Stereo mode in phone stage going out
I have a Pioneer SX-950 that had a near-complete restoration a few months ago. The issue I had taken it in for was the stereo mode when playing vinyl would cut out on the right channel. Thankfully, the mono mode stayed intact. Up until recently, all was well with stereo mode, but last week the same issue popped up again. My question is: would purchasing a separate phono stage correct this issue?
I tend to favor porchlight’s suggestion that the fault is in the selector switch, because OP says it doesn’t happen with other inputs. on the other hand, if the stereo/mono switch is only in the phono stage circuit, in that case it could be that stereo mono switch. But I think most of those old receivers and integrated amplifiers would have the stereo mono switch in the line stage circuit.
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When you say 98% out, is that 98% of the time or 98% of the volume? I suspect a loose contact around the base of the tonearm cable. Could it be that as the tonearm approaches the inner tracks, the tonearm cable is stretched enough to slightly dislodge a connector? Or maybe a wire in the tonearm is broken, but normally remains in contact - until reaching those inner tracks? Otherwise, it seems that the fault occurs as the amplifier warms up for a few tracks. Try starting playback at track four. What does this do to the onset point? Simplest test is to switch amplifiers - maybe borrow one from a dealer for a trial listen! |
Been a while since I posted here, but having restored a Pioneer SA-8500 II, thought I'd chime in. Some great suggestions so far. The thought of a dirty switch is a good suggestion, however, this unit does not have a rotary selector switch - it is all push buttons (pushing in one source pops out the currently selected source). See this pic of the 950 (its a beauty): https://www.classicaudio.com/forsale/pio/SX950.html Trying out the phono2 input to see if it has the same problem would likely determine if the problem exists on the switch board. All of these switches (rotary and push button) need to be cleaned in a restoration on these older units (and not just by spraying deoxit all over the place - they need to be pulled out, taken apart if possible, crud cleaned off, and the appropriate contact cleaner/enhancer applied). Also try connecting the turntable RCA leads in reverse (left to right and right to left) and make sure the sound in the right speaker still goes out. If the left channel goes out in that case, then the problem is before the 950 as @elliottbnewcombjr suggested - either the RCA connectors, the cables, or the cartridge leads or the cartridge are the issue. If it is not one of those, then it is could be something on the phono stage itself - the phono stage in this unit is very simple and uses six transistors, all of which are known to fail eventually. They have readily available and easy replacements too. This fellow on audiokarma had the same problem and fixed it by replacing those six transistors: https://audiokarma.org/forums/index.php?threads/pioneer-sx-950-no-right-channel-on-phono.1032652/ If you end up replacing the transistors, might as well replace all the electrolytic capacitors too on the board as well while you are in there. |
