Sinclair ZX80 / ZX81 / Z88 Forums

I've asked this on eevblog but so far no one has answered. Basically... what I read about Chinese desoldering heat guns has got me scared.

Being on a budget I have a ZD-915 desoldering tool, but as you know it gets 95% there and leaves enough pins with a small amount of led solder on, to prevent the chip from lifting clean.

It obviously needs a small amount of directed heat to do enough melting to allow the chip to lift, but I'm having a heck of a job trying to find something. Obviously I've got larger heaters for removing mobile phone backs, but that's too large and delivers too much heat.

I've been watching a number of videos and saw Adrian's Digital Basement where he uses a Gaoyue 858, but there seems to be little information about it. Looking it up on Amazon, I see reviews equally split across from 1 to 5 stars with people getting white smoke and destroying their units. https://www.amazon.com/GAOYUE-Rework-So ... B01L6U7032 Some of this sounds like it's down to not knowing how to use it properly... but that's another problem... I can't find any reliable information that would give me confidence to know that I wouldn't make the same mistake.

One that I've been looking at is this https://www.ebay.co.uk/itm/285632937860 ... SwbtdlknPP - hand held so can be put away after use, has nozzles and adjustment, etc. But there are desk "station" units with easier to handle nozzles for the same price.

Grateful for opinions and suggestions please.

I have something like the first link you provided.
But I never needed it.
I also have the zd915 and use the following steps:
First I apply flux gel
Next I desolder every pin. Not from the top but horizontal. This way I can see what I'm doing and it's not necessary to work against gravity.
After every pin is desoldered I try to move each Pin separately and if it doesn't move with some force (not bending the pin) I add more flux and try to desolder this Pin again.
This way I get all Pins moveable and can take out the chip.
In the worst case only one or two pins stay stuck and I only need to heat one pin at a time to take the chip out.

Again my apologies for my crude words, I'm not navtive English.

No need to apologise for your English... You speak more than one language, which is more than me!

Thanks very much for the advice. I think I need to get hold of more boards on which to practice.

I have one of those desolder stations. I don’t think I have made a chip just drop out more than once or twice after desoldering.

I apply heat, pull the trigger and then move the nozzle about until I can feel it moving the pin.

Once I have done all the pins I get the magnifying glass out to assess the pins and see if any need another go. If so I add more solder and plenty of flux.

Assuming the chip then does not lift easily I use a normal soldering iron to push the pins away from the sides of the holes to try and get them in the middle. This normally then allows easy chip removal.

Sometimes I put the end of a flat screwdriver under the chip and gently rotate it (as it is easy to control the pressure when rotating rather than lifting) while applying heat with the soldering iron to the pins.

I have removed a lot of chips this way without damage to the board or chips.

I have one of these, that with an electro magnet suck once, and when you release the button, blows all solder out again. So it's not very good. However it's better than none at all.

https://a.co/d/hodRSQB

Someone on EEVBlog kindly posted this video for me to have a look at, concerning vacuum desoldering...

https://www.youtube.com/watch?v=e8KRPFOD1RE

With through-hole plated holes on multilayer boards, how easy it is to get the solder out of a PCB hole that has a component leg/pin in depends on how big the diameter of it is compared to the component leg/pin. If it's a very tight fit, often the leg/pin and the PCB pad/track both need to be at the melting point of solder.

Even a little bit of solder will hold the leg/pin solid. Applying force is far more likely to wreak the through-hole plated hole than break the solder.

Also, as Lardo implies, using 'new' solder helps, as very old solder may be harder to remove.

As well as the tips above, if you can clamp or fix the PCB in a vertical position, and you can manage it, heat up the component side with a normal iron and keep it there, while using the desoldering tool on the non-component (underside).

Or if you are VERY, VERY careful, you could do what I sometimes do, use a electric paint stripper heat gun to remove the chip... (as long as the legs don't catch, the chip literally falls out when the pins are poked with a flat bladed screwdriver). Then use a desoldering tool to clear the PCB holes

Mark

It took my brain a while to take on board the notion that to remove solder first you must (sometimes) add solder!

Lardo Boffin wrote: ↑Sun Jan 21, 2024 7:23 pm It took my brain a while to take on board the notion that to remove solder first you must (sometimes) add solder!

Adrian, of Adrian's Digital Basement, does it on every joint he desolders.

I know I probably should but…