Vastelec and I are not friends right now

[osgoor]

A few weeks ago I set up my little fm transmiter to test and it worked just fine. I then took it apart to mount it in a hobby box from RS. When I inished soldering everything and before applying power ( I are smart) I ohmed out the ground and the 12V points and sure enough I hear the dreaded beep of a short. I carefully removed the board, checked every connection for a solder bridge under a loop and can see nothing wrong. There is no short on the antenna connection, that comes up clean as does the audio connectors, it's only the power. Is this thing caput or what else should I check?

Thanks!

[ErnieHorning]

It depends. Is it a dead short or does the resistance slowly go up if you hold the probes there for a few seconds. There could be an electrolytic capacitor on the input that you’re trying to charge up with your meter.

[Aurbo99]

Quick question;

Did you have the antenna connected when you applied power?

[osgoor]

I have only had it powered up once and yes, with the antenna attached. I tested to see if I could receive the transmitter signal and it worked. That's the only time power was applied.

I do appreciate the question.

[Aurbo99]

Can you take a few pictures of your board and post them for us? more than one set of eyes on a problem is always good.

[LabRat]

A few weeks ago I set up my little fm transmiter to test and it worked just fine. I then took it apart to mount it in a hobby box from RS. When I inished soldering everything and before applying power ( I are smart) I ohmed out the ground and the 12V points and sure enough I hear the dreaded beep of a short. I carefully removed the board, checked every connection for a solder bridge under a loop and can see nothing wrong. There is no short on the antenna connection, that comes up clean as does the audio connectors, it's only the power. Is this thing caput or what else should I check?

Thanks!

Change from continuity test to readingthe OHMS. It could be that there is a path but with a limited resistance. (Or had you done this same test previously? )

[jasonhuff]

Osgoor, I just ohmed my board and with red to gnd and black to +12v i get 1.1k ohms. With red to +12v and black to gnd I get open. It seems like the boards read back through something when checking ohms from +12v to gnd.

[osgoor]

Osgoor, I just ohmed my board and with red to gnd and black to +12v i get 1.1k ohms. With red to +12v and black to gnd I get open. It seems like the boards read back through something when checking ohms from +12v to gnd.

Thanks I will try that.

[dirknerkle]

I'd also check how it was mounted in the box. Sometimes you can bend a board and cause shorts that way if you screw mount it yet the mounts aren't level or your screw it down too tightly. Sometimes a board can short with a screw that's too large, as well.

You could also try un-mounting the board, and if it works when removed from the enclosure and it works, well... that means something...

[osgoor]

Here's the follow up. I waited till early evening to face the devil that is Vastelec. I ohmed out between power and ground and it was full deflection. I then de-soldered every wire from the board, still no go. I spent 30 minutes under a magnifier scouring every nano meter of this thing and could not find the problem. So in the humble words of Mr. John Cleese:

It's not pinin,' it's passed on! This board is no more! It has ceased to be! It's expired and gone to meet its maker! This is a late transmitter! It's a stiff! Bereft of life, it rests in peace! If you hadn't nailed him to the perch he would be pushing up the daisies! Its metabolical processes are of interest only to historians! It's hopped the twig! It's shuffled off this mortal coil! It's run down the curtain and joined the choir invisible! This.... is an EX-VASTELEC!

R.I.P

Of course if there are other thoughts a resurrection is always an option.

[klanger]

Did you actually try power to it, or just meter it?
Now that your resigned to it being a dead duck, rehook the wires and try power, if it lets the smoke out, yup you were right, if not and it works ok, you've lost nothing.

[ErnieHorning]

Well a short is a short and applying too much current could permanently fry something that otherwise could have been easily fixed.

If you’re throwing in the towel, I’m still local and willing to give it a try. It could very well be a shorted part but not necessarily a total lost cause.

[bmcgeeny]

Well a short is a short and applying too much current could permanently fry something that otherwise could have been easily fixed.

If you’re throwing in the towel, I’m still local and willing to give it a try. It could very well be a shorted part but not necessarily a total lost cause.

And if anybody can find it it's Ernie.

Had a chance to look at that LED sign yet? I just got my LED trix boards so I'll try and assemble without creating another "repair" project for you.

[ErnieHorning]

Well, I don’t know if I should just make something up or just chock it to the magic of Christmas but I found nothing wrong.

The first time that I measured across GND (Neg) and +12 (Pos) I got 4.6 Meg ohms. I put a 51.1 ohm resistor across the antenna output and connected a power supply. I slowly increase the voltage and current. It popped on at 6.00 volts drawing 52 milliamps.

I then checked it with an antenna connected to an RF spectrum analyzer. It appears to be fully operational at 6.00 volts with full output. I only transmitted with no audio, just a dead carrier. The center frequency was .4 MHz high from what was on the display. Maybe this gets pulled down when a real antenna is connected.

With a sample of one, the supply current is as follows:


87.5 MHz 108.0 MHz
6.00 volts 52 mA 58mA

12.00 volts 49 mA 56 mA
I cleaned up the pads so it should be ready for redeployment.

Edit: Oh and looking at your house, I see a nicely decorated gingerbread house.

[osgoor]

Ernie,

I don't know how to thanks you except "THANKS!!". I really appreciate you looking at this board for me. I will pm you on getting the board back.

I also appreciate your thoughts on what I can do for putting my show together :)