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MMR40_Kit vs Homebrew


MMR40_Kit vs Homebrew

On the MMR40 Yahoo Group, there came a question concerning R24 and R30.
Both are 1 Meg resistors, located close together. The confusion seems to stem from the fact that on the parts placement diagram, the two resistors are not labeled the same as on the schematic. This is true in both the Kit documentation and the ARRL Website Documentation.

So, R30 on parts placement = R24 on schematic, and R24 on parts placement = R30 on schematic.

The other problem brought up was that R30 (parts placement) had one end floating on the homebrew version of the PC board etching diagram (Available on the ARRL Website). After tracing out the circuit, I believe that the floating end should be connected to ground.

I have overlayed the homebrew PC board pattern with the parts placement, and marked the traces for each circuit. The R24 (Parts placement) is marked in Green. It should connect between the V5 potentiometer and C65. It appears to be connected that way on both the kit and the homebrew PC boards, so no changes are necessary there.

The other Resistor (R30 on the Parts placement diagram) is marked in Red. One side should be grounded and the other goes to the junction of Q4 gate, Q11 gate, D3 cathode and C59.

Here is the Parts Placement diagram overlayed on the homebrew PC board pattern:

Circuit Board overlay

Click on the image for a larger file.

And here is the schematic showing the connections:

Kit Schematic Markup

Click on the image for a larger picture.

And finally, in the Homebrew instructions, Steve shows that R24 should have one end grounded.

R24 Grounded

The Deadbug documentation also shows several other parts that should be grounded on one end, but the ground connection did not show up on the etching pattern for the homebrew PC board.

Finally, there was a question about whether the MMR40 really only used 4 1-Meg resistors, rather than the 6 in the parts inventory. The answer is that all 6 1-meg resistors are used:

  • R16 - Connects to U8, pin 1
  • R24(Parts Placement) – Connects to the V5 sidetone level pot ( It is R30 in the schematic)
  • R30(Parts Placement) - Connects to Q11 gate (it is R24 on the Schematic).
  • R2 - Connects to the Q14 PTO gate
  • R8 - Connects to U7 pins 9,10 and 11 (5 volts)
  • R44 - Is part of the RF Probe and is not shown on the schematic

Here they are on the schematic:

1 Meg Resistors

Migrated Comments:

3 Responses to “MMR40_Kit vs Homebrew”

  1. Randy wb0smx Says:

    Please note that the overlay drawing in this post is not perfectly overlayed. It seems that the component layout is not drawn to scale. I was able to get the portion of the board that was of interest to the discussion to line up pretty good, but in certain parts of the diagram, the components are not exactly where they belong. One area is particularly bad, near Q9 at the bottom center of the board. By looking closely, you can see that the components would need to move over to the right a bit to line up there. I just look for the transistor mounting holes, and move the corresponding transistor over to fit in my mind.

    Floyd, PD8F on the MMR40 Yahoo Group points out that:
    R19 is free floating at one side as well but should also be grounded.

    Pin 4 of U4 is floating freely as well but should also be connected to ground.

    And in case someone is using Steven’s first PDF file of Jan. 2nd 2007(like me): R14 is mistakenly named R34 here on the homebrew layout. I put the file on my own server: (PCB layout at bottom)
    In later documents and also the kit it is called R14.

  2. Floyd PD8F Says:

    Another thing I recently noticed: the source side of Q12 is a pad that is not connected to ground either.

    Q12 source pad should be connected to ground.

    Look for an update (Feb. 9, 2009) here:

    Thanks Randy, keep up the good work!

    73, Floyd PD8F


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