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:
Click on the image for a larger file.
And here is the schematic showing the connections:
Click on the image for a larger picture.
And finally, in the Homebrew instructions, Steve shows that R24 should have one end 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: