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Old 23rd Nov 2022, 2:19 pm   #1
HECTOR63
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Default Revox A77

I'm looking for a copy of the service manual and any complete upgrade or restoration kits or advices to get this one up to spec if possible.
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Old 23rd Nov 2022, 2:20 pm   #2
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Default Re: Revox A77

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Old 23rd Nov 2022, 4:01 pm   #3
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Default Re: Revox A77

Looks like a MK4 Dolby, probably 3.75 and 7.5 ips from the small photo. Definitely worth servicing as quite rare. Nagravox in Australia did do several complete refurbish kits depending on what needs doing. Not cheap however. What are the heads like as, if very worn, will add significant extra cost? I have a copy of the service manual, but need it for fixing my own machines which are still spread out over the floor of my study.
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Old 23rd Nov 2022, 4:21 pm   #4
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Default Re: Revox A77

Manual's are available online. It'll need those metalprint caps changing for a start, the skeleton presets on all the IP/OP/AMP cards swopping for Piher's after noting the resistance of each preset, the relay's contacts cleaning and any electrolytics changing after checking the power supply amongst other stuff.

Things to watch out for, you have to pull off the knobs etc to remove the front board, the switches have ball bearings that are really easy to lose, every SW is different, great care is needed with these. You need a really long screwdriver to get at a screw on the main board, it's a nightmare to get at.

As well as the source in Oz for the main caps I think there's a place in Germany that sells spares, buying stuff from the EU being now more difficult, spares located in Australia may be cheaper after taking into account customs charges, you need to do your research.

Andy.
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Old 23rd Nov 2022, 4:56 pm   #5
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Default Re: Revox A77

The metalprint capacitors Andy refers to I think are the 3 Rifa Miniprint capacitors (semi transparent yellow/gold) on your 4th photo in Post 1.

These have a bad reliability reputation and are prone to failure sooner or later.

They are on the Relay/Tape Drive board, namely C113, C114 & C115, these are 0.47uF (also the same as 470nF/474k).

They are used for suppression and recommended replacements are 0.47uF X2 Class (safety rating) Metallized Polypropylene ideally at 275VAC, a typical example are these -

https://uk.farnell.com/kemet/phe840m...ial/dp/1572160

Other types and suppliers of course are available.

There is a 4th Rifa 0.47uF, it is on the Servo/Speed Control board, this is the horizontal board above and to the left of the Tape Drive board, it is strongly recommended to change this one at the same time as the other three.

David
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Old 23rd Nov 2022, 8:12 pm   #6
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Default Re: Revox A77

No evidence in the photos (cannot see the 4th Rifa) but if any of them has actually failed (normally visually obvious) then the failed Rifa could also take out its serial 4.7 Ohm resistor (the 4th Rifa does not have the resistor).

The resistor is in series with the 0.47uF to form I think a serial CR snubber, namely C113/R121, C114/R122 & C115/R123.

If the Speed Control board is all transistor (no IC's) then the 0.47uF Rifa is C213.

David

Last edited by DMcMahon; 23rd Nov 2022 at 8:18 pm. Reason: Typo correction
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Old 24th Nov 2022, 6:25 am   #7
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Default Re: Revox A77

Miniprint, your right David, need to order some new eyes next time I put in an order at Farnell. There's what looks like a crack on one, they're potential time bombs, make sure you order the right lead spacing.

Andy.
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Old 24th Nov 2022, 1:00 pm   #8
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Default Re: Revox A77

Sincerest thanks for the replies folks greatly appreciated and points duly noted and shall update when ive done some more research into manual and parts advices.
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Old Yesterday, 12:17 am   #9
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Default Re: Revox A77

Quote:
Originally Posted by DMcMahon View Post
If the Speed Control board is all transistor (no IC's) then the 0.47uF Rifa is C213.

David
Update - If the Speed Control Board has ICs as well as transistors then the 0.47uF Rifa is C220.

David
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Old Yesterday, 11:34 am   #10
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Default Re: Revox A77

Quote:
Originally Posted by Diabolical Artificer View Post
Miniprint, your right David, need to order some new eyes next time I put in an order at Farnell. There's what looks like a crack on one, they're potential time bombs, make sure you order the right lead spacing.

Andy.
Yes Andy can see what looks like a crack.

I need to change mine on my A77, I have not done it yet because I am hardly ever using it, but I should change them soon before one or more fail.

David
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