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Dual 701 Left Channel Issues

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Dual 701 Left Channel Issues

Postby MtnBeachBum » 12 Jul 2018 18:48

Hello all.
Been chasing gremlins in my system since I moved to the new place. Ever since I set up the stereo system I swear that the left channel wasn't quite up to snuff with the right channel. I thought it was a speaker issue, probably because I have been wanting to upgrade the speakers for some time anyway. Then I noticed that everything sounded fine when playing cassettes. I then tried my other turntable and everything sounded fantastic!
I then turned my focus to the receiver because it hasn't had any work done to it since I purchased it. It has two phono inputs, so I swapped the inputs and plugged the Dual 701 into the Elac 50H inputs and still no left channel. So, now I know that it is a problem with the Dual 701 somewhere. I deoxed the pins coming out of the cartridge, the pins coming out of headshell insert, and the actual headshell itself, still no left channel.
My question to yall is what else should I concentrate on that may explain no left channel? I had a new RCA cable put on a year ago, I would be very surprised if it was bad already. I removed the 701 from the base for the first time ever to see if there was anything visually that looked odd but to no avail. I just had the turntable serviced a couple of months ago. I am hoping it's something simple I can do, I don't have any soldering skills or test equipment. Any ideas?
Chris
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Re: Dual 701 Left Channel Issues

Postby Dual_Jean » 13 Jul 2018 00:02

Hi Chris,

Usually the contacts between the headshell and the tonearm get tarnished.

Can you try another cartridge? I would also test conductivity with a meter each wires from the end of the RCA all the way to the tiny wires connecting to the cartridge.
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Re: Dual 701 Left Channel Issues

Postby Spinner45 » 13 Jul 2018 01:28

Possible issue with the muting switch contacts not opening.
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Re: Dual 701 Left Channel Issues

Postby MtnBeachBum » 14 Jul 2018 00:39

Dual_Jean wrote:Hi Chris,

Usually the contacts between the headshell and the tonearm get tarnished.

Can you try another cartridge? I would also test conductivity with a meter each wires from the end of the RCA all the way to the tiny wires connecting to the cartridge.

I don't have another cartridge, unfortunately. I also don't have a multi meter.
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Re: Dual 701 Left Channel Issues

Postby MtnBeachBum » 14 Jul 2018 00:57

muting.jpg
Spinner45 wrote:Possible issue with the muting switch contacts not opening.

Not very familiar with how the muting switch works. What exactly am I looking for and where do I clean?
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Re: Dual 701 Left Channel Issues

Postby Spinner45 » 14 Jul 2018 02:19

MtnBeachBum wrote:
muting.jpg
Spinner45 wrote:Possible issue with the muting switch contacts not opening.

Not very familiar with how the muting switch works. What exactly am I looking for and where do I clean?


When in play or stop/off mode that cam gear opens the contacts (right side of that photo)
The opening between contacts is perhaps a millimeter or so, and when the gear rotates during cycling, they should be closed.
Best to refer to the service manual for details, before messing the thing up.
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Re: Dual 701 Left Channel Issues

Postby MtnBeachBum » 14 Jul 2018 06:00

Ok. Thanks
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Re: Dual 701 Left Channel Issues

Postby Tinkaroo » 14 Jul 2018 10:41

It's probably a good idea to get a multimeter, even a cheap one since it is a valuable tool for many things around a household besides checking continuity and resistance.

A simple one with basic functions can be found for reasonable prices these days, so worth considering picking one up some time.
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Re: Dual 701 Left Channel Issues

Postby DSJR » 14 Jul 2018 11:04

Gawd, those solder connections look not too good when viewed close up (I'm sure they're just fine!) - at least I used heat-shrink on my 701 exit cables to try to smarten the look up even if it makes no darned difference. Exposed un-tinned copper will go off over the years and sadly, the original exit cables probably only needed fresh RCA plugs fitted at the amp end but I was an audiophool then and thought fresh cables would perform better 'cos the originals didn't look smart enough...

I appreciate different climate and storage can give differing results here. I have a number of used carriers here and one or two of them don't like my 701, but can work in the similar 1214 shell. One early carrier works in the 701 but not at all in the 1214 headshell - SO - maybe a fresh carrier would be useful, or at least to very lightly file the tips of the sprung pins on the back of the carrier even if they basically look shiny from the side - just a thought. A fibre pen gently used on the headshell contact strips too? the mute leaves are well described in the service manual (they stick out from the contact block pictured and should be open and not touching in 'play' mode and when cycling, they touch each other to 'short' the channels. They also

A note please - the 701 is a classic and becoming collectable now. Mine cost me £50 at a second hand store thirty years ago when it was already twelve to fifteen years old and is now worth several times that. The sonic performance just gets better and better as the cartridges improve and the arm will happily take pickups costing a grand or more and get great results from them too!!
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Re: Dual 701 Left Channel Issues

Postby mrow2 » 15 Jul 2018 22:16

All is true! Well you could resolve it just using careful procedures described in all the threads which relate to this here, but the common areas are to clean wherever there is tarnish from RCA plugs to the cartridge clips, wire crimps, headshell (cartridge carrier contacts), PCB on the tonearm head. The tarnish can get everywhere and even inside the microscopic clips where they are crimped. There is a way to chemically clean them (then re-crimp even tighter) but the absolute best is to pry open the clips with the smallest jewelers screwdrivers possible, clean the surfaces and the wires, and re-clamp. (If you do it chemically and it fails, you'll probably ruin the tiny clip trying to get it to release the tiny wires for proper cleaning). This is a real pain, but it does increase signal strength and reliability. Any nicks on those few soft copper wires inside each sheath and they'll fall off, so be sure they are strong before reassembling. If you solder them, don't allow the solder to run into the clamp portion of the clip or you'll have a mess. They don't really have to be soldered though if it's done well, it's probably the best result.

Muting switch keeps the system quiet during cycling. The cartridge is a form of microphone, similar principles involved. If not muted during cycling you will hear clunks and loud sounds from the table and stylus you'd rather not hear. So those contacts in the right of the pic need to be clean and make good contact in order to have it work well.
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Re: Dual 701 Left Channel Issues

Postby dualcan » 15 Jul 2018 22:37

Hi,
Please keep in mind that muting on the muting switch is a secondary function. The primary function is to set/hold the proper null point on the cam. The exception to this was the 1214 1216 and 1218 (perhaps a few more..). These had an extra "finger" from the platter bridge to perform the null function.
Regards,
k
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Re: Dual 701 Left Channel Issues

Postby MtnBeachBum » 16 Jul 2018 01:42

Found the culprit! It ended up being a combination of cleaning the small lead ends that clip onto cartridge pins thoroughly ( got quite a bit of black crud out of them) and fixing the white lead clip end.
After trying everything out and it still not being right i undid the leads from the cartridge and noticed it was very loose. I crimped it a bit and slid it back on. This time i could feel some resistance when i slid back onto post. Got everything back together and... hello left channel. Didn’t notice it was loose before, must have been because the crud was keeping it nice and tight until I decrudded it.
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Re: Dual 701 Left Channel Issues

Postby mrow2 » 16 Jul 2018 04:35

Exactly right! Decrudding and tightening the leads and clips goes a long way towards making things better!
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Re: Dual 701 Left Channel Issues

Postby Spinner45 » 16 Jul 2018 05:35

mrow2 wrote:Exactly right! Decrudding and tightening the leads and clips goes a long way towards making things better!


I apply a drop of Tarn-X into the clips, let it sit a while, then use a small stiff brush to "scrub" the inside of the clips.
Rinse with contact cleaner, crimp it closed a little, then call it a day.
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