Serit dying

M0VKK · Post by **M0VKK** » Fri Jun 21, 2019 12:39 pm

I built a V2 MiniTiouner a couple of days ago and noticed there was no +12V on the 'A' Ftype.

Not a problem - I used the 'B' one instead. This was fine for a couple of days till this morning when I switched on and noticed the PSU current dropping from 240mA down to about 120mA

I checked and found there was no 12V now on the 'B' f type. The thermal fuse (300mA) hadn't tripped.

I moved the LNB feed to my NB receiver setup and there were no issues and the LNB drawing was drawing about 100mA.

I've opened the serit and found what I presume to be the two tiny inductors that feed the +V to the Ftypes - on one end there was 12V and nothing on the other. There were splashes of solder/metal in there though

So in short does anyone know what the value of this inductor might be?

Richard

M5TXJ · Post by **M5TXJ** » Fri Jun 21, 2019 1:29 pm

Hi Richard,
I believe that quite a few have had this problem, me included. What I have done, others too I understand, is fit a through hole inductor and polyfuse inside the Serit NIM. I fitted a 10uH inductor and 300mA polyfuse in series between the centre pin of the F socket and theLNB voltage input pin of the NIM with the inductor as close as possible to the F socket. I don't know the original inductor specs but as 10uH has an impedance of around 50K ohms at the frequencies we're using I went with that.
There is this thread showing a fix, this OM has used a hairpin inductor rather than a through hole one as I did but you'll get the idea.
viewtopic.php?f=105&t=5942&hilit=lnb+voltage&start=10
73 Dave.

M5TXJ · Post by **M5TXJ** » Fri Jun 21, 2019 1:40 pm

Me again, I should add that using a 10uH inductor means its impedance at 146.5MHz is approaching 10K so can be used to feed a 2m masthead preamp as well as an LNB.
73 Dave.

M0VKK · Post by **M0VKK** » Fri Jun 21, 2019 4:29 pm

Thanks - that is brilliant. The parts only arrived for it on Wed morning and I built it in the evening - like any new toy I want it to be perfect and to have one socket DOA and the second dying after a days use was a bit upsetting.

time for a quick RS order then

G4uvz · Post by **G4uvz** » Sat Jun 22, 2019 2:41 pm

An alternative which is easier to replace in the confined space is a standard ferrite bead with a couple of turns of wire.

One end can go on the centre pin of the F socket

Adrian

M5TXJ · Post by **M5TXJ** » Sat Jun 22, 2019 3:14 pm

This is the mod to my Serit, I have since changed the 1uH for a 10uH for better performance at 146.5MHz as in my earlier post.
73 Dave.

gi7ugv · Post by **gi7ugv** » Fri Jun 28, 2019 10:43 pm

Thanks for that Dave, just did as you pictured there after losing voltage on that socket and it's working fine now.

HB9OBD · Post by **HB9OBD** » Mon Sep 09, 2019 9:28 am

Hi Dave,

just asking if you can provide more info about the 10uH inductance.

I tried to find RFC (Choke) in Digikey but no workable results.
Then I tried only Inductance and found something like M10135-ND

My question now, to decide what to buy, is how have to be the Auto-resonance Frequency or any other HF critical parameters?

Thank you!

73 Luca

M5TXJ · Post by **M5TXJ** » Mon Sep 09, 2019 9:55 am

Hi Luca,
the choke isn't critical, I just used one from a typical Chinese sellers 0307 size selection I bought from Ebay, something like this.

https://www.ebay.co.uk/itm/1-4W-Color-R ... 2052303138

73 Dave

g8gtz · Post by **g8gtz** » Mon Sep 09, 2019 11:23 am

Hi Dave

Can we add the picture of your mod to this wiki page: https://wiki.batc.org.uk/Serit_LNB_DC_supply

73
Noel - G8GTZ

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