Disassembly of HP-19C

[[kby]]

Are you using a temperature-controlled soldering iron and interchangeable tips? While it’s certainly easy to just blast the board with too much heat, often time it’s the length of time you heat as much as the temperature that causes damage. This can be more problematic of too low a power soldering iron thst can’t transfer heat in fast enough to exceed the transfer rate out: the solder never gets to the melting point, but the whole surrounding area is maintained at a high enough temp to lift traces or cause other damage.

Make sure your tip is clean. Tin the tip well (as Teenix suggested in different words). You might try paste rosin flux and/or a larger tip (like chisel rather than point)being more careful about the time), and using the solder wick.

I’ve gone to using a portable desoldering tool (Hakka Frp-301), but thst is a fairly expensive solution (like a few hundred $$$).-kby

(04-12-2021 04:24 PM)Jonas Sandstedt Wrote:  Hello and thanks for all tips. The new solder indeed "blobs" on the joint, and the joint won't melt to be sucked away bý either vacuum pump or desolder wick. The solder joints are most surely oxidized, having been rinsed from battery leakage with vinegar acid. Is there any other way to melt these joints without destroying PCB and components? Perhaps the safest way to continue is to try to re-assemble the calcualtor and see how it works before working more on the PCB.
best regards, Jonas