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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 2nd Aug 2021, 10:58 pm   #1
Gerry_Richards
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Default Revox F36 take up motor unprompted motion!

Hello,

Complete newbie here so please bear with...

Curiosity and love of sound recording equipment has led me to acquire a Revox F36. It's partly functional but has the 2 following problems:

1. I can load, record and play back a tape but after about 5 minutes after powering up, the take-up motor starts to spin by itself. Also tested it today without a tape loaded and the same problem occurred - didn't press any buttons, just switched on and after about 5 mins the motor starts to spin up... Any theories as to why this is happening please?

2. Tried recording a basic stereo track and track 2 didn't record a signal even though the level meters were functioning - what would be the basic things to check first?

Many thanks in anticipation for any help you might offer....

Gerry
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Old 2nd Aug 2021, 11:14 pm   #2
paulsherwin
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Default Re: Revox F36 take up motor unprompted motion!

No offence meant, but these are complex semiprofessional recorders and almost 60 years old. If you have no expertise in this area you would be well advised to find a professional who can restore it for you. Members here can tell you basic things like 'clean the switch contacts with Servisol', but there are likely to be much more complex electronic and mechanical problems that will need attention.
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Old 2nd Aug 2021, 11:31 pm   #3
Gerry_Richards
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Default Re: Revox F36 take up motor unprompted motion!

No offence taken - that's fair enough ; I have the skills to assemble a recording studio and passed my A level in electronics in 1989 (!) so I'm not naive enough to think it'd be an easy fix. But the Revox cost me little and at worst I'll have a valve pre-amp x2 for my studio even if I can't get it to record. With all things in life I take a 'learn by doing' approach so I just wondered whether there are any obvious things to check first, specific to this particular model?
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Old 3rd Aug 2021, 7:26 am   #4
Ted Kendall
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Default Re: Revox F36 take up motor unprompted motion!

There are shunting diodes in the switchpack which can go leaky and cause odd function problems like this. But Paul is right - these machines, although still capable of superb results, are difficult to work on, partly because they are tightly packaged. The later A77 series is much easier, but still doesn't respond well to a "poke it and see" approach.
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Old 3rd Aug 2021, 10:56 am   #5
ms660
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Default Re: Revox F36 take up motor unprompted motion!

Looking at a schematic the motor control circuits don't look complicated, basically just simple switching.

Lawrence
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Old 3rd Aug 2021, 11:04 am   #6
Ted Kendall
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Default Re: Revox F36 take up motor unprompted motion!

Granted, the switching is simple enough on the diagram, but dealing with the switchpack itself is a royal pain.
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Old 3rd Aug 2021, 11:12 am   #7
ms660
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Default Re: Revox F36 take up motor unprompted motion!

Quote:
Originally Posted by Ted Kendall View Post
Granted, the switching is simple enough on the diagram, but dealing with the switchpack itself is a royal pain.
Electronics wise the whole machine is relatively straight forward.

Lawrence.
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Old 3rd Aug 2021, 11:15 pm   #8
DMcMahon
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Talking Re: Revox F36 take up motor unprompted motion!

Quote:
Originally Posted by Gerry_Richards View Post

2. Tried recording a basic stereo track and track 2 didn't record a signal even though the level meters were functioning - what would be the basic things to check first?

Gerry
No easy answer to this, unless someone knows of a stock fault with the F36 that would explain this.

First make sure that Playback of a known good stereo recorded tape is good on both channels.

If Ok then it would be a case of downloading the schematic and working through it, monitoring the signals with a scope as required.

Main things it might be:-

1. Bad record head on track/channel 2, maybe open circuit (not very likely).

2. Very dirty record head, unlikely if track/channel 1 records OK but still worth giving the record head a good clean.

3. Generally for any recorder with playback or record issues always worthwhile cleaning the Play/Record switch contacts.

4. Record bias signal missing at the head in that channel, check by scoping it at the head.

5. Assuming that the EMM 801 stereo magic eye is telling the truth in that there is a good record level signal then the record signal must be bad (assuming head and record bias are good) in the last valve stage of the channel 2 record amplifier, i.e. ECC81 Ro6a/V6.1 (valve identification # varies depending upon which version schematic is checked). This stage is fed from/driven by signal line "V" which also goes off to the EMM 801.

David

Update - appreciate that some of the above may be much easier said than done due to difficult access.

Last edited by DMcMahon; 3rd Aug 2021 at 11:22 pm. Reason: Update
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