Quote:
Originally Posted by ldadipscm
Alan (owner of the HMV 2046) confirmed last evening that, using the balance slider, the sound does come out of both speakers and furthermore, when the balance fader is pushed fully to the left, the sound disappears from the right speaker (and vice versa).
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Interesting. This means that the earth connection between the amplifier and control PCBs is good. My prime suspect has just shown me a cast-iron alibi.
I've heard horror stories where people have tried to clean potentiometers using over-aggressive solvents that have wound up eating right through the carbon track
But the symptom then is that you don't get any signal coming through at all. To get your symptom of full volume all the time, the very bottom ends of both tracks would have to have come disconnected from Earth. It's still possible that the fault could lie outside the potentiometer, but it could be within. At any rate, the broken connection is definitely somewhere on the controls PCB.
Unfortunately, while I have seen the insides of the family stereo on a few occasions (only a very few occasions; it was very reliable), I can't for the life of me remember how the controls PCB comes off. Does anyone else know? It would be a shame to break anything in the course of disassembly.
Then we're going to need some pictures of both sides. With it being so long and narrow, you might be best off taking four or five shots along its length. This will ensure the best resolution, as the Forum software will automatically reduce pictures to no more than 800 pixels on the long edge. Also note anything printed or stamped on the potentiometers. Then, one of us will be able to suggest where to probe with your multimeter.
There is one more test you might be able to try before you open her up. You will need a record with noticeably different material on the left and right hand channels. There are some music records that are like that anyway, especially some early stereo pressings; there were also special test discs for setting up record players, with bursts of different frequencies, solo passages of certain instruments, and left-right test tracks. There is a famous recording of a steam train that starts coming from the left and goes across to the right. The owner of the player may well already have something suitable. Or maybe you could use something connected to the tape inputs. Anyway. The test is to set the treble, bass and balance to centre, volume to minimum, both speakers connected and make sure the "mono" button is out; turn on the power, and play something that should be different in each channel. Are you still getting proper stereo separation, or is some of the left-hand signal leaking into the right-hand channel and vice versa? If in doubt, try pressing and unpressing the "mono" button (which directly connects the left and right signals together, so killing any separation). If this makes an audible difference, then you have stereo separation.
If the two bottom ends of the carbon tracks were still connected to each other even although they were not then connected to earth, that would mean the fault could not be inside the pot. In this case, with the volume control set to minimum, the amplifier inputs would be connected together; so whichever track a signal was arriving along, it would end up being fed to both speakers -- no stereo separation. The link between the two pins of the potentiometer is doing the exact same job as the "mono" switch. As the control was slid towards maximum, the resistance between the two channels would increase, thus giving less of the "wrong" signal in each channel, i.e. better separation. Pressing the "mono" button should then make a difference.
If you are getting proper separation between the stereo channels, and pressing the "mono" button makes a difference, this means that the two bottom ends are not connected to each other. This still doesn't necessarily mean the pot is to blame, though.
Anyway, pictures will be a real help. Someone here will be able to devise a sequence telling you exactly where to put your meter probes, to determine exactly where the fault lies.