Low volume D-104

[namvet6971]

I just got a D-104. Mic looks great, but audio output is is very low. I have it turned up all the way and fresh battery. I have to hold it up to mouth, to get any swing on meter at all. My D-104 I had back in the early 70's, was super sensitive and super loud. Anyone have any idea what could be wrong with mic ? Thanks in advance.... John

[MDYoungblood]

Check to make sure the circuit is getting 9v, could be the battery connector is bad, there isn't much that can go wrong with the circuitry, open the head and see if the element has been damaged or possibly changed.

3's

Greg

[pabxone]

If it's not the battery - it will be either :-

The head element has had it or the 4.7uf Electrolytic on the circuit board has gone short circuit and needs replacing.

See if you can borrow another D104 head off someone and try it with a good working head.

The 4.7uf caps all fail eventually - so now would be a good time to replace it regardless of it's current condition.

[namvet6971]

Thanks for feedback guys. P.O. had left battery in it and it leaded. I had to replace battery and connector. Don't know anyone with a D-104 to swap head. Anyway to check head with a ohmmeter ? Will check caps.

[MDYoungblood]

If the battery had corroded that bad check to make sure there is no corrosion on any of the components, it could have even made its way up the grip bar to the contacts.

3's

Greg

[pabxone]

DON'T check the D104 head with an Ohmmeter - that's likely to destroy it being a crystal element.
You can check it with a voltmeter on the millivolt range but that won't help you a lot as you already have some output and measuring the millivolt output won't tell you a great deal.

Make sure when you replaced the battery snap lead that you put the Red & Black leads onto the correct spots.

If it's a D104 T-UG8 the Red wire should go to the top tag on the volume control with the Violet wire on it.
The black wire should go to the tag strip (2nd tag on the left counting from the volume control side) That tag should have a black wire on it coming from the switching contacts inside the microphone mast.

[GS19D3]

If by chance you have access to scope or an analog high impedance voltmeter, the unloaded voltage across a D-104 crystal element is about 200mv if you are humming or whistling into it. Just take the head off the the stand and stick the probes in the head socket holes. Also as the other poster said, do not measure it with an ohm meter. The test current may damage the element.

-- Sunday, 12 June 2016, 13:29 PM --

And I need to correct myself. Connect the instrument to the head PINS. The socket is on the stand side and will not do you much good.

[Stoneman]

Yeah I have a few of D 104 that are low also, most the head doesn't change it...I'd go with pabxone on that 4.7uf Electrolytic where-ever that is...Is this a cap replacement??

[pabxone]

Here are some pictures of the faulty 4.7uf electrolytic capacitor on D104 T-UG8 and D104 T-UG9 circuit boards.





The volume control pot can also give problems with low output level due to the pot being dirty ( try cleaning it with WD40 or contact cleaner ) and also with intermittent output due to loose crimping on the 3 tabs that the wires are soldered onto ( Try gently squeezing the crimps to tighten them up - But be careful as exact replacement pots are no longer in production )

The D104 T-UP9 mikes have the same problem with the capacitor - It is a different circuit board but the 4.7uf AXIAL electrolytic capacitor is easy to locate.

[Trapper267]

I had a intermittent no voice on a tug8 and found that large .1UF cap had came unsolderd from the board.
I cleaned up the board and resoldered it on, But i may have overheated the cap.
Anyway i just swapped out the amp board with another one and i'm up and running.