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Dual 701, start problems

O

Olderkongen

New Member
Dual 701, start problems HELP!

Has been (very?) Lucky to get hold of an almost unused Dual 701.
:D was great until I would try to spin the discs.
It is simply not going around, and it's a little shame when we talk board turntable...
At the same time I'm not super stressed out because I have understood that its not very much that can be destroyed on these players.
Someone who has ideas?

Could it be a fuse? Where do I find these?
 
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Can someone help me? I found a broken fuse. Changed it, i went out again almost immediately, a little burned smell. What can be wrong?
 
The motor and driving circuitry for the 701 are pretty complex. Matter of fact, even the service manual for the 701 states that if the motor and/or speed circuitry needs work, the unit must be returned to Dual for service. I don't know of anyone who knows enough about the motor to service it.

The only part of the motor circuitry that has potential for the novice to repair is the regulated 15V power supply. Here, the circuitry is straightforward and uses standard parts, such as a 1N4001 diode bridge, 7.5V zener diode, and common transistors & resistors. If the issue is due to a fault here, it can be fixed fairly easily. The service manual has a good schematic to work from. If you're lucky, the problem is a blown rectifier diode or one of the transistors in the 15V supply (although if you smelled something burnt, I'd look carefully at the resistors too).
 
Come on, Glenn - show me some love!!

There is a .0047 mF capicator in the power supply that has failed, causing a direct short. Will blow the fuse every time. New cap and fuse, and you are good to go. That's as far as you need to go, too, in the electronics.

However, there are many other mechanical issues that need to be addressed so that it is again in tip top condition. Any 35 year old piece of mechanical gear needs to be serviced.

Actually, the more you use a Dual, the better it operates.
 
bohhey said:
Come on, Glenn - show me some love!!

There is a .0047 mF capicator in the power supply that has failed, causing a direct short. Will blow the fuse every time. New cap and fuse, and you are good to go. That's as far as you need to go, too, in the electronics.

However, there are many other mechanical issues that need to be addressed so that it is again in tip top condition. Any 35 year old piece of mechanical gear needs to be serviced.

Actually, the more you use a Dual, the better it operates.
Click to expand...

You da man! I love it when people know their crap! :thmbsp: Almost makes me wish my 701 was broken so I could fix it and feel like the man!:yes:
 
Well, the total number of 701's I've worked on is zero...and I never heard of the fuse-blowing capacitor till now (I admit I knew Bill changed them, but now I know why... ;))
 
You may have...but how many years ago was that? :scratch2:

Glad you found the thread...might have saved another nice 701.
 
Open up the box where the fuse is. Desolder the power and strobe lamp connections. Remove the circuit board from the case - you need to splay the case sides to get it out. You do not need to desolder the 3 leads to the transformer. Locate the cap - clearly labeled as .0047 mF, desolder it and replace it with a new film cap. I've got 'em, if you need one. As part of a 701 rebuild, this cap is always changed out. They usually split one side out.

There's another cap in the KS-3 power connection box. It stops the spurrious "pop" that comes from your speakers. when it is turned on and off. Sometimes, this needs to be changed out as well. Also, the power cord mounting pins in this power supply frequently fail. Later Duals have the KS-4 power supply - and the caps always need to be changed out. Bad pins here, too.
 
bohhey said:
Open up the box where the fuse is. Desolder the power and strobe lamp connections. Remove the circuit board from the case - you need to splay the case sides to get it out. You do not need to desolder the 3 leads to the transformer. Locate the cap - clearly labeled as .0047 mF, desolder it and replace it with a new film cap. I've got 'em, if you need one. As part of a 701 rebuild, this cap is always changed out. They usually split one side out.

There's another cap in the KS-3 power connection box. It stops the spurrious "pop" that comes from your speakers. when it is turned on and off. Sometimes, this needs to be changed out as well. Also, the power cord mounting pins in this power supply frequently fail. Later Duals have the KS-4 power supply - and the caps always need to be changed out. Bad pins here, too.
Click to expand...

Thanks a lot for your help. The .0047mF capacitor (C52 in Scheme) looks OK?? I measure 25,5 VAC on secondary on the trafo if i disconnect the wires to the motor. A person in Norway told me that C3,electrolytic capacitor 470 mF on the print under motor could have dried out --> short. Does this sound reasonable? Should i change the other parts as well?
 
Good work.

I've been intending to change that cap and another 50µf cap shown in the schematic. but I have no idea how hard it is to get to the solder side of that board. Did you remove the board to get to the solder side? Or just tack your new cap to the old leads so you didn't have to remove the board?
 
I cut off the old cap soldered the new one in the old pins. It is a sort of lacquer coating on the solder side of the card and I did not take a chance to touch that. But its no problem to lift the card it you want.
 
Thanks to everyone who replied in this thread. I am working on a Dual 701 currently. It had a blown fuse. I replaced the fuse with one from the hardware store that was .250a instead of the needed .125A just to test it out. That may not have been a great idea as the unit powered on but began to smell like something was overloading a bit after a few moments, so I powered it down and am trying to order parts from Mouser. Can someone help me make sure I am ordering the right parts?

power supply capacitor C52 on schematic .0047 mF film cap???
https://www.mouser.com/Search/Produ...irtualkeyECQ-E2475JFvirtualkey667-ECQ-E2475JF

fuse .125A???
https://www.mouser.com/ProductDetai...=sGAEpiMZZMsZt0HrY5I79peG3sX9OZ38FTcaEm1SnTY=

I am not sure how to tell the size of the cartridge fuse. I know the one in the Dual 701 is smaller than most fuses I am used to seeing. Do I have the right size selected above?

many thanks. -Joe
 
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