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Old 17th December 2011, 03:40 AM   #1501
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Thanks RS for your help. I've narrowed my problem down to D1. It was reversed. I started tracking the voltage from D3 and downwards. D3 & D4 measured 18. C2, C3, C4, C5 also measured 18. Across D1 it's zero even after I've de-soldered and corrected the polarity. So I might have overcooked it while I'm trying to de-solder it.

Once thing that I don't quite understand is U6. Between in-out it's 5.8v and ground-out is 12v. Is that because the circuit before it is open?

Last edited by hbarradah; 17th December 2011 at 03:46 AM.
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Old 17th December 2011, 03:55 AM   #1502
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Matthaios, if you have a DMM you can run the voltage checks I'm working on publishing on my blog. If nothing is getting hot it sounds like there's a DC problem of some sort in one channel. Hopefully you're not using valuable headphones unless you're sure they're not seeing any DC. But the fuzzy sound might be a serious DC offset and when it stops completely it might be pure DC. If you don't have a DMM, turn off the amp immpediately after it stops playing in one channel. If you hear a big pop in the headphone when you turn it off, it's likely there's a large amount of DC on the output.
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Old 17th December 2011, 04:32 AM   #1503
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Actually I'll take that back about D1. When I test it using the diode mode on dmm I get 160 on the right direction and 0 on the opposite. So it should be fine. But across it I'm still getting 0V even though when I measure across C6 and D1's anode I'm getting 12V.
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Old 17th December 2011, 05:33 AM   #1504
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@RocketScientist: I double checked the temps of everything and from startup until a few minutes after it was turned on, all components were cool to touch. I then went ahead and checked the voltages with my dmm as follows.

AC - 12.8-13. I'm a bit confused on this, I thought I selected the wall wart from the BOM which is rated as a 12V, not the 13.5v+ that the testing states.
Battery - 11.9v on each, 23.3v across both
C8/C9 - 11.7v onv c8 and 11.6v on c9, 233v across both
U6 - 11.9v
U5 - 4.6v
C2/C - 16.6v
P2 - with the black pin in the square hole and red in the last hole it starts at 1.1v and slowly climbed up to 20v before I shut it off. Every other way I tried to measure P2 read 0.0v.

BTW, thanks for creating this project and for the help trying to figure this out.

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Old 17th December 2011, 06:35 AM   #1505
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Matthaios,

The AC power is a bit low but that's OK. The wall wart is rated at 12 volts, and depending on your home line voltage, should put out about 13.5 volts with no load.

I assume the battery voltages are with no batteries installed.

The pin outs are different on U5 and U6 and you're measuring is the voltage across U5--i.e. it's dropping 4.6 volts which is correct (16.6 - 12).

It's impossible for the DC offset at P2 to go past + or - 12 volts with respect to ground (the square hole). Do you mean 1.1 millivolts to 20 millivolts? (i.e. 0.001 - 0.02 volts)?

If the DC offset is really 1.1 volts or higher that's bad and would explain the distortion. Please don't use any headphones and wait for my revisions to the article.
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Old 17th December 2011, 06:57 AM   #1506
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RS, sorry I accidently measured p2 as ac not dc. It is actually starting at around 0.7v and rapidly climbs up to 11v I assume, and stopped measuring at around 9v.

No rush or anything, and but when should we expect the update to the article? And again, thanks for the help.

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Old 17th December 2011, 07:05 AM   #1507
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@Matthaios, @hbarradah, @kmc52087,

Please have a look at the following newly written section on my Blog. It's likely full of typos, formatting/editing problems, etc, as it's past my bedtime and I've been at it too long. But it should help quite a bit in many circumstances:

O2 Troubleshooting

Important! Please note I've also substantially revised the DIY Testing section as well and you need to make sure you follow what's there first:

O2 Initial DIY Testing

@Matthaios, I really can't think of what would cause a climbing DC offset like that but swap U3 and U4 and see if the problem swaps channels. If so you have a bad 4556. If it stays in the same channel, measure from ground to pin 5 of U3 and U4 and see if there's also an offset there? If so, check across C13 and C14. There's just not much to go wrong with the output stage that would cause a symptom like that besides the op amps themselves but you never know I guess.
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Old 17th December 2011, 02:43 PM   #1508
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Quote:
Originally Posted by hbarradah View Post
Actually I'll take that back about D1. When I test it using the diode mode on dmm I get 160 on the right direction and 0 on the opposite. So it should be fine. But across it I'm still getting 0V even though when I measure across C6 and D1's anode I'm getting 12V.
Make sure your power switch is on. You won't get a voltage drop across D1 unless there is some current going through it. Does your LED still light when the power switch is turned on? Since the voltage drop across D1 will be that 0.16V - or - so make sure your DMM is on a low range, if manual, like 2V and on DC volts.

0.16V is OK for D1 on the diode test mode since it is a Schottky. Try measuring between ground and D5's cathode, see if you are getting around -12V. Then measure the voltage drop across D5.
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Old 17th December 2011, 02:47 PM   #1509
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Thanks agdr. I should add there are three links to large diagrams of the O2 PC board called out in the links in post 1507 above. One has DMM in-circuit resistance measurements. The other two have voltage measurements including D5 to ground as agdr suggests.
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Old 17th December 2011, 05:36 PM   #1510
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I did what you said and worked my way backwards. I found that the voltage was bad at C15 (8 volts) and good at the battery terminals (24 volts). Decided it was a bad connection on the switch, resoldered the pins and its working great. Perfect voltages everywhere.


Thanks for your help RS.
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