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Mitsubishi LT-30 help - no output and I'm stumped

C

champversion

New Member
Hello,

I've recently purchased an LT-30 that simply doesn't make a sound. I've read through the 28 page master thread on this table, which was very helpful with changing the belts. Having done that everything seems to be working perfectly mechanically and electronically, but there's just no output.

I have checked the phono cables. I know that it's plugged in properly. It's not the amp - I've tested three separate amplifiers. It's not the cartridge. I am stumped in a way that I don't think I've ever quite been stumped.

My thought was that it might be the muting board. It appears to be as it should, but I wouldn't really have a way of knowing if there was an issue with it. Any help would be greatly appreciated.
 
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You would have to install a headshell with no cartridge and advance and then drop the arm, then power down the unit and check for continuity from the headshell wires to the various places that are available, first starting with the terminated tonearm leads where they first land after leaving the arm underneath. I can’t recall for absolutely sure, but as designed, the signal is only not muted in the down and play position. It is muted internally whenever raised. If you disassembled the Tonearm to change the internal belt and bulbs it is easy to screw up that switch. A lot of people delete all the muting for purity of signal so the headshells are wired directly to the output.

Oddly, my 2nd LT-30 had heavily oxidized (or something else contaminated them) contacts in the arm, where the headshell screws in and makes contact, so I too, had no sound. And checking the resistance from the headshell wires out, I found very high resistance, like 2k+ . I used contact cleaner on a wood tipped swab repeatedly and eventually got it to about 2-4ohms. Works perfectly now. Worth checking that out first.
 
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The muting function is a shorting action across each pair of pick-up wires. It should measure closed (near zero ohms) cued up, open (infinite) cued down without a pickup, the resistance of each pickup section with.
 
Thanks very much for the direction. I'm getting a closed reading no matter if the arm is cued up or down. I spent a while cleaning the arm contacts, but I would imagine there'd be some output, even if they were heavily oxidized. As it is there's absolutely no sound... This is how it functioned when I bought it (having been told it worked perfectly), and I seriously doubt the original owner had ever opened or modified the table. If anything I think it most likely sat unused for many years.

I've gone back through and checked the muting board, and as far as I can see, having compared it to the service manual and the photos in the larger AK thread, it looks to be properly aligned with not wires touching. I'm not at all electronically inclined, nor knowledgeable or proficient, so I'm a bit lost.

Would you know how to bypass the muting board? I read that this was common in the larger LT-30 thread, but didn't see anyone describe the process. I imagine it's obvious to most readers, but again, I'm basically a five year old when it comes to a PCB.
 
champversion said:
Thanks very much for the direction. I'm getting a closed reading no matter if the arm is cued up or down. I spent a while cleaning the arm contacts, but I would imagine there'd be some output, even if they were heavily oxidized. As it is there's absolutely no sound... This is how it functioned when I bought it (having been told it worked perfectly), and I seriously doubt the original owner had ever opened or modified the table. If anything I think it most likely sat unused for many years.

I've gone back through and checked the muting board, and as far as I can see, having compared it to the service manual and the photos in the larger AK thread, it looks to be properly aligned with not wires touching. I'm not at all electronically inclined, nor knowledgeable or proficient, so I'm a bit lost.

Would you know how to bypass the muting board? I read that this was common in the larger LT-30 thread, but didn't see anyone describe the process. I imagine it's obvious to most readers, but again, I'm basically a five year old when it comes to a PCB.
Click to expand...
It may be buried in the big thread on the LT-30.
https://www.audiokarma.org/forums/index.php?threads/mitsubishi-lt-30-restoration.298682/
 
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