Aleph 3 diy problem with one channel - diyAudio
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Old 23rd May 2015, 07:13 AM   #1
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Default Aleph 3 diy problem with one channel

I've been messing around with this long enough and I'm ready to seek help... That being said: I've built a Aleph 3 and I'm having a terrible time figuring out a problem I'm having with one channel. The unit starts up and I dialed in bias and offset and just when I plugged in my iPhone to check it, it went pop. My phone that is. The 3.5mm jack blew up on my phone.

I checked and found I had offset voltage on the input from one channel reaching .6volts and the other side was at 0. I blew a capacitor on the side with the voltage. After replacing it I checked input offset and found it had returned to 0 on both sides. I put the project down a couple days and thought it over.

Today I returned to it and I measured voltage at the input and found one channel to have 0, like it should, and the other to have -27volts! The one with the voltage issue is the one that has performed correctly all this time without any failure. I measured across the voltage rails and I have 55 volts, but 53 from the negative and 2 from the positive to chassis ground. I also have -27volts on the "ground" coming off my supply capacitor bank.

All my voltage reading are off on this channel and I have no idea where to start. I disconnected the power supply from the amplifier board and it performed as it should, + and -27 volts. As far as I can tell, the negative voltage is feeding back through the entire system through the ground and I'm not sure why or why the negative voltage is so high. One last piece of evidence is I found a blown diode on this channel as well, but after replacing it nothing changed.

Any ideas on where to start or what to check would be extremely helpful. Thank you.
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Old 23rd May 2015, 09:06 AM   #2
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For starters, as always, post pics. Ideally post a schematic of the actual build showing wiring and with voltage measurements annotated.

Check all solder joints for bridges.
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Old 23rd May 2015, 06:00 PM   #3
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Default schematic and pictures

Here are some pictures as well as a schematic with measurements. Only difference as far as I can tell in the schematic is that I'm using 2 variable resistors to adjust bias and offset. All the measurements are done checking voltage using chassis ground.
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Old 23rd May 2015, 06:09 PM   #4
Zen Mod is offline Zen Mod  Serbia
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using solid core fatties soldered to pcb is recipe for disaster

remove them , remove pcbs from heatsink and inspect is there any damage to traces


also - try power supply with some load

say that 100W bulb across one rail will be as 25W load
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Old 30th May 2015, 02:28 AM   #5
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I ran a couple 8ohm 25watt resistors across the rails and measured. They stated to smoke after about 30 seconds, but I got the measurements before. About 27volts on both sides. Will this suffice for testing the power supply under load? Clearly having no idea that solid core is bad for this situation, could you please explain why? I have the pcb off the heat sink and cannot see any damage. The diodes are good and the resistors measure good and are not burnt. Really all I can think to do is remove the transistors and check them as well as the board traces. I could also remove the capacitors and measure/replace them too.

I just really have no idea what would cause this to fail and then cause the voltage irregularities I'm measuring. My only guess would be the mofsets on the positive side? Is there a way to test them in the circuit? Maybe similar to matching then?
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Old 30th May 2015, 07:26 AM   #6
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-27volts on the "ground" coming off my supply capacitor bank. --> that mean isolate Mosfet to heatsink problem...i think.
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Old 31st May 2015, 12:46 AM   #7
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Quote:
Originally Posted by dungdochi1978 View Post
-27volts on the "ground" coming off my supply capacitor bank. --> that mean isolate Mosfet to heatsink problem...i think.
Yep! Thank you.
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Old 2nd June 2015, 10:22 PM   #8
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Quote:
Originally Posted by Zen Mod View Post
using solid core fatties soldered to pcb is recipe for disaster
Why is that, ZM?
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Old 2nd June 2015, 10:54 PM   #9
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Probably thermal expansion as they get hot, and break PCB traces.
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Old 2nd June 2015, 11:14 PM   #10
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1/100th of an inch, really ?
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