T&L Publications

Hi,
I just soldered together the DC-DC converter kit and I am having some problems. I can't get a square wave from the MOSFETs and when I supply power, Q2 gets extremely hot. Can anyone help me out?

Is the transformer connected into the circuit? I had a similar problem and found a short on the PC Board foil pattern.

Yep, I found the short on the trace and was sent this fix. I still have problems with the output. Initially i got the +/-12 volts, but for about 15 seconds before it dropped to 0, and then one of the MOSFETs tries to melt itself. I think that some of the components got toasted from the short.

Hello,

Try disconnecting the primary of the transformer and see if you still see the hot Q2. Better still would be to monitor the current if you have a meter. Sounds like you have a bad transistor though You should also be able to check for a Drain/Source short using a ohm meter with the primary disconnected.

I had the same problem with the shorted trace and should have been monitoring the current (my power supply had a current meter) when powering up and ended up finding out by the hot components. Luckily the circuit survived and is working once the short was removed.

Should see about 40mA with no load when its running normally.

I finally got the circuit working. Turns out that the short on my board did kill the MOSFETs. After double checking the board components vs the instructions, I found a few things that might make it a little easier.

-Before soldering anything to the board, check to see if it has the short. If it does, use the fix posted above. I would recommend you cut the trace first, solder the components in, then solder on the jumper wire.
-C2 is the brown capacitor, and C3 is the white/gray capacitor. The color photo on the page is correct, the list description is wrong. I followed the text the first time without measuring the values and had the capacitors in the wrong position.
-The R7 resistor has 5101 on it, not 5110 like the text says. That had me worried until I measured the value on the resistor.
-Remember: the Tantalum capacitors have the bar marking on the POSITIVE side. They get damaged if you reverse them.
-Before installing the MOSFETs, check with an oscilloscope (if you have access to one) that you do have a square wave coming from the IC.

Hopefully this helps.