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CTB16K Soldering Note / Caution


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I have been constructing electronic circuits for over 40 years and applaud LOR for their fine kits and easy to follow instructions.
After finishing my latest CTB16K (kit) I plugged it in and to my surprise it didn't work. :(
The 5 volt regulator was getting warm as was the transformer.
When the regulator and transformer get warm, it's a sure sign that something is shorted. I measured the 5 Volts and it was WAY low so it wasn't a "dead" short but pretty close to it. Using an accurate Ohm meter and starting from the 5 volt regulator, I measured around .5 ohms from the +5 volt regulator to ground. As I worked my way up the board toward U2, the resistance was dropping so I knew I was going the correct direction. To make a long story a bit shorter.... after an hour I found that C0 was shorted with a solder bridge on the COMPONENT side of the board. The bridge was a bit resistive because it wasn't a very good solder bridge but C0 was soldered to the circuit board properly.
Here is where I see the potential for problems.
C0 is a physically small capacitor and its leads are also small. The holes in the circuit board are big compared to the lead size. IF C0 is placed VERY close to the circuit board, solder can "wick" through the holes and form a short (or a resistive connection in my case) across the leads of C0 on the component side of the board. The solder connection on the solder side of the board looks fine.

What I suggest you do (and I do now) is keep C0 about 1/8 of an inch above the component side of the board. This will help by keeping the solder further away from the component and making it more visible to check for solder bridges. Capacitor C1 is probably another component that would benefit from a little spacing from the circuit board.

Again... LOR produces a fine product. Just be careful with solder flowing through the holes into the component side.

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Thanks for that note. I am on my third kit this month, and see what you mean. Also, does anybody really know if it mattes which way you solder the Risitor Networks in, like R1? I know the manual says doesn't matter. Is this true? On the one Kit that I solder it in the other way, I had problems getting Hardware Utility to regonize that board. Had to Manually Assign that board a Number first, than it worked. Is this a common problem?

THanks, Chuck

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If I remember correctly (I don't have the assembly manual in front of me) resistor network R2 is the only one that MUST have the DOT correctly positioned on the circuit board. R2 is a "bussed" type of resistor network. That means all resistors in the network have one side tied together and attached to a common pin. (see the photo below) Resistor network R2 is type 10X-1-103. The red number one indicates it's a "bussed" type of resistor network.

R1, R15, R16, R18, and R19 are "isolated" resistor networks. Each resistor in the pack does not connect with any other resistor in the pack. Resistor network type 8X-2-471 are "isolated" resistor networks. The red number two indicates it's an "isolated" resistor network.

In the picture below, this manufacture uses the number "101" as the "bussed" resistor network and "102" as the "isolated" resistor network.

Hope this helps!

Attached files 138357=8226-resistor_network.jpg

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Nice reply... You are correct, R2 is the only bussed resistor network in the kit and thus is the only one where position matters. Many kits, such as the PC kits do not have R2.

A common mistake with the network resistors is placing one of the 471s in the 472 place. The result is that a group of 4 lights does not work.


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