Headphone/microphone hearness for # 19

[Chris Suslowicz]

Originally Posted by Bob Carriere

Final questions.... are there any fuses inside the control box used on the wooden board for training... the control box has the 3 earphone connectors coming out the side and in the parts manual is referred to as .... control unit 3A MK II..

Bob C.

No, the only control units with a fuse inside are the No.1 family (1, 1A & 17). The No.4 does not have a fuse and has the 12V supply wired straight through. The fuse is present to protect the wiring harness against short circuiting pin 10 (+12V) to ground if _only_ a single control unit (1, 1A or 17) is in use and the control unit is switched to either the the IC or B position.

On the headset front, check the earpiece continuity with an ohmmeter, infinity means it's duff, remove and faulty ones (undo the nuts and disconnect the wiring then spring the headband clips to remove the earpiece from the headband), and replace the faulty one with a "known good" earpiece from another headset.

Chris.

[Bob Carriere]

...will disect the earphones tomorrow when the sun shines in the work room.....

Thanks for your help.....stay tuned.

Bob C.

[Bob Carriere]

Found a "minute" wisker of copper that WAS formerly connected to the voice coil..... broken....and so small as to make it impossible to mend..... copper wire is finer than a human hair.

So there were no continuity acroass the two ear piece..... which explains why only one earphone worked.

Much like when I dissected frogs in class I could never put the frog together again.... so that earphone is Kaput!!

Now will turn my attention to a more complete NO 1 set with chamois covers..... it also only works on one earphone..... but will tread lightly and not do a full irreversible dissection.

Meanwhile I have opened up the control box and using the previous schematic I beleive that I can installattach a more modern earphone, so looking at installing a 1/4 male/female jack. This should allow me to test further the rec/trans. and see if it work properly.

I fear that most of the rubber bellshaped connectors have corroded contacts and the rubber is as hard and brittle has hard wood. They may look OK for a static display but for actual use very impractical. I know of no means to make the rubber soft again. Installing a jack or having a female jack hang out of the control box is relatively easy as the boxes already have two soft rubber plugs to pass the wired through.

Bob