2 - PCB Assembly


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Post Fri Dec 01, 2017 6:34 am

2 - PCB Assembly

The exact order of assembly will depend on the preference of the builder but with SMD components and this PCB it may prove easier to cover as many pads as possible to make placing the smaller components a little easier. I would start with the 3-legged beasties.
A soft heatproof work mat will help as you'll be soldering onto both sides of the board alternately. Apologies for the slightly hairy PCB!.

Start with the MMBTA92 transistors which provide the nixie anode switching. These will be marked '2D, on a black antistatic strip of 5 3-legged plastic squares':

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Post Fri Dec 01, 2017 5:54 pm

Re: 2 - PCB Assembly

Next the MMBTA42 transistors which control the 92s. These will be marked '1D', a black antistatic strip of 5 3-legged plastic squares:

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Post Fri Dec 01, 2017 5:57 pm

Re: 2 - PCB Assembly

Now their 750k bias resistors. These will be marked '754' which is 75 0 000, on a paper strip of 10 or 11 tiny black rectangles:

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Post Fri Dec 01, 2017 6:02 pm

Re: 2 - PCB Assembly

Now the 10k resistors. These will be marked '103' which is 10 000, on a paper strip of 5 tiny black rectangles:

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Post Fri Dec 01, 2017 6:07 pm

Re: 2 - PCB Assembly

A large number of ll148 clamp and rectifier diodes next. These are copper coloured glass cylinders with metal ends on either a strip of 13-14 or 2 strip, one 10x and one 3x. They are the only diodes in the kit with a clear platic carrier strip. Make sure they're fitted with the black polarity band facing the same way as shown in the photographs:

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You may want to leave the single diode on the other side for later:

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Post Fri Dec 01, 2017 6:11 pm

Re: 2 - PCB Assembly

The 2x 75V zener doides now, these are copper coloured glass cylinders with metal ends on a black antistatic plastic strip of 2. Make sure they're fitted with the black polarity band facing the same way as shown in the photograph:

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Post Fri Dec 01, 2017 6:27 pm

Re: 2 - PCB Assembly

Now a modification before going any further. See the post here for further information:

http://www.lasermad.com/forums/viewtopic.php?t=155&f=36

It's under the resistor in the previous pictures but you can see where the PCB has been cut. Cut through this track as it's now connected to the HV supply by that resistor.

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Post Fri Dec 01, 2017 6:30 pm

Re: 2 - PCB Assembly

Now that's done we need to add the resistor that replaces it. You need the 2x 470r (marked 471) resistors on a paper strip of 2x black rectangles:

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Form a bridge using solder or a wire offcut between these 2 pads:

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Post Fri Dec 01, 2017 6:31 pm

Re: 2 - PCB Assembly

Followed by the HV ceramic capacitors. These are large beige rectangles which are on a clear plastic strip of 2:

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You'll need to put some hot glue or similar on these once the clock is finished and working as they tend to buzz due to the piezoelectric effect of the ceramic material.

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Post Fri Dec 01, 2017 6:33 pm

Re: 2 - PCB Assembly

One small 91r resistor, this supplies 3.9v to the IR receiver. It's on a cream paper strip of one and marked '910' :

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