Troubleshooting Help with LM3886 PCB - diyAudio
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Old 7th October 2008, 03:28 AM   #1
udailey is offline udailey  United States
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Default Troubleshooting Help with LM3886 PCB

If you folks could look at my board and give advice I would appreciate it.
I designed the board and populated it. I had forgotten to solder in my jumpers from 1 to 5 and from 4 to 11. I tried to fire it up and nothing. Tried a few more times thinking it was some other problem and then when checking the schematic I noticed I had forgotten my jumper wires. So I put them in and fired it up and I got a small turn on thump but nothing more. Maybe I fried the chips by having +voltage and no -voltage, but I doubt it. I have tested the pre amp and cd player by running another amp and the other amp runs fine.
I modeled my amp exactly after the schematic on DIYAudioProjects by Giovanni Miltano.
Here : http://diyaudioprojects.com/Chip/LM3.../LM3886_CA.htm
Here is the diagram I put together of the board with parts on it. The 1 pin is on the left side.
Here is the google album with a few pics in it
http://picasaweb.google.com/udailey/Troubleshooting#
Here is the pic of the board and labeled components
http://picasaweb.google.com/udailey/...28429490530530

Your help is sincerely appreciated.
THanks
Uriah
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Old 7th October 2008, 03:39 AM   #2
paulb is offline paulb  Canada
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Have you got a voltmeter? (If not, get one.)
Measure the voltage (relative to ground) on the speaker output and as many pins of the chip as you can, and post them here.
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Old 7th October 2008, 03:51 AM   #3
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I don't see any issues with your layout from a "it should make music" perspective. Pin 11 is not connected, but it should be fine if you have it connected to V- and jumper that to pin 4.

Do you have the isolated chip (LM3886TF), or non isolated (LM3886T)? If it's non isolated, you must make sure the back of the chip is not connected to ground through the heatsink/chassis.
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Old 7th October 2008, 04:00 AM   #4
udailey is offline udailey  United States
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Just got out the DMM. Really tough to get it in there to the pins. Nevertheless, the first thing I found was that my power supply is giving me +1.6V and -22.3. Now I have a 24V swing, but still this doesnt seem right. Its a regulated supply I bought. LZS-500-3
This is the one http://www.newark.com/jsp/search/pro...FC-GB100000001
Got it on ebay for NOT that price
Anyway if I am supposed to give 24V is it okay to have 1.6 and 22.3 to add up to 24?

Uriah

I will try more measurements in the meantime.
Thanks guys.
EDIT: LM3886TF = Isolated.
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Old 7th October 2008, 04:18 AM   #5
udailey is offline udailey  United States
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Nothing across speaker outputs.
Nothing at all on any pins except obviously on the +/- pins.

I was thinking maybe my mute resistor was wrong but both are 10k.
If you look at my board
HERE
http://picasaweb.google.com/udailey/...28429490530530
Does it appear to have any issues. It seems right to me but thats probably the problem. That I have looked at it so many times I cant see the mistake.
Uriah
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Old 7th October 2008, 04:34 AM   #6
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If you are only getting +1.6V, that is likely your problem. Positive and negative must be close to the same (within a volt). That power supply is a single supply (only positive voltage). To use it, you must have a virtual ground setup. You need to have positive and negative power rails with ground about half way between them.
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Old 7th October 2008, 04:36 AM   #7
udailey is offline udailey  United States
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Yeah. At the amp I get 1.6 and 22.3 and also right at the power supply output.
I will call Lambda tomorrow and ask them what the deal is. Maybe it is supposed to be this way and I just bought some application specific supply.
I will update tomorrow after I talk to their techs.
Uriah
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Old 7th October 2008, 05:20 AM   #8
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Quote:
Originally posted by udailey
Yeah. At the amp I get 1.6 and 22.3 and also right at the power supply output.
I will call Lambda tomorrow and ask them what the deal is. Maybe it is supposed to be this way and I just bought some application specific supply.
I will update tomorrow after I talk to their techs.
Uriah

Hi,
I'm confused. Where are you measuring the 1.6V from?
That Lamda supply is single - 24VDC. For your amp to work you need a split supply - + and -24VDC. That's a total of 48 volts with ground (0volts) in the middle.
Understand?
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Old 7th October 2008, 01:18 PM   #9
udailey is offline udailey  United States
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Join Date: Mar 2008
I am measuring the 1.6 from the positive rail and the 22.3 from negative.
Hmm, if its single supply maybe I could use two of them for a dual supply. I did buy two of them which could either be a disaster or if it is a single supply maybe it could be a good thing.
I will call Lambda in a few hours when they open and ask whats up.
Thanks for your response I hadnt thought that it might be a single supply like you said.
Uriah
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Old 7th October 2008, 01:43 PM   #10
AndrewT is offline AndrewT  Scotland
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Location: Scottish Borders
build a simple unregulated supply and get the amp working first.

If you use a light bulb tester for each power up you will not need to ask
Quote:
Maybe I fried the chips by having +voltage and no -voltage, but I doubt it.
__________________
regards Andrew T.
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