sundance-communications.com/forum Forums General General Telephone & Systems Information Magic Jack with external CID

Look at getting a watt resistor next time. Looks like it might be sending more current then the rated resistor can handle.

OK Ed, gotcha.

I concur with the others... but I'd of never guessed you'd blow a resistor. Since you got them at RS, I'm guessing you got 1/4 watt resistors, and at 100K ohms.... well, just... wow.

I'm a bit concerned that putting in a higher wattage resistor will fix your resistor blowing problem, but might cause a "insert component name here" burning up problem.

Might be worth a post out in the resistor thread on the MJ forum to see if that's happened to anyone else. I just browsed it again, and people were putting in 1/2 watt resistors, as well as 1/4 watt, all the way down to whatever wattage the resistor in the picture above is.

Maybe even an email to sandman is in order; his bulletin stated he went through a fairly high number of the gizmos doing his testing.

One other thing - did it blow while hooked to an SLT or to your KSU? I'd be curious to know what the current draw is for each of them.

In the meantime, if you decide you want to go the higher wattage route, you can put 2 of the 1/4 watts in parallel and you'll have 1/2 watt - I'm sure you knew that.... but just in case.

While you're enjoying all that, I'll have a look at the thin client you pointed out.

- Matt

The resistors I purchased are 1/2 watt. I guess I may have just had a bad one, so I'll have to let this replacement one sit for a while to see if that is the case.

I just have it connected to a CO port of my Panasonic KX-TD system at home. The resistor is just bridged across the line on a 66 block.

Sounds like a plan. For even more fun, you might see if the resistor warms up both when the MJ is idle and in use.

I guess it could be a bad resistor, as I'm sure they come from China, and are prolly made out of lead and recalled sheetrock.

Might as well stick a straight piece of wire in!
Rt= 1 /R1 + R2 A good rule of thumb in figuring resistance in parallel is the total resistance will be less than the least!!

oops

Sorry, my bad. Thanks for the heads up... and for saving Ed's MJ!

RT = R1 X R2 / R1 + R2 = 100,000 X 100,000 / 100,000 + 100,000 = 10,000,000,000 / 200,000 = 50,000. Much more than a straight wire! And actually easy to figure out in this case, since any time you parallel identical resistances, the result is attained by dividing the original individual resistance of 1 resistor by the total number of resistors. 100,000 / 2 = 50,000. BUT, the circuit will still be wattage limited by the LOWEST wattage resistor! If you paralleled 4 100,000 ohm resistors, the net resistance would be 25,000 ohms. If the resistor wattages were 1/4, 1/2, 1, and 2, the 1/4 watt resistor would be the limiting factor. So, the circuit could dissipate 1 Watt total, 1/4 watt for each of the 4 resistors.

SMT resistors are in the 1/10th watt range and below. Going up in wattage is like going up in current rating in a fuse, it will just let the smoke out of the next weakest link! If you are burning a 1/2 watt resistor up in that short period of time then something is drawing way too much current. Sounds to me that if it (MJ) was working fine and started to develop problems, then a 100k ohm resistor fixes the issue then something is slowly going bad in the MJ and the 100k ohm resistor is compensating for the degradation of the failing component.

It also sounds like due to the postings of this problem on the MJ forum then its probably a design oversight where a part was used too close to its max operating specs and is now failing and/or its so close to its max rating that some work fine and some need a lil help via 100k ohm resistor.

After checking my MJ on-hook voltage (51.5 VDC), I calculated the current thru a 100.000 ohm resistor and then calculated the wattage at .02575 watt. That is way less than 1/4 watt, like about a factor of 10 smaller. Even assuming a ring voltage of 100 VAC added 'on top' rather than 'meshed' like it should be, that is still less than 1/4 watt! Somebody check my numbers, PLEASE. That HAD to be a defective resistor! (Or a defective mathematician! )