SP-10 Mk2 #3

The SP-10 as it arrived, not working.  The power supply seemed to be working okay, just voltages a bit off.  The speed and power switches were damaged and quite gummed up.  Shorting in the switch assembly was the primary cause of failure in this unit.  

The chassis, although not perfect, was not bad, mostly just scratched up, no corrosion.   

Power supply refurb:

This shows the power supply after being recapped with Nichicon and Vishay parts.  I increased the main cap (C413) from 1,000uf to 3,300uf, and most caps are 105 degree rated.  I also replaced the voltage adjustment trimpots with 25 turn Bourns cermet pots.

I also added a simple DC supply (diode & cap) to power the front panel LED indicator (stock bulb was dead).

Lastly I adjusted the voltages to the target 5.0 and 32.5VDC.

Chassis refurb: 

Although I had planned to powder coat the chassis, since there was no corrosion, I thought I'd try something simpler.  This shows the chassis after disassembly.  I sanded it with 220 then 320 sandpaper, then sprayed a couple coats of gloss polyurethane after which it looks much better.

Motor refurb:

I replaced the thrust pad with a new Torlon pad and the ball bearing with a SI3N4 silicon nitride (ceramic) ball bearing, shown here.  I've seen corrosion in the stock bearings, hence the change.  The blue liquid is Loctite Blue 242 threadlocker on the bearing end cap threads.  It's a special version that allows removal in the future if needed.

The correct size bearing is 9/32, and I bought mine from Boca Bearings.

Start/Stop and speed assembly refurb:

This assembly (bottom view) was in bad shape - had been modified, assembled incorrectly, and connections were shorting.  I replaced all 4 switches (Omron SS-5D), cleaned and reassembled.  This got the turntable working.  The 3 speed selectors and the Start-Stop switch are on the other side of this assembly...

The Start-Stop switch after refinishing and mounting in the SP10 chassis.

Like the main chassis, I also lightly sanded the Start-Stop button and coated it with gloss polyurethane.  On all the units I've seen, that switch cover seems to take the most abuse, but this one cleaned up pretty well.

The speed switches also have a fresh coat of white paint for the speed markings.

PCB Recap:

Next step was recapping all of the electrolytics on all 4 PCBs, show here after completion.  I also replaced the PLL trimmer pots (VR101 and 102) with 20 turn trimpots, visible on the left.

Strobe light:

Like my previous SP-10 projects, I replaced the hard-to-find neon bulb for the strobe with an array of 4 orange LEDs, shown here from the bottom.

PLL adjustment:

This screenshot of my oscilloscope shows the PLL adjustment for 33RPM.

Brake: 

I cleaned and replaced the rubber parts on the brake solenoid mechanism, as the original parts were worn out.

Plinth construction:

Now that the SP-10 and power supply were working well, I needed to build a plinth for it.

I wanted something lower profile than my previous projects, but still well damped.  This is my drawing for the plinth.  I planned to re-use the Jelco 10" arm from my last project and the dust cover as well.

The core of the plinth is made of 2 layers of 3/4" MDF (different types) with an aluminum layer between them to help dampen the base.  They're glued together with Aleene's Tacky Glue, which stays a bit pliant, which I've also used often to laminate speaker panels together.  There's also a 3/8" layer of Baltic birch ply on top to give the arm mount something to solidly screw into.

Here's a view do the core of the plinth (back is up in this photo), before any finishing or drilling for mounting the table, arm, feet and dust cover.

Adding solid cherry trim around the perimeter of the plinth.   The edges were then rounded over with a 1/4" router bit to take off that sharp edge.

After the cherry trim was added, I painted the top semi-gloss black.   The whole unit was then sprayed with several coats of polyurethane.

The tool in the center is for installing threaded inserts for the feet in the bottom, shown below.

Another view of the completed plinth, after drilling holes to mount the arm (with the Jelco tonearm base shown in place here) and holes for mounting the SP-10 itself.  

Since full-sized templates are no longer available, the easiest way to locate the SP-10 mounting holes is to lay the bottom of the SP10 chassis in place and mark the mounting holes thru the openings.

The assembled setup with the SP-10 and Jelco SA-750E tonearm mounted (and aligned).

Front view, showing the Stillpoints footers and dust cover in place.

View from the right side.