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Mitsubishi LT-30 restoration

Renfield72 said:
So, how do i fix it? I presume replacement switches are unobtanium. Bypass it? Eek, hate to open it up again.

Also, the tonearm is not tracking/moving along with the record. :(
Click to expand...

After my latest adventure inside my LT-30, which was to replace the output RCAs with SignalCable Silver Resolutions, I had an issue where the tonearm would not lift and move over to the record. But if I gave it a nudge, it would move. It turned out I just needed to relevel the table, I had bumped one of the feet I suppose. Make sure it's level.

As for the muting switch, yes, it's in the tonearm base. I've drawn a red circle around it. It's the little pcb where the tonearm wires terminate, and has a little white switch that sticks into the opening of the white gear thing. I removed that switch from my turntable and spliced the wires coming from the tonearm with the ones going from the relay board to the output RCA.
 

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Pio1980 said:
The clue to whether the tracking lamps and detectors are working is whether moving the arm left-right caused the arrows to light appropriately, whether or not the arm moves. Next the shuttle buttons should move the arm left/right when pressed with the arm cued up and not down. Lastly, cued down the arm's deflection should cause the arm to move appropriately with no effect from the shuttle buttons when cued down. The shuttle buttons should cause the arm to cue up before moving in the appropriate direction.
Get back with observations to go further.
Click to expand...
The shuttle buttons appear to be working perfectly. When tonearm is down and playing, hitting the shuttle buttons causes the tone arm to raise and go in the correct direction. The arrows and center position lights are functioning. However the tonearm will not move or track when cued in the down position and manual moving of the tonearm does not make the tonearm motor activate.
 
Contrary to impressions this is actually a pretty simple & straightforward system.
As it happens my TT has an intermittent identical problem which I've been diagnosing, the fact the tracking light are working sez that the part of the system associated with the tracking shutter and detectors in the arm base is working OK.
There is a relay RL101 on the main board that is the tracking servo function transfer relay, it switches control of the tracking motor from the shuttle buttons to the tracking shutter circuits when the arm is cued down on the record. There is another micro-switch in the arm base that works off the lift cam that 'tells' the circuits whether the arm is up or down, which CPU IC102 validates, and causes IC-101 to switch Q137 relay driver on or off to effect the relay control function transfer. This arm base switch may not be working properly via maladjustment or malfunction, connector 6 may have a contact or board solder pad problem, the relay may not be functioning, or the relay contacts or board solder pads may be intermittent or fouled. If the relay clicks when the arm is cue-raised or lowered it will then be either fouled relay contacts or board relay contact terminal solder pad(s) needing to be checked and reflowed.
 
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I picked up an inoperative LT-30 the other day and thought I'd follow up this thread over here, since this is the amazingly informative LT-30 thread with which I'd not have placed my wager. I must extend a huge thank-you to OP and Pio1980, and everyone who has contributed with excellent tech advice and photos.

So far the progress has been minimal, but the process interesting and enjoyable. I evicted a spider and a several egg sacks from under the bottom access panel, but other than that she's clean and shiny with no signs of high-moisture basement living, or a dirty/dusty environment, and only minimal signs of being previously worked on by a hack (other than myself of course.) More on that in a minute. The wire that moves the tonearm laterally was off its pulleys, but it went back on without a hitch. Surprisingly, the feet are in great shape and are not sagging to the point of the plinth touching their bases, so they were using some good rubber compared to Pioneer or Kenwood.

I had an SBS3.5 belt on hand since several of my Pioneer decks use one, so I got the tonearm lift belt swapped out as a matter of indoctrination and only lost my will to live two or three times in the process. The SM photos are truly bad and instructions typically vague, and the LT-30 is complicated, but thanks to the tips and photos from this thread, it got done in short time with minimal shifting of parts. Next time I'll be able to knock it out in fifteen minutes in case the new belt doesn't outlive me. The larger linear tracking belt seemed excellent and easily swappable later, so I left it alone. I did order the SBS3.5 and SBS5.1 belts it uses from turntableneedles.com, so I'm covered, and they've already shipped. Kudo to them for their responsiveness.

What I have now is an LT-30 with a platter that spins, locks speed, and detects record size properly, but the tonearm doesn't move up, down, or laterally from its resting position. I'd be thankful for any input.

- All the lights on the panel work and the green arrows which show left, right, and center all correctly indicate tonearm pivot position.

- From initial power-on, neither the up nor down arrows illuminate, but if I press the "up" button the "up" arrow illuminates. If I then press "down", the "up" arrow stays illuminated. There is no noise from the lift motor.

- The "start" and "stop" buttons do nothing. There is no noise from the tracking motor.

I guess the next thing I should do is look for bad wires and check solder joints. I did notice that one white wire to the tonearm base, where the lift assembly resides, got squashed by a previous technician (just as has been warned about here and in the SM), so repairing that will be step one. If anything else I should do jumps out at you, please let me know.

As has been stated, and I agree, this thing is a masterpiece of engineering and a pleasure to work on. Not a huge fan of the incandescent lamp choice over LEDs, but there's certainly nothing cheap or mundane about the design. I just hope I can get it working so it doesn't become a parts donor. It's too nice for that.
 
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There are range endpoint limit switches on the lift cam gears and rail ends that have to be ordered correctly for the CPU to allow proper functioning of the servo systems. If something has been incorrectly adjusted out-of-range or improperly re-assembled the system will hang up or stall, lacking confirmation of completion of the initiated function and "permission" of the CPU to allow manual or automatic operation of subsequent functions. Confirm that these endpoint limit switches are in proper adjustment, working, and that the wiring in these ckts is good.
 
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Led

I did a LED-conversion for the display-board only (yet).
Easy, there are a thick common + trace (however, it shifts side half-way).
Orange lead (from 4-pin-plug) supplies the +, I put a 800-something ohm resistor on that wire.
I used white 5mm diodes, could maybe been prettier (greener) with yellow, as the display-paint is blue-greenish.

Arne K
 
Hi,
New to the forum .Does anyone know if the control chip MSM5831RS used in this turntable is a dedicated device or a programmable device,
If it needs programming the turntable will be a write off if it fails.
Asking as I am looking at a faulty one.
Cheers
 
crumbly said:
Hi,
New to the forum .Does anyone know if the control chip MSM5831RS used in this turntable is a dedicated device or a programmable device,
If it needs programming the turntable will be a write off if it fails.
Asking as I am looking at a faulty one.
Cheers
Click to expand...

I'm pretty sure it's dedicated. The LT-5V, LT-20/22, LT-30, X-10, and LT-640 and their Diatone equivalents all used the same chip.
 
I have bought a non working lt30 and am struggling with it.It has none of the bulb faults and sensors all seem ok.
I had to rebuild the tonearm as someone had been there before me and left it a mess.
Screws lying loose, trapped wiring, mis aligned tracking sensors.
I have replaced the micro, IC102.
The problem I now have, and is taking some pinning down ,is that when the tonearm lifts it only goes a fraction of an inch when it moves to the left.
I can hear the relay click when it stops! Any Ideas anyone please?
Mike
 
Thnx! Thinking it over. This is a pretty simple servo system with interlocking 'permission' sensors and systems, the relay is a tracking function transfer switch that takes the carriage movement control from manual shuttle cued-up to auto-tracking cued-down. Are you absolutely sure that the timing of the gears in the carriage base is correct and that all wiring is in it's proper place?
 
The tonearm is set up as per the service manual.It raises and lowers to order.I seen to get different symptons.Now the tonearm just raises with no sideways motion.
The relay has been changed.
 
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