Monotron problem

Yoa · Post by **Yoa** » Thu Jul 12, 2012 5:37 am

Hey, awesome KF users, I need your help.

My poor little monotron's output jack has severe connection problems. If I jiggle a plug in there and leave it at one precise position, it will output to that, but only the right side. Otherwise, there's either no output anywhere or output to the main speaker.

I have two questions: 1) can I fix this? and 2) could I just use a banana plug? I just figure since it's wider and squeezes into the jack it might work.

I know it's a cheap little thing, but if I can spend but a few bucks to fix it I'd rather do that than buy a new one. Otherwise it works.

billbaker · Post by **billbaker** » Thu Jul 12, 2012 6:21 am

Yoa,

Banana plug is not recommended.

Its a 1/8" mini plug, right? I sometimes see the same issue on other equipment - you might want to be more selective about whether your plugs are engish or metric standard (inch v. millimeter). Also, since the output is a stereo (headphone) jack, you want to use a RTS (ring-ti-sleeve) stereo cable to get both sides, and you need to plug into a system that will carry both sides of the signal to mains. You may need to get a rts-to L/R splitter cable. A mono cable in a stereo jack might give you sub-optimum noise like you're experiencing.

BTW: The speaker is supposed to cut off when anything is plugged in, so that at least is behaving to spec.

BB

MarcusCarab · Post by **MarcusCarab** » Thu Jul 12, 2012 3:56 pm

Just sounds like a standard loose connection on the jack. Luckily, the monotron is *designed* to be opened and tinkered with so fixing it should be extremely easy. If you have no experience with electronics soldering find someone who does - but it's not tough. Once you open it up, the loose connection from the jack to the board will probably be immediately visible - and you just need to solder it up nice and solid again.

Of course, before you do that, make sure it's not just the /cable/ with a loose connection... And, worst case scenario, you need to grab a new jack from an electronics store to replace the one that's in there. If you're not sure how to do it and don't know anyone, maybe throw an ad up on craigslist or something and find someone to do it for a beer or something - anything to avoid taking it to an actual repair place, since that will cost WAY more than such a tiny fix is worth.

Incidentally, the full schematics of the monotron circuitry are available - though you shouldn't need them for this:

http://www.korg-datastorage.jp/Manual/monotron_sch.pdf

Yoa · Post by **Yoa** » Thu Jul 12, 2012 6:00 pm

Billbaker,

But banana plugs are cool! Well, fun to say, anyway. It is a 3.5mm jack, but I'm using that same size plug. and I know the plugs I've tried work because they can carry any other sound. I am using a TRS (same deal) for both in and out into a mixer or headphones, same problem. I know it's supposed to cut, that's why I think maybe the jack's connectors are maybe bent outwards. I can (and this is usual) plug something in there and it still goes through the speaker. Thanks!

Marcus,

Is the actual jack loose from the board or the connectors inside the jack bent out? I've looked at the board around the jacks and everything seems fine. I do have some minor experience doing electronics, and even had my former quality tech father look at it under a microscope, and it's connected solidly. The cables are fine. I currently have the one I was using carry my VL-Tone's signal and it works fine. I actually have all the scematics for every analogue KORG ever made, including the monotron haha! I'll look again at the board and jack and see if I find anything.

Thanks to both of you!

MarcusCarab · Post by **MarcusCarab** » Thu Jul 12, 2012 6:07 pm

Sounds like it's something inside the jack then, yeah, if all the contacts look fine... hopefully it's easy enough to find the right switching jack to replace it. I suppose you could try taking it out and using some tweezers to fix it if it's bent, but that might be really tough... Either way I'd be pretty surprised if it was anything /other/ than the jack or its connection to the board...

BTW - you say every analog schematic... does that by any chance include the Monotribe schematics OTHER than the publicly released rhythm section? Because if so.... I have a favour to ask :)

MarcusCarab · Post by **MarcusCarab** » Thu Jul 12, 2012 6:09 pm

Btw a banana plug is definitely off the table - you wouldn't be able to separate the signal and the ground!

Yoa · Post by **Yoa** » Thu Jul 12, 2012 6:19 pm

Maybe... If nothing else, I can just record the speaker and have no low end. And, sadly, all I have is pics of the boards and a block diagram. Oh, and the trigger used by the sequencer, which I think may be slightly off. I'm pretty sure it uses the same stuff as the monotron, though.

So I guess you could say banana plugs have a very "down to earth" signal! wow that was a lame joke...

MarcusCarab · Post by **MarcusCarab** » Thu Jul 12, 2012 6:21 pm

hahahaha yes that was a lame joke but the BEST KIND of lame joke

Yoa · Post by **Yoa** » Thu Jul 12, 2012 6:22 pm

haha!

kvnvk · Post by **kvnvk** » Thu Jul 12, 2012 8:31 pm

I hear this is a common problem with the Monotrons, have to treat the jacks as if they're as fragile as they actually are. just opened mine up and the jacks appear to have solder points on both the top and bottom of the board. the ones on the top are likely making connection with the circuit, while those underneath look like they're just helping to secure the jacks to the board. if you or a friend have any soldering skills it would be worth a shot resoldering all the connections to see if you can get it working properly again.

teracide · Post by **teracide** » Wed Oct 30, 2013 9:40 am

Yoa wrote:Hey, awesome KF users, I need your help.

My poor little monotron's output jack has severe connection problems. If I jiggle a plug in there and leave it at one precise position, it will output to that, but only the right side. Otherwise, there's either no output anywhere or output to the main speaker.

I have two questions: 1) can I fix this? and 2) could I just use a banana plug? I just figure since it's wider and squeezes into the jack it might work.

I know it's a cheap little thing, but if I can spend but a few bucks to fix it I'd rather do that than buy a new one. Otherwise it works.

Hey, did you ever get anywhere with this? Exactly the same issue here. I'm gonna replace it myself, but it'd be nice to know if anyone knew exactly what jack plug to use.

Thanks,

Robin

Jon1268 · Post by **Jon1268** » Sat Aug 15, 2015 9:31 am

I noticed when downward pressure was applied to the broken port, it reattaches the circuits/feet and makes sound. So my solution was to drill a 2mm hole on either edge of the exterior plastic housing, slightly below the height level of the ports, then insert a 2mm steel rod right through the two holes, overlapping the ports, which applies permanent downward pressure. Soldering would be an additional option, but now it's clamped down it doesn't seem to need it. Epoxy glue didn't work for me, not strong enough, those ports get some abuse.[/img]

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