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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 17th Jun 2021, 11:02 am   #1
boy1904
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Default Revox A77 aficionados in Scotland ?

Hello

Anyone have any leads on anyone in Scotland who know's about the Revox A77 ? I've got an MK1 that needs a look at - the person doesn't need to be a hifi expert, just needs to know this machine and be based in Scotland!

Would appreciate any help, thank you.

Theo
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Old 17th Jun 2021, 12:21 pm   #2
Ted Kendall
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Default Re: Revox A77 aficionados in Scotland ?

What do you want to know? Can it be done by photos?
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Old 19th Jun 2021, 4:02 pm   #3
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Default Revox A77 playback head issue

Hi all,

I’m wondering if anyone can help with my Revox A77 MK1 issue.

I recently got my heads relapped and realigned and upon taking off the headblock I took note of all the wires and their connection spots. When the headblock came back I reconnected everything and upon switching the machine back on the playback head doesn’t seem to be playing but the record head seems to be okay on both channels. Before sending the heads off they were both working perfectly.

One thing I stupidly did was reconnect the “end of tape” bulb to the incorrect spot, and an issue I encountered was when I turned the machine back on the “end of tape” bulb seemed to blow along with the red power on light and Channel 2 VU metre light. Not sure if this would have an effect on the playback head ? All of these were lighting up before disconnecting the headblock initially. I have reconnected the “end of tape” bulb to the correct spot now, but it still doesn’t light up.

I’ve attached some images of how I’ve reconnected the playback head, along with images of the lights that no longer light up.

I’m at a bit of a loss as to what to do so any help would be hugely appreciated, thank you !


Theo
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Old 20th Jun 2021, 7:36 am   #4
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Default Re: Revox A77 aficionados in Scotland ?

The fuse maybe?
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Old 20th Jun 2021, 9:41 am   #5
Michael Maurice
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Default Re: Revox A77 aficionados in Scotland ?

It’s a pity, you didn’t post this a couple of weeks ago as I was in Edinburgh.

There are two main power lines in these recorders, the unregulated 24V and the regulated 21V. Each has their own winding on the mains transformer and their own fuse.

The 24V powers the replays, solenoids and lamps.

The 21V powers the audio electronics, the End Of Tape lamp and the capstan control board.

Check both fuses, you’ll probably find one is blown.

Come back to us when you’ve done this.
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Old 20th Jun 2021, 12:01 pm   #6
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Default Re: Revox A77 aficionados in Scotland ?

Hi there - thanks for the tip. Struggling to find where these fuses are located, could you give me an idea of where they are ?
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Old 20th Jun 2021, 12:10 pm   #7
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Default Re: Revox A77 aficionados in Scotland ?

If I am removing just the record and play heads I normally remove the small rectangular plate on which the record and play heads are mounted (after unsoldering the eight signal wires from the back of the heads). No need to remove the chassis from the case, let alone having to mess with the other leads and their small spade connectors going to the motherboard.
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Old 20th Jun 2021, 12:15 pm   #8
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Default Re: Revox A77 aficionados in Scotland ?

I think I've found the fuses! Is it these?
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Old 20th Jun 2021, 12:55 pm   #9
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Default Re: Revox A77 aficionados in Scotland ?

Yes they're the fuses. Inspect them visually to make sure that the wire running between the end caps isn't broken.

Better still check them (out of circuit) for continuity using a meter on a low resistance range.
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Old 20th Jun 2021, 1:04 pm   #10
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Default Re: Revox A77 aficionados in Scotland ?

Only remove one at a time to measure them. This way you can be sure to not get them mixed up.

It's important if they are different values.

It's still important if they're both the same value, because which one's blown tells you which system you may have to track down a fault on.

With experience in fault-finding, you develop lots of little careful tricks that may add a little time, but which protect you from easily made mistakes and confusions.

David
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Old 20th Jun 2021, 4:15 pm   #11
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Default Re: Revox A77 aficionados in Scotland ?

Quote:
Originally Posted by Station X View Post
Yes they're the fuses. Inspect them visually to make sure that the wire running between the end caps isn't broken.

Better still check them (out of circuit) for continuity using a meter on a low resistance range.

Doesn't look like the wires are broken on either fuse, and no sign of them being burnt either. Have yet to test them with an electrical meter.

The top fuse reads : T630mA 250V

The bottom reads : T2A 250V
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Old 20th Jun 2021, 6:37 pm   #12
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Default Re: Revox A77 aficionados in Scotland ?

They'll need a check with an ohmmeter to be really sure.

If neither have blown, then it's a logical progression of checking supplies and tracing the bad one back looking for damage or errors.

David
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Old 21st Jun 2021, 12:40 am   #13
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Default Re: Revox A77 aficionados in Scotland ?

The top fuse (F102) 630mA is for the regulated +21V supply, the bottom fuse (F103) 2A is for the unregulated +24V (designated +27V) supply.

The bead on the top fuse looks a little suspicious, although some glass fuses do have such a bead.

David
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Old 21st Jun 2021, 7:31 am   #14
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Default Re: Revox A77 aficionados in Scotland ?

There may also be some splatter showing on the glass. So it does look dodgy. With luck, this fuse might have popped and saved the regulator.

But a check with a meter on its Ohms range will find out if it's blown or not.

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Old 21st Jun 2021, 1:01 pm   #15
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Default Re: Revox A77 aficionados in Scotland ?

The top fuse seems to have a consistent reading of 00.2/00.1, so I think that one is okay.

The bottom fuse is more inconsistent - it does also read 00.2/00.1 but also intermittently also reads "0L." depending on where I place the metal caps on the metal of the fuse.

Would this mean the bottom fuse needs replaced?

Thanks,
Theo
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Old 21st Jun 2021, 1:06 pm   #16
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Default Re: Revox A77 aficionados in Scotland ?

OL indicates infinite resistance, so either your probes aren't making good contact with the end caps or the fuse is intermittent.

You could put both fuses back and measure the DC voltage wrt ground on all four end caps
caps.
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Old 21st Jun 2021, 1:20 pm   #17
boy1904
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Default Re: Revox A77 aficionados in Scotland ?

It actually seems as if both fuses are okay, on second inspection with the multimeter.

Is there a next place I should look for any issues ?

Thank you!
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Old 21st Jun 2021, 1:37 pm   #18
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Default Re: Revox A77 aficionados in Scotland ?

Don't forget the interlock and the remote plug if you decide to do any voltage checks or try to operate the machine with the cabinet removed.

Lawrence.
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Old 21st Jun 2021, 1:47 pm   #19
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Default Re: Revox A77 aficionados in Scotland ?

Quote:
Originally Posted by boy1904 View Post
It actually seems as if both fuses are okay, on second inspection with the multimeter.

Is there a next place I should look for any issues ?

Thank you!
See the second paragraph in post #16.
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Old 21st Jun 2021, 2:21 pm   #20
boy1904
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Default Re: Revox A77 aficionados in Scotland ?

Quote:
Originally Posted by Station X View Post
OL indicates infinite resistance, so either your probes aren't making good contact with the end caps or the fuse is intermittent.

You could put both fuses back and measure the DC voltage wrt ground on all four end caps
caps.
Okay so can you measure the DC voltage on the end caps using the multimeter also ?
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