When good meters go bad.

[space cowboy]

I was thinking I had a major mobile equipment failure. very low output I was glad it happened while I was doing the upgrades and not while driving. so I pull it out and put in my backups planning on diagnosing the other stuff later. backups working great.
later I give the other equipment the once over and it's all working fine. checked a few times, no issues.
so yesterday I'm yacking on the base and my output drops, just like I saw in the car...

my meters haven't died, but they're seriously wounded. the swr function works fine but the power section is dead.better that than the radio, but annoying none the less.

kind of seems like that frikking knob is glued on, I was afraid the plastic was going to shatter when I was pulling on it. and the circuit board won't come out even after pulling the four mounting screws. it doesn't seem to be directly connected to the calibration pot...


I'll give it another go later, right now I just want to take a prybar to it.
anyone else have this problem? were you able to repair it?

 

[Robb]

Check the diodes; that is the first thing I would check.
To replace a bad diode would be pretty easy AND cheap too.

 

[psycho]

Worst case scenario, spend $40 on a replacement meter. I have one of those meters and it is surprisingly accurate.

 

[222DBFL]

Same here. Those meters are pretty tough. And mine is about as accurate as any other meter of its type. Better than many that are way more expensive IMO. If was to really want a nice one, the lp-100 would be a nice one to have!!

 

[space cowboy]

wow, there sure isn't much to this thing.

3 switches
4 variable resistors
2 caps
1 resistor (1.5K)

I'm going to go out on a limb and get a replacement for the cap on the board. the resistor and switch both test ok.

 

[RatsoW8]

Like Robb said...did you check the sensing diodes? Those regularly go bad in an older MFJ tuner I have. When they do it shows no output and the cross needle swr side barely moves.

 

[AudioShockwav]

Is it me or do we not see a sensing diode anywhere on the top/bottom of that board......
Me thinks you should look at the bridge in the back of it.
Gonna have to look in that metal box.


73
Jeff

 

[space cowboy]

here's the back side of the box. still no diode. the circuit board is soldered to the metal box so this is where I'm stopping tonight. I'm not sure if I've got enough braid left.

 

[Robb]

I don't know the part # for the diode you find. Might be a 1N34A/germanium diode. As these diodes have a very low turn-on voltage, making them fairly sensetive. And cheap too; you might be able to salvage one out of an old junk radio for nothing . . .

Take a pic of that diode so we can look at it . . .

 

[space cowboy]

ok, according to radio shack I've got lots of extra parts in this thing. and no diodes either.

http://support.radioshack.com/support_electronics/doc45/45754.htm

 

[Captain Kilowatt]

There are diodes in that meter. All RF meter have detection diodes in them. Show us the component side of the board that has the coax connectors on it. My guess is that they are located where I have drawn circles. I have the same meter in a small go-kit but I don't want to open it up to check. The gray item in the middle above the connectors is a toroid that picks up the RF and the diodes should be connected to it's windings.

 

[Robb]

ok, according to radio shack I've got lots of extra parts in this thing. and no diodes either.

http://support.radioshack.com/support_electronics/doc45/45754.htm

That part list is for one board; not both boards. Why they left the other board that has the diodes, ferrite, and SO-239 connectors - off of that parts list - is a mystery.

Buck up amigo; you are almost there . . .

 

[space cowboy]

CK got the positioning right.


there we go. 2 1n60 diodes.
after I pulled them from the board one tested OL and .209V, the other OL and .216V.

 

[Robb]

Xlnt.
The diodes look like 1N4148; the ~.2v turn on voltage makes me think that too.
But they did check OK.

What is on that board below the ferrite that is out of focus?
Did you check the continuity of each part on these boards yet?

 

[space cowboy]

nope, no testing. got bored working on it, so I took a break to break my toe and just never got back to it.
that's another coil and some caps. I'll get some shots later, I don't feel like getting up.

The diodes look like 1N4148

diodes say 1n60 on them.