Hot Air & desoldering soon.

[Naysayer]

I’m preparing to attempt a repair on an Alinco DX-70T that needs SMT diodes replaced on the Band Pass Filter boards. There are 5 boards, one for each HF band and each board has a few SMT diodes on it. Over the past several months, I’ve been gathering Hot Air & De-Soldering equip. This is all new to me.

The original RLS135 SMT diodes were problematic for many DX-70 owners. Based on an old thread, I planned on replacing them (a few each BPF board) with RN731v and ordered 30x 5-6 years ago. These things are smaller than a rice grain.

I posed my circumstance to Co-Pilot and it suggested 1N4148, regular axial diodes that anyone reading this likely has a lot of. Not the same package but small enough to be do-able if I bend & cut the leads just right.

I need hot air practice just to get the BPF boards out. The DX-70 has been disassembled for a decade and not knowing how to go further is what stopped me (BPF boards soldered-in with heavy braid that needs more than an iron to free). I can see my way through this ‘in my head’ now, which I couldn’t do a decade ago. I learned a lot from this forum. Thank you for all the advice as I floundered through this & that.

Neil

 

[N8YX]

Chip Quik is your friend.

What type of hot air station do you have? Nozzle size?

 

[brandon7861]

You could preheat the area at a lower temp before blasting the solder joints with hot air. The board will wick away some of the heat leading many to crank up the temp and potentially lift traces.

Assuming they used lead-free solder (which has a ridiculously high melting point), you might want to flow some 60-40 into the joints to lower the melting point. It doesn't take much. Kapton tape can be used to shield the electrolytics and plastic parts but try not to stick it tightly to what it's protecting.

ChipQuik can definitely be your friend, but it contains bismuth, and when mixed with lead-based solder, it makes the alloy brittle. If you do use chipquik, flood the pads with solder and re-wick them to remove as much of the chip quik as you can before soldering the parts back in.

4148s come in surface mount packages too.

 

[N8YX]

ChipQuik can definitely be your friend, but it contains bismuth, and when mixed with lead-based solder, it makes the alloy brittle. If you do use chipquik, flood the pads with solder and re-wick them to remove as much of the chip quik as you can before soldering the parts back in.

What I do is apply some with the solder pencil of my rework station, hit the part with hot air (lower temp than required to melt 60/40 or similar solder) or use a Thermo-Tweez handpiece with the appropriate tips. After the part is removed, flux and clean pads with a Sodr-Xtractor, melt some 60/40 on the pads with the pencil and repeat. Then flux before putting new part on the board for soldering.

 

[Naysayer]

IDK it's all new to me. The Co-Pilot reply was surprising and yesterday I forgot to post it. Attached below. The C-Pilot reply about component selection was impressive.

Thank you, Brandon on the SMT version diode availability point. I'm still learning and acquiring what I need to do SMT work. Watching it on YT is my sum total experience there.

The air station is the cheaper copy of the Quick / Atten 861DW. So it is a no name 861SW. It has the air pump in the base and does not have the current filter on the inside of the back wall. I've never used one before so my knowledge of same is from web reading only. Have not tried it yet beyond powering On to see it light up. All told with shipping about $130. from AliExpress.

 

[Naysayer]

Playing w/ it today some cover off. The auto-cool down when nozzle placed into cradle is nice (case mounted and free-standing). I measured temps on the heatsinks on pcb and will add a small 5020 cooling fan to be safe. Quieter than I thought it would be.