Revox B77 MKII - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Redders03 · 26th Apr 2012, 8:05 pm

checked the Control Board and it contains a 6.8k resistor. The board version is .81 so the attched diagram is for the wrong board. Any how the resistor is working within tollerance

Refugee · 26th Apr 2012, 9:01 pm

The resistor should have 22-24 volts across it for the IR LED to be taking current. There should be something close to 2 volts across the LED. Measure all the wires and PCB tracks that carry the signals. It has been tested with more than one sensor unit and still has the problem. If you are not sure try an ordinary LED in series with the one in the sensor. It should stay on all the time.

Redders03 · 26th Apr 2012, 9:11 pm

just took a reading and gained 27 v

Redders03 · 26th Apr 2012, 9:18 pm

at the sensor i gained a reading of around 1.5v !!

Refugee · 26th Apr 2012, 9:54 pm

That sounds OK.
The sensor assembly needs to be tested with an LED and resistor in each arm while it is out of the recorder from an external power supply. 12 volts with 1k resistors will do for this. Then you will be able to see the LEDs both light up and when you put something in the gap one LED will go out. That is the end that needs to be wired to the location that was linked out to get the machine to stop. This will prove that something has worked loose between the sensor location and the location on the PCB where the resistor is.

Michael Maurice · 28th Apr 2012, 10:32 am

I actually gave you the manual from a PR99 not knowing the differences, here is the circuit from the B77 II.

You will see there is a preset, marked with an arrow.

Check its intact and that its slider hasn't fallen off!

Redders03 · 28th Apr 2012, 3:52 pm

Checked the sensor and checks out fine, changing preset and zener diodes. Preset looks abit dodgey

Redders03 · 5th May 2012, 7:59 pm

Changed preset and both Zenor diodes and it's still not working
Where next ?
When the optisensor contacts are shorted at the the sensor it stops to I guess their is no problem between sensor and card.

Refugee · 5th May 2012, 8:50 pm

Have you tried a TV remote with the LED end offered close up to the sensor to see if it operates then?
The sensor may also have been rotated by mistake to that the "eye" part of it is facing the wrong way.

Redders03 · 6th May 2012, 9:00 pm

Tried this and still nothing

Michael Maurice · 7th May 2012, 9:09 pm

The circuits are quite simple so they cant be too much wrong with it.

What you have to understand is that the photocell voltage will change when light falls on it, but not by a huge amount and certainly not to 0V.

What I want you to do is the following test:

Switch the machine on and connect your multimeter set to volts, on to the output of the photocell (the one that goes to pin 7 of the transport board)

Measure the voltage both with and without a tape (or cover the sensor up) and let us know if there is a difference. If there is and there should be then that part of it is working and its likely the preset hasn't been properly set, if there isn't repeat the exercise while shining a bright torch into the sensor.

Redders03 · 7th May 2012, 10:49 pm

The machine is working corectly when torch is placed in front of sensor, When led is placed on violet and grey it lights when placed on violent and brown does not light, measuring around 2 volts around violet and brown

Redders03 · 7th May 2012, 11:31 pm

from this i believe the ground for the ir emitter is open and Changing R2, in Service manual, three figures are given for this resistor 1.5k, 3.3k and 6.8k. Which is the correct one for 1.177.317.81 ?

Refugee · 8th May 2012, 3:01 am

Quote:

Originally Posted by Redders03

The machine is working corectly when torch is placed in front of sensor, When led is placed on violet and grey it lights when placed on violent and brown does not light, measuring around 2 volts around violet and brown

The LED and sensor are not matched.
You need to find an LED and sensor that have the same wavelength measured in nano meters often shown nm in data sheets. Try and stick to non visible light and part size for convenience.

Michael Maurice · 8th May 2012, 7:44 am

In post 18, you state that you have replaced the sensor twice.

Did the replacement sensors come complete with wiring loom? If so did you fit it with wiring loom or did you cut wires off and solder the original wires to the new sensor?

It would appear that the IR receiver part is working and that fault lies with the LED only.

According to my manual R2 on your transport card is 1.5K but it isn't critical.

I'm wondering if somehow you've got the LED's wires reversed.

Redders03 · 8th May 2012, 6:17 pm

Changed the resistor and now working properly many thanks to all who contributed !!

26th Apr 2012, 8:05 pm	#21
Redders03 Pentode Join Date: Apr 2012 Location: Bromley UK. Posts: 161	Re: Revox B77 MKII checked the Control Board and it contains a 6.8k resistor. The board version is .81 so the attched diagram is for the wrong board. Any how the resistor is working within tollerance

26th Apr 2012, 9:01 pm	#22
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,554	Re: Revox B77 MKII The resistor should have 22-24 volts across it for the IR LED to be taking current. There should be something close to 2 volts across the LED. Measure all the wires and PCB tracks that carry the signals. It has been tested with more than one sensor unit and still has the problem. If you are not sure try an ordinary LED in series with the one in the sensor. It should stay on all the time.

