Revox B710 Mk2 problems.. - UK Vintage Radio Repair and Restoration Discussion Forum

QUADGOD · 6th May 2020, 10:48 pm

Should my newly acquired B710 have an led permanently on to aid stopping the tape like on my B215?
I've just been looking at YouTube and all the ones on there are like mine but one has this red light just like my B215.
I was checking to find out why my led record indicators were on full when switching on today. After a while they dropped to a few above zero but when turning back on they were all back on.
Any ideas for either issue?
Thanks..

DMcMahon · 7th May 2020, 9:33 am

I am not familiar with either of your cassette decks.

Looking at the service manual for the B215, I can see that it has an EOT (End Of Tape) sensor, which is a photo electric device (a photo LED with a photo transistor in one package) designated QP5. Have not been able to find out what QP5 actually is (device wise) but can see that it will always be powered as long as the unit is switched on.

The photo LED is powered from +5Volts and 0V, the 0V for some reason is provided via a transistor that is switched by a +22 volt supply (that will be present when unit is switched on).

Cannot tell what type of LED it is, visible/invisible (like infra red) but if you can see it, it must be visible (red most likely).

Have yet to see the B710 manual, but would presume it would have a EOT sensor.

DMcMahon · 7th May 2020, 10:17 am

Can now see that the B710 has a similar EOT arrangement which is normally always powered.

The photo LED and transistor are discrete components mounted in one assembly, the LED is designated QP500 (a TIL 78 device) and the photo transistor OP 160 (a TIL 32 device).

The same sensors are used for the Move left and Move right sensor assemblies.

Have yet to see if these TIL devices are visible or invisible light.

QUADGOD · 7th May 2020, 11:45 am

Every 710 on YouTube and tests more than 20 shows one like mine which has no visible light. There is just one that has one apparently purchased off the bay and that has a visible one. I'm guessing the one with the visible light has had a restoration using the innards from a b215 which would make sense? I'm no engineer so most of what you've said I understand but not enough to strip and test.... I was informed on another site this could be a rare model as it has Telefunken Hi com noise reduction not Dolby.
As it seems to stop ok I'm assuming it's normal. I'm more concerned with the led record play indicators staying on full when I switch on. My guess if a dirty contact somewhere because they do slowly retract once playing and fiddling with switches.
Now the MPX filter light wont come on! I think I need an expert to look at it and also to remove those gold caps I keep hearing about?

DMcMahon · 7th May 2020, 12:12 pm

Yes looks like the B710 parts are infra red so will not be visible light. Maybe earlier revisions (Mk. 1 ?) used the visible red part like the B215. So if no operational problem then all is good.

Have not had time to look at the record indicators to be able to make any comment yet.

QUADGOD · 7th May 2020, 10:26 pm

Ok thanks

mole42uk · 8th May 2020, 7:48 am

The main problem with the B710 is that it uses two capstans, flywheels & motors and if they don’t revolve at the same speed the machine throws a hissy fit. The mechanism is built to very close tolerance and has Oilite bearings for each flywheel which may or may not remain in alignment!

QUADGOD · 8th May 2020, 8:53 am

Fortunately speed and replay are not a problem. It sounds superb and works perfectly accept where mentioned thanks

6th May 2020, 10:48 pm	#1
QUADGOD Tetrode Join Date: Aug 2016 Location: Bedford, Beds. UK. Posts: 59	Revox B710 Mk2 problems.. Should my newly acquired B710 have an led permanently on to aid stopping the tape like on my B215? I've just been looking at YouTube and all the ones on there are like mine but one has this red light just like my B215. I was checking to find out why my led record indicators were on full when switching on today. After a while they dropped to a few above zero but when turning back on they were all back on. Any ideas for either issue? Thanks..

7th May 2020, 9:33 am	#2
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,604	Re: Revox B710 Mk2 problems.. I am not familiar with either of your cassette decks. Looking at the service manual for the B215, I can see that it has an EOT (End Of Tape) sensor, which is a photo electric device (a photo LED with a photo transistor in one package) designated QP5. Have not been able to find out what QP5 actually is (device wise) but can see that it will always be powered as long as the unit is switched on. The photo LED is powered from +5Volts and 0V, the 0V for some reason is provided via a transistor that is switched by a +22 volt supply (that will be present when unit is switched on). Cannot tell what type of LED it is, visible/invisible (like infra red) but if you can see it, it must be visible (red most likely). Have yet to see the B710 manual, but would presume it would have a EOT sensor.

7th May 2020, 10:17 am	#3
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,604	Re: Revox B710 Mk2 problems.. Can now see that the B710 has a similar EOT arrangement which is normally always powered. The photo LED and transistor are discrete components mounted in one assembly, the LED is designated QP500 (a TIL 78 device) and the photo transistor OP 160 (a TIL 32 device). The same sensors are used for the Move left and Move right sensor assemblies. Have yet to see if these TIL devices are visible or invisible light.

7th May 2020, 11:45 am	#4
QUADGOD Tetrode Join Date: Aug 2016 Location: Bedford, Beds. UK. Posts: 59	Re: Revox B710 Mk2 problems.. Every 710 on YouTube and tests more than 20 shows one like mine which has no visible light. There is just one that has one apparently purchased off the bay and that has a visible one. I'm guessing the one with the visible light has had a restoration using the innards from a b215 which would make sense? I'm no engineer so most of what you've said I understand but not enough to strip and test.... I was informed on another site this could be a rare model as it has Telefunken Hi com noise reduction not Dolby. As it seems to stop ok I'm assuming it's normal. I'm more concerned with the led record play indicators staying on full when I switch on. My guess if a dirty contact somewhere because they do slowly retract once playing and fiddling with switches. Now the MPX filter light wont come on! I think I need an expert to look at it and also to remove those gold caps I keep hearing about?

7th May 2020, 12:12 pm	#5
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,604	Re: Revox B710 Mk2 problems.. Yes looks like the B710 parts are infra red so will not be visible light. Maybe earlier revisions (Mk. 1 ?) used the visible red part like the B215. So if no operational problem then all is good. Have not had time to look at the record indicators to be able to make any comment yet.

7th May 2020, 10:26 pm	#6
QUADGOD Tetrode Join Date: Aug 2016 Location: Bedford, Beds. UK. Posts: 59	Re: Revox B710 Mk2 problems.. Ok thanks

8th May 2020, 7:48 am	#7
mole42uk Nonode Join Date: Aug 2010 Location: Resolven, Wales; and Bristol, England Posts: 2,614	Re: Revox B710 Mk2 problems.. The main problem with the B710 is that it uses two capstans, flywheels & motors and if they don’t revolve at the same speed the machine throws a hissy fit. The mechanism is built to very close tolerance and has Oilite bearings for each flywheel which may or may not remain in alignment! __________________ Richard Index: recursive loop: see recursive loop

8th May 2020, 8:53 am	#8
QUADGOD Tetrode Join Date: Aug 2016 Location: Bedford, Beds. UK. Posts: 59	Re: Revox B710 Mk2 problems.. Fortunately speed and replay are not a problem. It sounds superb and works perfectly accept where mentioned thanks