An unusual Revox A77?

[Jay Pemberton]

I've had this machine for about 10 years. It's in terrible shape, and I know the record head is bad, one of the VU meters is dead, and it will need a comprehensive recap job and extensive cleanup work to get it up to the level of performance befitting a Revox. (I'd love to get it totally refurbed, though I know I'd have to part with a few other machines to fund doing this. It would be worth it, mind you.)

Has anyone else ever seen one of these with the aluminum bit behind the upper part, where the reels go? This is the only one like it I've ever seen. The lighting is crap here, so please excuse the bad quality of this pic:

http://i150.photobucket.com/albums/s88/Perisphere-photo/A77.jpg

[gab73]

Not me, i have 2 and both are grey plastic.

[Jay Pemberton]

I'm thinking of taking this thread and making it a bit of a 'rebirth of a legend' thing. I haven't fired this deck up in about 5 years, and I also was reminded of one of it's other troubles: the machine wouldn't go into rewind mode any more.

Since getting my own computer about 3 years ago, I was able to download a service manual for the deck as a PDF, so I now have lots of valuable information as to what's inside this thing. I was able to at least track down a problem inside one of the relays, and fix it. Now, though, the control buttons work except for the fast forward button; you have to hold it in to keep it in FF mode. Hopefully I'll have that sorted as well soon.

http://i150.photobucket.com/albums/s88/Perisphere-photo/A77servo.jpg

That service manual is for one of the later versions of this deck, which shows a very different servo circuit to this one. However, I have managed to write down all the sizes of capacitors on this circuit board, so I can get new ones to re-cap it with. (Now all I have to do is get a screwdriver small enough to fit inside that space, to remove the board!)

At least the audio circuits seem fine.

More later....

[user510]

I'm thinking of taking this thread and making it a bit of a 'rebirth of a legend' thing. I haven't fired this deck up in about 5 years, and I also was reminded of one of it's other troubles: the machine wouldn't go into rewind mode any more.

Hi Jay.
I for one am looking forward to your future installments re: "rebirth of a legend.."

I also have an (early) A77 and look forward to delving into its innards sometime this coming winter.
http://www.theanalogdept.com/images/spp6_pics/User510/DSC_3415.jpg
Here's a shot of mine. At present it has one dead vu meter (needle fell off!) and it wants to go into fast forward mode when it should be in play. That should be fun sorting out.

-Steve

[Jay Pemberton]

Thanks! They still look cool, even after 40+ years, don't they? I found the link to the Studer ftp site, from which you can download a pdf of the service manual, if you want it. I posted it over in the DIY section here as well:

ftp://ftp.studer.ch/Public/Products/Revox/Revox_A77/Manuals/Revox_A77_Serv.pdf

[Jay Pemberton]

<snip>and it wants to go into fast forward mode when it should be in play. That should be fun sorting out.

-Steve

For future reference--sounds like there may be a problem with the pinch roller solenoid or it's pertinent circuitry on the control board.

When the deck is first put into play or record mode, it is normal for the right hand reel motor to be fed full voltage for a fraction of a second (just the same as if you put it in fast forward mode), to take up any loops of tape thrown from the capstan when the tape is started. You should hear a relay click, and the higher motor torque drop out just an instant afterward.

Now, to check the status of the pinch roller solenoid and pinch roller arm assembly: make sure the moving parts of the pinch roller and solenoid assembly can move freely. (No, thankfully, this deck doesn't suffer the Teac syndrome of a grease that turns to bad Super Glue after 3 or 4 decades!) Not usually a problem, but it doesn't hurt to make sure.

You'll have to defeat the interlock near the power cord connector to do the next bit; I did it with a couple of small screw-in pencil soldering iron tips from Radio Shack. Just use one per hole. Each one carries one side of the AC line.

BE EXTREMELY CAREFUL--THESE WILL CARRY FULL LINE VOLTAGE WHEN THE DECK IS CONNECTED TO THE POWER!

Looking into the back of the deck, you will find the pinch roller solenoid to the left, about 40% of the way up from the bottom of the deck. Two wires are attached to it, with a small diode across them. To determine you're getting voltage to the solenoid, attach a DC voltmeter to the two wires, where they're connected to the solenoid. Positive lead is nearest the outside of the deck. With the deck powered up--and you don't need tape on the machine to do this--press play whilst watching your volt meter. You should get approximately 24 volts at the solenoid. (Mine's doing fine with 23.2 volts.) If the voltage is getting to the solenoid and everything is free to move mechanically, I'd say the solenoid is open. It's a good idea also to check the diode across those terminals for a short, then work your way back into the control circuitry.

Good luck!

[hakka26]

I have two A-77's. The one in my system pic is a "Suitcase" model with onboard amp and speakers and the other in a conventional wood case. Both have the aluminum backs. BTW they sound great. Keep us informed.