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Mini3 troubleshooting help

post #1 of 24
3/20/10 at 6:12pm
Thread Starter 
Hello,

Finished my mini3 build last and....

For some reason the battery starts to heat up heaps when it is in use. Also the front LED doesn't light up.

It does produce sound (and sounded good in the brief period I used it), but with a battery running so hot and no glowing led I don't think it's a good idea to use it...

Checked the circuit, looks to be clean with no solder bridges.
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post #2 of 24
3/20/10 at 6:37pm
Do all steps of the Initial Check on amb's site and report your findings:
The Mini³ Portable Stereo Headphone Amplifier

For the battery to get hot, you must be drawing way more current than you should be.
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post #3 of 24
3/20/10 at 8:12pm
Reversed or shorted D4 diode?
Is the LED installed backwards?
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post #4 of 24
3/20/10 at 8:22pm
Thread Starter 
Quote:
Originally Posted by amb View Post
Reversed or shorted D4 diode?
Is the LED installed backwards?
Oh!.... didn't know leds have a polarity. On the silkscreen which is positive for the led?

Hope I haven't blown anything in my board due to that.

D4 diode has got the black ring side of it facing the battery.
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post #5 of 24
3/20/10 at 8:28pm
Quote:
Originally Posted by rayk View Post
Oh!.... didn't know leds have a polarity. On the silkscreen which is positive for the led?
The cathode ("negative") side of the LED should be oriented to the pad with the straight line on the silkscreen.

Quote:
Hope I haven't blown anything in my board due to that.
Mounting the LED backward shouldn't cause any damage.

Quote:
D4 diode has got the black ring side of it facing the battery.
That's correct, but measure it (while the battery is removed) to make sure it's not shorted. Also make sure the mounting screw for your 7812 voltage regulator isn't shorting to the ground plane on the bottom of the board.
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post #6 of 24
3/20/10 at 8:36pm
Thread Starter 
Quote:
Originally Posted by amb View Post
The cathode ("negative") side of the LED should be oriented to the pad with the straight line on the silkscreen.

That's correct, but measure it (while the battery is removed) to make sure it's not shorted. Also make sure the mounting screw for your 7812 voltage regulator isn't shorting to the ground plane on the bottom of the board.
Thanks! What should the diode measure?
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post #7 of 24
3/20/10 at 8:44pm
With your DMM in ohms mode, it should basically measure open circuit ("infinite resistance") after the reading settles.
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post #8 of 24
3/21/10 at 12:46am
Hi, thought it was fair to piggyback on this thread, rather than starting a new one. If I should start a new one, please let me know.

I finished assembling my mini three, and I'm getting really high DC offset on the left channel (5.000v) and about 0.5v on the ground channel, which according to the test guide, I have a blown opamp. Should I replace U4, U5, or both?

Also, how close should the electrolytic caps be in capacitance? the 100uf ones are very close (98.2 and 98.6) but the 470uf's arent (465 and 510 or so.) Does this matter?
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post #9 of 24
3/21/10 at 3:04am
Quote:
Originally Posted by barnaclebeau View Post
I finished assembling my mini three, and I'm getting really high DC offset on the left channel (5.000v) and about 0.5v on the ground channel, which according to the test guide, I have a blown opamp. Should I replace U4, U5, or both?
High DC offset on the left channel indicates a problem with U5, high DC offset on the ground channel indicates a problem with U4. That said, it might not necessarily be a problem with the opamps. Bad soldering could also cause it. Try reflowing the solder joints first, then go through the initial check steps again.

Quote:
Also, how close should the electrolytic caps be in capacitance? the 100uf ones are very close (98.2 and 98.6) but the 470uf's arent (465 and 510 or so.) Does this matter?
The two 470uF caps are in parallel (see schematic), their capacitances are additive, it doesn't matter if one of them is a little higher than the other.
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post #10 of 24
3/21/10 at 3:21am
AMB,

Thanks for the quick reply. Already reflowed all joints, good to go, I'll double-check but it looks like I'll be ordering new chips from you soon.

Ah, didn't even look at the schematic yet, am going to study it while listening to the amp
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post #11 of 24
3/23/10 at 6:31pm
Thread Starter 
Ok so,

D4 reads 0, while D1, D2 and D3 all read 1 after the counting stops. Well for some reason only D1 counts for a while while the other 2 just show up 1 straight away.

Checked soldering on D4 - looks good, no solder bridges or touching of any kind. Faulty diode?
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post #12 of 24
3/23/10 at 6:38pm
rayk, your D4 is definitely shorted: "0 ohms".

Many DMMs read "1" when it's in over-range condition. For ohms mode this means "open circuit". That's what I expect them to measure.
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post #13 of 24
3/23/10 at 7:16pm
Thread Starter 
Hmm I'll try to take pictures of it tonight then, but it looks so clean around it - can't see where it's shorting out unless the diode is broken somehow...
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post #14 of 24
3/23/10 at 7:26pm
rayk, the D4 diode is most likely shorted out internally. You need to replace it.
This usually happens if you connected the battery backwards.
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post #15 of 24
3/23/10 at 7:57pm
Thread Starter 
Ah! Thank you, well things you learn .

What the difference between BZX55-C12 and BZX55C12 ? Both seem to have identical specs - cept there is only stock of BZX55-C12 in AU.
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