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Old 20th January 2005, 11:39 PM   #1
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Default No left channel on Technics SA-303

I just got a Technics SA-303 receiver. Everything on it works great, except I have no sound on the left channel (this includes FM/AM radio and external inputs).
I've checked and tried switching the fuses on the back, and that isn't the problem. The balance knob just fades out the right side, but twisting either it or the volume knob back and forth quickly generates some light scratching/static from the left speaker (only if I do it quickly, not during normal movement)
What might be wrong with this? Do I have a specific bad part/connection/switch I can check out, or are there several things I can volt/continuity check to figure out what's wrong?
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Old 21st January 2005, 12:09 AM   #2
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A simple first check would be the solder joints on the volume and balance pots. Possible that one cracked, but I would think jarring them around you would at least get an intermittent signal. A physical instpection of the boards is always step one.
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Old 21st January 2005, 12:48 AM   #3
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I can't get down to the balance knob without completely taking out the front tuner assembly, which looks rather difficult. I took off the bottom and couldn't see anything wrong, and the volume knob connections look fine from the top, too.
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Old 21st January 2005, 01:00 AM   #4
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This is strange... when listening to the radio, I flipped both of the tape switches from Source to Tape. After I flipped them back up, no audio came back. I flipped one or both of them up and down a few times, but then the sound came back on only the LEFT channel. Now the right doesn't work.
What does this suggest? I'm not at all an expert on even the most basic of these types of units.

Second try; I had to flip the two tape, remote/main/remote+main, and power switch up and down in random order before the sound came back, it's still only on the left channel now.
It may be a delay of some sort; I flipped the tape switches down and up, and waited about 10 seconds. I diddled the volume knob a little and it came back on; that was with a station tuned but FM muting on.
With FM muting off, I briefly had it come in on both channels while fine-tuning the dial.

I turned muting back on, tuned it a little, and I got it coming through on both channels. It kind of randomly cuts out. For awhile I was getting full stereo, then the right channel started crackling a little, and now it's only on the right channel.

Now when I use a CD player on the Aux setting, I'm able to get a slight left channel and full right channel.

Depending on something to do with the tape switches; either it's if I slide them up or let them snap up and down normally, or the sequence, or some combination, I get different performance. Full left, no right, full left and partial right, scratchy left and full right, and so on.

Perhaps I just have dirty switches that I need to work around to clear up?
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Old 21st January 2005, 01:33 AM   #5
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Hi Secret Chimp,
Yes, you have dirty switches. If your unit has a speaker relay, those contacts may need cleaning as well.
-Chris
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Old 21st January 2005, 01:37 AM   #6
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Alright... there's how it seems to work.
If I switch the tape source switches on or off (either one or together) it usually messes up the audio output. Sometimes flipping the loudness switch on causes a loss of audio.
However, this problem is ALWAYS fixed by grabbing one of the tape source switches and moving it slightly down its travel; maybe halfway. For some reason, this "clears out" whatever is fuzzing up or cutting out the audio.
If I flip the Tape 1 switch to Tape (from Source) and flip it back on, it usually causes the left channel to come back on fully and the right only slightly. A half-dip clear out fixes this. The opposite for the Tape 2 switch; it seems to affect the left channel (the right channel generally comes on full and the left needs a little help)
Sometimes both will come back in fully by themselves, but if that's the case, it's always the channel closest to the switch first, and then the next channel (left then right for the left Tape 1 switch, right then left with the right Tape 2 switch)

Why are the tape switches quasi-linked to specific channels?

However, now that this problem is solved, on to the only other thing that seems to be wrong:
The SA-303 has an LED display below the tuner face. The LEDs connected to the tuner - FM Tuning, Signal Strength, and FM stereo - all work fine.
However, there's also a power level meter on the left. The center green LED is always lit, but the only time I see any activity is if the thing has been off for a bit (maybe 40 seconds to a minute) and I turn it on. Then, there's a little bit of a "bounce" on both channels about 2-3 steps out on the scale right after I power it up. Otherwise, it doesn't register anything.
The Display switch won't even switch the thing off; I'm guessing this is another switch issue, or does the fact that the channel power meter light up a little after a post-rest power up suggest that something else is wrong?
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Old 21st January 2005, 01:48 AM   #7
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Hi Secret Chimp,
The tape monitor switches are in the audio path. All your switches need cleaning before you can troubleshoot anything else.
The reason you get a reaction from the level meter is the power on surge. This might be fixed withthe switch cleaning or the behaviour may change. Clean first and continue troubleshooting if you need to.
-Chris
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Old 22nd January 2005, 12:57 AM   #8
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The internals of this thing aren't put together very conveniently; it looks like I'd have to remove the heat sink (and break a lot of big thermal paste bonds) or take apart the tuner needle assembly (I have no idea how it's put together beneath the top shields) somehow disassemble the entire front face (which may end up requiring disassembling the whole thing) in order to get a cleaner squirty tube down into the switch boxes/pots.
Is there a way to get cleaner into the switches without any kind of drastic mechanical operation? The only thing I can access with just the top cover off is the volume knob, but the apparently most dirty switches are stuck under the series of shelf things that apparently hold the tuning needle slider.
I'd be more up for trying to take apart the needle carriage if I had any idea what was going on in there, but I have no idea how difficult it would be to put back together after I got the switches exposed.
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Old 22nd January 2005, 03:02 AM   #9
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Hi Secret Chimp,
Sorry to inform you that sometimes you need to get things apart to get into the switches and controls. That's why it sometimes costs 2 - 3 Hrs labour to clean these contacts. I have had to do this and it's not normally fun.
See if you can get the faceplate and tuner dial off. Relax and keep looking at what you are doing.
Do not use TV tuner cleaner. Use as little as possible as it will wash out the lubricants also.
-Chris
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Old 23rd January 2005, 06:11 AM   #10
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What cleaner should I use? I've never bought any of this stuff before, and there seems to be a ton of different kinds out there; some claim to de-oxidize and lubricate (and a whole bunch of other stuff) at once, others I can't tell if they're right for cleaning these pots and switches.
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