QRPLabs_Replace_Si5351

My QRP Labs U3S stopped working with a message "Error: Si5351A"

The 5 volt regulator on the Synth board was hot and I realised the Si5351 was taking a lot of current.

I found a source of Si5351s from Malaysia on eBay, post free these were about the same price as a UK supplier excluding postage.. Make sure you get the correct one!

About 3 weeks later they arrived.

My removal of Si5351. Other techniques may be used, I show the one most suited to me and my resources. This needs a lot of care, planning and patience. You need a steady hand and magnification depending on your eyesight. I use some +4 reading glasses, another pair with a watchmaker's lens for the fine work. An eyeglass for final inspection.

First I removed C2, C3 and the crystal. It is safest to destroy the capacitors and remove each lead separately. The crystal may be removed by heating each pad in turn and edging it out.

Then I masked everything other than the Si5351 with aluminium foil and used a hot air embossing tool (ebay) to melt all the solder on the pins. When certain all is melted the Si5351 may be lifted with tweezers.

Note pad 5 top left seems to have moved. I left it like that, it is not touching anything .

Very carefully position the new Si5351 over the pads and tack it on with solder on a corner. Extra flux helps, I did not have any. A delicate job to position it and ensure it does not move.

Then, if still located solder the corner pin on the other side. Then flood the first side, I used rather more than necessary.

Flood the second side, try to use less than I did. Flux would help!

Then remove excess solder with wick. Do not be afraid about heating the Si5351, do not remove the braid unless it is fully heated.

The bottom pins looked better than the photo when I used an eyeglass. I replaced C2, 3 with surface mount.

Testing in the QRP Labs VFO this Si5351 worked from about 3.4KHz up to about 306MHz, did not seem to be bad.

G4ZFQ September 2019