Emexar DOD 250 issues

[Alan]

Hello all,

This is my first build of this nature, I tried a vero board layout that failed and that’s a completely different issue, so after finishing up this project and anticipating the big moment of plugging in and applying power I was highly disappointed. I had inadvertently put resistor 9 on the main board so I removed it and put it on the switchboard, didn’t seem like such a big deal at the time. Onwards to the testing there was volume but the gain really didn’t take effect until about 3:00 position. I started looking over everything to see if I missed anything, I even had to slightly disassemble to double check I had the proper pots in the correct position, I started to check continuity and I did find from power jack positive to clr there was not continuity. There is a bicolor LED that is lit properly.

I went into this with the intention of it being fun and I invested quite a bit in parts, equipment and many boards right off the bat, but this setback has made me not want to even attempt another pedal at this point. I’d really like to get this first pedal 100% operational. What could be the cause of low gain? I have beginner knowledge of electronics but I’m usually a good diagnostic minded problem solver, this one has me stumped, any input would be highly appreciated. I know I should take this as a learning experience but the frustration level right now is not helping.

[Barry]

Hi Alan.

The hobby is fantastic, especially after solving problems which make you better each step along the way. Electronics is very much about troubleshooting, and problem solving, which I consider a large part of its appeal since if everyone could do it then it would be no big deal that you can.

That said I see a major problem area for you to fix.

You need to fill the solder pads with solder. Do not create blobs of solder but be sure you heat the pads first from the (opposite side as the components) and apply the solder letting it go into each pad. It should look like a hershey kiss on the pad. If you look at your build there are many unfilled pads and in this case particularly the clipping diodes.

This is easily solved by carefully reflowing the entire PCB to make sure every pad has solder forming a good solder joint. Be sure to re-flow everything. Then retest it.

Here is a video I did for proper solder joints.

 

Everything else about you build looks great so I believe that will help tremendously and get you having some fun.

[Alan]

Thank you Barry, I know my soldering skills need to be improved, so I will go through and do as you said. I didn’t think filling the holes was that critical but obviously it is. I will see what happens after I do this.

[Playsforfun]

I second those emotions. I solder at about 650-700 degrees and use a pointy tip which is great for Barry’s boards. And I swear, after a bunch of years, I still count seconds to be sure I gave enough heat for a good melt but don’t overdo it. Thousand one thousand two…  It’s important enough that I do it all the time. For example no more than 4 seconds on a mini switch tab or you will start to melt it. A full 6-8 seconds for a pot tab. Try to go too fast and you can get a cold joint which will allow the wire to pull right out. But for the boards be aware that the ground connections and many others connect to a plane of copper in the middle of the board instead of traces, the ground plane. I notice that these solder pads can take an extra second or two because you are heating a large area around the pad. They are visible with their crisscross design. If the solder looks weird it is weird and worth a second look.

This IS fun. Lots to learn and that’s what I like about it. But to learn everything that I just told you, I had to make the mistakes. Troubleshooting can be a long pta. But it is so interesting how to find some of these problems we run in to. Most of them are really dumb things we do at times. It happens. Rule of thumb, don’t double check, triple check. I’m a learn as I go guy. Built about 100 or whatever and I still don’t expect that it fires up right away. I make them kind of complicated to torture myself maybe but if it fires right up I’m thrilled like its ten years ago. Don’t give up yet. You’ll get on a roll and have a ton of fun. Happiness is a warm soldering iron.

[Author]

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