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Old 22nd September 2015, 05:17 AM   #1
Hogwild is offline Hogwild  Canada
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Join Date: Oct 2010
Unhappy Overheating and voltage issues

Hi everyone:

Electronics newbie here, with soldering skills, and some ability to use a meter. Assume nothing more in terms of knowledge. This stuff confuses the daylights out of me, so please be patient.

I finished soldering four Chipamp.com LM3886 amp boards and one pair of same company's PSU boards.

A friend helped me test three of the four amp boards and one of the PSU boards with a True RMS meter. Something is very wrong.

Transformer used: 300VA 18.00V dual secondary toroidal.
PSU board A: measured approx. 27V DC stable on both rails (under no load). OK, not too bad.

It appears that when the circuit is turned off then on again, we blew fuses.

First two amp boards (I soldered)
Amp board 1. Output 2V AC with no input.
Amp board 2. Output 5V AC with no input. Sometimes peaked as high as 16V AC with no load.

Frequency checks on amp board (2.) were all over the place.

Connecting either amp board to a speaker resulted in a bad hum which sounded like AC. However, the metered frequency was all over the place.

Amp board 2. heatsink got quite hot. It was only on for about 30 seconds, but took about 15 minutes to cool down.

Amp board 3. (soldered by someone else.) It seemed to display voltage measurement problems similar to the other two, but the heatsink remained cool. It also showed hum on the output. Third power on for that board blew a 2A fuse.

Scoping is not practical at the moment due to heat concerns after only a few seconds.

My friend also has only an analog scope, not one with storage.

Finally, both amp boards 1. and 2. have coaxial input wires, as recommended to me by people here. Amp board 3. has only single conductor wires for input.

Earlier posts I made told the story of how I started out with a solder process that didn't work right. Lead-free solder was just not
wetting. So I kept heating. Maybe I burned out some components?

Any help would be appreciated. So far, my journey with this has been long and painful.

Last edited by Hogwild; 22nd September 2015 at 05:20 AM.
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Old 22nd September 2015, 05:53 AM   #2
diyAudio Member
Join Date: Sep 2004
Location: New Zealand
You will need to provide some diagrams and images of your
LM3886 build. Nat Semi provide excellent instructions here:

Are you trying to run these all at the same time, from the one psu
or separately ? How much capacitance are you using on the rails?

Check your bridge rectifier if it is still alive, possibly the 300VA
transformer has taken out one or some the rectifier bridge diodes
a thing called in rush current. Take a measurement of AC content
on the supply without the amplifiers connected. 18VAC should be
25.45V DC, up and down a bit of course with mains voltage flucuations.

Cheers / Chris
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Old 22nd September 2015, 06:14 AM   #3
Philfr is offline Philfr  France
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I agree with Chris, post some picts with both side of pcb.
Check R3 (amp board), page 8 :
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Old 22nd September 2015, 09:33 AM   #4
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Few pictures would be good.
Short the input of the amp and check the output again.
You can check the psu part with scope if it is steady voltage without amps connected to it.
With shorted input there shouldn't be any AC at the output, or something is seriously wrong.

Last edited by mrWagner; 22nd September 2015 at 09:37 AM.
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Old 22nd September 2015, 03:19 PM   #5
Hogwild is offline Hogwild  Canada
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Join Date: Oct 2010
Hi there:

Thanks for the info. The boards are, as I said, stock Chipamp.com LM3886 boards. Nothing's been modded. Sorry, I really should've specified dual mono.

Not meaning to sound snide, but is there a need to post pictures if everything is stock?

My first posting about this project, including pictures, is here. They area lousy pictures, I think. Let me know if I should post better ones. In fact, I'll go to take some today, if I can.

Help troubleshooting PSUs from Chipamp.com

No need to read that entire post. It was newbie confusion and mega problems with lead-free soldering. In the end, I switched to leaded, but maybe I damaged some components?
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Old 22nd September 2015, 05:09 PM   #6
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On the PC, it would be the "Go Advanced" button below, and then next, click on the "Manage Attachments" button to upload your pictures.

We do still need some more clues, and hopefully they'd be in the pictures that you upload into diyaudio.com.
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Old 22nd September 2015, 07:05 PM   #7
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Hi, it's not clear whether you bought complete kits from Chipamp. com or just the boards. If it was just the boards, I suggest that you check all the components for the correct values.

I've built the Chipamp LM3886 amps and they worked fine right off.
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Old 23rd September 2015, 01:21 AM   #8
Hogwild is offline Hogwild  Canada
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levistubby: Oh darn, I can't believe I didn't think of specifying. Yes, everything came from the Chipamp.com kit. Absolutely 100% stock. I tested all the components before soldering. Did you mean I should test them again now?

Here are some better pictures of the boards. Let's call the amp boards (acc. to who soldered them) b1, b2 and a1 for now. Let's call the PSU boards ps1 and ps2.

Here are some pics. In order, b1, b2, and ps1. I'll take photos of amp a1 and ps2 tomorrow and submit then as soon as I am able.
Attached Images
File Type: jpg amp b1-top.jpg (710.5 KB, 140 views)
File Type: jpg amp b1-top-rotated.jpg (756.9 KB, 134 views)
File Type: jpg amp b1-bottom.jpg (443.9 KB, 130 views)
File Type: jpg b2-top-rightside up.jpg (776.3 KB, 127 views)
File Type: jpg b2-top-upside down.jpg (972.8 KB, 124 views)
File Type: jpg b2-bottom.jpg (707.2 KB, 52 views)
File Type: jpg ps1-top-front.jpg (631.8 KB, 44 views)
File Type: jpg ps1-top-rear.jpg (649.4 KB, 36 views)
File Type: jpg ps1-bottom.jpg (643.0 KB, 44 views)
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Old 23rd September 2015, 02:21 AM   #9
Alekk is offline Alekk  United States
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Some of the solder joins on the board look like they need a little bit more solder. Other than that, everything looks in place. Double check the polarities on the capacitors to make sure everything is in the correct direction. If none of that seems to be working, then I would point to the transformer connections with those terminal screws. Make sure the screws are good and tight, and that the transformer leads are in order (one winding connected to one set, one connected to the other). If the transformer has more than two secondary coils, make sure that the secondaries are isolated (not soldered to other coils. I had similar symptoms to yours, except if it weren't for me noticing the solder melting on one of the terminals, I would have fried the rest of my power supply! Culprit was a third secondary soldered to my second secondary coil. )
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Old 23rd September 2015, 03:37 AM   #10
infinia is offline infinia  United States
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Id much rather see the whole test set up. the PCB s/b OK since you built according to the kit. did you use volume control pot with DC block cap?

you used the coax is used improperly. use the center conductor to 'In" and outside shield to'SG'. don't need 2 coax cables for each amp.
please dress lead wires>
twist pairs of wires from the transformer outputs to the power PCB. 2 pairs.
\Twist pairs from power supply ( 2 pairs for each amp pcb.)
\Twist speaker output pair.
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like the whisper of the termites building castles in the dust
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