HFU HF Underground
Technical Topics => Equipment => Topic started by: kris on January 03, 2022, 0005 UTC
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Hola All
Maybe some of you have the same fault, then listen - maybe we can find a solution.
I was delighted with its possibilities, until after about a year of use it started to turn off shortly after starting the measurements - dark screen. The working time on subsequent launches was getting shorter and shorter. It happened even after freshly charging and disconnecting the charger, and finally the battery did not hold voltage and could not be charged either from an external charger or via USB from a laptop. .
I installed a new battery for the VNA, fully charged it (green LED) and started convinced of the success. And here's a disappointment - the battery can only last a quarter of an hour of work, charging via USB from a laptop does not keep up. The removed battery, after being charged and reinstalled, discharges even without turning the instrument on. Something went wrong with the VNA system!
After opening the housing, it turns out that the 1R5 ohm resistor gets very hot (you can burn yourself) and the FM9688AA chip that manages the power supply.
I do not see any electrolytic capacitors on the board that could cause a short circuit.
I will try to save this graceful device by replacing the suspect IC.
Do you have any more ideas?
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By any chance had you updated the DFU?
I did and my battery problems only started since then. It now goes flat when not in use. Something must be drawing current. Also, the battery symbol, which wasn't in the original firmware but is part of the update, doesn't actually do anything. This a known issue and needs a hardware mod to get it working, which I'm not keen on doing.
I have a second VNA so i'm not too bothered.
I received my TinySA a few weeks ago so I've another toy to play with :)
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Interesting. I have charged my NanoVNA H4 like maybe two or three times in several months of intermittent usage. The battery status icon seems to work as intended. I am not sure on the exact firmware revision, but I have not even bothered it.... yet? Now even less incentive to bother updating, so thanks for the FYI.
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I cannot check the software version with the battery removed.
Its presence is probably detected and necessary for the VNA to take off.
The battery status indicator is working properly.
Brian - I haven't done a software update. Maybe it's just a time coincidence with you and not the software's fault. The fact is that although the VNA is turned off, current is drawn from the battery and this problem increases over time.
On the forum of Polish hams, one of the members said he has the same problem. This week he is to replace the IC FM9688. I haven't had the opportunity to explain the details yet, but he made a jumper and the device is powered by a power bank.
I will write about the repair progress.
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Yes - after replacing the IC FM9688 with a new one, the VNA returned to normal operation.
The short circuit (in damaged ) of pins 1 to 8 of this IC allows the VNA to operate on the power bank power supply. I don't try it until IC replacement.
I am grateful to my colleague SP9FK for help! ;D
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Nano VNA rescued after IC FM replacement ;D
The manufacturer probably knows the problem that arises with this IC, because the protective resistor has as much as 5 W of power. It gets terribly hot, but it has saved the meter from damage.