Refreshing a Marantz SLT-12 Turntable

[atlackey]

I stumbled upon a local ad for a Marantz SLT-12 -- I'd never heard of this turntable prior and after spending some time reading archived threads and anything else I could find on it decided it would be a really interesting TT to own. The previous (I think original) owner had it in storage for decades. It included the original owner's manual with a matched serial #, but no dust cover. The plywood, motor, platter, buttons and tracking mechanics all seem to be working well although it definitely needs some TLC.

As a lot of the other threads have mentioned, it's a beautiful albeit finicky machine. I managed to get it leveled and it skipped like crazy, after I made sure the tonearm wire had clearance from the mechanics and RCA cable it played the first track on my test LP before losing tracking force and skipping out. The dampening mechanism isn't working, I've ordered some Dow Corning 111 silicone compound to fix it - the service manual calls for #11, but I couldn't find that, hoping it's equivalent. I can't imagine the dampener causing the skipping, but I'd like it fixed nonetheless. I don't own a caliper yet and haven't gotten the bearing out to check for flat spots, but it seemed to spin fine without any noise. I did order some molly spindle oil as well for the platter shaft although it seems to have plenty of lubrication in it already. Wanted to share and am interested to see what others have learned.

Pictures attached

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[ltbetty]

Beautiful! I'm not quite finished with mine but close. Still need to get into the electronics and (I'm guessing) swap in a new capacitor. Belt from LPGEAR was perfect! Info about setting the tracking force is conflicting. The service manual states to move counterweight towards cueing tab to increase pressure. But mine only tracks at 1g when right up against the cueing tab. In my opinion, the "skating" is all about balance. If it is not balanced perfectly, the arm will skate. All the mechanics underneath were set properly at the factory. Unless someone prior has messed around underneath, there should be no adjustments necessary. I was able to balance mine just from the adjustable foot underneath. Adjusting the platter from the 3 nuts underneath complicates matters as that also adjusts the clearance of gears as well as the cueing tab gap from the belt. In regards to cueing, I disassembled according to service manual and used 200000 weight oil. It works great now. A couple things I still need to fix:

1: Transformer buzzing (could be the motor)
2: Slight ground hum (I found a ground wire connected at one of the wing nuts!)
3: increase tracking force (another manual I stumbled upon said to move the weight away from cueing tab to increase pressure so I need to play with this some more)

Interestingly, the 12u version appears to have a fine adjustment weight on the cartridge arm (similar to a Philips table).

 

[atlackey]

Beautiful! I'm not quite finished with mine but close. Still need to get into the electronics and (I'm guessing) swap in a new capacitor. Belt from LPGEAR was perfect! Info about setting the tracking force is conflicting. The service manual states to move counterweight towards cueing tab to increase pressure. But mine only tracks at 1g when right up against the cueing tab. In my opinion, the "skating" is all about balance. If it is not balanced perfectly, the arm will skate. All the mechanics underneath were set properly at the factory. Unless someone prior has messed around underneath, there should be no adjustments necessary. I was able to balance mine just from the adjustable foot underneath. Adjusting the platter from the 3 nuts underneath complicates matters as that also adjusts the clearance of gears as well as the cueing tab gap from the belt. In regards to cueing, I disassembled according to service manual and used 200000 weight oil. It works great now. A couple things I still need to fix:

1: Transformer buzzing (could be the motor)
2: Slight ground hum (I found a ground wire connected at one of the wing nuts!)
3: increase tracking force (another manual I stumbled upon said to move the weight away from cueing tab to increase pressure so I need to play with this some more)

Interestingly, the 12u version appears to have a fine adjustment weight on the cartridge arm (similar to a Philips table).View attachment 1937293 View attachment 1937296

Yours looks great thanks for sharing! Is that a new Marantz next to it?
I really like your display cover. Is something like that easy to come by?
You're right about the second counter balance on the tone arm for the U model. I saw someone mention the U tonearm may also be shorter to make up for the larger cart head.\

Hopefully you get to the bottom of your issues. I've noticed some pictures with the grounds attached in different spots, maybe some came from the factory with different placements? There are also a couple of small allen screws on the backside of the tone arm that I'm a little afraid to mess with.

 

[ltbetty]

Yes atlackey, that's the new 15s next to it. That dustcover fits over both Marantz turntables perfectly. It's made by JnB near me here in Grand Rapids Michigan. He sells on eBay. I'm working with him on replicating the original dustcover. I know it's a stupid question but did you release the suspension wing nuts underneath when it was skipping after first song? If so, in one of your photos it looks like the platter is too high up. The manual says something about it being relatively flush with the deck.

 

[atlackey]

Oh cool, I'll check JnB out. I had the suspension released when I was testing it, you're correct though in the pictures the wing nuts are tightened. Thanks for the suggestion.

