Revox A77 Electrical Interlock Question
ARTHUR...@mpa15ab.mv-oc.unisys.com
mechanical interlock on a Revox A77 open reel deck, which keeps power
from being applied when the case is removed? The service manual
doesn't seem to have any specifics.
I took my A77 pretty well apart to clean out a couple decades of the
usual grime, grit, dust, etc that settles into any electronic
component over time, no matter how well covered it might be. (It was
scary how the wiring harnesses failed to correspond to the service
manual, but I made good notes). Upon reassembly, I turned it on with
fire extinguisher in hand, expecting either an explosion, smoke,
capstan ejection, or at least meltdown of my house's aluminum wiring.
Rather surprisingly, I got absolutely no indication of any power- no
lamps or motors were actuated, no hum, smell, etc. I haven't managed
to defeat the interlock to see if power is getting through to the
power supply, an obvious first step. Thus this question. For those
reading this out of idle curiosity, the interlock consists of a block
with two hefty metal rods loosely mounted (via rivets, unfortunately)
on the back of the cabinet or of the rackmount cage. They push deeply
into corresponding holes on the chassis, adjacent to the actual AC
connection. There is no electrical conductivity between the two rods,
so something mechanical is involved which isn't immediately obvious.
Using narrow screwdriver shanks into the holes doesn't seem to release
the interlock.
Art
Arthur L. Shapiro Art...@mpa15c.mv-oc.unisys.com
Rarely an official Unisys corporate spokesman, and certainly not now.
Richard D Pierce
<ARTHUR%MPA...@mpa15ab.mv-oc.unisys.com> wrote:
>By any miracle are any of you readers familiar with the rather strange
>mechanical interlock on a Revox A77 open reel deck, which keeps power
>from being applied when the case is removed? The service manual
>doesn't seem to have any specifics.
Yup, I am, serviced maybe 100 of these guys.
>manual, but I made good notes). Upon reassembly, I turned it on with
>fire extinguisher in hand, expecting either an explosion, smoke,
>capstan ejection, or at least meltdown of my house's aluminum wiring.
>Rather surprisingly, I got absolutely no indication of any power- no
>lamps or motors were actuated, no hum, smell, etc. I haven't managed
>to defeat the interlock to see if power is getting through to the
>power supply, an obvious first step. Thus this question. For those
>reading this out of idle curiosity, the interlock consists of a block
>with two hefty metal rods loosely mounted (via rivets, unfortunately)
>on the back of the cabinet or of the rackmount cage. They push deeply
>into corresponding holes on the chassis, adjacent to the actual AC
>connection. There is no electrical conductivity between the two rods,
>so something mechanical is involved which isn't immediately obvious.
>Using narrow screwdriver shanks into the holes doesn't seem to release
>the interlock.
The interlock is electrical, not mechanical. The two rods you see are
definitely not connected to each other. Rather, each of them, when
inserted into their respective holes, shorts TWO contacts and connects
them. Two rods are used, one for each side of the AC line. The
arrangement looks like:
| interlock |
| |
| |
v v
hot ----| |- -| |---- neutral
+---| |- -| |----+
| |
| <- to power switch -> |
hot neutral
Inserting the bar connects the hot side of the AC line to the hot
contact of the power switch and connects the neutra; side of the line
with the neutral contact of the switch.
You can accomplish the same thing by inserting a dual banana plug into
the socket (making sure it's not a SHORTING plug!). Anything
sufficientlyu conduction with enough current carrying capacity that's
of the right diameter and length to connect the two sets of contacts
will work.
| Dick Pierce |
| Loudspeaker and Software Consulting |
| 17 Sartelle Street Pepperell, MA 01463 |
| (508) 433-9183 (Voice and FAX) |
JohnAFR
<ARTHUR%MPA...@mpa15ab.mv-oc.unisys.com> wrote:
>By any miracle are any of you readers familiar with the rather strange
>mechanical interlock on a Revox A77 open reel deck, which keeps power
>from being applied when the case is removed? The service manual
>doesn't seem to have any specifics.
Yup, I am, serviced maybe 1 of these guys, years ago; been a long time,
though.
Just read the mighty Dick Pierce's response and, as usual, I can't
dissagree with a word he says. Just wanted to add something I think I
remember from years ago when I owned one of those guys. I seem to
remember a remote control shorting plug that had to be installed before
any power would magically appear at the power supply. It seemed like
magic when I owned it. I know better now. Just a thought.
John Elison
David J. Carlstrom
> In article <3pcup6$3...@eyrie.graphics.cornell.edu>,
> <ARTHUR%MPA...@mpa15ab.mv-oc.unisys.com> wrote:
>>By any miracle are any of you readers familiar with the rather strange
>>mechanical interlock on a Revox A77 open reel deck, which keeps power
>>from being applied when the case is removed?
> contact of the power switch and connects the neutra; side of the line
> sufficientlyu conduction with enough current carrying capacity that's
> of the right diameter and length to connect the two sets of contacts
> will work.
The Revox screws that hold the wood case on are handy (you just took them
out!) and screw right into the interlock holes. I have used this trick
from the first A77 I opened.
--
"The more cutting the verbal thrust, .-. / \
the more elaborate was the courtesy .-. / \ / \
employed." _Up At Oxford_ -Ved Mehta / \ / \ / \
' \ / \ / -DJC
David J. Carlstrom
[quoted text cut by dsb]
> remember a remote control shorting plug that had to be installed before
> any power would magically appear at the power supply.
Half-right: The remote plug is needed for the transport to run, but has
nothing to do with power supply.
Richard D Pierce
David J. Carlstrom <as...@freenet.carleton.ca> wrote:
>Richard D Pierce (DPi...@world.std.com) writes:
>> sufficientlyu conduction with enough current carrying capacity that's
>> of the right diameter and length to connect the two sets of contacts
>> will work.
>
>The Revox screws that hold the wood case on are handy (you just took them
>out!) and screw right into the interlock holes. I have used this trick
>from the first A77 I opened.
YOUCH! Gee, Dave, two exposed screw heads hangin off the back of the
chassis, sitting at line voltage with respect to one another! Golly,
that'll straighten my hair right out! (maybe that's why it's straight
already!).
Yeah, this will work, BUT IT'S NOT SAFE!!!. It's extremely hazardous in
my view. The banana plug trick will at least afford a measure of
insulating material betwixt your hands and the line voltage.
The prefered method is to call up Revox and simply order a spare
interlock bar. I have one I bought about 20 years ago. Ran a string
through the rivet holes and ran that through a hole in an index-card
sized piece of plexiglass that has big red stripes on it. I'll never
loose that sucker!
Please don't use the screw method here, while it works, it's not very
safe!
--
