Rust and Rot: Pioneer PL-518 Turntable Restoration Fail

I recently came into the possession of a vintage Pioneer turntable. Specifically the semi-automatic, direct drive PL-518, one of their most venerable turntables of the late 1970s. Despite it's initial, relatively innocent appearance however, this deck was a long way from spinning LPs again thanks to the horrors of unchecked humidity. Unfortunately for me, the rust and rot was just the tip of the iceberg.

I bought this PL-518 along with the Technics SL-1600 MK1 I wrote about previously for $60. Either one of these turntables would've been a steal at that price, and I was still pinching myself even after I loaded them into the car and drove home. While it was clear they both needed work, it was very evident the minute I touched the Pioneer that it was screwed up in ways the Technics certainly wasn't.

The nice woman I bought them from said that both turntables were in storage for around twenty years. She didn't specify what kind of storage, but the condition of the Pioneer's plinth made it clear that it was somewhere quite humid. Shit kept falling off the bottom of the turntable as I carried it out to the car, and once I got it to my workbench and flipped it on it's side, the extent of the damage became clear.

The Pioneer's plinth is made out of a thick slab of MDF that had absorbed ambient moisture like a sponge, swelling up and causing the bottom pan directly attached to it to rust. This was in contrast to the Technics, which has a powder coated aluminum plinth that did a far better job of withstanding the moisture whilst it was in storage. As I began tearing the turntable apart, it became more and more obvious how deeply this moisture penetrated.

The PL-518 is thankfully very easy to tear apart. Pop the platter off, undo the screws holding the covers to the plinth, and the entire thing separates from the plinth in two neat pieces. Or... at least it would have been, were the screws not rusted to oblivion. The bottom cover was practically welded to the MDF with rust, and one I finally chiseled it free, I was able to fully take in the horrors that two decades of humid storage could impart onto a turntable.

Shit.

That bottom pan was so rusty around the edges that the Autopian's David Tracy probably would've come knocking, cash in hand. Thankfully, the internals were untouched by corrosion, having been separated from the plinth, but it was evident that getting all that rust off was going to take quite a bit of elbow grease. Still, I felt better about restoring that piece than I did the plinth itself.

The condition of the plinth was so bad that I was afraid that I might need to replace it entirely. And since I don't have the tools or skills to effectively fabricate a new one myself, I was almost ready to chalk this one up as a bust. After studying it a bit more though, I figured there still might be some hope of making it work. The portions of MDF in the middle of the board seemed more solid than the visibly swollen and flaking pieces on the outer edges. My theory was if I dried the MDF out sufficiently, I could remove the rot, fill in the gaps with wood filler, then plane it flat. I had no idea if this method would work, but I decided it was worth at least trying.

This also raised the question of what to do about the grey veneer attached to the MDF. I'm a sucker for originality and as much as I'd like to keep it, it seemed far too worn and discolored to rescue it. Even if I could reuse it, if the dimensions of the MDF change slightly after the repair, it would no longer be a proper fit. I decided the best thing to do was to replace the veneer entirely. I opted for some nice-looking cherry veneer that I was going to seal with polyacrylic to give it a nice, thick shine.

My first order of business was attempting to dry out the plinth. I had to get the old veneer off, and that was as easy as heating each side up with a heat gun and peeling it off, after removing the hardware still in it of course. From there, I stuck it inside of a storage tub with a bag's worth of calcium chloride moisture absorber (otherwise known as Damp-Rid) to hopefully draw any remaining moisture out of the MDF. I really had no idea if this would work, so I opted to leave it alone while I worked on refurbishing the bottom pan.

Rust removal is not something I regularly do, and this thing had no shortage of the brown stuff to clear off it. I don't have any fancy tools at my disposal for this task, so I masked up and went medieval on it with the wire brush, file, and heavy grit sandpaper.

Pitted. So pitted.

After sweating my ass off in the sweltering sun, I managed to get the bulk of the rust off. Though there was still a little bit left within the pitting it caused, I was satisfied enough with the surface to start painting. I selected a rust preventative primer, following it up with a layer of black, then a gloss enamel clear coat. I sanded the entire pan down, cleaned the surface with IPA, then got to painting.

I'm far from an expert at spray painting, but since this pan was going to be on the underside of the unit anyways, I wasn't too concerned about making it look perfect. The most important thing was making sure the pan was protected from future corrosion, so adequate coverage - especially where the pan contacts the plinth was a far greater priority than a perfect mirror finish.

With the pan done, it was back to the plinth. A week has passed since I left it in the container with the desiccant and while it was hard to tell what extent the plinth had dried out, the swollen, flaking edges of the MDF did seem pretty dry and less 'spongy'. Unfortunately, I didn't weigh the plinth prior to it going in the desiccant box, and I had no idea if the moisture droplets I saw were actually from the MDF, or the surrounding air. 

To make matters worse, the desiccant left behind a huge mess. Droplets seemed to crystallize on the surface of the MDF and a good chunk of the calcium chloride itself had gotten stuck to the surface. Chalking this idea up to a bust, I cleaned all the residue off the plinth, weighed it, and baked it in the over at 225 degrees Fahrenheit, reweighing it every hour to see how much moisture was evaporated from the plinth.

