Revox PR99 Mk 1 dead capstan motor questions

[Riley Casey]

I've just finished swapping out the electrolytic & motor caps in my PR99 along with all the trim pots, put it back together, turned it on and discovered the capstan motor wasn't turning. Checked voltages at the motor leads where they attach at PSU board and got 130 VAC there as it should, checked the DC supply voltages on the board and all seemed in order there so I measured the resistance on the windings. I found 92 ohms between the outside windings but the center winding connected to the yellow lead showed open to both of the outer leads. This is very odd as the motor was fine before I started the overhaul. Now its been a few decades since I worked on these machines on a regular basis so I'd like to check a couple of things before I go in search of another capstan motor.

Am I correct in thinking that I should see continuity across all three winding on an AC sync motor like this? Second question is on the wiring. When I disassembled the machine I took plenty of pictures so as to not miss any connection details BUT when I reassembled it I went by the wiring as detailed in the schematic. Only after discovering the motor wasn't running while I was measuring voltages did I realize that the original connections were different from those shown on the schematic. I had marked the PCB with yellow paint next to the far wire terminal to show where the yellow lead was initially and as you can see in the photo the schematic called it out as being in the middle position. I'd imagine that the windings were all good for seeing 130 VAC so that wiring them out of order shouldn't burn a winding open but that certainly seems to be what has happened.

This machine was essentially a back up deck so had very low hours compared to some so it seems unlikely that the motor winding went out from hard use. I'm the original owner & I've never worked on the capstan or actually any part of the machine before it went into storage twenty years ago so the motor wiring is from the factory. I've attached a picture of the motor terminals as they land on the power supply board as well as a pic of the capstan wiring part of the schematic. If anyone has a PR99 with the back off and could let me know how yours is wired that would be helpful.

Thanks for any suggestions

 

[guy_4]

Hello Riley,

I have ckecked on one of my capstan motors for PR99 MKI.
Studer 1.021.302. 7,5 / 15 IPS

When unplugged from the board the coils resistance are :

Yel / Grey : 90 ohms
Yel / Green : 96 ohms
Grey / Green : 92 ohms

For the wires plugged on the board the colors are :

Yellow / Green / Grey , from the front panel to the inside of the PR
( Grey near the white connector )

Hope it will help.

Best,
Guy

PS : do you still have some splitter XFER available ?

 

[Riley Casey]

Hello Riley,

I have ckecked on one of my capstan motors for PR99 MKI.
Studer 1.021.302. 7,5 / 15 IPS

When unplugged from the board the coils resistance are :

Yel / Grey : 90 ohms
Yel / Green : 96 ohms
Grey / Green : 92 ohms

For the wires plugged on the board the colors are :

Yellow / Green / Grey , from the front panel to the inside of the PR
( Grey near the white connector )

Hope it will help.

Best,
Guy

PS : do you still have some splitter XFER available ?

Thanks for those readings. After posting I disassemble the motor again and discovered a burned open winding on the surface. After exposing some bare copper at each end I solder a jumper in and the motor seems to be running fine. Not sure thats a permanent fix but it'll get me thru testing the machine.

A couple of people have messaged me about the iso transformers so you're third in line if they don't come thru. Can't deal with them til January anyway. Unless of course you have a spare PR99 motor you want to let go. That'd change the equation ;-).

 

[guy_4]

Thanks for those readings. After posting I disassemble the motor again and discovered a burned open winding on the surface. After exposing some bare copper at each end I solder a jumper in and the motor seems to be running fine. Not sure thats a permanent fix but it'll get me thru testing the machine.

A couple of people have messaged me about the iso transformers so you're third in line if they don't come thru. Can't deal with them til January anyway. Unless of course you have a spare PR99 motor you want to let go. That'd change the equation ;-).

That's fine if you are able to save your motor with soldering a jumper.
About the iso transformers : thanks for your proposal for a spare PR99 motor in exchange
...I can let one go..
Are you located in Europe ?

Best,
Guy