I've got this RCD-951 which is in good condition and seems to play fine however one channel is faulty. If I turn the volume up that channel goes from silent to DC popping and pushing the cone of the test speaker.Just finished reflowing all joints.
Does anyone have any ideas to help me out with this one?
Thanks!
Does anyone have any ideas to help me out with this one?
Thanks!
Thanks for replying! I've checked most of the caps, I was wondering if anyone will recognise the distortion in the video.
I assume your amp is OK with other CD players?
Have you measured the DC offset at the CD player output terminals?
Have you measured the DC offset at the CD player output terminals?
Check the offset here (arrowed) and also measure and report back what voltage you have on pins 6 and 7 of each opamp. So four readings.
Are the opamps the correct ones or have they been swapped?
Are the opamps the correct ones or have they been swapped?
Thanks Mooly!
Yeah that's my test amp and is all fine, I keep it checked for these sort of jobs.
The opamps (OPA2604AP) are original and all original Black Gate caps too (good old Rotel!)
Will do as you suggested and report my findings, thank you for your help!
Yeah that's my test amp and is all fine, I keep it checked for these sort of jobs.
The opamps (OPA2604AP) are original and all original Black Gate caps too (good old Rotel!)
Will do as you suggested and report my findings, thank you for your help!
Offset:Check the offset here (arrowed) and also measure and report back what voltage you have on pins 6 and 7 of each opamp. So four readings.
Are the opamps the correct ones or have they been swapped?
2.8mv, 1.1mv
Opamps:
0.7mv, 0.7mv (left)
0.7mv, 0.7mv (right)
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Thanks, I just connected the RCD-951 to another amp just to be certain and the same problem.
Would this all point to a failing DAC chip or a Black Gate cap is bad and I missed it?
It doesn't really make sense tbh because the crackling and cone jumping you show suggests DC is present up to and including the point where the volume control is on the amp and yet you have measured the offset of the CD player at zero. It may just be that a meter is averaging all this and not showing what is really happening.
If you disconnect the speaker that is not jumping around do you get music from the bad channel or is it just noise?
Its difficult diagnose without a scope as that would show instantly anything going on with the output from the player. If the player has been modified then I would first look really carefully at anything that has been altered or changed and also look for solder splashes etc.
You can prove if the problem is the DAC or before the DAC by isolating the two signal feeds to each opamp and then cross linking them so you feed DAC Left into opamp RIGHT and see if the fault swaps channels or not.
If you disconnect the speaker that is not jumping around do you get music from the bad channel or is it just noise?
Its difficult diagnose without a scope as that would show instantly anything going on with the output from the player. If the player has been modified then I would first look really carefully at anything that has been altered or changed and also look for solder splashes etc.
You can prove if the problem is the DAC or before the DAC by isolating the two signal feeds to each opamp and then cross linking them so you feed DAC Left into opamp RIGHT and see if the fault swaps channels or not.
Just replace all lytics in the output stage before jumping to any further conclusions and wasting time on all sorts of measurements.
If you really like them then you can always solder them back one by one.
If you really like them then you can always solder them back one by one.
I would also look for bad solder joints and the output relay. Can you bypass the relay also?
After you've done what others have suggested and/if you haven't found the issue.
After you've done what others have suggested and/if you haven't found the issue.
Thanks for all the replies. Here's a second short video of the channel. I also wondered about this tiny output relay, it makes the bad channel pop the cone when pushed down with my thumb.
Rotel RCD-951 Faulty Channel
Rotel RCD-951 Faulty Channel
Thanks. I asked that because it wasn't obvious from the video whether that channel had audio as well.
When you push down the relay then you probably also bend the circuit board and some micro crack opens or closes due to that action.
Or the board makes contact with something that it should not do.
I've installed new opamps with no change. And today ordered that dac chip as a blind replacement. Solder joints are all reflowed and checked. The previous owner provided no clues just that they used it for a long time and got good use and then suddenly one channel drops out.