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nanoVNA-H no boot screen flickers then black

Al Holt All Messages By This Member #24887 Hello all, I'd had this nanoVNA-H for a few years, h/w v.3.4, and it's had this startup trouble for a long time. At power on, the screen lights up, a blank screen flickers as if trying to boot and after ~30 seconds goes dark. For a long time I've been able to get it to boot by repeatedly flicking power switch off and on. Researching the trouble on this forum I have found I can attach external power to USB port and then after ~30 seconds pull the connector and it will boot. Symptoms were there with the original firmware. I've updated it to v.1.0.64. Battery voltage is 4.16 volts. I've read about a troublesome IC or cap, but I can't find those on my board, a blue PCB that looks official. When it does boot, it works well enough. What the best course of action? I wouldn't mind a larger screen, but I'm reluctant about purchasing a -H4 model if I can get this one to reliably start. Thanks! --Al WD4AH
William Smith #24888 Try disconnecting the battery, disconnecting the USB cable, powering it on to discharge any caps, and then boot it with just the USB as power supply? Battery might be getting soft... 73, Willie N1JBJ toggle quoted message Show quoted text On Sep 25, 2021, at 7:24 AM, Al Holt <grovekid2@...> wrote: Hello all, I'd had this nanoVNA-H for a few years, h/w v.3.4, and it's had this startup trouble for a long time. At power on, the screen lights up, a blank screen flickers as if trying to boot and after ~30 seconds goes dark. For a long time I've been able to get it to boot by repeatedly flicking power switch off and on. Researching the trouble on this forum I have found I can attach external power to USB port and then after ~30 seconds pull the connector and it will boot. Symptoms were there with the original firmware. I've updated it to v.1.0.64. Battery voltage is 4.16 volts. I've read about a troublesome IC or cap, but I can't find those on my board, a blue PCB that looks official. When it does boot, it works well enough. What the best course of action? I wouldn't mind a larger screen, but I'm reluctant about purchasing a -H4 model if I can get this one to reliably start. Thanks! --Al WD4AH
Hugen All Messages By This Member #24889 It looks like the power IC is malfunctioning, so if you are willing to work without the battery, try removing the FM9688 and shorting pin4 and pin8 of the FM9688 location on the PCB.
Al Holt All Messages By This Member #24890 On Sat, Sep 25, 2021 at 07:57 AM, William Smith wrote: Try disconnecting the battery, disconnecting the USB cable, powering it on to discharge any caps, and then boot it with just the USB as power supply? Battery might be getting soft... Thanks for the suggestion. I tried it, but all I get is a more dramatic flickering of the display at a slower rate. --Al
Al Holt All Messages By This Member #24891 On Sat, Sep 25, 2021 at 08:43 AM, Hugen wrote: It looks like the power IC is malfunctioning, so if you are willing to work without the battery, try removing the FM9688 and shorting pin4 and pin8 of the FM9688 location on the PCB. Hugen, thank you for your reply. Do you think it's worth trying to replace the FM9688 IC? I have some experience and equipment to work on SMD and that chip has enough spacing of its leads to make it seem reasonable to give it a try. --Al
Hugen All Messages By This Member #24892 You can try to remove the FM9688 first in order to confirm if it is caused by a fault in the FM9688.
Al Holt All Messages By This Member #24893 Success! Removal of the FM9688 and adding the jumper did the trick. The nVNA starts up every time. I'm using an external battery pack with it. Thanks! --Al

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