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Old 22nd Sep 2016, 7:55 pm   #1
edmonius
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Default Revox A700 problem with PLAY, FF and REW

Hi,

I have a Revox A700 on the bench. After some repairing on the power supply I now have a problem with the PLAY, FF and REW keys. They operate the machine but only while are pressed. If released the A700 stops working.

Can you please give me some help?

Best Regards
Eduardo Fonseca
OldBack Productions
Portugal

Last edited by edmonius; 22nd Sep 2016 at 8:11 pm.
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Old 22nd Sep 2016, 8:13 pm   #2
Amraduk
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Default Re: Revox A700 problem with PLAY, FF and REW

Do you have a tape on the machine? If not, then it might just be the end-of-tape sensor doing its job.

Regards,
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Old 22nd Sep 2016, 8:13 pm   #3
Michael Maurice
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Default Re: Revox A700 problem with PLAY, FF and REW

You need to check that the EOT sensor is working by following the instructions in the service manual to ensure the threshold level is correct.

Once you've eliminated that, check the output from the tape move module.

If that's ok, check that the stop line itself is at 0V.

I take it you've replace all the RIFA caps on the speed, capstan and relay boards, if not change them.

Let us know your findings.
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Old 22nd Sep 2016, 8:27 pm   #4
Ted Kendall
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Default Re: Revox A700 problem with PLAY, FF and REW

Depending on the age of the machine there may also be microswitches on the tension arms which activate autostop when at the end of their travel. And do replace those Rifas, unless you like firework displays...
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Old 23rd Sep 2016, 1:05 am   #5
Michael Maurice
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Default Re: Revox A700 problem with PLAY, FF and REW

Quote:
Originally Posted by Ted Kendall View Post
Depending on the age of the machine there may also be microswitches on the tension arms which activate autostop when at the end of their travel.
Was that early versions or late versions? Doesn't seem to be any reference in the service manual
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Old 23rd Sep 2016, 10:47 am   #6
Ted Kendall
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Default Re: Revox A700 problem with PLAY, FF and REW

If memory serves, this was quite late - S/No 15000 or thereabouts. It was standard on the related Studer A67 from the off, and replacement tension arms were so equipped. The mod was simple enough - some wire and a couple of diodes - I have the bit of paper somewhere - but it was a while ago...
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Old 24th Sep 2016, 7:16 pm   #7
edmonius
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Default Re: Revox A700 problem with PLAY, FF and REW

Now I have a new problem... the F5 fuse is blowing out as soon as i hit the play/ff/rew... and afert that the capstan motor stops...
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Old 25th Sep 2016, 12:07 am   #8
Ted Kendall
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Default Re: Revox A700 problem with PLAY, FF and REW

A piece of the story missing here - have you fixed the original fault? Did you change the Rifas, and if so, are you confident you haven't introduced a fault in the process?

First thought is that you should check the shunting diode across the brake solenoid - this is the common component which comes to mind for these three operations.
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Old 25th Sep 2016, 8:55 am   #9
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Default Re: Revox A700 problem with PLAY, FF and REW

You should have the service manual, if you don't have it you can download it from various sites including hi fi engine.

F5 is the supply to the -20V and -12V supplies
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Old 25th Sep 2016, 5:53 pm   #10
edmonius
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Default Re: Revox A700 problem with PLAY, FF and REW

Hi,

Rifas are out. No more blowing fuses. On to the next step.
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Old 25th Sep 2016, 9:49 pm   #11
edmonius
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Default Re: Revox A700 problem with PLAY, FF and REW

Quote:
Originally Posted by Ted Kendall View Post
First thought is that you should check the shunting diode across the brake solenoid - this is the common component which comes to mind for these three operations.
Shunting diode checked!
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