[OZAPRS] THD7 users

Ron and Val Smith rsmitj at tpgi.com.au
Wed Dec 22 06:20:15 EST 2004

Hi All,
My THD7 has been running fine for a couple of years now.  When I bought it
also purchased a SMC 33 microphone but the microphone has had virtually no
use.  About 6 months ago while travelling in a hire car I connected the
microphone which worked until I parked and the the interior of the car
became hot.  I had no loudspeaker sound from the hot microphone although
actual electret microphone was fine as I had tx audio.
Experimentation showed that keeping the microphone cool kept the receive
audio and wriggling the cable where it enters the microphone occasionally
brought back sound.
When I went to Brisbane for my initial cancer diagnosis and treatment the
receive audio died totally.
Home now I became motivated to fix it. I suspected a broken wire in the
cable, a common microphone fault.  So I was set up to fit new cables.
When I opened the case to make the connections I found the fault.  The pcb
which is mounted around the loudspeaker and holds the minor components had
split at its narrowest point breaking the earth connection to the speaker.
The track ends had been intermittently touching with heating and cooling
cable movement.  Looking at the construction it had most likely been like
this since manufacture with the hole the loudspeaker magnets come through
being slightly too small, stressing the pcb.  Naturally it was relatively
easy to solder a bridge across the break and re-establish the connection.
So my conclusion about the cable was wrong in spite of all the indicators
this common fault with microphones.

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