Prog Rock board voltages


KI7MWA
 

The assembly manual, page 10, says "If there is any problem with the measured voltages then you have GOT to investigate and find the problem before going any further!." 

I did, and got +5.3V, and +3.7V, at the locations specified. Are these within spec?  And, if not, what needs correcting?

I built according to section 4.3.1, with the LM317LZ on the Prog Rock board, not on the Synth board.  I did screw up, however, and had to purchase a replacement LM317LZ.

My supply voltage is +9V

Thanks


KI7MWA
 

Measuring R1 and R2, in the board, I'm getting 0.968kOhms and 2.82KOhms, which, should be giving me 1.25V(1+(2.82/0.968)) = 4.89V.  But I'm not good enough at reading schematics to conclude whether or not my measurements are being affected by some other part of the circuit (e.g. the LM317LZ).

I'm inclined to try adding some parallel resistance to R2, just to see if I'm understanding the voltage regulator part of the circuit.


Alan G4ZFQ
 

I did, and got +5.3V, and +3.7V, at the locations specified. Are these within spec?  And, if not, what needs correcting?
Hans has said before that the voltages are somewhat higher than nominal. I'm not sure about measuring resistances when fitted, other paths might be involved. If you use the formula for the regulator it comes out at around 5.15V. The 3V3 also calculates at around 3.6 so your readings are as expected.

73 Alan G4ZFQ


KI7MWA
 

So, just for fun, I added a 47KOhm resistor in parallel with the 3K at position R2 (for a net of 2.82K, theoretically). The fitted resistances are now 0.968K and 2.66K, and the board voltages are 5.15V and 3.57V.

My only remaining question is whether the decreased resistance at R2 will negatively affect anything else.


Alan G4ZFQ
 

My only remaining question is whether the decreased resistance at R2 will negatively affect anything else.
Hans says the higher voltages have never been known to do any harm, give a little more power out when used in the U3. (I have wondered how little.)
On the other hand I use a 1.8V TCXO with a maximum rating of 3.3V so I have reduced voltage further so my 3.3V is actually 3.1.
I have never thought this a problem.

73 Alan G4ZFQ