It was a slow, stinky process but after six hours of baking, I ended up removing about 100 grams of water from the plinth, or a bit less than half a cup. Not a huge amount of water and I accepted that I was never going to get this thing to stay completely dry, but the excess moisture was out, and I felt like it was ready for filler.

This was easily the part where I wound up wasting the most money and time; trying to figure out the best way to repair the rot in this MDF. I first experimented with a tub of standard DAP latex wood filler, being that it was cheap, and hell it seemed like it was practically made for the job at hand. I started off by breaking off and brushing away chunks off rot on the bottom edges of the plinth and laying a heaping amount of filler into the gaps.

DAP wood filler on the left, and JB Weld Quik Wood on the right.

While the DAP filler dried fast and was really easy to sand, it was so viscous that it was nearly impossible to shape while applying it, hence why I had to glob it on in large amounts before I planed and sanded it flat. After I started breaking huge chunks off the board during that process, I quickly realized this stuff was extremely ill suited for building pieces that require structure - such as corners and edges. It was far too brittle, and after removing all of it from the edges of the plinth, I moved onto something I was a little more accustomed to using.

The magic stuff that ended up getting the job done was JB Weld Quik Wood: a two-part epoxy putty formulated to match the density of wood. This stuff wasn't cheap - it took me two tubes at $7 a pop to fill all the edges, but it worked. I was able to sand it all down to a nice strong, sharp edge. With that out of the way, I painted the bottom of the plinth flat black, and decided it was time to try applying the new veneer.

And being my first time doing this - I fucked it all up. Bad.

What I did wrong, was just squeeze a bunch of wood glue onto the plinth without spreading it evenly, and then weight the veneer down with a big crate full of junk. It dried extremely unevenly thanks to the excess glue, and no amount of heat was able to level it out. I had no choice but to rip it all up, and it took an entire 1mm thick layer and several chunks from the once pristine top side of the MDF.

I ended up having to fill the entire top layer with automotive body filler just to give myself a flat surface to work with again. This time a around, I spread the glue evenly using a foam brush on both the veneer and the MDF, and then bonded the two pieces with a clothes iron. I then trimmed off the excess with an Xacto knife before sanding the edges flush. The finished product looks like it just came off a table saw, which is more than I would've hoped for.

Pioneer PL-518 Replacement Foot by YALE70 - Thingiverse

Before I got to finishing the plinth, I needed to deal with another pressing issue my PL-518 had: rotted feet. The originals were completely gone and replacements were generally pretty expensive. I went ahead and modeled a replacement set in Inventor and 3D printed them in TPU - first in blue, then in black. The new feet would help keep the plinth off the workbench while I finished it, plus I hoped that the soft-ish TPU would retain at least some of the vibration dampening aspects of the original spring-loaded feet in actual use.

Afterwards, I got started with the staining and sealing of the plinth. I first stained the cherry with some teak oil, which didn't darken the wood too much but made the colors pop a whole lot more. After that dried, I then sealed it off with several layers of polyacrylic. I couldn't quite get the super glossy finish I was envisioning, but the plinth ended up getting this kind of lightly weathered look that I thought complimented the vintage nature of the turntable pretty well.

With the horrific state of the plinth finally addressed, I turned my attention to the actual guts of the turntable. There wasn't anything mechanically wrong with the turntable - hardly surprising because it's so simple, but the motor was struggling to start and sustain rotation. Mind you, this was with the platter on the spindle. This type of behavior is actually pretty normal with the platter off since without the mass of the platter, there isn't enough inertia for the motor to keep spinning.

All signs then pointed to this being an electrical issue. I checked the continuity of both switches and the impedance of the speed control pot after a good contact cleaning. I also checked the voltages of the power board. Nothing appeared to be out of the ordinary which left the motor as the odd component out. Underneath the PL-518's motor is it's control PCB, on which the trim pots and several capacitors are mounted. This board is a pain in the ass to access, since it's connected to the motor coil by several hair thin wires that you absolutely don't want to break.

Pioneer never intended for this part to be serviceable and all of the circuit components are omitted from the parts list on the service manual. I had to dig through the actual schematic to determine the spec of each capacitor on this board. It's a pretty unfortunate design choice on their part, but what can you do. I figured just maybe, a contact cleaning on the trim pots and a full re-cap of both the motor and power boards would finally bring this this thing back to life.

Except, it didn't. The problem still persisted.

It was evident by this point that the motor was shot, possibly due to bad windings. At this point, I decided to throw in the towel. I had already poured enough time and money into this deck to see if there were any hopes of repairing or replacing the motor. Plus, secondhand PXM-058 motors are rare and there's no real guarantee they will work. I'm glad that I managed to rescue the plinth though, and I was able to sell the turntable on to someone who had the spare parts to put it to use. So while my overall restoration attempt was a bust, I'm glad that it wasn't all entirely a waste. You can't fix em' all.