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Thread: Deluxe Electric Mistress

  1. #1
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    Deluxe Electric Mistress

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    Next project from generalguitargadgets.com

    Wanted to try UV pcb board manufacture.

    Step one is to create the NEGATIVE design on an overhead film. I tried just printing from the pdf from the website but it seemd to scale to a very large picture. Copied it into MS Word and scaled it by printing and measuring the printout (there are inch scales on the pdf)..

    Step 2 is to use a UV light for 3 or so minutes to 'set' the pcb tracks.
    I taped the plastic on. Get it very flat onto the pcb for best results. Some people use a thin glass sheet over the top.

    The clear parts on the overhead (for the type of UV pcb kit I am using) remain after you use the 'AE' resist developer. Took about 2 minutes to take the exposed plastic off the copper pcb.

    Photos and more soon.

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    The PCB Etching

    The overhead negative:



    The Resist Developer and Ferric Chloride etchant:



    You swish in the Resist Developer until all of the areas to be etched are bright copper colour.

    Then into the etchant. When it goes very dark, pour it out and replace:



    When all copper taken off (that should be taken off), wash off with water.
    Drill the holes and then use the resist stripper to clean off the plastic covered tracks ready for soldering:



    Look for shorts (I had one) and get ready to stuff the board.

    Garry

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    Stuffed Board

    Only a few components missing:



    I had to work out which direction the 7815AC faced.

    Looking at the 'dmistlo.gif' diagram (and in the pic above), it faces towards the right.
    ie pin 1 (input) is towards the bottom of the diagram/picture.

    Wires on tomorrow.

    Finding an SAD1024A is a problem. They are very expensive. Have some quotes coming.

    Spent about $50 so far (already had the UV pcb makings).

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    Wires on and Started Enclosure

    I wanted to fit everything into as small a box as possible.

    Found a box, but needed to do some minor changes to the pcb. Cut off a track, so put in a jumper on each side of the pcb:


    Found a toroidal 18V transformer that would JUST fit. Mounted the pcb to the top plate:

    Garry

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    Power Supply Installed

    Shrink wrapped everything and put a plastic cover over the 240V wires.

    Earth is in between the power connector and the transformer.

    Just connected to the pcb so I can check voltage runs and ensure that there are no shorts to audio circuit:


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    Found a pcb Error

    I have been testing the power circuit prior to connecting any other wires.
    Found I had a short between the D1/D2 pads and R21. Could not see a short, but running a knife between the pads fixed it.

    Then went and tested every IC pinout to earth, looking for unnexpected voltages.

    Found no voltage at pin 5 of IC5 (LM311). The layout gif shows that it should be connected to pin 6, then pin 8.

    Then checked a schematic that showed that pin 5 should be connected to 6.

    The pcb design just has a pad. No connection at all. Soldered together and that was all for today.

    I will drop message to generalguitargadgets.com. Who can you trust these days?

    Also you should note that you need to have a centre tap on the transformer.

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    You Must Use LN4001 Diodes

    I could not source LN4001 diodes so I tried LN4004s.

    They cause too large a voltage drop for the MC7814AC voltage regulator to work.

    The spec sheet for the voltage reg says that the Vin must be 2V higher than Vout. Therefore must have at least 17V at Vin.

    I am getting 15.75V at Vin by using the LN4004 diodes.

    Now trying to source LN4001 NOS. Could be a while.

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    All Connected Up

    While I wait on 1N4001 diodes (still looking...), I have connected up all of the wiring.



    Thought I had found a reasonably priced SAD1024A, but they are out of stock...

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    50th Post!

    Woo Hoo.
    Have sourced 1N4001 (x25 and 25 of all other values from 1N4001 to 1N4007...) Only way I could source small numbers, though Radio Shack has them in stock in the US.

    Cannot find a cheap SAD1024A. Cheapest is $100US! Other venders have large minimum orders. I can buy a genuine Mistress for not much more!

    May take a while to find a cheap one. Wish I had known this before I started.
    Last edited by Neve1073lover; 03-26-2009 at 23:46.

  10. #10
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    Found a 'Cheap' SAD1024A

    Been looking for a while and getting quotes. Some places are asking $200US!
    Most places make out they have them but don't when asked for a quote. Big waste of time.

    Found a place in Germany that has some stock and actually had a price.

    So SAD1024A is on its way at a cost of $120AUS delivered.

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