Step 12: R1 overheats

General discussion and support for the Peaberry SDR V1.

Step 12: R1 overheats

Postby vk2ijc » Sat Jan 05, 2013 4:21 am

Hello,

I started working on my Peaberry SDR kit today. After finishing off step 12, I applied power using my ICOM PS-300 power supply (voltage set to 13.4V, measured with a voltmeter). Something didn't seem right, less 5 seconds after I connected the power plug, I spotted R1's soldered joints about to come off. I immediately unplugged the power supply.

I have checked the soldered components for dry joints, checked if U1 & U2 are swapped over (they are not), checked the polarity of D1 (mark on the case aligned with the mark on the PCB), I have all the 0.1uF bypass capacitors soldered (Step 10). I have checked the polarity of the DC power supply socket, it is as per the circuit diagram. I went ahead and tested once again , this time applying power with a 12V DC power pack, again, the same problem - R1 heats up!

My board came pre-soldered with U10 & U11, am I not supposed to apply power till Step 18? I hope I haven't done any damage to the board & the soldered components. I'll appreciate if someone could help.

Thanks very much,
73
Indy VK2IJC
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Re: Step 12: R1 overheats

Postby AE9RB » Sat Jan 05, 2013 6:49 am

You have a solder bridge somewhere. Perhaps under one of the electrolytics. Find it, fix it, and you'll be good to go.
73 David AE9RB
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Re: Step 12: R1 overheats

Postby vk2ijc » Sun Jan 06, 2013 9:06 am

David,


Thank you for your help.

I desoldered the electrolytics (all four of them for the stage), desoldered U1 & U2, checked for bad solder, shorts, etc. Then, I soldered them back all. When I powered the board up, same problem. With board safely packed up, I headed to a friend of mine (in the PCB design industry). He had a very fancy PCB tool that I haven't seen before, one that magnifies several hundred times. We found a solder bridge between pins 36 and 37 of U11, it grounded the +5V rail in the PCB. My friend helped fix it with his fancy SMD tools, I heaved a sigh of relief and headed back to carry on with the build. I had opted for U10 & U11 to be pre-soldered, so, I had ruled out any issues with them. It is probably a good idea to check for shorts before powering up the board. The voltages on the tabs of U1 and U2 are exactly as per the documentation, so, I am excited to proceed with the next steps!

Thank you for attention.
73,
Indy VK2IJC
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Re: Step 12: R1 overheats

Postby AE9RB » Sun Jan 06, 2013 6:39 pm

Awesome. Sorry about that. I have no way of electrically testing those chips. After the initial soldering, I clean them and check again with magnification. A small amount of errors are bound to slip by. You are the first to find one!
73 David AE9RB
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Re: Step 12: R1 overheats

Postby vk2ijc » Mon Jan 07, 2013 5:14 am

No problems at all David. The progress till Step 18 has been fantastic, I paused there last night and I look forward to resuming from there on. I do not think I can ever progress this fast with a through-hole component PCB! Yes, people say soldering SMD is painful, however, after building my Softrock RxTx ensemble a year ago, it is not really true.

To avoid any surprises with poor soldering of Si570, I dabbed some solder on the 6 pads and then touched some solder up on the PCB mount pads, I think I have better chance to avoid problems related to poor soldering of Si570.

One small thing about Step 18 - in order to expect 2.5V in pins 2 & 14 of U6, I found audio needs to be played through the "Peaberry Soundcard", otherwise, the voltage on both pins are zero. I have added a comment in the Make manual.

Above all, great kit and awesome board, thank you for your great work. I hope to be on the air soon.

73,
Indy VK2IJC
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Re: Step 12: R1 overheats

Postby k4fxn » Sat Jan 12, 2013 8:56 pm

I had the same problem. I had U7 in backwards.

Thanks to all for posting even the most obvious problems. It helps all of us. A the same time, the step by step check points are another lifesaver. Don't skip them!

Dan K4FXN
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