Defunct MM+ (pics)

[AilSnail]

I had a functional MM+adj with a nick in the ferrite which I wanted to try out the variable resistance foam with. I removed the pot, but the wiper lead came with it. So I scraped off the FP pin (pin 1) and soldered a 10k resistor from it to gnd, and one to Vout (J5). This resulted in no output at all, and no power consumption. I tried to short the FB to ground resistor, but to no avail. I am eager to try out the Iadj pin on a BB, but I would like to get some suggestions that may explain why this one failed. Possibly I have cooked one of the components.

 

[shankus]

The one I fried, smoked and stank. I'm inclined to say that if you didn't noticed signs of it's demise, it may be O.K. still (minus whatever the other problem may be).

 

[dat2zip]

What is the voltage across the LED when you apply the input voltage? What input voltage did you apply?

Two equal value resistors will set the output voltage to approximately 2.6V (1.3V * 2). This may not be enough voltage to cross the LED threshold to light it up.

Shorting the FB pin to either GND or Vout should light it up.

If you are still having trouble with this I can be available on CPF chat or can be reached via Instant messenging.

 

[AilSnail]

The Component DeComposer is back! (me)

Voltage across the led is nil, I think. I'll recheck it another day.

I did run a wire across the resistor from FB to ground to get it WO, still no light. I also resoldered the joints several times, and plucked away foreign matter that became apparent when I looked at the big pictures (which is on imagestation).

I have never tried chatting, I am setting it up as per saaby's instructions right now.

 

[AilSnail]

Update: Doug_S found the problem, it was a bad solder joint between the FB and ground, apparently.

It ran unefficiently after he fixed it, until he broke the FB pin when he was going to replace the resistors with smt.

 

[dat2zip]

Dang, those pins on the IC can be bent about 1 time before they wanna break off. Sounds like you got lucky and got more life out of it then normal. /ubbthreads/images/graemlins/smile.gif

The inductor could be a real problem since the IC ramps to 1A on each cycle as I recall. If that is true, having a broken inductor is asking for saturation. How much and how it will affect it is beyond my scope of imagination at this point.

Wayne