oscillating spindle sander help?

[mark smith 20Participant @marksmith20]

joseph its fixed i think I reflowed all the solder joints on the pcb and `vroom` it started , dont know if it was a bad solder joint or brushes badly seated , i suspect the pcb.

Thankyou for you help

Edited By mark smith 20 on 28/05/2020 16:51:58

[Joseph Noci 1Participant @josephnoci1]

I thought it had to be a bad joint on the PCB..Thats great! Happy Sanding.

Joe

[mark smith 20Participant @marksmith20]

Thanks.

I dont understand these bad/or dry joints though, how does it suddenly happen when it was working fine. I can understand vibration loosening things but not dry joints or whatever.

[Dave HalfordParticipant @davehalford22513]

A dry joint is a soldered joint that has not properly flowed between the two parts. Typically you get the solder on the wire, but not the board, essentially the two are touching, not soldered. The joint seems firm as the resin flux acts as a glue.

Sometimes bad joints are duller where the rest are shiny or it's more of a blob than a pyramid.

[mark smith 20Participant @marksmith20]

Dave thanks for the explanation, i couldnt picture what was meant by dry joint.

[Anthony KnightsParticipant @anthonyknights16741]

Dry joints happen when the solder fails to "wet" the two parts of the joint. They are held mechanically in contact, but can fail electrically at any time. It seems to happen more with the new lead-free solder, than the old 60/40 lead -tin solder I used most of my working life. Such is progress.

[Joseph Noci 1Participant @josephnoci1]

Sometimes more that that – the joint may start out perfectly good, ie, a well made, properly flowed joint. But a lot depends of the actually mechanics of the parts soldered together. For example, a double sided through-hole plated connection of the PCB, with a snugly fitting wire in the hole, properly soldered will have a miniscule chance of failing under tension or vibration from the motor, etc.

However, that PCB is single sided it seems, and a single sided joint, with heavy wires soldered whilst inserted into a hole notably larger than the wire, relies on both electrical connection, and mechanical strength ONLY via the solder, a soft tin/lead combo ( yes, that one still has lots of lead..). all the stress is on the solder itself, and with vibration it fractures and the inter-joint becomes crystalline and either open circuit or high(er) resistance. A further cause is when the perfect joint is made during soldering, but the technician moves the wire , even a little, before the solder has properly solidified – the joint may look good, but internals it is already crystalline and waiting to fail.

That is why, on high reliability requirements for wire connections, the connections are crimped and not soldered..

In the High-Rel world, you will never find wires directly inserted into a hole and soldered – if not crimped, the hole will have a termination pin or pillar inserted and soldered, and the wire wrapped around the pillar and then soldered. Mechanical stability or strength should NEVER rely on the solder itself.

Joe

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