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 :)

  • 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 ;-)

  • 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 ;-)

  • 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 :D

  • @toneburst

    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)!

  • currently im in a state where i do no soldering at all, only thinking, thats the reason why you hear no cries for help from me :-)

  • shall i recommend some projects then? ;)

  • @rosch

    just throw them on the pile’o projects ….

  • i’m not gonna post mine….

  • you need a fisheye or something to stitch the pics together…

  • :D

    Impressive pile you have there, fcd72!

    Right, it's now working!!

    I think I might need to change my case order to an opaque one though- don't want anyone to see my circuitboard now... :(

    I had to cut off the legs of the 7905, put big blobs of solder on the pads on the component side, and try and melt the solder on all three pads at the same time, and jam the regulator legs onto the melted solder blobs. It works, but it's certainly not pretty (or reliable, probably).

  • Oh, yeah, and having trashed one of the pads at the top, I also had to poke a tiny section of resistor leg through and solder it to the bottom of the board to make the connection to the ground plane.

  • maybe verify in the eagle board files that there isn’t an additional connection

  • Additional connection?

  • i also tore off a pad at the vreg and soldered it on top. i looked in the brd file if there possibly had to be a connection on the bottom also. but there was just one (it was the SSM2044 board).
    i just wanted to make sure i don’t have to do it once again.

  • Ah, OK.
    Well, all the voltages checked out OK on the relevant pins of the IC sockets, so I guess everything is OK.
    Just realised I forgot to order the 33n film caps C14 C30 C31... :(

  • i have some. if you like i can send you some. you can drop me a pm/email (profile)

  • That's very kind rosch. Don't worry though, have just realised there is an RS Components Trade Counter here in London. I can order some from there and pick them up on Monday.

  • cool, you’re at the source!

  • OTish but thanks for the heads up, never thought of trade counters, theres an RS one about 15 minutes from me. That will prob be very useful to know.

    Nice one.

  • :D
    Definitely worth knowing. RS have a pretty good range, I think, ParadigmX.
    I hate paying £1.50 for components, and £15 delivery- especially when the parts are coming from a warehouse that's probably only a few miles away...

    Shame Farnell or Mouser don't have any trade counters in the UK....

    Are you in London?

  • Farnell have one in leeds – i use them mostly, or rapid (counter in essex). I googled out of interest.

    Im near stockport.

  • The Source:


  • Single-sided board (no solder pads on the top), which should make desoldering easier. It’s pretty crowded on the bottom of the board though.


  • If you don’t care for the board just use a saw or a dremel to free the 3109s right to their legs…. should make desoldering easier.

    Can i have these Knobs??? ;-)

  • what are you doing with the second chip?
    :D drool

  • I think I'd better keep both of them until I find out if I've melted one of them... (if that makes sense)
    fcd72, I can send you the knobs if you want. They're for a splined shaft, rather than a D though. Don't know if this makes any difference to you.

  • if they both work just grab another board and get into polyshruthi-ism

  • Re. your idea of chopping the board up, fcd72: I might do that. In fact, if I carefully cut between each leg, I could get the little bit around each pair of legs off individually. That might help a lot.

    Before I get the hacksaw out though, can anyone spot any other chips or components they might find a use for? There’s a circuit diagram which is probably a bit clearer than my photos.

    No guarantee I can get them off intact, of course, and I only have a cheap voltmeter to test them with.


  • Is this the result of your DremelMassacre?

  • looks refurbished ;D

  • Nice job!
    I used to be good at desoldering IC’s.. I used to work for a large mixing console manufacturer.. When we got faulty batches of IC’s.. We couldn’t just cut them out, bin and replace. We had to desolder them, to keep them intact so they could be evaluated. It was a chore, but I could do it.
    Now I can’t do it at all.. So well done to you!

    I’ve not got my (cheaty) IR3109 chip yet. But apparently it is on it’s way..

  • :D

    I cheated a bit. I basically cut it out, cutting the board around it, then nibbling away the remaining PCB around the legs with some small wire cutters. I used the soldering-iron to get rid of the remaining little bits of solder and board. Hopefully the chip didn’t get too hot. I’m going to try it in a few minutes, so fingers crossed.


  • IT LIVES!!!!

    And sounds good!


  • well done!!

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