Thursday, September 18, 2008

Repairing the finals in an Alinco DR-150

Several years ago I replaced the “finals” in an older 2m ham transceiver. As I recall, it was fairly obvious that it was the finals that were shot, so I ordered a replacement, slipped them in, and the radio went back out the door. After it left, I noticed that the output module had a removable cover, curiosity got the best of me and I took it off. Under the cover with a circuit board of sorts with several discreet components soldered together and basically mounted to a heat sink. As I got to looking, it appeared that there was a hair-line crack in one of the traces. It made me wonder…

Skip ahead about five years and I put a surplus 2m rig in my wife’s car. I got the installation all buttoned up, keyed up the repeater but couldn’t get anyone to respond to me. A little checking and it showed the classic signs of burned up finals - barely kerchuck the repeater, but not readable on the other end. A watt meter confirmed my suspicions, but I noticed that the first time I keyed up (i.e. when it was good and cool), I got about 20 watts out for a few seconds.




I brought it back inside, and cracked the top and bottom covers. I found a familiar looking Toshiba S-AV17 power module in the back.

I’d been curious to know if that old rig just had a hairline crack or if it was more serious than that, but since it had already been repaired and returned, I’d never had the chance to find out. This time however, I popped the cover first. Initially, I didn’t see the problem, although it was fairly obvious. Since I knew I had a heat-related problem, I shot a bit of circuit cooler on the module to see if that would “fix” it. What I noticed was the frost from the cooler causing a red glow at the bottom. Sure enough, I had another crack in a trace.

The repair in the photo looks a little crude. This was my first attempt with a 15 watt iron, which I found to be pitifully inadequate since I was quite literally soldering a heat-sink. But, the fix worked.



I cleaned up the joint a little bit with a larger iron, and re-installed the rig in the car. I've only been using it sparsely for a few weeks now, but so far, so good.

6 comments:

goooooood girl said...
This comment has been removed by a blog administrator.
Rick said...

I have a DR-150 that puts out only about 25 watts, and I have wondered if it was the finals. The microphone need to be soldered to the connector too. I finally just bought a new radio. but I have thought about using it on APRS and I wondered it would take to get it back to full power.

AD5DU

Zack said...

That doesn't really sound like finals to me. My (albeit limited) experience with the finals is that when they go out, you'll drop down to a quarter-watt or so, not just half-power.

Are you sure it has a good match on the antenna? I'm sure that it's designed to throttle back in the case of a bad match. Are all of the power settings (low-medium-high) running at half power, or are the others about right?

Unknown said...

Hello. Interest page about DR150. If the transceiver has the S-AV21L the power output 25w its normal, if not try do measurement the dc voltage at 3 pin VCC1 VCC2 and B+. IF in lower, medium range power its ok and full power was 25w only try to test with another module power.

73 from Hugo CT2HMX

Unknown said...

Hello. Interest page about DR150. If the transceiver has the S-AV21L the power output 25w its normal, if not try do measurement the dc voltage at 3 pin VCC1 VCC2 and B+. IF in lower, medium range power its ok and full power was 25w only try to test with another module power.

73 from Hugo CT2HMX

Unknown said...

Hello. Interest page about DR150. If the transceiver has the S-AV21L the power output 25w its normal, if not try do measurement the dc voltage at 3 pin VCC1 VCC2 and B+. IF in lower, medium range power its ok and full power was 25w only try to test with another module power.

73 from Hugo CT2HMX