when I unplug the cable, the + 15V and -15V pins are OK
I guess the preamp is out of order.
HK audio offers reconditioned spare parts. But before ordering a preamp, I would like to be shure that the amplifier operates normally. But without wiring diagram, I do not see what to do. Does anyone have any advice?
Thanks in advance.
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Old 12th March 2021, 10:08 PM   #8
kevinaston1 is offline kevinaston1  United Kingdom
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Join Date: Oct 2010
As above, I have the manual, but it is too big to post here. PM me with your E-mail address.


Kevin
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Old 13th March 2021, 09:18 PM   #9
mijoub is offline mijoub  France
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Join Date: Feb 2021
Location: France
Quote:
As above, I have the manual, but it is too big to post here. PM me with your E-mail address.
Kevin
Thank you so much for your help
Michel

Last edited by mijoub; 13th March 2021 at 09:28 PM.
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Old 5th April 2021, 11:29 AM   #10
DSinaga is offline DSinaga
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Join Date: Apr 2021
Quote:
Originally Posted by kevinaston1 View Post
I have a service manual, but at 7MB it exceeds the limit. PM me


Kevin
Dear Kevin,


I sent you message to ask you if you could send me the sevice manual for the Lucas nano 300. I do not know if it arrived to you . In this case ignore this new message....
Recently I got problem with my nano300 and I try to find doc to guide me to troubleshoot the amp. If you could help my bysending me the service manual it would be great.
Here my email address: dgb.sinaga@gmail.com
Thanks a lot ,
Didier
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