 

[ltbetty]

Just curious if you've worked on the circuit board at all. I'm in the midst of this at the moment. There's two larger caps on the board but there's no indication of whether or not they're polarized caps (no marking on the board either). I also replaced the crumbling foam pads under the control buttons this morning.

 

[atlackey]

Thankfully I haven't had to touch the circuit board. My general circuit knowledge is limited, but I have a cheap multi-meter. If there's any way I can help with that let me know. Looks like the foam pad replacement went well for you. I didn't realize they were there, my buttons seem to work well, but I'd be surprised if the foam wasn't disintegrated.

 

[ltbetty]

Hi atlackey, thanks for the reply. I'm almost done. There's a 1uf cap and a .1uf cap, a 300 ohm block resistor and a couple smaller resistors. I've replaced the larger cap and am waiting for the smaller cap to arrive. The resistors are all good. Should be done and reassembled by mid week. I think the foam just helps the buttons feel more soft and maybe spring back better. Do all your buttons light up?

 

[ltbetty]

I'd be happy to help when you decide to refresh the circuit board. It's super easy.

Well, it's done and sounding great! A couple tips...the crossbar that changes the speed goes on the inside of the brass plate. Do not put the two pins through the two holes. The ball bearing rides in those holes. Also, one of the L shaped brackets is smaller than the others and goes in the corner by RCA connectors. Images attached.

 

[sbaudio]

Fun tables these. I have several and pick up used tables for parts when I can find them. When shipped, if not in the original packaging, the platter can be hammered enough to slip up or down on the spindle. If the top of the shoulder on the spindle is not flush with the platter it can cause a misalignment between the stylus and the record groove causing skating. This can also occur when a mat of thickness different from that of the original is used. The short length of the tonearm exacerbates this as it pivots in an arc. Originally the tables were shipped with cardboard wedges placed between the lip of the platter and the black metal frame. With the shipping screws tightened the weight of the platter is hammering on the ball bearing in the bottom of the spindle bearing well. I have had to tap several spindles out with a hard rubber or leather mallet, clean the platter and spindle, and then reassemble with Locktite red. Gentle tapping is usually all that is needed and a small socket can be placed on the spindle shoulder to prevent damage. With the original Shure V15 type 1 the adhesive fails and the diamond falls out. Very hard to find. Marantz had belts specifically made and ground on one side for precision. Todays belts do not come close to the originals. I have also decreased motor hum by running the motor and carefully adjusting the four nuts that hold it together. The rubber motor mounts usually need to be replaced too. Even with some motor hum the rumble was not very loud. The SLT12 is much more adjustable but somewhat more boxy in appearance. It does allow for use of many more cartridges that are more robust. The Shure M55E seems right at home in these tables. Let me know if the Dow 111 works for the cuing. I have gotten used to carefully cuing records and havent tried the Dow yet. I would not try to increase the length of the cuing spring as this can prevent a complete landing also resulting in mistracking. I hope you enjoy the table. I have to level the deck on top of 2 milk crates to set it up. Hours of fun!

 

[Bill Sohne]

Fun tables these. I have several and pick up used tables for parts when I can find them. When shipped, if not in the original packaging, the platter can be hammered enough to slip up or down on the spindle. If the top of the shoulder on the spindle is not flush with the platter it can cause a misalignment between the stylus and the record groove causing skating. This can also occur when a mat of thickness different from that of the original is used. The short length of the tonearm exacerbates this as it pivots in an arc. Originally the tables were shipped with cardboard wedges placed between the lip of the platter and the black metal frame. With the shipping screws tightened the weight of the platter is hammering on the ball bearing in the bottom of the spindle bearing well. I have had to tap several spindles out with a hard rubber or leather mallet, clean the platter and spindle, and then reassemble with Locktite red. Gentle tapping is usually all that is needed and a small socket can be placed on the spindle shoulder to prevent damage. With the original Shure V15 type 1 the adhesive fails and the diamond falls out. Very hard to find. Marantz had belts specifically made and ground on one side for precision. Todays belts do not come close to the originals. I have also decreased motor hum by running the motor and carefully adjusting the four nuts that hold it together. The rubber motor mounts usually need to be replaced too. Even with some motor hum the rumble was not very loud. The SLT12 is much more adjustable but somewhat more boxy in appearance. It does allow for use of many more cartridges that are more robust. The Shure M55E seems right at home in these tables. Let me know if the Dow 111 works for the cuing. I have gotten used to carefully cuing records and havent tried the Dow yet. I would not try to increase the length of the cuing spring as this can prevent a complete landing also resulting in mistracking. I hope you enjoy the table. I have to level the deck on top of 2 milk crates to set it up. Hours of fun!

Hi

I am in the middle of acquiring a 12u but seller telling me the motor was failing when he went to test it before shipping .
Anyone have any suggestions for replacement ?

thanks
Bill