Cumulus Support

Ok guys i am another person getting the dreaded "Lost Sensor Contact" message. If i lieave the unit alone for an hour and put batterys back in it will function for a few hours fine. I've found the cause of the issue though have no idear what the part is. I can solder fine and if someone can tell me what it is i will replace it and see how it goes. On a side note completly bypassing the part make the unit function as intended.

I've attached a picture and a video of the bypass hope you guys can help

Video Link

As a small update I've resisded to the fact that if i cant fix this i will be forced to go to ebay and buy another TX unit. there for I've put a temp solder across it to test over night for Signal loss.

Its a switching diode probably a IN4148 or similar

Hi,

Well, it's almost certainly a silicon diode, in Surface Mounting (SMD) style, perhaps intended to protect against reversed battery connection. Almost any "General Purpose" wire-ended diode should be a fine subsitute, e.g. 1N4148, but such devices very rarely fail.

Maybe it's the lighting, but all the soldering on that board looks really shoddy, perhaps there's (another) bad solder joint . There's a similar photo towards the bottom of the page here ("Transmitter backside").

If you can't repair it, there have been several recent posts on this forum for sources of new "spares", I believe the transmitter is generally £20. Make sure you get a version with the correct radio frequency.

Cheers, Alan.

How do you know it has failed? Testing a diode with an ohmeter wil show infinite resistance in one direction, and a low resistance in the other, equating to about a 0.6 volt drop.

If you had watched the small video you would see it works fine when bypassed. Also I have had it running all night as a test bypassed and i still have sensor contact this morning.

I've concluded it must be that as using a Multimeter on it does nothing either way.

I shall look for a part for that later thanks guys.

Feel free to take a look at the station you can see for yourself its working again.

http://weather.retro-hosting.co.uk/trends.htm

EDIT:-

Ok so its just to stop reverse current damage ? At least that's what it seems. If so i wont bother with putting a replacement in there.

Jim

Hi Jim,

The multimeter test is not absolutely conclusive, but changing the diode is certainly worth a punt.

You will need to connect the diode the correct way around. The cathode end should be marked with a line on the package (probably RHS on your photo), or measure the voltage across the circuit board pads (cathode to negative).

RE EDIT: The FO battery holder doesn't have any physical protection against reversed battery insertion (often the positive end is recessed) so you're taking a risk. On the other hand, if the diode is in series with the supply, then the transmitter might get another 0.6 volts and give more range.

Cheers, Alan.

Is this the correct diode i would need to get ? http://www.maplin.co.uk/signal-diodes-1 ... tpanel=off

Hi Jim,

Yes, that's what we had in mind, probably the best substitute if you can't see any markings on the original device (when removed). Might be cheaper from eBay if you can't get to a Maplin shop (or combine it with other items that you want).

It's not obvious from the photo that it is just for reverse-voltage protection (for example it appears to be conducting current AWAY from the microchip under the black "blob"). But if it is, then something like the 1N4001 (lower series resistance) or even a Schottky barrier device (lower voltage drop) might give marginally better performance.

Cheers, Alan.

Have you measured your battery voltage?

Shorting out a protection diode bumps the voltage up by 0.6V - 0.7 V, so you can move a voltage that's too low to power the device back into a working range temporarily...

Hi,

Yes, I thought the same as Charlie. Note that the transmitter draws a short pulse of current (about 20mA) so a simple "Open Circuit" voltage test isn't always reliable. You need a "battery test" mode on the multimeter, or check the batteries with about 100 ohms across the terminals.

Cheers, Alan

Charlie wrote:Have you measured your battery voltage?

Shorting out a protection diode bumps the voltage up by 0.6V - 0.7 V, so you can move a voltage that's too low to power the device back into a working range temporarily...

Yes m8 both where brand new batterys 1.5v ( replaced two rechargable 1.2v batterys ) because i read about issues and batterys. There pumping out 1.58v each.

AllyCat wrote:Hi Jim,

Yes, that's what we had in mind, probably the best substitute if you can't see any markings on the original device (when removed). Might be cheaper from eBay if you can't get to a Maplin shop (or combine it with other items that you want).

It's not obvious from the photo that it is just for reverse-voltage protection (for example it appears to be conducting current AWAY from the microchip under the black "blob"). But if it is, then something like the 1N4001 (lower series resistance) or even a Schottky barrier device (lower voltage drop) might give marginally better performance.

Cheers, Alan.

I'll get both from Maplins later as there store is kinda near me

I'll update when i get there lol

Also Im still collecting data strongly a good 12 hours after starting the test. Alot different from the two hours MAX i was getting before.

I tried the ohm meter test on that component and got 0.1 ohm no matter which way I connected the meter leads - which leads me to think it is almost a dead short.

A little further left and down than is shown in jimmyo6's photo is another identical component.
Again a reading of 0.1 ohm both ways.

These measurements were done on a 265NC transmitter which no longer connects to the console, so these components are both possibly dead.

Both are marked only with a squared off "O". No indication of a cathode or anode end. So, are they diodes?
Or are both of mine shorted out? What do others find?

Hi,

I haven't opened up mine as it's still potentially under warranty, and there do seem to be a number of different printboard layouts.

However, the boards do appear to have several "zero ohm" links (cheaper than making a double-sided printboard), there's one (marked 'o') just below the yellow-bounded "mystery" component (which I'm fairly sure is a diode of some type) in Jim's photo.

Cheers, Alan.

Uhhhm I measured the wrong component. Yes, zero ohm links make sense as you explain.

So when I measured the RIGHT component, as outlined in yellow, I find
+ 4.2M ohm -
- infinity +

So even on my suspect unit, 4.2 M ohms is too high for a diode. It is "almost" open circuit one way, and perhaps correct the other at infinity.

What's next?