IR3109 Board Soldering Order

Anyone any tips about the best order to solder components of the IR3109 board? I’m thinking power-supply section first. Would be great to have some ideas of what points on the board to test for voltage, before inserting the ICs. Sorry, newbie here…


Here’s how I do it:

  • Start by the 100nF bypass cap. They are the most boring part.
  • Power supply section.
  • Then, bring the meter and check the voltages. I won’t solder a single component on a board whose power supply is not tested. Best way to damage chips!
  • Resistors in the order of the BOM.
  • Ceramic capacitors.
  • IC sockets
  • Then the rest of the capacitors, the “tall” parts and the connectors.

For power supply testing, look at the image of the board (or better, load it in the freeware version of Eagle):

Power traces are the largest one, they are easy to follow. Or you can simply refer to the datasheets of all the ICs!

Thanks for that, pichenettes.
I can see the power traces, now. So should the voltage at the power input of each of the ICs be the same? Sorry if this is a naive question…


Each IC has a positive and negative power supply. Voltages should be 5V at all the positive supply pins, - 5V at all the negative supply pins./- a few per cents because 78xx and 79xx and not the fanciest regulators out there.

I see, thanks, that’s very helpful :slight_smile:


Hmm… something must be wrong. I’m getting 7.68v/-7.68v at the test points. Is this likely to fry my ICs?


It won’t fry the chips, but the circuit won’t work.

7.68 looks like the voltage delivered by your power supply, so it looks like both your regulators are not doing their job. Do they get hot? Maybe you have swapped them?

Hmm… it’s not quite the PSU voltage. I’ve just checked that and it’s 9.02v with no load.

I DID get the voltage regulators the wrong way around initially, and my attempts to desolder them, predictably, didn’t go terribly well. The regulators don’t appear to be getting warm at all now I’ve swapped them around, so I guess they’re not doing anything…

Is there somewhere I can check more specifically where the problem might be?


ok, i deleted my last post, but here it is again:
you could try to put some load there. check this thread, i had a similar problam and almost destroyed a board:

maybe that’s it? good luck!

Currently, the right-most + pin of my 7905 and the centre pin of my 7805 aren’t connected to the PCB. I was giving trouble clearing solder from the holes, so I looked at the circuit diagram, and those pins didn’t seem to be connected to anything, so I didn’t solder them to the board. Could this be the reason the regulators aren’t doing their job?

I also used a replacement 7805 I had lying around, as I cut the legs off the original too short to resolder it. The replacement is labelled ‘7805CV’, rather than the original’s ‘7805CT’. I don’t know if this is significant…


Yo alex,

nothing to see means they are connected to the ground plane… and without ground theres no regulation. Now go solder and it will work… old Jedi Trick :wink:

Hi rosch.

interesting. Would you happen to know where I could try putting a resistor on the IR3109 board to test that theory?


Just use something like 10k from some +5V rail to GND . . . but first solder these regulators :wink:

Ah, OK fcd72… sorry, that was a silly mistake of mine! I’ll see if I can get some solder in there, and see what happens. My board looks terrible now…


if you have soldered the ic sockets find the + and - supply pins of any ic, or GND also.
then just put them in the sockets, no soldering required. that helped, and my psu works fine now.

but seriously, the gnd pins of the vregs HAVE to be soldered to work!

Gotta keep telling myself

‘desoldering is BAD, get it right the 1st time…!
desoldering is BAD, get it right the 1st time…!
desoldering is BAD, get it right the 1st time…!
desoldering is BAD, get it right the 1st time…!
desoldering is BAD, get it right the 1st time…!’


mine looks terrible too, but it works. i had to solder the 7905 from the top side, it’s sitting there at a weird angle :smiley:


You may use my patented Slogan to make a banner for your workspace:

First think, then solder, else socket™

you’d be surprised, frank, that requires thinking too (proto)!