Author Topic: Dual 721 repair  (Read 357 times)

Offline scorpio333

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Dual 721 repair
« on: April 25, 2018, 05:23:05 PM »
For the past week and a half I've been repairing and/or fighting my 721. I've only tackled the mechanical side of it, there are some electrical tune ups that need made. This all started because I was trying to adjust the VTA and things got weird. After inspecting it, I found the following part was broken.



Luckily I found what is believed to be the last two available, right here in the Burgh from dual-parts. I bought both, one is going to Quebec to Klaus, a former Dual service manager and good human. His guidance in this has been amazing. Klaus was a driving force to getting new dearings made for 12xx series tables, a broken dearing was fatal to those tables and now there are brand new parts available. The broken and new pieces are going his way to hopefully make new helixes for the 721's. They'll sort of work with the broken part, but it can be insanely finicky.

Along the way I found out there was a missing ball bearing in one of the races in the gimbal, I lost a spring (I HATE SPRINGS) and damaged a tracking force wheel. Everything is coming back to together slowly. I took pics along way of the disassembly (reassemble in reverse order!). Figured I might as well share in case anyone likes torture pictures or gets bored and wants to tear down their table which I don't necessarily recommend.

pix.sfly.com/CEXQt9Yj

Offline Sir Thrift-a-Lot

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Re: Dual 721 repair
« Reply #1 on: April 25, 2018, 09:27:02 PM »
You are infinitely more patient than I.   I curse at pens when I'm putting in a refill and the spring gets lost.   One more reason to be a direct drive guy.

Offline scorpio333

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Re: Dual 721 repair
« Reply #2 on: April 25, 2018, 10:46:21 PM »
Patience isn't my strong suit. However, this is one of the more regarded Duals. When it was introduced it was the quietest table rumble-wise available.

This table was covered in nicotine so a near complete teardown to clean it was in order.

The 721 is a direct drive, but also a full automatic table. There a nearly a dozen springs on it. I shouldn't have mentioned springs because the tracking wheel i tried from a 1237 won't work so now I need to pull out the tweezers to try and repair the original. The 1237 is on the left and has a nice tight 90 degree bend on the end of the spring. The 721 wheel on the right is out of square enough that it slips out of a notch on the dearing. There's plenty of cursing going on here.


Offline Sir Thrift-a-Lot

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Re: Dual 721 repair
« Reply #3 on: April 25, 2018, 10:50:15 PM »
If it were mine it would be in the bottom of the Mon by now.

Offline EmperorNorton

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Re: Dual 721 repair
« Reply #4 on: April 26, 2018, 08:25:28 AM »
Scorpio,

The 721 I bought recently apparently needs some attention.  The on/off switch has a lot of play in it, for one thing.  Not sure if the "fully automatic" function works consistently, as I've been manually placing the needle down to begin playing records.

Mike
Yamaha PF800/Dual 721
DBX D5/Sony CA8ES
Yamaha C-2X
Hafler Five Hundred/Sansui AU9500/Heathkit SA-2
Canton CT800s/Vandersteen 2CE/Klipsch Heresy

Offline scorpio333

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Re: Dual 721 repair
« Reply #5 on: April 26, 2018, 12:53:35 PM »
Mike,

I have a good suspicion what the issue with the auto start feature. If you feel adventurous you can take a look inside. Here are instructions on how to get inside. Lock the tonearm down and remove the platter first! https://www.vinylengine.com/turntable_forum/viewtopic.php?f=37&t=26556&sid=22370a70826c6e07c637ab9aa0e4d987

Then look at this pic. About an 1.5 inches down from the top of the pic and 1.5 inches in from the right, you'll see a silver nut with blue loctite. That white plastic piece under the nut has a tendency to crack around the hole right under the nut. Once it does, it's no longer a "lever" and will either have lots of play when using the start lever or not work at all. That was the first thing I had to fix way back when I got mine.

If you don't want to mess with it, no problem. I'll give you a call in a few hours.

Offline scorpio333

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Re: Dual 721 repair
« Reply #6 on: May 04, 2018, 06:48:00 PM »
If it were mine it would be in the bottom of the Mon by now.

Do you know a good spot to toss it in the Mon??? My patience is just about shot with this table. It's just insane how sensitive some of the screws and springs are...the gimbal on this table and the tracking force (SPRING) and then the auto start mechanism are ridiculously sensitive. I'm getting close, but still seems so far to go.

Offline Sir Thrift-a-Lot

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Re: Dual 721 repair
« Reply #7 on: May 04, 2018, 08:01:59 PM »
I like the Rankin Bridge.

Offline EmperorNorton

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Re: Dual 721 repair
« Reply #8 on: May 05, 2018, 05:50:42 AM »
It's not over the Mon but like they say, you can be sure if its Westinghouse.
Yamaha PF800/Dual 721
DBX D5/Sony CA8ES
Yamaha C-2X
Hafler Five Hundred/Sansui AU9500/Heathkit SA-2
Canton CT800s/Vandersteen 2CE/Klipsch Heresy

Offline Kingman

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Re: Dual 721 repair
« Reply #9 on: May 05, 2018, 09:13:07 AM »
Good luck with the repair or welcome to the make a wish club!  :laugh:
IN REALITY IT ONLY MATTERS WHAT IT SOUNDS LIKE TO YOU!!!!!

Offline scorpio333

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Re: Dual 721 repair
« Reply #10 on: June 01, 2018, 12:41:28 AM »
Been awhile since I updated this, outdoor stuff just won't quit growing! The turntable is still on the jig, just waiting to grab some paint for touch ups. Mechanically it's running great. I had EN's 721 here for a week or two and got it tuned up for him. While testing his. I can't wait to get mine back running full time. The tonearm gimbal on minecouldn't be saved, so I grabbed a parts table which came with a wrecked base. It definitely looked dropped at some point. So I got to thinking how much I don't like the bases Dual or United Audio decided to use. So I set out to make one better at least looks wise, if it adds 10 watts to my tubes it's a win win. I made a base for a 1229 awhile back and the mounting of the deck to the base is a pain to recreate with wood, so I decided to rip off the particle board sides off the junked 721 to get the top plastic mount separated.



After removing all the wood, glue and staples I grabbed some scrap wood and made a first draft



I didn't set the plastic mount low enough which caused the dustcover to not line up well. Back to the drawing board and came up with this.



After a few coats of danish oil and two light coats of poly it's almost there


Once I get the poly done, the plastic chassis slides in from the rear and gets secured. More pics to come as time allows, hopefully soon.

Offline Sir Thrift-a-Lot

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Re: Dual 721 repair
« Reply #11 on: June 01, 2018, 02:00:23 AM »
That looks great.   Here's a tip if you ever decide to do that to another table.   I would take that flakeboard plinth and throw it in a tub of water for a day or two before trying to liberate the plastic.   I'm sure it would practically fall off on it's own and there would be much less chance of breaking the plastic as you work.

Offline scorpio333

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Re: Dual 721 repair
« Reply #12 on: July 09, 2018, 10:58:18 PM »
Geesh over a month since I posted any updates on this. I believe I cleared the last major hurdle tonight. Hopefully another couple sides on it and I'll know for sure. Need to get it cleaned up and post some pics later.

Here's a teaser pic: