Mitsubishi LT-30 restoration

[kotofei]

Added July20, 2011: New Feet!

Greetings everyone,

Recently I acquired a Mitsubishi LT-30 linear tracking turntable off Ebay. This TT was on my short list of linear trackers (see thread http://www.audiokarma.org/forums/showthread.php?t=291585); however, I did not expect that the opportunity will surface that fast.

The LT-30 was cosmetically in very good conditions but the tonearm lift did not work; it also doesn’t have a bottom.

The seller followed my instructions for packing and she arrived undamaged. A scratch on a veneer and a couple of small scratches on a dust cover; otherwise, great-looking table. Now it needs to be fixed.

This thread will document the repair process with pictures, information about getting spare parts and how it all ends up.

Update: fixed! All what was required are one belt, six mini bulbs and ten or so hours of a free time.

 

[kotofei]

Before the LT-30 purchase, I asked here what might be the reason for non-working tonearm lift. The most likely reason was considered a broken or worn tonearm lift belt. This belt is located inside the tonearm and can’t be seen from outside. Upon pressing the “Start” button, I’ve heard the sound of a working motor inside the tonearm so at least the motor seems to be OK.

I ordered two Mitsubishi LT-30 belts from turntableneedles.com upon the advice of koseltri. Both belts (for the vertical and horizontal movement) were around $7 with free shipping (many thanks for the advice Scott!). They arrived extremely fast, 3 days after placing the order. The service manual was downloaded from vinylengine.com; it describe din details the tonearm disassembly procedure.

The process of disassembling the tonearm, removing it, replacing the belt and assembling everything back took approximately 3 hours. Yes, this was a belt- the old one was just worn and provided no friction. I was very happy that the belt was intact and did not decompose into the belt goo, unlike those on Mitsubishi LT-20 that I had.

Few notes on the belt replacement:

- there is no need to desolder any wires as SM recommends; all boards with wires that should be removed could be moved to the side(s) safely so they don’t interfere. However, if you would like to remove the tonearm completely, not just change the belt, you have to desolder wires;
- Getting a new belt on a motor and a pulley is difficult since the belt is tight and the space around there is tight too. I managed to get a belt in place using a tool made from a staple;
- Assembling everything back, one should be very cautious not to get one of many wires going into the tonearm between the tonearm base and one of the plates (see “precaution #4 in the service manual).
- It’s a good idea to make pictures during the disassembly process, download them on a laptop and use during assembly as a guide.

Changing of the horizontal drive belt is a piece of cake.

 

[kotofei]

After both belts were changed, I put the LT-30 upright, installed a platter, rubber mat, counterweight and a headshell and started her. Now the tonearm was lifted, then it moved to the left, but did not land on a leading groove: instead, it traveled all the way to the spindle and stopped there. The horizontal motor continued to work and it was no way to turn it off. In order to stop that motor and return the tonearm, I pressed “stop” and it traveled back to the rest and went down there.

After a few repeats of the above, I realized what bothers me- there was no light from the prism at the upper left corner. This prism is a part of a system for disk size detection and I remember the light was on when I powered up my “old” Mitsubishi LT-20.

I checked the bulbs- there are two of them mounted under the prism in a rubber holder. Neither lightens up upon powering the TT. The schematics showed that both lamps are powered by transformer windings that should provide 13.8 V AC. The DMM showed that ~14V was supplied to lamps, so the winding seems to be OK.

So I need to get new bulbs, 5V 0.06A each, most likely with “wire terminal” base since they should be soldered in the PCB.

I ordered them from bulbtown.com:

Code Item
680 #680 MINIATURE BULB WIRE TERMINAL BASE- 2 each
6833 #6833 MINIATURE BULB WIRE TERMINAL BASE- 2 each
2174 #2174 MINIATURE BULB WIRE TERMINAL BASE
7219 #7219 MINIATURE BULB WIRE TERMINAL BASE
.
The bulbtown.com has 5V 0.06 A bulbs in the sizes, 0.25" and 0.20” overall length. I ordered both sizes since I don’t know which one will fit the best. Two other lamps are for the broken 33RPM indicator bulb. The original is 12V 0.05A but bulbtown has them in 0.04 or 0.06 A.

I will post here results of the bulb replacement when they will arrive. What worries me though that the tonearm didn’t stop at the end or the record (i.e. where the final groove is) but traveled all the way over the label across the spindle. Perhaps, another sensor that detects the “end position” is not working. The LT-30 has few of such sensors and all requires a 12V, 0.05 A bulb.

 

[tmarx]

Thanks for the informative thread. If this is the unit that was on eBay just a few weeks ago I nearly put an offer in on it myself.

