ASR 33 buzzing
vintagecomputer at bettercomputing.net
Fri Oct 14 14:53:53 CDT 2016
Okay here's an interesting one.
With the 2A fuse near the motor currently blown, I tried plugging in with
the switch in the Off position, just trying to see what's going on with the
PSU. To my surprise, the motor started buzzing as though there were a fuse
in. But there's nothing?! Something's messed up here.
I might just swallow hard and buy the darned books. I hate trying to read
on my ipad or computer.
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of tony duell
Sent: Friday, October 14, 2016 10:38 AM
To: General Discussion: On-Topic and Off-Topic Posts <cctalk at classiccmp.org>
Subject: RE: ASR 33 buzzing
> Check that all the clutches lock up. You can do this by hand. If
> they drag it can stall the motor.
It may be worth removing the belt from the motor :
If an air deflector is fitted over the fan remove it by loosening thw 2
screws between the fan and the motor and removing the screw on top. Then
unhook it from under the 2 screws and take it out.
Undo the 2 screws on the clamps at each end of the motor (2 are the 2
screws refered to above) and lift off the clamps.
Lift out the motor and free the belt from the sprocket. Hold the belt out of
the way (with a bit of wire or something), put the motor back in place and
fit the clamps to hold it. You can now get the motor running with no load,
if there is a problem in the rest of the mechanism it can't stall the motor.
The motor is fed via 2 pins of plug 4 at the back of the control unit. You
can try disconnecting this to see if the control unit behaves.
According to the diagrams I have, the motor is not powered with the switch
in the 'Off' position. So you may have a problem with the switch or a
shorted snubber network in parallel with it.
There were various motors fitted to the Model 33 over the years.
Some had a current-operated relay to disconnect the starter winding when the
motor was up to speed (and drawing less current), If this is not closing at
switch-on, the starter winding will not be powered, the motor can't run. The
relay is a black plastic box on the mechanism chassis (IIRC to the left of
the motor) with 3 wires going to it.
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