26th Apr 2012, 9:11 pm	#23
Redders03 Pentode Join Date: Apr 2012 Location: Bromley UK. Posts: 161	Re: Revox B77 MKII just took a reading and gained 27 v

26th Apr 2012, 9:18 pm	#24
Redders03 Pentode Join Date: Apr 2012 Location: Bromley UK. Posts: 161	Re: Revox B77 MKII at the sensor i gained a reading of around 1.5v !!

26th Apr 2012, 9:54 pm	#25
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,554	Re: Revox B77 MKII That sounds OK. The sensor assembly needs to be tested with an LED and resistor in each arm while it is out of the recorder from an external power supply. 12 volts with 1k resistors will do for this. Then you will be able to see the LEDs both light up and when you put something in the gap one LED will go out. That is the end that needs to be wired to the location that was linked out to get the machine to stop. This will prove that something has worked loose between the sensor location and the location on the PCB where the resistor is.

28th Apr 2012, 10:32 am	#26
Michael Maurice Moderator Join Date: Feb 2006 Location: Wembley, Middlesex Posts: 7,225	Re: Revox B77 MKII I actually gave you the manual from a PR99 not knowing the differences, here is the circuit from the B77 II. You will see there is a preset, marked with an arrow. Check its intact and that its slider hasn't fallen off! Attached Thumbnails __________________ Forum Moderator http://www.michaelmauricerepairs.co.uk/

28th Apr 2012, 3:52 pm	#27
Redders03 Pentode Join Date: Apr 2012 Location: Bromley UK. Posts: 161	Re: Revox B77 MKII Checked the sensor and checks out fine, changing preset and zener diodes. Preset looks abit dodgey

5th May 2012, 7:59 pm	#28
Redders03 Pentode Join Date: Apr 2012 Location: Bromley UK. Posts: 161	Re: Revox B77 MKII Changed preset and both Zenor diodes and it's still not working Where next ? When the optisensor contacts are shorted at the the sensor it stops to I guess their is no problem between sensor and card.

5th May 2012, 8:50 pm	#29
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,554	Re: Revox B77 MKII Have you tried a TV remote with the LED end offered close up to the sensor to see if it operates then? The sensor may also have been rotated by mistake to that the "eye" part of it is facing the wrong way.

6th May 2012, 9:00 pm	#30
Redders03 Pentode Join Date: Apr 2012 Location: Bromley UK. Posts: 161	Re: Revox B77 MKII Tried this and still nothing

7th May 2012, 9:09 pm	#31
Michael Maurice Moderator Join Date: Feb 2006 Location: Wembley, Middlesex Posts: 7,225	Re: Revox B77 MKII The circuits are quite simple so they cant be too much wrong with it. What you have to understand is that the photocell voltage will change when light falls on it, but not by a huge amount and certainly not to 0V. What I want you to do is the following test: Switch the machine on and connect your multimeter set to volts, on to the output of the photocell (the one that goes to pin 7 of the transport board) Measure the voltage both with and without a tape (or cover the sensor up) and let us know if there is a difference. If there is and there should be then that part of it is working and its likely the preset hasn't been properly set, if there isn't repeat the exercise while shining a bright torch into the sensor. __________________ Forum Moderator http://www.michaelmauricerepairs.co.uk/

7th May 2012, 10:49 pm	#32
Redders03 Pentode Join Date: Apr 2012 Location: Bromley UK. Posts: 161	Re: Revox B77 MKII The machine is working corectly when torch is placed in front of sensor, When led is placed on violet and grey it lights when placed on violent and brown does not light, measuring around 2 volts around violet and brown Last edited by Redders03; 7th May 2012 at 11:03 pm.

7th May 2012, 11:31 pm	#33
Redders03 Pentode Join Date: Apr 2012 Location: Bromley UK. Posts: 161	Re: Revox B77 MKII from this i believe the ground for the ir emitter is open and Changing R2, in Service manual, three figures are given for this resistor 1.5k, 3.3k and 6.8k. Which is the correct one for 1.177.317.81 ?

8th May 2012, 7:44 am	#35
Michael Maurice Moderator Join Date: Feb 2006 Location: Wembley, Middlesex Posts: 7,225	Re: Revox B77 MKII In post 18, you state that you have replaced the sensor twice. Did the replacement sensors come complete with wiring loom? If so did you fit it with wiring loom or did you cut wires off and solder the original wires to the new sensor? It would appear that the IR receiver part is working and that fault lies with the LED only. According to my manual R2 on your transport card is 1.5K but it isn't critical. I'm wondering if somehow you've got the LED's wires reversed. __________________ Forum Moderator http://www.michaelmauricerepairs.co.uk/

8th May 2012, 6:17 pm	#36
Redders03 Pentode Join Date: Apr 2012 Location: Bromley UK. Posts: 161	Re: Revox B77 MKII Changed the resistor and now working properly many thanks to all who contributed !!