 

[jason12]

Glad to hear that your restoration proceeding well. My LT-30 arrived with steel cord snapped due to poor seller's packaging. I got new one made from the bead string that I got from JoAnn's store.

I would say overall this TT is very much restorable from about any condition.

On 12V bulbs - Radioshack has miniature 12V bulbs that fit nicely in the tonearm section. They also might work in the prizm.

http://www.radioshack.com/product/index.jsp?productId=2103780

 

[kotofei]

Update:

Bulbs arrived 5 days after placing an order. It took bulbtown.com 3 days to process the order and ship and shipping itself by USPS Priority took 2 days.

To change the two bulbs that light up the prism, I decided to remove first the white rubber lamp holder. This apparently easy task turns out difficult since the holder was glued to the lamp PCB. The glue Mitsubishi used is extremely strong so I just cut off the holder from the PCB (see picture). Now I am not sure that holder should be removed at all since there are holes for bulb leads in the holder so bulbs probably could be inserted from thr top with holder attached to the PCB. On the other hand, it’s very difficult to grab the bulb that is in the holder.

Anyways, I de-soldered both bulbs and compared them with replacements I have. The bulbs p/n 680 looks exactly as the original ones (see picture) so I soldered them in. That was easy wearing magnifying googles and using the “third hand” devise that holds the PCB horizontally. The other 5V I got are a bit smaller but could also be used.

The bulbs fit perfectly in the holes of the white rubber lamp holder. First I thought about gluing the holder back to the PCB but it turns out not necessary. The two long screws that attach holder, the PCB and the prism to the plinth hold everything together very well.

Then I changed the burnt 33RPM bulb that sits in the bulbholder at the right of the TT. The bulbholder is very easy to remove for inspection and bulb replacement without desoldering any wires. Upon close inspection, it turns out yet another bulb is burnt: the one that shows there is no tracking error. Testing with DMM confirmed this.

Of two 12V bulbs I got, only one, p/n 7219, was of the right size (see picture). The other one was just too big.

De-soldering of the old bulb and soldering in the new one was very easy with googles and the “third hand”. I attached the holder back and tested the turntable.

Now the prism light was on and the TT recognized that the record installed is 30 cm and set up speed at 33RPM. The speed indicator lightens up.

However, upon pressing start the tonearm did not drop at the beginning of the record. As before, it traveled all the way to the left without attempting to return when it was close to the spindle.

So the problem is not in the prism light...

 

[kotofei]

I studied the service manual and found that the tonearm positioning circuit is mounted at the base of the tonearm. The circuit uses three sensors: one for 30 cm record, another for 17 cm record, and the last one for detecting the end of record. Each sensor consists of a light source and a photo detector (on the second picture taken during tonearm belt change detector PCB is at the left and lamp PCB at the right) ; they are separated by a plate with long horizontal holes. When the tonearm moves far enough to the left, the positioning circuit reaches the hole and light from the lamp gets to the detector, triggering tonearm dropdown or liftup.

Fortunately, the plate with three bulbs that serve as light sources for positioning circuit is easily accessible from the bottom; in fact, it’s one of the first thing I removed in order to change the tonearm belt. I disconnected the “CONN 1” that connects this plate to the logic PC board and tested bulbs with DMM. Two out of three were burnt out; not surprisingly, these were for 30 cm LP tonearm positioning and the end source light detector.

I also tested the tracking servo bulbs. This servo uses two bulbs connected in parallel; they are of the same 12V, 0.05A type as others it LT-30. Tracking servo is connected to the logic PCB through CONN 5; I disconnected it and tested the resistance between red and purple wires. It was 13.7 or so Ohms, as it should be if both lamps are OK. So hopefully I shouldn’t change these since the tracking servo is deep inside the tonearm and it will be a PITA to get to it.

Now I need a trip to Rat Shack to get the bulbs as jason12 suggested; will keep you updated.

 

[kotofei]

Finally Fixed!

Update:

Got two pairs of bulbs from Rat Shack. They did not have 12 V 0.05 A, only 0.04A and 0.06A; I got 0.06A. Bulbs are a little bit longer that the original ones but they fit. Soldering two in tonearm positioning circuit was very easy, no need to remove or unscrew anything. Another one went in the bulbholder but it was easy to replace it too.

Started the turntable; the tonearm moved to the beginning of the record , went down...and jumped back up. Oops! It appeared that the tonearm was elevated all the way up and needs to be lowered. Lowering it fixed the problem. The liftup at the end of the record worked too. The Mitsubishi is up and running!

