Revox A77 - auto stop at end of tape? - UK Vintage Radio Repair and Restoration Discussion Forum

stevehertz · 7th Feb 2016, 5:11 pm

I'm using my A77 again, and just rewinding a tape I noticed that it does not auto stop once the tape has all been wound back on to the original spool, so you have to press 'stop'. Without digging out the user manual, is that correct? Maybe I'm getting mixed up with a TEAC 3440S that I had years ago, I think that auto stopped at the end of a tape.

Radio Wrangler · 7th Feb 2016, 5:44 pm

it will not autostop if the little light bulb by the tape path isn't working.

David

johnny english · 7th Feb 2016, 5:46 pm

Not too sure about the a77 but on my b77 there is a photo electric cell to the left of the erase head. Sometimes the speed of the rewind if you have`nt got miles of leader tape all the tape will spool off the opposite reel

Radio Wrangler · 7th Feb 2016, 6:42 pm

I interpreted it as the spool motor kept going even after the tape un-threaded and the stop button was needed, so it isn't a matter of not enough transparent leader.

David

stevehertz · 7th Feb 2016, 7:41 pm

Your interpretation is correct David. So I need to check to see if a lamp is illuminated by the side of the erase head?

8 Tracker · 7th Feb 2016, 8:01 pm

Yes, mine does this, but only when it's warmed up. It's very annoying. If I start a reel with clear leader tape playing and the machine is cold, it will not stay in play mode until the leader has passed the bulb and sensor, indicating all is well. However, when it gets to the end of the tape it won't stop even when the tape has run off the reel. I come in to find it flapping about all over. I suspect some resistor values have drifted a little over time, but I haven't investigated yet.
Mark.

Phil G4SPZ · 8th Feb 2016, 12:05 am

This may be a common problem with the A77. Mine arrived minus the auto-stop mechanism; the previous owner had had the machine since new, and found the auto-stop function so unreliable that he stripped it out.

vidjoman · 8th Feb 2016, 9:59 am

From memory the machine senses the current through the lamp and senses the light falling on the receptor. The lamp may be just dirty or full of dust around it. The sensing of the end of the tape can then be erratic. I think there was also a slight delay built in to prevent false triggering and that may also be at fault due to failing capacitors or resistors changed in value.

johnny english · 8th Feb 2016, 1:32 pm

You can download from revox the schematic for free.

ben · 8th Feb 2016, 1:57 pm

See attached. Check the voltages at Q111, 1v and 22v for light /dark.The sensor may have gone high, should read less than 2kOhm for light.

Michael Maurice · 8th Feb 2016, 2:55 pm

Quote:

Originally Posted by vidjoman

From memory the machine senses the current through the lamp and senses the light falling on the receptor.

No the lamp is an ordinary 24V lamp connected across the stabilised 21V rail.

The autostop is activated by light falling on the sensor.

TIMTAPE · 8th Feb 2016, 4:14 pm

The small 24 volt bulbs have rather fragile filaments and can often fail.

I found an LED with suitable current limiting resistor can be made to substitute for the 24v incandescent lamp. It needs to be manually aligned for maximum illumination on the sensor as it is more directional than the lamp.

stevehertz · 8th Feb 2016, 8:18 pm

Thanks guys for all your help. I'll report back in due course.

Restoration73 · 10th Feb 2016, 5:30 pm

Note that some leaders are more translucent than others; particularly some found on
Zonal brand tapes.

7th Feb 2016, 5:11 pm	#1
stevehertz Dekatron Join Date: Sep 2011 Location: Rugeley, Staffordshire, UK. Posts: 8,833	Revox A77 - auto stop at end of tape? I'm using my A77 again, and just rewinding a tape I noticed that it does not auto stop once the tape has all been wound back on to the original spool, so you have to press 'stop'. Without digging out the user manual, is that correct? Maybe I'm getting mixed up with a TEAC 3440S that I had years ago, I think that auto stopped at the end of a tape. __________________ A digital radio is the latest thing, but a vintage wireless is forever..

