Lost RH channel

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   I have a Dual 701 acquired last year from Freecycle which was working fine, apart from an annoying hum. The output lead terminated in a male 5-pin DIN connector which was connected to 2 phono plugs via an adaptor, but it had no separate earth lead. 

After doing a bit of research, I decided to fit an earth lead which could connect to the earth terminal on the phono stage of my amp (an Arcam Alpha 9). I also removed the cartridge (Shure V15 III) and carrier from the headshell and cleaned all the pins, and also the metal strip contacts at the back of the headshell (which were black with filth) with a fine emery paper. 

I reassembled everything, reconnected and switched on. The hum issue was improved slightly, although I found it actually became worse if I connected the newly fitted earth lead to the earth terminal on the amp. However I then discovered a major new problem - there was now no output at all on the left-hand channel. I tried reversing the left/right cartridge connections, but that made no difference so the problem had to be either with the connections between the cartridge and headshell, or with the lead somewhere. 

The original female DIN to phono adaptor was old and corroded, so I replaced it with a brand new one. Even so, if I moved the cable, or touched the metal outer sleeves of the connectors, the hum would became really loud. I therefore decided to replace the entire cable, and fitted push-connectors to the stripped end wires of a twin-phono lead which I fitted on to the appropriate flat terminal posts inside the turntable. I now have a signal on the LH channel - but nothing on the right!

The four spring pins at the rear of the cartridge carrier appear to be making good contact with the now gleaming metal strip contacts in the headshell. Two of the fine wires from the cartridge/tonearm were kinked and very floppy where the kinks were, so I cut them off at that point and resoldered them to the relevant posts, in case there was a break in the wires. I also checked that the correct gaps were being maintained in the short-circuiter strips (which make contact when engaged by the camwheel to prevent noises during the automatic operation of the tonearm). 

All to no avail, and I have now run out of ideas. I don't have any kind of electrical testing equipment. Any suggestions as to how I can diagnose where the problem lies, or failing that, can anyone recommend a reasonably-priced turntable/hi-fi repair specialist in the Worcester Park, Surrey area of the UK?

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hotmog Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 14 Jun 2010 Location: Worcester Park Status: Offline Points: 178	Post Options Post Reply Quote hotmog Report Post Thanks(0) Quote Reply Topic: Lost RH channel Posted: 16 Jun 2010 at 7:27pm
	I have a Dual 701 acquired last year from Freecycle which was working fine, apart from an annoying hum. The output lead terminated in a male 5-pin DIN connector which was connected to 2 phono plugs via an adaptor, but it had no separate earth lead. After doing a bit of research, I decided to fit an earth lead which could connect to the earth terminal on the phono stage of my amp (an Arcam Alpha 9). I also removed the cartridge (Shure V15 III) and carrier from the headshell and cleaned all the pins, and also the metal strip contacts at the back of the headshell (which were black with filth) with a fine emery paper. I reassembled everything, reconnected and switched on. The hum issue was improved slightly, although I found it actually became worse if I connected the newly fitted earth lead to the earth terminal on the amp. However I then discovered a major new problem - there was now no output at all on the left-hand channel. I tried reversing the left/right cartridge connections, but that made no difference so the problem had to be either with the connections between the cartridge and headshell, or with the lead somewhere. The original female DIN to phono adaptor was old and corroded, so I replaced it with a brand new one. Even so, if I moved the cable, or touched the metal outer sleeves of the connectors, the hum would became really loud. I therefore decided to replace the entire cable, and fitted push-connectors to the stripped end wires of a twin-phono lead which I fitted on to the appropriate flat terminal posts inside the turntable. I now have a signal on the LH channel - but nothing on the right! The four spring pins at the rear of the cartridge carrier appear to be making good contact with the now gleaming metal strip contacts in the headshell. Two of the fine wires from the cartridge/tonearm were kinked and very floppy where the kinks were, so I cut them off at that point and resoldered them to the relevant posts, in case there was a break in the wires. I also checked that the correct gaps were being maintained in the short-circuiter strips (which make contact when engaged by the camwheel to prevent noises during the automatic operation of the tonearm). All to no avail, and I have now run out of ideas. I don't have any kind of electrical testing equipment. Any suggestions as to how I can diagnose where the problem lies, or failing that, can anyone recommend a reasonably-priced turntable/hi-fi repair specialist in the Worcester Park, Surrey area of the UK?

