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Ham Radio

Ten-Tec Century 21 power supply repairs

[Yesterday’s run: Watson Road; Today’s run: 2 miles plus 10×100]

Over the weekend there was a VHF radio contest.  VHF contests are kind of slow around here so I also dug into my Ten-Tec Century 21 to make some repairs.

When I first got this radio the power supply was not working.  I ended up replacing a large 2n3055 pass transistor and that seemed to do it.

Then here recently I turned it on and it came on for a little bit, then the lights dimmed down and it went off.  Kind of like if it were on a mostly-dead battery.  But this rig plugs into the wall, no battery.  A bad sign.  After that, no life at all.

So I pulled the cover off and found a burnt trace on the power supply circuit board.  Fuse was fine (!), and everything else looked Ok.  Pulled out the power supply board and put a jumper over the burned trace (today’s picture) using some solder-wick.

After putting it together, it burned out the fuse.  It was a 5 A slow blow fuse  (too big).  I took the power supply board back out.  Poking around, I discovered that the voltage rectifier pack was not working correctly; one leg was shorted to another.  And those legs were the ones which would cause that circuit board trace to have lots of current on it.  Imagine that!

Went to Radio Shack and purchased a new rectifier.  The new one is slightly bigger but I made it fit ok.  I purchased a new 2n3055 pass transistor also but did not end up using it.

I put in a 1 Amp fuse this time.

Now the Century 21 is back on the air.