No DC voltage on Lm3886 chipamp.com

JohnnyP00 · 25th August 2009, 04:35 AM

I'm stumped.

Everything up to the transformers secondary rails work perfect but once I attach the power supplies I get no voltage. My secondaries read around 25V ac to 27V ac. I attach the snubberized power supplies from chipamp.com and read no DC voltage on the P+ and V+. The LED doesn't light either. Do I have just bad diodes? Can't seem to get past this problem.

Thanks for anyones help... JohnnyP.

ikoflexer · 25th August 2009, 04:43 AM

There's something to be gained by going a step at a time. Connect just the diodes to the transformer, and measure again. If OK, connect the next stage (might be an RC filter) and measure again.

sangram · 25th August 2009, 05:56 AM

Supplies? Are there more than one connected to the same transformer?

I remember going crazy (and driving PD crazy) trying to troubleshoot the exact same problem. It turned out that you can't actually connect the AC1 and AC2 of two different PSU boards to the same secondary, it shorts out. It needs to be AC1 and AC1 together, and AC2 and AC2.

I don't know if that's your problem though.

Redshift187 · 25th August 2009, 11:37 AM

Can you post quality, close up photos of the power supply board, top and bottom? They don't have to be large, but you have to be able to tell what you're looking at.

Also, are you using a light bulb tester? If you are, whether the bulb is lit will tell us whether you have a short or an open.

JohnnyP00 · 25th August 2009, 12:44 PM

I'm doing a dual mono configuration from chipamp.com. It looks exactly like the photo there. I'm only attaching one power supply for one transformer. I'm not doing the light bulb test. As far as I measured everything is perfect up to PS boards. How can you test if diodes are bad... Thanks JohnnyP.

Redshift187 · 25th August 2009, 02:21 PM

First, we don't need photos of what the board looks like, we need photos of what you've done during assembly of the board.

Second, the light bulb tester will protect you and the equipment in the case of a mistake, and give a signal indicating when you have something wrong that would otherwise end up in a lot of smoke or worse. It's not for the transformer, they rarely have problems. It's for the power supply boards and amp boards after that.

audio1st · 02:58 PM

Quote:

Originally Posted by JohnnyP00

I'm doing a dual mono configuration from chipamp.com. It looks exactly like the photo there. I'm only attaching one power supply for one transformer. I'm not doing the light bulb test. As far as I measured everything is perfect up to PS boards. How can you test if diodes are bad... Thanks JohnnyP.

The LED connects pre the diodes so your problem is probably your AC1 and AC 2 connections...If you can't show a picture, then what make of transformer and colour wires connect to AC1 and AC2.

JohnnyP00 · 25th August 2009, 05:25 PM

Hi. Here is some pics. Ignore the chip boards because they're not set up yet. Didn't get that far

audio1st · 25th August 2009, 07:42 PM

Between which points did you measure the 25, 27AC voltages?

audio1st · 25th August 2009, 08:09 PM

It seems you need a green and blue to AC1 and a green and blue to AC2.
So thats a green and blue with a reading of 25Vac between them..

25th August 2009, 04:35 AM	#1
JohnnyP00 diyAudio Member Join Date: Nov 2007	No DC voltage on Lm3886 chipamp.com I'm stumped. Everything up to the transformers secondary rails work perfect but once I attach the power supplies I get no voltage. My secondaries read around 25V ac to 27V ac. I attach the snubberized power supplies from chipamp.com and read no DC voltage on the P+ and V+. The LED doesn't light either. Do I have just bad diodes? Can't seem to get past this problem. Thanks for anyones help... JohnnyP.

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25th August 2009, 04:43 AM	#2
ikoflexer diyAudio Moderator Join Date: May 2008 Location: Toronto	There's something to be gained by going a step at a time. Connect just the diodes to the transformer, and measure again. If OK, connect the next stage (might be an RC filter) and measure again.

25th August 2009, 05:56 AM	#3
sangram diyAudio Member Join Date: Sep 2002 Location: India	Supplies? Are there more than one connected to the same transformer? I remember going crazy (and driving PD crazy) trying to troubleshoot the exact same problem. It turned out that you can't actually connect the AC1 and AC2 of two different PSU boards to the same secondary, it shorts out. It needs to be AC1 and AC1 together, and AC2 and AC2. I don't know if that's your problem though.

25th August 2009, 11:37 AM	#4
Redshift187 diyAudio Member Join Date: Aug 2008	Can you post quality, close up photos of the power supply board, top and bottom? They don't have to be large, but you have to be able to tell what you're looking at. Also, are you using a light bulb tester? If you are, whether the bulb is lit will tell us whether you have a short or an open.

25th August 2009, 12:44 PM	#5
JohnnyP00 diyAudio Member Join Date: Nov 2007	I'm doing a dual mono configuration from chipamp.com. It looks exactly like the photo there. I'm only attaching one power supply for one transformer. I'm not doing the light bulb test. As far as I measured everything is perfect up to PS boards. How can you test if diodes are bad... Thanks JohnnyP.

25th August 2009, 02:21 PM	#6
Redshift187 diyAudio Member Join Date: Aug 2008	First, we don't need photos of what the board looks like, we need photos of what you've done during assembly of the board. Second, the light bulb tester will protect you and the equipment in the case of a mistake, and give a signal indicating when you have something wrong that would otherwise end up in a lot of smoke or worse. It's not for the transformer, they rarely have problems. It's for the power supply boards and amp boards after that.

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