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Guide me through assembling DAC board?
Guide me through assembling DAC board?
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Old 14th November 2019, 04:34 PM   #11
PaulFrost is offline PaulFrost  United States
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Join Date: Aug 2017
Location: Tucson, AZ
It is important to understand what flux you are using. All solder and solder wick have flux added to it.

I only use Kester Leaded Water-soluble solder:24-6337-6401 Kester Solder | Soldering, Desoldering, Rework Products | DigiKey
If I find any other solder (besides lead-free water-soluble solder) in my lab I go and recycle it immediately. Not all solder is equal.

I use a water-soluble flux pen:83-1097-2331 Kester Solder | Soldering, Desoldering, Rework Products | DigiKey
You use it as a highlighter. You highlight the pin or pad you soldering.

As they are both water-soluble, you can clean the board by just rinsing it.
You will not be able to find a solder wick that has water-soluble flux. You will mostly find rosen core wick: 2-5L Chemtronics | Soldering, Desoldering, Rework Products | DigiKey
This is not too much of a problem, but if you use it you will need to clean the areas with alcohol, not water. A small paintbrush can help with cleaning.

The tip-tinner is important to preserve your tip quality. If I put the iron down for more than 10 seconds, I tin the tip. I always tin it before I turn off the iron. Soldering iron tips should be shiny, not dull. If it is dull, tin it. If solder will not stick to it, then it is possible that the tip is over oxidized. You can try sanding it with some fine-grit sandpaper or throw it away.
T0051303199N Apex Tool Group | Soldering, Desoldering, Rework Products | DigiKey

Basically, my process while soldering is:
1. Turn on iron.
2. Apply flux to the joint I will be soldering.
3. Pick up iron, and wipe it on the moist sponge.
4. Apply the iron tip to pin and then add the solder.
5. Tin my tip and put down iron.
6. Go to step 2. Repeat
Turning off iron?
1. Tin tip.
2. Turn off.
3. Clean board using water, blow-dry the board with compressed air. If you can get it all, use a heat gun on a low setting or an actual hairdryer to warm the board and evaporate all the water.
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Old 14th November 2019, 05:18 PM   #12
Markw4 is online now Markw4  United States
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Join Date: Jul 2016
Location: California
For flux cleaning I use:
https://www.amazon.com/MG-Chemicals-...%2C217&sr=8-15

And: https://www.amazon.com/ALAZCO-Brushe...3751262&sr=8-4

The alcohol goes into a clear plastic cup, that sits inside a coffee mug (so the clear cup won't tip over easily). Once alcohol in plastic cup dries up, often the brush will be stiff with dried flux. In that case I replace the clear plastic up and the brush.

When cleaning flux off a board I put a folded paper towel under the board and hold the board up on its edge so that flux and alcohol will drip onto the towel.

Just pointing out there are multiple ways to solder and produce good joints.

One thing that may not have been mentioned yet is that solder should be clean and shiny before attempting to use it. I wipe it inside a folded paper towel until gray colored streaks stop coming off onto the towel. The cleaning needs to be done with each length of solder to be used. Don't squeeze the towel too tight around the solder or it will break off.

Also, the very thin solder I mentioned previously is for small joints like SMD parts or opamp adapter mounting pins. (It would have been much better if your opamps had the pins soldered only on the adapter end, socket should have been installed on the main board where the pins can plug in. That makes certain troubleshooting procedures much easier, for one thing.)

For larger joints on circuit boards I usually use about .6mm diameter solder. That's what I would use for the RCA connectors.

Basically, if solder diameter is too big then its very hard to get the right amount on small joints. On the other hand if diameter is too small it is hard to feed in the solder fast enough to get the soldering done quickly before the the first of the flux burns off.
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Old 14th November 2019, 09:06 PM   #13
weissi is offline weissi  Austria
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Location: Austria
While I've found IPA to be quite useful for everyday cleaning, nothing beats KONTAKT LR. I'm quite sure that this very product is not available over the ocean, there might be some substitute you're able to get. I'd say I need only 1/5 of that compared to IPA to get the same results.
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Old 17th November 2019, 06:43 PM   #14
mark3141 is offline mark3141  United States
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Join Date: Feb 2013
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Guide me through assembling DAC board?
Thanks for all the good info. I've ordered all the recommended items I don't already have that I can get here in the U.S. and will use these going forward. (Paul, based on your earlier post, I am the using Kester flux pin you recommended and Kester water soluble solder. However, I was using 0.031in (0.8mm) diameter solder and have now ordered 0.015in (0.4mm) diameter solder.) I've also made a note of all the recommendations on technique and process and will continue to practice those as well as watch more instructional videos.



