What we're sharing here is extensive experience with the varied quality of finished boards in the same series or family. Some of us have seen hundreds of some models. This gives us a critical eye for trouble spots that the casual but intuitive hobbyist wouldn't have.
I'll skip over the lighter, heavier part thing since Andy was already there. Likewise the shift and bump thing.
Next is are the TO220 regulator, driver, final,. Although not usually placed under stress when soldered occasionally the board will shift during its lifetime and the legs will separate from the trace.
The infamous circular separation (crack) around a pin that defies visual examination. The crack appears as a dark circle slightly larger than the protruding pin unless it's right up on the pin's outside diameter. Under good lighting and magnification it does jump out at you. Electrically the signal will just stop at the trace but will be visible at the pin! A good example would be the RF/IF transformers in early 29LTD and 148GTL, VCO area of the 92A SSB radios (13-892, 6241 JCP etc) and the uPD858 mixers.
Some parts are not wave soldered as they won't survive the process. These were or used to be some varactors, 1N34's 1N60's and early CMOS for static rather than heat reasons. These parts were installed by hand. Quality may vary.
In later years RoHS lead free crept into everything and was a game changer. It's upper and lower limits for proper flow are closer together. It is prone to rapid chill fracture. It doesn't play nice with real solder. It will occasionally repel real solder used in rework. Some components tinned with lead will not bond to lead free. Short, sharp, shocks will fracture bonds. In close spaced surface mount applications tin whiskers will grow, easily spanning a tenth of an inch.
Old radios, I tell ya. You just can't get a break some days.
New radios hide their sins in surface mount LSI and lead free solder those microscopically spaced pins down with a evolved cousin of the original lead free solder that sometimes defies flow on manual rework and resists bond on hot air rework.
Then vias and multi layer boards ....
Okay done for now. I guess the point is complete diagnosis and examine why rather than just repair. The lesson will serve you well later. On the other hand a poor solder joint is often times just that so don't over think it.
I'll skip over the lighter, heavier part thing since Andy was already there. Likewise the shift and bump thing.
Next is are the TO220 regulator, driver, final,. Although not usually placed under stress when soldered occasionally the board will shift during its lifetime and the legs will separate from the trace.
The infamous circular separation (crack) around a pin that defies visual examination. The crack appears as a dark circle slightly larger than the protruding pin unless it's right up on the pin's outside diameter. Under good lighting and magnification it does jump out at you. Electrically the signal will just stop at the trace but will be visible at the pin! A good example would be the RF/IF transformers in early 29LTD and 148GTL, VCO area of the 92A SSB radios (13-892, 6241 JCP etc) and the uPD858 mixers.
Some parts are not wave soldered as they won't survive the process. These were or used to be some varactors, 1N34's 1N60's and early CMOS for static rather than heat reasons. These parts were installed by hand. Quality may vary.
In later years RoHS lead free crept into everything and was a game changer. It's upper and lower limits for proper flow are closer together. It is prone to rapid chill fracture. It doesn't play nice with real solder. It will occasionally repel real solder used in rework. Some components tinned with lead will not bond to lead free. Short, sharp, shocks will fracture bonds. In close spaced surface mount applications tin whiskers will grow, easily spanning a tenth of an inch.
Old radios, I tell ya. You just can't get a break some days.
New radios hide their sins in surface mount LSI and lead free solder those microscopically spaced pins down with a evolved cousin of the original lead free solder that sometimes defies flow on manual rework and resists bond on hot air rework.
Then vias and multi layer boards ....
Okay done for now. I guess the point is complete diagnosis and examine why rather than just repair. The lesson will serve you well later. On the other hand a poor solder joint is often times just that so don't over think it.