tg [RIP] Members Profile Send Private Message Find Members Posts Add to Buddy List Moderator Group Joined: 19 Jan 2008 Location: Sydney Status: Offline Points: 1866	Post Options Post Reply Quote tg [RIP] Report Post Thanks(0) Quote Reply Posted: 17 Jun 2010 at 3:33am
	I am not familiar with your TT and would not have a clue re repairers in your vicinity. What I would suggest is to purchase a fairly cheap DMM from your nearest Jaycar/Radio Shack/whatever. Make sure it includes a continuity test (although normal resistance readings will tell the story, the buzzer just makes it much easier) and use it to check for continuity and correct connection from the cartridge tags to the phono plugs, you can also use it to check if your ground wire is correctly connected or grounds to another lead at some point. It can also tell you if any of the leads is shorting to something else.

hotmog Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 14 Jun 2010 Location: Worcester Park Status: Offline Points: 178	Post Options Post Reply Quote hotmog Report Post Thanks(0) Quote Reply Posted: 17 Jun 2010 at 10:44am
	Thanks tg - They are pretty cheap, aren't they! I've just had a look around and found one with audible continuity test for £4.34. It's £8.50 postage though, so I'll wait until Monday when I shall be going up to London anyway, and will pick one up from the shop in person. Things went from bad to worse last night . In order to check the gaps on the short-circuiters I had to remove the cam wheel. In the course of putting it back and trying to synchronise it with the auto start/stop mechanism, I managed to rotate it the wrong way which not only bent the short-circuiters strips to buggery, but also the tiny upward projection on the pawl (which engages with the cam follower lever). Inevitably that broke off completely when I tried to bend it back. My futile attempts to solder it back on ended in utter frustration and dark mutterings about the whole thing now being a lost cause . Even if I can identify which of the tonearm wires is the problem, correcting it could be another matter. Especially so if it is where it soldered to the strip contacts at the back of the headshell, since there is no obvious way of detaching the headshell from the tonearm. I may well end up just salvaging the cartridge, ditching the 701, and looking for another TT, which is a shame because there's nothing that much wrong with it. I have a copy of the Dual 701 Service Manual and have identified the offending part no, but getting hold of one is easier said than done. Well, it cost me nothing (Freecycle's a wonderful thing!) and I've had a year's use out of it. To paraphrase (very badly) the opening lyrics of the Hot Chocolate song: It started with a hum, Never knew it would end like this

hotmog Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 14 Jun 2010 Location: Worcester Park Status: Offline Points: 178	Post Options Post Reply Quote hotmog Report Post Thanks(0) Quote Reply Posted: 03 Jul 2010 at 1:11pm
	UPDATE: Now sorted! I bought the DMM, but have been away on holiday since so I've only just had a chance this morning to have another go at the turntable to see what the problem might be. All the connections from the cartridge pins to the soldered posts on the powerplate checked out OK. Now I am absolutely sure I had connected the three push-terminals (red, yellow & earth) from the new phono lead to the exactly the same positions on the powerplate as the originals had been. However I reconnected the red to one of the other free posts, adjacent to the yellow, et voila both channels now worked. Simple enough in hindsight, but I'd never have worked it out without the DMM. The only issue arising from the damaged pawl appears to be that the auto-start mechanism no longer manouevres the arm into position above the first track on the record. I have to do that manually, but otherwise the auto-stop still works. I can live with that, and that means the UL upgrade can hopefully happen sooner rather than later. Edited by hotmog - 03 Jul 2010 at 2:11pm

tg [RIP] Members Profile Send Private Message Find Members Posts Add to Buddy List Moderator Group Joined: 19 Jan 2008 Location: Sydney Status: Offline Points: 1866	Post Options Post Reply Quote tg [RIP] Report Post Thanks(0) Quote Reply Posted: 03 Jul 2010 at 3:08pm
	Always good to hear when someone reports their particular problem is resolved. There may always be someone else with a similar one who happens along looking for clues. Thanks for letting us know

Lost RH channel

Cadman Enterprises Limited
7 Kirkstall Close
South Anston
Sheffield S25 5BA
England

+44 (0) 1909 568739
+44 (0) 7947 107188

john at gspaudio.co.uk

Lost RH channel

Cadman Enterprises Limited7 Kirkstall CloseSouth AnstonSheffield S25 5BAEngland

+44 (0) 1909 568739+44 (0) 7947 107188

john at gspaudio.co.uk

Cadman Enterprises Limited
7 Kirkstall Close
South Anston
Sheffield S25 5BA
England

+44 (0) 1909 568739
+44 (0) 7947 107188