Bad Cap

I dug out the Morsemaster II, last mentioned here:

https://wb9kzy.blogspot.com/2023/11/morsemaster-switches-part-ii.html

I tried it out but it didn't seem to be working.  After fiddling with it a little I could hear a really faint stream of Morse code.  After opening it up I decided that the earphone jack might be bad so I took it out - WRONG.

The sidetone uses a 555 timer circuit, some variation of which has been used by many hams for a CPO.  I finally realized it was the 220 uF output cap.  So I replaced it with a 100 uF cap (all I had at hand) and bingo, it worked, very loud and thumpy !  I had to turn down the volume.

it wasn't born bad - it became bad  :)

I decided to check the cap value, the AADE LC Meter manual cautions against polarized caps so I dug out the B&K 810C cap meter.  Here is the reading:

So sometime along the line that cap lost almost all of the original value.  And since capacitive reactance is inversely related to capacitance the result was very little audio:

  

the cap should have been 1.2 ohms instead of 189,000 ohms - a big difference

source: https://www.omnicalculator.com/physics/capacitive-reactance

I'm not sure who made the cap or where it was from, probably taken from another piece of equipment 40 years ago.  The 555 CPO board pre-dated the Morsemaster article from 1987 and because I had it on hand I used it instead of the tone generator in the article.  The cap positive polarity is marked which is unusual these days since the electrolytic caps I buy usually have a negative stripe to indicate polarity.

Best Regards,
Chuck, WB9KZY
http://wb9kzy.com/ham.htm