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FAQ Schematics for Board V1.41 (blown D1B/D2B diodes) (1 Viewer)


Junior Boarder
X-108 Member
25 Mai 2015
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Hi fellow OM's

After my X108g broke the second time I threw it into the 'spare parts' bin.

Now (about 3 years later) I decided to have a go and debug the issue. I supposed the RD16HHF1 to be blown, desoldered them, but my component tester showed they have both similar and matching characteristics.

So I went on checking component on the TX path until I came across D1B and D2B on the SWR measuring circuit towards the antenna socket. One being open, and the other acting as a 6ohm resistor, that is not quite right! :)
So I went looking for a schematics to find what kind of diode this should be. Unfortunately I only find schematics for newer revisions of this board, where those were replaced by SMA shottky diodes.

Does anyone know, what they used on my board? Does anyone know where to find schematics for my revision? Or could I just use any shottky diode? I guess they all have similar specs.

73 de HB9EUE

Chris Wilson

X-108 Member
30 Mai 2020
Punkte Reaktionen
I know its been a while, but there is a list of parts in the service manual that you can use as hints for what they're likely to be. The service manual I have doesn't show the component numbers nor values on the diagram. Later versions have different components and or completely different circuits for that part of the radio

From memory the SWR compensation / protection circuit sends a signal back to the small signal board. If you disconnect the SWR it may default to full output, it may not.

You can try feeding a signal into the input of the power amp chain. That's how I found the 2SC5551 surface mount that buffers the signal from the small signal board to the mosfets in the PA, was open circuit.

The radio seems to be a slightly better engineered uBitx without the documentation, and a bunch of surface mount, so it isn't the easiest to troubleshoot, but all the issues I have had which are:
* The backup battery
* Front panel buttons not working
* The PA input buffer open circuit ( pictured below)
* A dodgy TX/RX relay
* Replacement screen
* Replacement mic curly cord
* RF Preamp soft switch (posted)
Have all been findable and fixable. I picked mine up second hand as a part payment for a bad debt....and it had the first three problems

However, my noise blanker is next to useless. The base noise vs RX sensitivity is a little below average, and I could do with a little more volume / clarity from the speaker, but I use earbuds as a work around.

That said, it does TX all the way down to 100KHz so it makes for a sweet signal generator, the compressor gives the 20W of voice a nice kick, and I am sure I can use it with some filters and such for 630m and 2200m when I get around to updating my "middle" license. 20W of CW carrier for the win. Shame about the RX sensitivity v noise floor.

Good luck

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