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Post by punkjr on Apr 30, 2010 11:21:11 GMT
Hi all
I have just carried the mods to my Jaycar PSU, and upon reconnecting, I had only two of the four LED's working, and a humm from my PSU. I checked the voltage, and I have 14.96 on the -, and .7 on the +. I have checked for bridges, but cannot see any. Can anyone help, and have I likely damaged something on either boards?
Tom
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Deleted
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Post by Deleted on Apr 30, 2010 11:33:56 GMT
Hi all I have just carried the mods to my Jaycar PSU, and upon reconnecting, I had only two of the four LED's working, and a humm from my PSU. I checked the voltage, and I have 14.96 on the -, and .7 on the +. I have checked for bridges, but cannot see any. Can anyone help, and have I likely damaged something on either boards? Tom Tom Remove the leads from the PSU to the main PCB before you go any further. Are you able to post photos of both sides of the PSU PCB, or at least the top ? If you don't know how to post a photo, email it to me. Please try and make sure the photo is of a reasonable resolution. Alex
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Post by punkjr on Apr 30, 2010 11:59:26 GMT
Hi again Alex
I think I jumped the gun. Whilst I was waiting for a response, I reread one of your previous posts, asking someone to check the orientation of the electrolytics. I did find a small black with a stripe at one end that was the wrong way around. There were four that I fitted, the 4004 things, and by luck, I only fitted one around the wrong way (could of been worse). I have refitted another small black thing, and everything is working fine.
Thanks for the help though.
Tom
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Post by punkjr on May 3, 2010 22:37:17 GMT
Oh no, so now I have a new problem. In my haste to listen to the mods to my rig, I wired the negative to the positive and vice versa. I had only four LED's light up, there was a hum, then a loud 'pop' and some smoke. I disconnected, inspected, and after finding nothing, I reattached the PSU. It appeared to work fine, with normal volume in both ears. I could hear nothing wrong with the unit.
So last night I put some shielded cable from my RCA's to the amp. When I reconnected, I discovered that my left channel has an extremely low volume, and is inaudible when the right channel is playing.
Now I'm not sure if this issue is related to my incompetance the previous night, or whether this is another issue altogether. Does anyone have any suggestions as to what to check? I have rechecked the wiring on my RCA's to PCB.
EDIT: Okay, so it turns out that I have only one channel working, and the sound I was hearing in the left channel was a mono of the right channel. I can get full noise from both channels if I pull my headphone plug partway out of the jack.
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Deleted
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Post by Deleted on May 4, 2010 11:01:14 GMT
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robertkd
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Electronics Engineer from sunny Queensland
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Post by robertkd on May 4, 2010 12:25:03 GMT
Tom, what you've let the magic smoke out,.... that's never a good sign
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Post by Deleted on May 4, 2010 21:56:03 GMT
Tom Despite the fact that all 4 LEDs are working, the fact that there was a loud "crack"and smoke, before you rectified the wiring fault, indicates that damage has been done. You need to check that none of the electrolytic capacitors are bulging or have "domed" tops. Especially check for the presence of more than a few millivolts of DC between both of the resistors in the centre of where the wire wound chokes were originally, to an earth point. Also check that the 4 x 4.7ohm resistors associated with the big output transistors have fairly similar DC voltage readings across them.If you have a Millivolts scale on your meter, select that option for those readings.The readings across the 4.7 ohm resistors should be a maximum of around 90 millivolts, and fairly similar across all 4 x 4.7 ohm resistors. Alex
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leo
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Team wtf is it?
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Post by leo on May 4, 2010 23:27:14 GMT
Did you try another op-amp? its not very often an op-amp will survive after reverse polarity
You need to locate where the smake came out and let us know, look very closely at the transistors, op-amp etc , look for small cracks/split
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Post by punkjr on May 5, 2010 13:14:33 GMT
Thanks for the tips guys. I have looked and have not been able to see anything obvious. One of the 470uF 25v capacitors had a slight bulge at the top! So I replaced the two caps with 100uF's, and installed to new output 68ohm resistors. I have a second amp that I have constructed, just waiting on the Toshiba transistors and the LME49720HA. I have also installed the Wima 470pF 100v capacitor across the two outside terminals on the input of the power supply (?). I hope that's correct. Thanks all for your help.
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Post by punkjr on May 12, 2010 14:13:52 GMT
I now have a new HA board fitted with the full array of mods, including the Toshiba's and the LM4562. Thank you all for your help, and I would like to especially convey my gratitude to Alex who, although rather busy atm, has found the time to help me with some self inflicted problems that I have encountered over the last couple of weeks.
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