Author Topic: Wurlitzer 140b Speaker Worked Until Connecting / Disconnecting Instrument Cable  (Read 509 times)

Offline nathancripps

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Hi - I just purchased a 140b. The built-in speaker was working without issue until I plugged a 1/4" instrument cable into the back, tested it (works), then disconnected.

Is there a switch in the jack that turns off the speaker during connection? Perhaps that's stuck?

Any help/ideas would be greatly appreciated!

Offline cinnanon

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The 1/4" jack on the back is *supposed to be* a Speaker out jack (same signal that goes to the internal speaker) but should not disengage the internal speaker. The 1/4" jack on the cheek block is supposed to be a Headphone jack (this is the one that mutes the internal speaker). What did you plug into the back jack?

Offline nathancripps

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I plugged in a pair of headphones (it's all I had when testing it out at the seller's house).

FWIW, the headphone jack doesn't work either.

Offline nathancripps

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Ah! I just had an idea and tested it: I plugged just the 1/4" adapter into the headphone port and played around with the connection tolerance and… bam, the speaker came back to life. There was some crackle, and then it seems to have stopped working again. So I think this is the general location of the problem.

Knowing this, any thoughts on the remedy?

Offline nathancripps

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I opened up the left keyblock where the volume, vibe, and headphone jack is located and found that the jack itself was disconnected from the port/hole/cutout in the block. Not sure what the next step here is but at least the problem is isolated.

Offline nathancripps

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If anyone has a picture of what an intact headphone connection looks like from the inside, please post a pic! Thanks!

Offline cinnanon

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the jack itself was disconnected from the port/hole/cutout in the block.
This really isn't an issue for anything other than proper grounding (unless you have some wires crossing or touching something they shouldn't be).

It sounds like you have some loose connections or someone has had their hands in there.  I would study the schematic until it makes sense, and then troubleshoot.

As a quick reference, when nothing is plugged into the cheekblock headphone jack, the speaker signal passes through the jack and to the positive terminals on the speakers.

When anything is plugged into this jack, the signal is sent two ways:
1. Through an 8 ohm 5 watt resistor (for loading the amp) and then to the negative terminal of the speakers.
2. Through a 470-ohm resistor (this resistor may only be present on 200 models) and then to the tip of the jack (to be sent to headphones).

Take a moment to research schematic symbols and it will help you out tremendously.
« Last Edit: February 24, 2021, 03:15:29 PM by cinnanon »

Offline nathancripps

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Thanks cinnanon!! That's super helpful.

Offline cinnanon

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How did you fare?

Offline danwpo

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Hi Cinnanon. I sent you a pm regarding your 3D print project. Would really really appreciate it if you could take a look at it. Thanks!