Quote:
Originally Posted by SiriusHardware
I've never taken the speaker-microphone apart on one of those but it may be worth having a look to see if any internal screening has come adrift, maybe foil-backed card which should be bonded to 0V or some kind of coating or screening on the inside of the casing which is meant to be bonded to 0V / GND.
Also on the microphone socket connections (on the inside of the radio) check that capacitors C302, C303, C305 which go from microphone socket pins to chassis are all intact, none broken, and check that L201, L202 and L121 and C153 (all on the radio PCB) are intact and have not been broken, tampered with or bypassed.
All of the components mentioned are involved in filtering out any RF which gets picked up by the strands in the microphone cable.
Is there any sign that the microphone cable has ever been replaced? Maybe with one with a less dense / less effective screen than the original cable?
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OK, I got around to doing an inspection & the 3 x 10nf ceramic cap's on the mic' socket are all in place, well soldered, and none shorted.
There doesn't appear to be any screening in the microphone, and there is continuity between the DIN plug ground pin & the ground at the mic' end.
There was a resistance when undoing the mic' screws, like hard glue/tamper glue cracking, so I'd say I'm the 1st person to gain access to the internals.
I've also checked C153, the tiny green Ceramic, and that's not shorted & well soldered.
L201 hasn't been tampered with & looks good - and being thick enamelled copper wire I presume it wouldn't be open circuit. I only pulled off the top casing, so didn't check the track side due to time constraints.
I couldn't locate the remaining 2 inductors, but I expect those are also the large vertical ones in close proximity to L201, also made from thick enamelled copper wire? They looked good & untouched, too.
I can check the the track side tomorrow if necessary & use a meter set to continuity, and will find the exact locations of the 2 inductors I couldn't see (L202 and L121).
One other thing - I strapped the transmit to common again with a wire, and anything longer than about 9 inches exhibits the transmit problem. 7 > 8 inches make the rig sort of motorboat on transmit (like attempting to lock), and anything shorter than 6 inches - the rig works fine.
The rig component side is very cramped & compact with tiny component ID print, hence me struggling to find the 2 aforementioned inductors.
I'm sure I've seen little Ferrite beads on the mic' socket on other rigs in the past, but please don't quote me on this.
Would it be worthwhile fitting some of these do you think?