looking for trouble

part one: when stuff breaks

tshoot_040717

de Bill, K7WXW

While tuning through the 40 meter band, I notice the SWR meter spike and return to zero. Ten minutes later, it happens while I am not touching the rig. That’s weird, I think, but the net starts in twenty minutes. I don’t want to start taking things apart. I decide look into it later.

I drop to 80 meters, lower the RF power to five watts, and switch to AM. When I key up, the SWR meter goes to max and stays there. Adjusting the matchbox makes no difference. I move back to 40 meters. The same thing happens. Weirder. It worked ten minutes ago. Looks like I am taking things apart. With the meter out of line, I match the dipole on both bands. Putting it back in, I don’t.

Bad cable? I swap in a new one and check the old one with a ohmmeter. The new cable doesn’t make a difference and the old one is good, at least at DC. While I am switching the cables, I bump the meter and the receive audio gets a lot louder. I try to match the antenna again. Success. Could my third hand meter, an Autek WM-1, be the source of my woes?  I take it out of line and get ready for the net. For now, I can use the rig’s SWR meter.

I am embarrassed to admit this, but in an earlier life, I would have chucked the WM-1 and ordered something shiny and new. I was a busy guy.  Who had time to figure out why something didn’t work, right? In this life, I finish the net, put the meter on the bench and start taking the case apart.

I look for obvious problems: loose wires, cracked components, bad solder joints. The solder work is questionable and the sensing toroid isn’t glued down but there are no glaring (that is, easy to see) faults. I make a note to reflow the solder on all the connections and glue the toroid into place.

The instruction manual notes that unexplained SWR spikes aren’t anything to worry about. I speculate for a moment about career path of whoever approved the manual. There’s a schematic for the detection circuit but none for the main board and no explanation as to how it works. Not helpful.

I do a quick web search and turn up a few posts about the odd behavior I am seeing. Unfortunately, none include a fix or schematics of the base unit. I can’t call customer support; Autek disappeared years ago. I am not sure what to try other than cleaning up the bad soldering, so I go to plan usual: asking for help from people who know a lot more than me.  I send an email to the QRP list and set the meter aside for the night.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s