Troubleshooting Help with LM3886 PCB

[udailey]

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/LM3886_CA/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/Troubleshooting#5254228429490530530

Your help is sincerely appreciated.
THanks
Uriah

 

[paulb]

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.

 

[Redshift187]

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.

 

[udailey]

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/productdetail.jsp?SKU=83F2586&CMP=AFC-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.

 

[udailey]

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/Troubleshooting#5254228429490530530
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

 

[Redshift187]

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.

 

[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

 

[MJL21193]

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?

 

[udailey]

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

 

[AndrewT]

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

Maybe I fried the chips by having +voltage and no -voltage, but I doubt it.

 

[pacificblue]

Switch mode power supplies are usually internally grounded. You cannot simply connect them together for a split power supply.

 

[BWRX]

Switch mode power supplies are usually internally grounded. You cannot simply connect them together for a split power supply.

And it is not recommended to take apart a switching supply because there can be lethal voltages inside and you can seriously injure or kill yourself if you do not know what you are doing.

As mentioned, you need a split rail supply. That Lambda supply is only a single rail and seriously overkill for an LM3886 based amp.

 

[udailey]

Thanks for the good suggestions and safety tips. I will not be opening up the case.
I have two of these units. Yes, its so much overkill that its close to if not totally ridiculous. But, thats what I have to get 24V with so I need to try to use it.
I spoke with the tech guy at Lambda and he confirmed that using two units I can get +/-24V. What I have to do is tie - on one of the units to ground and + on the other unit to ground. The lug tied to ground will reference ground and create 0Volts and the other lug will generate 24V.
So, I just have to try it out. Will let you guys know what happens.
Uriah

 

[AndrewT]

Hi,
Is there a safety Earth connection in those SMPS units?
If so, then both must be connected to Safety Earth and that will prevent you connecting +ve output to Zero Volts.

If not, then the units should be treated as double insulated. Are they labeled as such?

 

[udailey]

Thank you AndrewT. You are certainly our OSHA guy here on DIY and we do appreciate it.
There is a Chassis Ground. The mains comes in and connects to L and N then you take ground to a chassis ground 6/32 screw. This is the same ground that I am to connect to one of the lugs. So it will be referencing earth ground. There is no specific mention of a "safety ground" in the documentation or on the unit.
Uriah

 

[udailey]

AndrewT could you explain double insulated? There is no mention of this either.
Uriah

 

[udailey]

Its WORKING

Thanks guys for the help/support. It all came down to it being a single supply and figuring out how to turn two of them into a dual supply.

So, what I did was take earth ground to chassis ground. I took - from PSU1 to its own chassis ground and I took + from PSU2 to its own chassis ground. Then I took the other two power outputs and took them to the amp and took ground to the amp by tying leads from both PSU's Chassis Ground to the amps ground.
Its getting 24V on each rail now and its happy.

Now I have .8V DC on the input which of course manifests itself at the output. But I have been fighting this problem for a while on a different amp and I think its the fault of the junky little wallwart I use to power my B1 PreAmp. I am going to replace that supply with 2 9V batteries and see if the problem persists.

Uriah