Quote:
Originally Posted by crackle
There is a 1k pot on the output from the desk mic which can be turned down to zero in effect shorting the input to the radio, and the mike can be latched on.
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I can't really add anything to the excellent and logical fault finding advice that's already being given. However, it's interesting that the circuit area being investigated has moved to the audio input and microphone area of the radio and it's always been said that the these particular radios should only ever be used with their original stock microphone, otherwise serious damage can be caused. I've never been able to see the logic in this statement or been able to see how connecting a non-standard mic can literally "blow the rig up", (as the common statement you hear goes). As it happens, I was on 'air' with a small group late last night and this model radio was discussed. One of the chaps who I've actually known for probably 40 odd years and who has recently retired, has spent some of his pension money on two of these radios. I think one is the Anytone version which he was using last night and the other is a 9900, which he says he hasn't yet used and is still in the box it came in. He has reasonably good electronic knowledge and has always been a bit of a 'homebrewer' building up stuff etc. He was insistent that using a non standard microphone would be the reason for the rigs failure, but couldn't offer a logical reason other than a voltage being fed back to somewhere it shouldn't. I said that this tended to apply to some of the older sets with an extra 'live' pin in the mic socket and I have actually come across radios where a section of print has been blown O/C by the miss-connection of a microphone, but I can't see how this could apply to the apparent damage to the particular radio in question on this thread.
Those that remember the Anytone 5555 that I repaired sometime last year, will remember that the owner of the radio told me that a friend of his had borrowed it and that he was talking to him on it when the chap said that he was just going to swap the original mic over for a power mic that he had to hand. The radio's owner said whatever you do don't plug that non-original mic into the radio or you'll blow it up, but he was too late and the chap had already plugged the other mic into the set and that was the last heard of his friend on air that night. The next day a phone call between him and his friend confirmed that the radio had failed when the power mic was connected, it was then that I was asked to look at the radio for a possible repair. Regardless of what I tried to explain to the owner of that radio, he was absolutely insistent that the cause of the radios failure was the fitting of the aftermarket microphone by his pal. When I had repaired the radio, I actually found that the stock microphone supplied with the radio was completely unusable, so had to dismantle it to clean up the switch contacts within to get it to work properly, so I can now understand perhaps why the chap wanted to try another mic on the radio. The original mics supplied with these sets do seem to suffer with bad PTT contacts, as I've heard a few on air that have been cutting in and out - probably why people want to replace the original mic with a supposed better one. But universally the advice is "don't do it - you'll blow it up", but with no real reason given.
Perhaps there really is some quirk of these radios and some obscure reason why connecting a non-original mic apparently causes damage, or is it just a myth, as I have to confess I've always thought it was? Stranger things have happened, as they say!