I did, but thankfully I averted what could have been a China Syndrome-style meltdown.
In the process of preparing for the recent hamfest, I had moved my MFJ-490 Bencher/DeLuxe Memory keyer combo aside. I had been wanting to install a 9 volt battery in the thing so I wouldn't have to tie it to a power supply all the time, and I remembered last night I located the appropriate battery for the thing.
The keyer consists of a Bencher BY-1 key with an MFJ box-like thing that has the electronics inside. The 490 keyer is the deluxe version that has memories and lots of nice options controlled by a series of momentary contact pushbuttons on top. The keyer has worked well hooked up to a 12v supply, but I wanted to try it on battery power.
I installed a battery, and found that the key was working only intermittently at best. Apparently it likes 12v or more instead of 9. I disassembled the unit and removed the battery. While reassembling the unit, I apparently didn't notice the “hot” side of the 9v battery clip was touching the case. It's hard to see what goes on in the case during assembly because you have to slide the BY-1 into the box opening.
I have a cable that runs from my MFJ DC power strip to the MFJ keyer, and I next plugged in the supply. I turned my attention to something to my left when I smelled smoke. The keyer was enveloped in thick smoke that had the distinct smell of overheated vinyl insulation. I jerked the plug loose from the power strip.
I suspect the fuse in the power strip was just about ready to go. I don't know why it did not — other than the fact perhaps it wasn't drawing enough current to trip it.
On inspection, the long battery clip lead was charred black — where there was something left to hang onto the copper wire. The wiring had served as a resistance of sorts, and probably was glowing red at the time I pulled the plug. The battery lead was toast from start to finish, so I cut it from the PC board.
I wasn't sure what damage had been done to the keyer, so while I had it apart I though I better try it out. Luckily there was no damage to the circuitry and the keyer worked fine.
One thing I never realized was there is a large lithium-ion battery that is used to retain the keyer's memory. The battery is on the underside of the PC board, and not visible until you totally disassemble the unit. I know that battery needs replacing, and its probably responsible for the rather screwy operation of the key sometimes when you turn it off and turn it back on. I usually just reset the keyer every time I turn it on by holding down the Menu button on power on.
I thought I was done, but Mr. Murphy intervened. After powering the keyer on, it began sending alternating dits and dahs nonstop. Uh-oh, I've screwed it up. No fiddling with the programming keys or the paddle could stop it. Was there a short? Where the heck was it?
The only hint I had was if I whapped the keyer hard enough with my hand — actually banging it upside down into my hand — the pattern of dits and dahs would pause or change momentarily. Gotta be a short inside.
And there was. Because I've had the case off the Bencher so much, I didn't realize that the cable was being rotated or twisted each time. Up where the cable connects to the PC board began twisted, with the extra long ground wire wrapping around both the dit and dah wires.
The cable was old and rigid, and the wiring frayed. I made it more 'fraid with a pair of diagonal cutters before tossing it in the trash. I replaced it with a thinnner, more flexible cable. The key works better now than ever. I suspect the cable had been shorted in the past or nearly so — enough to make the keyer send unwanted characters at times. It's a solid key now, and I've got enough confidence to actually use the thing on the air … provided I can get back my keyer fist. It's funny how little movement the Bencher needs. I'm a bull in a china shop for a few minutes until I get reacquainted with the Bencher.
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