Revox A77 Capstan motor control board schematic - UK Vintage Radio Repair and Restoration Discussion Forum

DJH83004 · 11th Dec 2017, 11:44 pm

Hi Guys, I have a Revox A77 service manual, but the motor control schematic is the later 555 IC version. Could anyone point me to the early discrete board schematic please.
The problem I have is the motor is permanently running up to full speed irrespective of the speed selected. I am getting +21v on the red AE1 pin on slow select, the 2SC782 tests Ok as does the bridge rectifier. Swapped the 0.47uf Rifa and I am getting AC on the tacho input when the motor is rotating.
Help greatly appreciated,

Many Thanks, Dave
sorry about the typo Revoc = Revox !

Humber888 · 12th Dec 2017, 5:21 pm

I had a look online and can only find the 10th edition service manual at either Electrotanaya or the Studer FTP site. The contents list says it has the circuit for the 1.077.725 board but does not - only showing the later circuit diagram. If you can find an 8th edition manual, this contains both circuits. My manual is not easily accessible at the moment, but someone on here may have what you need to hand.

Mike

KeithsTV · 12th Dec 2017, 6:15 pm

I've sent Dave a copy of the earlier motor control circuit.

Keith

11th Dec 2017, 11:44 pm	#1
DJH83004 Triode Join Date: Sep 2016 Location: Nottingham, Notts. UK. Posts: 15	Revox A77 Capstan motor control board schematic Hi Guys, I have a Revox A77 service manual, but the motor control schematic is the later 555 IC version. Could anyone point me to the early discrete board schematic please. The problem I have is the motor is permanently running up to full speed irrespective of the speed selected. I am getting +21v on the red AE1 pin on slow select, the 2SC782 tests Ok as does the bridge rectifier. Swapped the 0.47uf Rifa and I am getting AC on the tacho input when the motor is rotating. Help greatly appreciated, Many Thanks, Dave sorry about the typo Revoc = Revox !

12th Dec 2017, 5:21 pm	#2
Humber888 Heptode Join Date: Jul 2012 Location: Bromley, London, UK. Posts: 702	Re: Revox A77 Capstan motor control board schematic I had a look online and can only find the 10th edition service manual at either Electrotanaya or the Studer FTP site. The contents list says it has the circuit for the 1.077.725 board but does not - only showing the later circuit diagram. If you can find an 8th edition manual, this contains both circuits. My manual is not easily accessible at the moment, but someone on here may have what you need to hand. Mike

12th Dec 2017, 6:15 pm	#3
KeithsTV Nonode Join Date: Aug 2007 Location: South Bradford, West Yorkshire, UK. Posts: 2,573	Re: Revox A77 Capstan motor control board schematic I've sent Dave a copy of the earlier motor control circuit. Keith