Hi All,
Been listening to my LM3875 premium kit for a week, and it was sounding great. But today the right channel faded out suddenly. There is still faint volume there but not much. I've eliminated speakers and source as problem. Voltages on rails and dc offsets are normal. and all continuity tests are checking out. I will need to remove chip from the board to test...correct? Star grounds are set up exactly as Peter suggests. Speakers are 8 ohms and there has been little detectable heat coming from the chips all week. I'm using a PEC 25K pot. Any thoughts are much appreciated. Thanks.
Been listening to my LM3875 premium kit for a week, and it was sounding great. But today the right channel faded out suddenly. There is still faint volume there but not much. I've eliminated speakers and source as problem. Voltages on rails and dc offsets are normal. and all continuity tests are checking out. I will need to remove chip from the board to test...correct? Star grounds are set up exactly as Peter suggests. Speakers are 8 ohms and there has been little detectable heat coming from the chips all week. I'm using a PEC 25K pot. Any thoughts are much appreciated. Thanks.
Additional Info
Forgot to mention that I'm using Avel 330/25+25 transformer. Rail voltages measure about 37V. For heatsink, I'm using 2.5"X1.5"X1/8" alum u-channel in almost same configuration as Peter's build instructions. Any advice is welcome. Thanks.
Forgot to mention that I'm using Avel 330/25+25 transformer. Rail voltages measure about 37V. For heatsink, I'm using 2.5"X1.5"X1/8" alum u-channel in almost same configuration as Peter's build instructions. Any advice is welcome. Thanks.
If the chip shows normal offset (20-70 mV) it's usually not damaged. Check if the offset changes when adjusting volume.
I would suggest swapping complete boards between both channels first and see what happens; removing chips might be tricky.
I would suggest swapping complete boards between both channels first and see what happens; removing chips might be tricky.
Thanks, Peter
Will do the swap. With full volume I'm getting 24mv on right channel 5.5mv on left. With volume off, 3.7mv on right, 33.1 on left. I'm pretty sure these are similar numbers when I brought it up initially. sound ok?
Will do the swap. With full volume I'm getting 24mv on right channel 5.5mv on left. With volume off, 3.7mv on right, 33.1 on left. I'm pretty sure these are similar numbers when I brought it up initially. sound ok?
Peter. I swapped the boards and the right channel still lacked proper volume. I swapped wiring on pins of the pot and low volume shifted to left channel, which means the problem seems to be in front channel of the PEC. Please let me know if you think I've missed something. Is it possible to repair the PEC? Thanks.
If it's the PEC, I assume you changed the wires after the pot?
Here's the link showing how PEC pot is built:http://www.diyaudio.com/forums/chip...-photo-ignore-my-ugly-pinky-2.html#post471619
One way to damage it is by overheating the pins which may disrupt internal connections.
Here's the link showing how PEC pot is built:http://www.diyaudio.com/forums/chip...-photo-ignore-my-ugly-pinky-2.html#post471619
One way to damage it is by overheating the pins which may disrupt internal connections.
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