7th Feb 2016, 5:44 pm	#2
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,901	Re: Revox A77 - auto stop at end of tape? it will not autostop if the little light bulb by the tape path isn't working. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

7th Feb 2016, 5:46 pm	#3
johnny english Retired Dormant Member Join Date: Nov 2013 Location: Liverpool, Merseyside, UK. Posts: 160	Re: Revox A77 - auto stop at end of tape? Not too sure about the a77 but on my b77 there is a photo electric cell to the left of the erase head. Sometimes the speed of the rewind if you have`nt got miles of leader tape all the tape will spool off the opposite reel

7th Feb 2016, 6:42 pm	#4
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,901	Re: Revox A77 - auto stop at end of tape? I interpreted it as the spool motor kept going even after the tape un-threaded and the stop button was needed, so it isn't a matter of not enough transparent leader. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

7th Feb 2016, 7:41 pm	#5
stevehertz Dekatron Join Date: Sep 2011 Location: Rugeley, Staffordshire, UK. Posts: 8,833	Re: Revox A77 - auto stop at end of tape? Your interpretation is correct David. So I need to check to see if a lamp is illuminated by the side of the erase head? __________________ A digital radio is the latest thing, but a vintage wireless is forever..

7th Feb 2016, 8:01 pm	#6
8 Tracker Hexode Join Date: Jul 2009 Location: Mablethorpe, Lincolnshire, UK. Posts: 286	Re: Revox A77 - auto stop at end of tape? Yes, mine does this, but only when it's warmed up. It's very annoying. If I start a reel with clear leader tape playing and the machine is cold, it will not stay in play mode until the leader has passed the bulb and sensor, indicating all is well. However, when it gets to the end of the tape it won't stop even when the tape has run off the reel. I come in to find it flapping about all over. I suspect some resistor values have drifted a little over time, but I haven't investigated yet. Mark.

8th Feb 2016, 12:05 am	#7
Phil G4SPZ Dekatron Join Date: Apr 2005 Location: Bewdley, Worcestershire, UK. Posts: 4,748	Re: Revox A77 - auto stop at end of tape? This may be a common problem with the A77. Mine arrived minus the auto-stop mechanism; the previous owner had had the machine since new, and found the auto-stop function so unreliable that he stripped it out. __________________ Phil Optimist [n]: One who is not in possession of the full facts

8th Feb 2016, 9:59 am	#8
vidjoman Dekatron Join Date: Jun 2013 Location: East Sussex, UK. Posts: 3,326	Re: Revox A77 - auto stop at end of tape? From memory the machine senses the current through the lamp and senses the light falling on the receptor. The lamp may be just dirty or full of dust around it. The sensing of the end of the tape can then be erratic. I think there was also a slight delay built in to prevent false triggering and that may also be at fault due to failing capacitors or resistors changed in value.

8th Feb 2016, 1:32 pm	#9
johnny english Retired Dormant Member Join Date: Nov 2013 Location: Liverpool, Merseyside, UK. Posts: 160	Re: Revox A77 - auto stop at end of tape? You can download from revox the schematic for free.

8th Feb 2016, 1:57 pm	#10
ben Dekatron Join Date: Aug 2006 Location: Madrid, Spain / Wirral, UK Posts: 7,498	Re: Revox A77 - auto stop at end of tape? See attached. Check the voltages at Q111, 1v and 22v for light /dark.The sensor may have gone high, should read less than 2kOhm for light. Attached Thumbnails __________________ Regards, Ben.

8th Feb 2016, 4:14 pm	#12
TIMTAPE Octode Join Date: Jul 2006 Location: Perth, Western Australia Posts: 1,970	Re: Revox A77 - auto stop at end of tape? The small 24 volt bulbs have rather fragile filaments and can often fail. I found an LED with suitable current limiting resistor can be made to substitute for the 24v incandescent lamp. It needs to be manually aligned for maximum illumination on the sensor as it is more directional than the lamp.

8th Feb 2016, 8:18 pm	#13
stevehertz Dekatron Join Date: Sep 2011 Location: Rugeley, Staffordshire, UK. Posts: 8,833	Re: Revox A77 - auto stop at end of tape? Thanks guys for all your help. I'll report back in due course. __________________ A digital radio is the latest thing, but a vintage wireless is forever..

10th Feb 2016, 5:30 pm	#14
Restoration73 Nonode Join Date: Jun 2013 Location: Surbiton, SW London, UK. Posts: 2,801	Re: Revox A77 - auto stop at end of tape? Note that some leaders are more translucent than others; particularly some found on Zonal brand tapes.