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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 13th Jan 2022, 1:25 pm   #1
OldKitMan64
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Default Removal of Chassis from Case Revox A77

OK so this might be a basic question but I have a Revox A77 (maybe Mk3 or 4) where I just cannot get the chassis out of the case! I have removed the four rear screws but the right hand side (as you look at the front) seems stuck for some reason.

I do not want to force it but has anyone encountered this issue before? I need to get it open to investigate some smoke and possible component failure on a previously working machine.

Any help to get the chassis out (without harm) welcome.

Thanks.
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Old 13th Jan 2022, 1:44 pm   #2
vidjoman
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Default Re: Removal of Chassis from Case Revox A77

I usually lay it face down on a cushion or something soft then tap the sides and bottom which will loosen the case then lift the case off the mech.
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Old 13th Jan 2022, 1:59 pm   #3
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Default Re: Removal of Chassis from Case Revox A77

Welcome to the forum!

The component that has failed may well be a Rifa capacitor across the terminals of the mains in socket. If you search for Rifa in the search engine at the top of the page you'll find that they are timebombs waiting to fill your room with a smelly smoke! It's easy to replace with a new decent make, I'd suggest Wima but others may have a better supplier in mind.
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Old 13th Jan 2022, 2:48 pm   #4
Ted Kendall
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Default Re: Removal of Chassis from Case Revox A77

Should you want to test the machine out of its case, you will need to insert a 4mm plug in each of the sockets which pick up on the pins in the case. Do not short them together - one is line and one neutral!
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Old 13th Jan 2022, 4:14 pm   #5
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Default Re: Removal of Chassis from Case Revox A77

Silly question I know, but have you removed the “dummy” remote plug from the top rear?

Regards Mike A.
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Old 13th Jan 2022, 10:49 pm   #6
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Default Re: Removal of Chassis from Case Revox A77

In my experience the case is much more reluctant to come off on an A77 compared to a B77. Laying it face down on something soft and encouraging it out was the only way I found to do it. I seem to remember removing the plastic part that contains the pins from the case and plugging it in to the socket on the chassis in order to run the machine out of its case. I used some grey Kemet X2 rated capacitors to replace the Rifas.
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Old 14th Jan 2022, 8:09 am   #7
Michael Maurice
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Default Re: Removal of Chassis from Case Revox A77

Quote:
Originally Posted by Kentode View Post
Welcome to the forum!

The component that has failed may well be a Rifa capacitor across the terminals of the mains in socket. If you search for Rifa in the search engine at the top of the page you'll find that they are timebombs waiting to fill your room with a smelly smoke! It's easy to replace with a new decent make, I'd suggest Wima but others may have a better supplier in mind.
Not on an A77
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Old 14th Jan 2022, 10:08 am   #8
Ted Kendall
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Default Re: Removal of Chassis from Case Revox A77

Quote:
Originally Posted by Michael Maurice View Post
Quote:
Originally Posted by Kentode View Post
Welcome to the forum!

The component that has failed may well be a Rifa capacitor across the terminals of the mains in socket. If you search for Rifa in the search engine at the top of the page you'll find that they are timebombs waiting to fill your room with a smelly smoke! It's easy to replace with a new decent make, I'd suggest Wima but others may have a better supplier in mind.
Not on an A77
Agreed, but there are Rifas elsewhere in the machine which can cause alarm and despondency if they have a mind to.
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Old 14th Jan 2022, 12:21 pm   #9
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Default Re: Removal of Chassis from Case Revox A77

And when the Revox is out of the case, another problem arises. The power button.
Don't pull it or it will break. But tap it from behind with a blunt screwdriver along the shaft against it. The button will then be released.

Jack Marotick
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Old 14th Jan 2022, 12:31 pm   #10
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Default Re: Removal of Chassis from Case Revox A77

Quote:
Originally Posted by Ted Kendall View Post
Quote:
Originally Posted by Michael Maurice View Post
Quote:
Originally Posted by Kentode View Post
Welcome to the forum!

The component that has failed may well be a Rifa capacitor across the terminals of the mains in socket. If you search for Rifa in the search engine at the top of the page you'll find that they are timebombs waiting to fill your room with a smelly smoke! It's easy to replace with a new decent make, I'd suggest Wima but others may have a better supplier in mind.
Not on an A77
Agreed, but there are Rifas elsewhere in the machine which can cause alarm and despondency if they have a mind to.
I bow to the superior knowledge of Michael and Ted.

If there are Rifa's anywhere in this recorder, they probably will be cracked and expanding, 'cos that's what they do!
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Old 14th Jan 2022, 3:39 pm   #11
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Default Re: Removal of Chassis from Case Revox A77

Even though I have seen it referenced in older Threads I do not believe there is a Rifa suppression capacitor on the mains wiring on a standard A77.

The three Rifa's that often fail are C113-C115 on the Tape Drive board (location F), if original they are typically Rifa Miniprint 0.47uF. They are connected in series with 4.7 Ohm resistors R121/R122/R123 respectively to form RC snubbers across the relevant mains transformer and motor windings. If the capacitor fails/blows it may also take out its 4.7 Ohm resistor.

Typically X2 suppression capacitors are used to replace them, typically at 275VAC rating.

There is a fourth 0.47uF Rifa (not part of a snubber network) that may fail, I think it is C213 on the later Speed Control/Servo board (with IC2) or C220 on the earlier Speed Control/Servo board (non IC version).

David
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Old 14th Jan 2022, 5:10 pm   #12
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Default Re: Removal of Chassis from Case Revox A77

Just to echo Ted's advice in post#4 - you'll need two separate 4mm plugs. I, er, knew someone who connected them together which results in flash a loud bang. I've no idea who that was...
You'll also need to re-inset the dummy plug or else it won't play.
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Old 15th Jan 2022, 11:15 am   #13
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Default Re: Removal of Chassis from Case Revox A77

As Ted references in Post 4 the switched contacts are at mains potential so you have to be very careful when plugging in (or removing) the 4mm plugs not touch any of the exposed metalwork on the 4mm plugs.

David
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Old 15th Jan 2022, 12:23 pm   #14
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Default Re: Removal of Chassis from Case Revox A77

Quote:
Originally Posted by Welsh Anorak View Post
Just to echo Ted's advice in post#4 - you'll need two separate 4mm plugs. I, er, knew someone who connected them together which results in flash a loud bang. I've no idea who that was...
You'll also need to re-inset the dummy plug or else it won't play.
You wouldn't be the first or the last to do this.....
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Old 22nd Jan 2022, 2:39 pm   #15
OldKitMan64
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Smile Re: Removal of Chassis from Case Revox A77

Thanks to all so far who have replied to my post
Well I can now reveal why the case would not free up on the right hand side of the chassis
I removed the front plastic face of the machine and managed to get in a right angle lever between the aluminium chassis holes so I could lever between the back case chassis and the wooden cabinet -
Success !
I found out the mystery. - The previous owner of this machine had broken the plastic spacer that exists between the chassis and the case. It had been stuck back together with Araldite (or similar) but it had not been allowed to dry before putting it back in the case, hence the case was stuck to the chassis (quite solid !).
I've inspected all the components and have found no scorched capacitors but have found a melted/broken windings in the right reel motor.
I'm about to make a new post on that.
So thanks again for replies - I hope someone can help me out on replacing my reel motor.
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