On 2/17/22 3:41 PM, Jim Lux wrote:
On 2/17/22 12:57 PM, Larry Rothman wrote:
? Alan,
The schematics are in the Wiki.
There are only resistors in the input pad. You need to measure them to see which is fried. Hopefully, you didn't fry the SA612 input.
If you have 2 soldering irons with fine tips, you can lift each off the board easily but remember the display is on the other side of the PCB - so not too much heat.
It's not that hard - I flipped the resistors on my Nano-H to see if it helped with the noise (msg thread on that in 2019).
If you have a junk box, you might be able to find replace SMT resistors on scrap boards.
???? On Thursday, February 17, 2022, 03:44:55 p.m. EST, Alan Brown via groups.io <va3aqb@...> wrote:
? ? So S21 has been damaged when I was checking a LNA, i gapped it for 2 seconds and hooked the attenuator on the wrong side.
It is a H4, I was going to order a new one as needed pass through on most things I use it for.
Anyone know how to fix, is there a diode or anything that blows when input is to high?
The resistors are cheap, too. I just heat them, and scrape them off with an xacto knife.? Before surgery, you can check: If you cooked one, the resistance will be wrong.? The SA612 is DC blocked, so you can calculate what DC resistance you should see from the CH1 connector (56 ohms , in parallel with 2*240+50 ohms - probably pretty close to 50 ohms)
I just measured about 50.5 ohms dc resistance.
