If it ain't broke, then don't fix it.

The term, “If it ain’t broke, then don’t fix it” reared its ugly head the last couple of days.  In an effort to improve the noise floor readings on my SNA, I installed a shield around the AD8307 circuits.

Problem number 1:

After installing the shield, I could not make the appropriate adjustments to calibrate the power meter. After several tries, considerable reading and thought, I removed the shield as a last ditch effort.  Since that did not solve the issue, no surprise, I was advised, “Don’t forget to press the alt key when making the measurements” Duh!! Problem #1 solved.

Problem number 2:

Shield interferes with the touchscreen and sd card. Not so easy of a fix, but trimmed the shield down, trimmed the L1 loop a little to lower its profile.

This is where I decided to put it all back to original, make some baseline measurements and then have another go at the shield mod. This now takes us to problem #3.

Problem #3:

I noticed that a resistor and a capacitor were not fixed to the pcb properly.  In fact they were off kilter by a fair bit so I knew I had done something. Must have happened while de-soldering the shield.

No problem, while they are 805 smd’s I was able to reattach easily. No pinging either.  Well, this lead to problem #4.

Problem #4:

Trying to calibrate the SNA was going much better now until I got to the part of the 3dbm level settings confirmation.  The readings I was getting looked like the AD8307 circuit was not working. Troubleshooting was easy enough with the screen removed and I quickly determined that the 6.8 ohm 805 resistor was toast.  This leads to problem #5.

Problem #5:

While I have a pretty good supply of on-hand parts, what were the odds of 6.8 ohm in the 805 package? Well as it turns out I have 4.7 and 8.2 in the 805 package. And as luck will have it, the designer told me either value would suffice.

No problem # 6, yet, but I’ve done enough for today and tomorrow can only get better.  I’m sure I’ll quickly forget the if it ain’t broke saying.  After all, the breaking of things offer a good learning opportunity.

73, Peter