Buchla LEM218 - Troubleshooting Question

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REcDeso12oi
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Buchla LEM218 - Troubleshooting Question

Post by REcDeso12oi » Fri Jul 26, 2019 2:16 pm

So, The last couple days I've been fortunate enough to have some time to dig into all these unresolved Buchla issues I've had over the years and my project today was to get the Sustain on my LEM218 to work.

I opened it up and took out the Power supply and saw that one of the prongs from the sustain input (prong 3) just doesnt exist. I see there's 3 holes for the prongs to be soldered into and Prong 3's hole had solder in it.. just no prong. Here's a photo:

Image

Is this normal?

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@green
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Post by @green » Fri Jul 26, 2019 11:16 pm

You may have cracked a years long case my friend. We have been trying to figure this out for quite a while. Mine never worked either. Haven’t unsoldered my input jack, but that seems like a possible cause for concern. Be interested to see where this goes for you.

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Post by jimfowler » Sat Jul 27, 2019 6:40 am

No horse in this race but is there a trace on the board where this missing prong would connect to? A pic of the board would answer that question...or a schematic. Most sustain pedals are just momentary on/off switches which would only require tip and sleeve connections and no ring.

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Post by REcDeso12oi » Sun Jul 28, 2019 1:49 pm

From what I can see there's no trace going to the missing pin, which is funny since theres solder there and no pin. Either way, I ordered a couple Tegg 6.35mm headphone jacks off of amazon. They have the correct pin configuration. I soldered one of them in there and surprise my sustain input now works.. ONLY when the sustain pedal is plugged almost all the way in. If I plug the sustain pedal fully into the jack, the sustain is on all of the time. So obviously the issue w/ this specific jack is that its a stereo jack.

Now all this being said, since it now works, I think the sustain jack that I pulled out was faulty.. not necessarily because of the missing pin, but maybe because of something else. But I also went through and touched up all the soldering, and cleaned all the flux off the board, so its also possible that there was a cold solder connection somewhere.

Either way, I think if your sustain input isn’t working, pull out the board and touch up all the solder joints and replace the jack (with the correct replacement haha, not the one I used).. hopefully you’ll have the same luck I did.

BTW this is a BEMI 218e.

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Post by Drillionaire » Sun Jul 28, 2019 5:48 pm

REcDeso12oi wrote:So obviously the issue w/ this specific jack is that its a stereo jack.
If I had to guess I'd say the issue is that your sustain pedal is a normally closed pedal, whereas the 218e requires a normally open pedal for sustain to work correctly.

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Post by @green » Mon Jul 29, 2019 10:24 am

Drillionaire wrote:
REcDeso12oi wrote:So obviously the issue w/ this specific jack is that its a stereo jack.
If I had to guess I'd say the issue is that your sustain pedal is a normally closed pedal, whereas the 218e requires a normally open pedal for sustain to work correctly.
That was what they originally suggested to try as a possible solution when I contacted Buchla. However, my jack is probably faulty as well. my sustain pedal is one of the switching variety and doesn't work in any configuration.

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Post by Drillionaire » Mon Jul 29, 2019 1:47 pm

@green wrote:
Drillionaire wrote:
REcDeso12oi wrote:So obviously the issue w/ this specific jack is that its a stereo jack.
If I had to guess I'd say the issue is that your sustain pedal is a normally closed pedal, whereas the 218e requires a normally open pedal for sustain to work correctly.
That was what they originally suggested to try as a possible solution when I contacted Buchla. However, my jack is probably faulty as well. my sustain pedal is one of the switching variety and doesn't work in any configuration.
It's certainly possible, I was simply stating that the replacement jack is probably not problematic due to it being stereo, the issue is with the sustain pedal.

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Post by jimfowler » Mon Jul 29, 2019 3:04 pm

Testing this is very simple: plug a TS cable into the sustain input and bridge the other end with a paper clip or anything conductive. That will close the circuit and you should have sustain.

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