I spent some time then on adjustments of the tracking servo, vertical tracking angle, lead-in lowering position and so on. All of the procedures are explained very well in owners or service manuals, and all of the screws that should be adjusted are in easy access. Of five or so turntables of mine, those of LT-30 were the easiest ones. Some adjustments such as VTA are cartridge-specific so I did them with the new Denon DL-160.

The most difficult was the tracking servo adjustment, since I did not have the piece of paper (“jig”) that is required for this process. However, the sole purpose of this jig is to provide a template with lanes perpendicular to the horizontal axis of tonearm movement; the tonearm should be adjusted parallel to them. I took the angle tool, glue a piece of tape on the turntable between the armrest and the platter, draw a line on it that was perpendicular to the axes (see picture) and oriented the tonearm parallel to it.

I also changed output cables to Petra Digital interconnectors; same thing done with my previous TT improved high frequences.

I have other plans for upgrades: install new tonearm wirings (Kardas?), bypass the muting relay, make new feet… Make bottom, of course. Get good LOMC cartridge. But now I am a happy camper.

Isn’t she a beauty?

 

[manpikin]

Beautiful. How does it sound? What needle are you using?

 

[Stanton681EEES]

Bravo wonderful post Thanks

 

[kotofei]

Beautiful. How does it sound? What needle are you using?

The LT-30 sounds great, at least I like it better than any of my previous turntables. I use the Denon DL-160 cartridge that I bought new and just installed on her. The soundstage is very "defined" , i.e. musical instrument are well separated from each other.

The Denon should be opened up after 80 or so hours so I expect further sound improvements.

 

[kmulkey]

Goo

OK, so I followed Kotofei's stellar instructions (Thanks!), along with those from the SM. Both pulleys have dead belt goo on them. To avoid having to remove the motor assembly from the arm housing, what works well to remove melted/decomposed/whatever rubber from plastic and metal? I'll have to do it in a very confined space, so I'm thinking the end of a toothpick wetted with something.
Thanks in advance.

 

[kotofei]

I've had this goo problem with a Mitsubishi LT-20; you can find a thread about her earlier on this year. IIRC, I used 70% or pure alcohol and a Q-tips (a LOT of them!) to remove the goo. You might start with a toothpick and follow with Q-tips/alcohol. It took some time but it works.

OK, so I followed Kotofei's stellar instructions (Thanks!), along with those from the SM. Both pulleys have dead belt goo on them. To avoid having to remove the motor assembly from the arm housing, what works well to remove melted/decomposed/whatever rubber from plastic and metal? I'll have to do it in a very confined space, so I'm thinking the end of a toothpick wetted with something.
Thanks in advance.

 

[kmulkey]

OK, I think I got it working sort of. I used a combination of goo gone, alcohol, q-tips and toothpick. Now when I press start, the arm moves over, cues the record but then the base of the tonearm moves back toward the base a bit. The display is showing this as perfect tracking as you can see from the pic. Any ideas? It's like there is some sort of sensor in the tonearm that is seeing the tonearm slightly askew as being perfect.

ttp://www.audiokarma.org/forums/picture.php?albumid=1119&pictureid=6956

 

[kmulkey]

Lets try this again...here are the pics

 

[kmulkey]

OK, scratch that, I figured it out...read the manual next time, Keith. There is a tracking adjustment right on the base. Very convenient.

 

[Jobman]

I have another question regarding the LT-30.
Mine works almost perfectly, BUT, when the arm reaches the end of the record, it will not automatically raise and return. I can manually lift and return it. I did change both belts.
Is this an electronic issue? I do not see anything about it in the manual or service manual.
Thanks for the help.
Jobman

 

[jason12]

I have another question regarding the LT-30.
Mine works almost perfectly, BUT, when the arm reaches the end of the record, it will not automatically raise and return. I can manually lift and return it. I did change both belts.
Is this an electronic issue? I do not see anything about it in the manual or service manual.
Thanks for the help.
Jobman

There are three micro bulbs in the tone arm (you need to open the TT bottom). One of them probably is out. You can use DVM to see which one is open. Replacement can be purchased from Radioshack (12v bulbs)

 

[Jobman]

Tonearm Lift

Ok, now I see the issue and the thread that describes it. I did not connect that the lift at the end was a light issue. I thought the lights were only for platter speed. Silly me.
Time to get back under the TT and do some checking.
Thanks
jobman

 

[jason12]

The third picture in the first post in this thread clearly shows the little board that is attached to the tonearm. It slides with the tonearm over the steel plate with three slots of different length. That board has three bulbs I am talking about.

Radioshack 12 V bulbs are slightly bigger but they do fit.