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Post by deltaqueenriverrat on Apr 18, 2009 16:35:15 GMT -5
Hey guys, I got a Tram 201,receives ok, no transmit, then noticed the 2amp fuse on the ba board is popped, what might have caused this type of failure, lots of miles on this Tram... Thanks for any help...don't want to put a new board in and have it fail again, DQRR
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Post by 2600 on Apr 19, 2009 3:39:53 GMT -5
The fuse on the BA board was added to that model after the first production run had already been shipped to customers. It prevents the audio tube and the modulation transformer from flaming out if there is a major fault in the audio-output circuit. It was a "mandatory" upgrade. Meaning that even if a radio came in to get the meter lamp replaced you were supposed to install this fuse in any radio that didn't have one in it already. Tram would mail you a "kit" free that contained a fuse with wire leads welded onto it, and teflon sleeve to cover the fuse. It came with directions showing where to cut one trace, drill two holes and solder it in. Always figured they were pretty worried about expensive warranty claims if they didn't encourage you to install this "upgrade". My shop was not a warranty station for them, but they would send us a half-dozen kits at a time just so we wouldn't let a radio go home without it.
The factory fuse on that board is one-tenth of an Amp.
For radios that have been "cranked", a 1/8-Amp fuse (125mA) is better. Anything bigger than that is a bad idea.
Once the 220-ohm 2-Watt resistor alongside that fuse, and the one just above it run for the first few years, the resistance value will drift with age. This pushes up the current in the audio tube and blows the fuse. Darkened color bands on these resistors are a clue. We use 5-Watt wirewound parts to replace them.
A bad 6L6GC audio tube will blow it. If you don't have a way to test it, just assume that tube is bad.
Always, always be certain that the pins under the main audio board are soldered securely. They develop cracks the first year or two out of the factory. Likewise, the socket pins on the BA board can also do this. A BA board that crackles when you tap it may have oxidized pins on the BA socket, the pins on the main board, or both. Once the bright plating on these contacts wears away, you have to replace them. Or clean them up every week or three. A BA board that has intermittent connections will get you some LOUD noises, and can also pop that fuse.
There are other things that can blow that fuse, but those causes are the top three you'll see.
73
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Post by 2600 on Apr 19, 2009 3:43:51 GMT -5
Ooohh. Just re-read your post. You said it receives okay.
This means that somebody has soldered a jumper wire across your blown fuse.
Bad idea.
But your "no transmit" problem is not being caused by this. The fuse soldered onto the BA board will only kill the audio. If the radio won't transmit, the reason lies elsewhere.
Like the relay, maybe? If you have a spare, this is easy to find out. And if you don't, it's time to get one. Setting up to properly test the relay may cost more than the spare part.
Maycom is the only source I know.
73
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