Nagra III restoration question

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Rwm8088

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Hi all, this forum has been a great source of info in the past, now I have a question I can't seem to find an answer to anywhere, figured I'd post it here. I've always wanted an old Nagra to play around with, and a couple weeks ago acquired one, a Nagra III (1963). I bought it with a missing pinch roller and pin, figured it would have other issues if someone was pulling parts from it. I was right. It won't go into playback mode. The amp turns on but the transport won't run. It won't rewind either. It works fine in record mode, and will rewind if I use the speed control bypass button. I have a used pinch roller coming, and I'm looking forward to doing a full electronic restoration on it but want to get the transport functioning first. According to the manual, the rewind lockout in record mode is intentional, so I'm guessing the function switch is the problem, possibly a broken contact or wire on a solder tab, the switch has 5 or 6 wafers each with at least 6 contacts. Here's the problem: I want to remove the switch, check the contacts and wiring, but the switch shaft nut is behind the front panel, and it looks to me like the panel is glued to the case. Is there a trick to removing the panel without butchering it?
 
Hello and welcome.

You may get some replies here, but are likely to get more in the Analog Only forum.

I have a III myself, awesome little machines. First, get a copy of the manual. Then start with a meter and check out the motor wiring and control functions...before we start taking that switch out.

Im at work so I dont have mine in front of me, but I'll look it over tonite and see what is involved.
 
"Here's the problem: I want to remove the switch, check the contacts and wiring, but the switch shaft nut is behind the front panel, and it looks to me like the panel is glued to the case."





That is one RtoR machine I have never owned, but don't you have enough clearance to check the switch without removing it?
 
THanks for the welcome and replies. I've got the operation manual, pretty detailed, but I can't find an actual service manual and doubt I will be able to. But the manual wasn't much help except for the schematic. When I got the machine, I opened it up to find someone had removed the shield from the motor, and cut 2 of the 3 motor wires at the PCB. I checked the motor windings, they seem to be fine and the machine does run in record mode. From what I can tell, the switch over to rewind is done mechanically instead of with reverse polarity to the motor. THe switch itself is a multi-pole multi-position rotary switch with 4 wafers, 12 contacts per wafer. THe way the thing is built, the bottom case is one piece and the electronics are set down inside of it. The transport is a separate assembly, the top deck is hinged so with loosening 4 screws on one side the whole thing can be opened up like a book with the transport on the left and the bottom shell with electronics on the right. Thanks to this design, I can only get to 24 of the 48 contacts on the switch because the bottom shell doesn't come apart. To get meter probes to the other contacts I would either have to remove the switch, drill holes in the bottom shell right below the switch, or pick apart the wire looms to trace the wires from the switch to the other ends at the boards. I'll get some pics of it later and post a couple when I get it back on the bench tonight. I moved it out of the way so I could finish recapping a Tandberg 74b. Once that is done and off my bench, it's back to the Nagra.
I probly should clarify... Everything works in record, but when the switch is moved to any function on the playback side, the transport is dead. THe amps come on, and I can manually run a tape through, the battery meter works. I can only run it on battery, I don't have an AC adapter for it, so I can only test it in battery mode. I loaned out my variable power supply, when (if) I get it back I will check to see if it runs when switched over to external.
 
Try this:

No tape loaded. Deck switch to where the two black dots are aligned. Switch set to "playback +battery meter".
Then depress the high speed switch. Does the motor take off then?
 
Hmm. It is looking like the front rotary switch could be the problem. pressing the high speed switch puts full battery voltage across the motor, bypassing the tachometer amplifier, frequency Discriminator and motor servo amplifier out of the equation.

have you tried some deoxit on the rotary switch?
 
Yep. Its brought stuff back from the dead for me numerous times! Using it just this morning. Bringing a couple of vintage Mcintosh amps back to snuff for the studio.
 
I've tried Deoxit, it didn't help. That is good stuff, I do work for a recording studio here in FLorida, and use the stuff pretty frequently. THey bought a vintage Quad Eight Electronics 24-24 console made about '69 or '70, and I've gone through a dozen or so cans of the stuff on the edge connectors for the line amp cards and fader pots in the past year. It's worked especially well on the patch bay and the bus selector connectors that have had various substances spilled and dumped into them over the years. I've heard that the newer formula doesn't work as well as the original recipe that was banned (so I've heard), if there is any truth to that I'd love to find an old can of it somewhere.
But no help on the rotary switch. THe one set of contacts I can see 100% actually look pretty clean. I wonder if someone hasn't already gone this route before I ended up with the machine. ANd since I last messed with it, now when I switch it to playback mode, no power to the amps. I can no longer get a signal from the heads to the line outs or speaker, no voltage at all on the connectors for the playback amp. The heads on this thing don't look that great, I believe it has seen more than enough use to have a couple broken contacts in the switch. FOrtunately there seem to be a few Nagra III parts popping up on Ebay lately. Overpriced, but at least they are there.
 
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