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Old 19th December 2014, 05:46 AM   #1
Hogwild is offline Hogwild  Canada
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Default Help troubleshooting PSUs from Chipamp.com

Hi everyone:

Well, it's a case of classic Newbie here. I assembled two Chipamp.com LM3886 Snubber PSU boards.
The output of both boards is 0 Volts. When measuring that voltage,
the 40W lightbulb in my dim bulb tester briefly and dimly lit up for a second or two and then went off.

I must've really messed something up. I'm guessing I damaged
some components with heat, as my soldering process was a nightmare. I had some serious problems
wetting lead-free solder with the combination of solder and the station I had. My soldering skills are actually
fairly good, but there was some strange combination of factors which made soldering really hard in this case.

My skillsets are limited to following instructions, soldering, and some basics of using a DMM.

I'm using the transformer shown just for testing the PSUs. I know it will not provide enough power to run amplifiers,
but I found them for next to nothing. So I'm using them just to test the PSU boards to figure out where I messed up.

DSCN1276-web ready.jpg

DSCN1278-web ready.jpg

DSCN1280-web ready.jpg

DSCN1282-web ready.jpg

Transfomers to PSU board connections.jpg

I've read that in the case of this circuit, it can be useful to test some of the components while still on the boards.
I did that. So far, almost every component I tested
measured approx. its rated value. IIRC, The only exception was the large capacitors, which counted up and then restarted and then
counted up again in a cyclical manner when I measured capacitance.

I'm hoping to do as little desoldering of components as possible to figure out where I went wrong. Let's just say that
I don't have the most steady hands for that.

I'd be very grateful for any help. Thanks in advance.
Click the image to open in full size.

Last edited by Hogwild; 19th December 2014 at 06:16 AM.
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Old 19th December 2014, 06:56 AM   #2
Philfr is offline Philfr  France
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Hi,
Your transformer must have two separate secondary..
I don't see anything wrong on boards.
Phil.
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Old 19th December 2014, 12:46 PM   #3
AndrewT is offline AndrewT  Scotland
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the PSU PCB has 4 terminals for power input.
It also has 8 rectifier diodes.

Those two pieces of information tell you it is actually TWO PSUs each with a discrete 4 diode bridge rectifier.
You MUST NOT use a centre tapped transformer.
You MUST use a dual secondary transformer.
Each secondary has TWO wires and those two wire feed the two input terminals of ONE PSU.

OR
look up previous Threads that describe how to convert the PCB to allow it to work with a CT.
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Old 19th December 2014, 01:30 PM   #4
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where are you measuring? ( i hope your not reading across the entire supply and wondering why you've got zero? algebra dictates this would be so.)
if nothing is releasing "magic white smoke" and the caps haven't exploded congrats!
what are the T220 devices regulators or transistors?
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Old 19th December 2014, 02:16 PM   #5
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in looking things over where's the bridge rectifier?
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Old 19th December 2014, 02:31 PM   #6
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Check the chipamp.com website for more info and the schematic.
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Old 19th December 2014, 04:07 PM   #7
Hogwild is offline Hogwild  Canada
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Hi:

Thanks for all the comments. One person says I should be using transformer with more than one secondary. Another says I absolutely should not. Can we get some kind of consensus on this?

I measured with probes at:
V+ and PG
V- and PG-

Sheesh, I can't believe I didn't think of the fact that of course I'm not going to get anything at V- and PG- when I had transformer wires attached at only AC1 and AC1| . OK, first dumb mistake. But why didn't I get any voltage measurements at all, regardless of where probes touched?

Any diodes are the standard ones that came with the kit.

I doubt looking at a schematic will help, since I don't really understand how to read one.
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Old 19th December 2014, 05:54 PM   #8
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Quote:
Originally Posted by Hogwild View Post
I doubt looking at a schematic will help, since I don't really understand how to read one.
You have misunderstood the advice that has been given. The answer is in the user manual in the form of a schematic. The schematic shows the type of transformer and how it should be connected.

Youtube is a good source on how to use a DMM. measuring AC, DC, R and diodes.
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Last edited by Mark Whitney; 19th December 2014 at 06:00 PM.
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Old 20th December 2014, 01:48 AM   #9
Hogwild is offline Hogwild  Canada
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So, this would be one way to test with a Centre-tap transformer, then?
Dangerously wrong diagram at apexjr?

I had a h*ll of a time soldering these components due to whatever was going on with lead-free solder issues. Do I have to desolder those diodes, as in the picture or could I just bypass them with some wires attached to the correct places for testing purposes?

Thanks
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Old 20th December 2014, 06:56 AM   #10
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I would not convert the boards for centre-tap use. Get the right transformer!
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