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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 6th Dec 2017, 4:17 pm   #1
rtbcomp's Avatar
Join Date: Aug 2007
Location: Sheffield, South Yorkshire, UK.
Posts: 48
Default Decca Deccalian Motor Mounting Replacement.

Further to my amplifier problems

I now have a loud graunching sound at 78 rpm coming from beneath the turntable. On inspection the motor mounting grommets have rotted away causing the motor to drop which in turn caused part of the speed change mechanism to bind on the brass motor pulley, you can see the brass filings in this picture:

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And the state of the grommets:

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Preliminary steps:

Remove the pickup and tie the tone arm to its suppport

Remove the 2 wooden fillets fore and aft of the deck and the deck will lift off the wooden supports at each side. Note how the fillets are located. Lift the deck vertically until the springs it sits on clear the supports before tilting it, otherwise the springs will get distorted. Tilt and twist the deck towards the rear of the machine taking care not to stretch any wires. Unplug the 3 pin plug connecting the pickup to the amplifier and tilt the deck further until you can get to the wires connected to the motor. Mine were connected to a 2 way chocolate block. Remove the amplifier switch, use a 3/8 BSF (5/46 BSW) spanner on the nut beneath the baseplate, this saves marking the knurled nut on the top. The deck can now be lifted away from the case.

The motor and speed change assembly come away as one unit:

1) Disconnect the motor, remove the switch if neccessary; there is a descrepancy between the circuit diagram and they way my motor was connected.

2) Remove the circlip from the peg where the link from the speed-change knob is connected to the speed change mechanism. This peg isn't fixed, so be careful not to lose it. Lift the link off the peg.

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3) Remove the turntable, there's a grub screw (or 2) in a hole on the side of the bearing, slacken this off sufficiently to release the turntable.

4) Remove the idler pulley, take care not to lose the brass spacer.

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4) Undo the cheese-head screws and nuts that hold the assembly to the deck, there are spacers inside the black grommets, they may fall out.

5) Remove the three dome-headed screws that fasten the speed change mechanism to the motor mounting plate. Note the large spacers, the mounting plate is tapped to take these screws.
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Old 6th Dec 2017, 4:22 pm   #2
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Location: Sheffield, South Yorkshire, UK.
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Default Re: Decca Deccalian Motor Mounting Replacement.

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6) Note the relative positions of the motor and its mounting plate and undo the three screws holding the motor to its mounting plate, these are tapped into the motor, there are three spacers and washers which will most likely be embedded in the gunge that was once the mounting grommets. Clean all the gunge off, I used a sharp chisel.

Putting it back together:

1) Acquire

3 off grommets 6mm

2 off grommets 9mm

6 off M5 Washers

2) Slice the 9mm grommets in half so that they form rubber washers.

3) Install the new washers/grommets and original screws/washers/spacers like this:

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The bits in blue are the new grommets; green, the original fixings and purple the M5 washers.

1) Fit the motor to the plate, don't forget the spacers, these are essential, if you omit them there is a risk that the screws will screw in too far and damage the motor windings.

2) Re-assemble it all but don't fit to the deck, fit the idler (don't forget the brass spacer, no need for the circlip yet)

3) Check the clearance between the bottom of the idler and the top of the 78rpm pulley on the motor shaft:

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If there isn't enough clearance move one of the M5 washers from above the motor plate to below, this will lower the motor slightly relative to the idler.

4) When the clearance is OK assemble it all, less the idler, and install back on the baseplate using the 2 screws and nuts furthest away from the speed-change link, leaving them slack, omit the screw nearest the link.

5) Raise the short link on the assembly away from the deck and insert the pivot peg. Slide some folded paper between the deck and the head of the peg, this will stop it moving when fitting the link.

6) Fit the 3rd screw and tighten up

7) Refit the motor switch, insert it in its hole and fit the knurled nut so it's flush with the top of the threaded boss then screw the hexagonal nut up to secure the switch. Note it's orietnation so that the lever points forward when switched on.

At this point it's worth paying some attention to the speed-change control, mine was gunged up with dried grease.

1) Remove the knob by pulling upwards

2) Remove the circlip from below the knob and push the shaft downwards through its bush.

3) Clean all the grease off and re-assemble, a drop of light oil should be applied to the shaft prior to inserting it into the bush.

4) Fit the end of the link to peg, fit the circlip and remove the paper.

5) Lightly oil the rubbing surfaces of the speed-change mechanism

6) Re-fit the idler & circlip, putting a drop of oil on the shaft

7) Put a drop of oil in the turntable bearing and refit the turntable.

8) Tighten the grub screw then turn it back a full turn, check the turntable runs free and won't lift off. If there was a 2nd grub screw tighten it up against the first one to lock it.

9) Re connect the motor supply and pickup connector

At this point it may be a good idea to slip some sleeving on the rubber wires carrying mains to the motor and the two switches, I used spiral binding as this can be fitted without disconnecting the wires.

Refit the deck:

1) Lower it vertically so the springs seat in the pockets on the side runners, it may be necessary to move the deck about a bit to get the springs to locate correctly.

2) Check the turntable runs quietly on both speeds.

3) Refit the front and rear fillets

4) Release the tone arm and refit the pickup.
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Old 6th Dec 2017, 5:19 pm   #3
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Join Date: Jun 2014
Location: Bristol, UK.
Posts: 1,595
Default Re: Decca Deccalian Motor Mounting Replacement.

Really helpful! Especially as I have still to finish tackling mine.
'....don't go mistaking Paradise for that home across the road!' (Bob Dylan)
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