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.

Coralife Aquarium Lighting

A few years ago I bought my wife a Coralife light fixture for her salt water aquarium. It’s a four-bulb fixture, intended for a pair of Actinic lights, and a pair of daylight balanced (she runs 10k’s). The first year or two, it ran fine, although she never replaced the bulbs.

About two years ago, we started having problems with the lights not coming on, and from the looks of these four-conductor plugs, I assumed that it was corrosion. It took a while, but I was finally able to pry the bulb off of the connector with a blade screw driver, but in the process, I destroyed one or two bulbs. The pins from the bulb were so corroded that they broke right off. This obviously was no good.

I did some asking around, but didn’t really like any of the answers I got, so after re-investing in a new set of bulbs, I set out to try to stop this corrosion.

What I decided to try was some Silicone Grease that I purchased at the automotive store. They call it Spark Plug Grease or Dielectric Grease. About a year ago I replaced two of the four bulbs. After removing the old ones, I cleaned up the plug with an acid brush (although a pipe cleaner would have worked better I think). I squeazed some grease into the plug, and put a good healthy lather on the pins coming out of the bulb.

When I plugged the bulb in, I was careful to make sure that the plug was on as far as I could get it. Not only that, I also made sure that the metal contacts were not exposed to the (salty) air, but were instead all gooped up in grease.

So now, a year later, how has it gone? Well, overall pretty good. This time when I went to change the bulbs, I had very little problem disconnecting the pair that had been cleaned and greased. The un-greased pair was more difficult to remove. Also, you can sort of see in the photo below the difference between a bulb that had grease applied (top) versus one that didn’t have any grease. It’s hard to see, but the top one is more yellow or brassy colored. The bottom one is more reddish-orange from the corrosion.

The only bad news is that on one of the plugs that was greased, it appears that the plug got very hot and actually melted the side of the plug away. At this point, I don’t believe that it was directly related to the grease, although I’m not ruling out the possibility yet. Of the eight pins that were greased (four pins times two bulbs), only one pair had this heat damage. The other six were in good condition.

Below is a photo of the newly greased plug on the right, and on the left is the bulb with a bad plug. The green you see is the bare copper wire that had corroded. This plug will have to be replaced.

Welcome to my blog

I’ve been wanting to try blogging for quite some time, and I’ve finally decided to jump in. You’ll probably find a of everything in here, but most of it related to computers, electronics, and probably bit of flying.

As a full-time IT guy, and a consultant on the side, I find myself constantly searching the web for solutions to my problems. I’ve gained so much from other people’s experiences that they’ve shared, I occasionally find that I want to share my own. Given the broad spectrum of my projects and hobbies, I couldn’t come up with a single better place to put them then just this…

So without further ado, here goes nothing!