Aside from practice, is my next step to remove the opamps. For this, will I need to remove them from the board entirely, or will I simply need to remove the solder I used to attach the opamps to the mount?



Mark, can you explain what you mean by this: "It would have been much better if your opamps had the pins soldered only on the adapter end, socket should have been installed on the main board where the pins can plug in"? I mainly don't know the terminology - what is mean by adapter end, and what is considered the socket here?
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Old 17th November 2019, 08:37 PM   #15
Markw4 is online now Markw4  United States
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Quote:
Originally Posted by mark3141 View Post
Mark, can you explain what you mean by this: "It would have been much better if your opamps had the pins soldered only on the adapter end, socket should have been installed on the main board where the pins can plug in"? I mainly don't know the terminology - what is mean by adapter end, and what is considered the socket here?
Pin headers can be soldered onto an opamp to dip adapter so that it looks like the one in the picture at:
SO8 to DIP8 Adapter | BrownDog 970601

Then instead of soldering those adapter pins to your dac board, you solder a socket to your dac board and plug the adapter-with-pins into the socket.
Mill-Max 8 pin DIP Socket

That way you can plug in the opamps to the dac board. It can be helpful if you want to remove the opamps at some point for troublshooting or if you want to try different opamps. (Remember not to plug/unplug opamps while the dac is powered on. That can damage things.)

Last edited by Markw4; 17th November 2019 at 08:40 PM.
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Old 20th November 2019, 01:49 PM   #16
mark3141 is offline mark3141  United States
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Join Date: Feb 2013
Location: Texas transplant in MD
Guide me through assembling DAC board?
Got it. I screwed that up then as it came with sockets, but I thought that was specific to a different set of opamps. Given all the mistakes I've made and the difficulty I've had in trying to redo the original board, I've ordered a new one. I hope to start on that this weekend. I hope that with the new solder tips, smaller gauge solder, and the other supplies I've picked up, after spending some time working on technique, this round will be much easier.
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Old 20th November 2019, 02:00 PM   #17
Markw4 is online now Markw4  United States
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IME, even .4mm is a bit thicker than optimal for small SMD soldering (such as soldering opamps to adapters). Prefer .3mm for that, myself. For even smaller work such as soldering a broken pin back onto an IC there is some .2mm here, but only use that rarely.

That movie I linked to in earlier in this thread was with .3mm solder. Usually its easier for me to solder those than it looks in the movie. Its just that soldering under the digital camera was awkward. Since I'm old and can't see close up anymore without help, normally wear one of these: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
If something is too small to see it with those then I go to: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1 ...Unfortunately, looks like the price for one has gone up some.

Also useful:
https://www.amazon.com/Hakko-7-SA-St...sr=1-3-catcorr
PREMIUM O.R GRADE AUTOCLAVABLE BARRAQUER NEEDLE HOLDER W/ NO LOCK 4" CURVED | eBay

Last edited by Markw4; 20th November 2019 at 02:13 PM.
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Old 23rd November 2019, 09:12 PM   #18
mark3141 is offline mark3141  United States
Still learning...
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Join Date: Feb 2013
Location: Texas transplant in MD
Guide me through assembling DAC board?
Thanks again for all the recommendations. I've been able to get output on all channels with the new board using a test set of opamps that plug directly into the sockets.
Next, I'd like to solder the RCA jacks to the board. Do I need to solder each 'leg' of the RCA jacks to board, or only some of them?
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Old 23rd November 2019, 11:12 PM   #19
Markw4 is online now Markw4  United States
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Solder all the tabs on the RCA jacks, but best to use a larger solder iron tip to easily get enough heat in there so you can solder quickly without producing cold or oxidized joints. I use the same rule I do with screwdrivers (especially Phillips head !) which is to use the largest tip that fits (without being too big). For soldering the tabs, that would likely be a tip approximately the same width as the tabs are.

If no tip like that in your collection, you might check with a cold iron to see if you can fit a smaller tip in there laying on its side so that it makes good contact with tab and its solder pad along where to two meet at the edge of the via hole. That might work well enough, perhaps with the iron temp turned up higher than usual. Remember, the idea is to heat up the joint fast, solder quickly, and get out before the flux starts burning off too much. Yet, you need to stay there long enough for the solder to fully liquefy and flow freely. Always practice on scrap material if unsure.
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Old 24th November 2019, 12:50 AM   #20
mark3141 is offline mark3141  United States
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Guide me through assembling DAC board?
Am I heating up the tab and the pad like in the pictures here and placing the solder on the other side of the tab?
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