Is my Vaillant PCB dying?

[Roddy Young]

Why on earth did he not resolder it. Worked on TVs for years and never replaced a PCB for a dry joint. Most TV guys can resolder a dry joint so it won't fail again.

As for £180 for a PCB that probably costs a fiver to make!

Some of the SMD ICs used these days have 12 soldered connections along each of 4 sides only 9mm (3/8”) long. Once upon a time, the friendly TV repair man would study a PCB and, indeed, resolder a dry joint or remove and replace a dead capacitor. Nowadays, though, his job would be very difficult. He would be hard pressed to see any fault, let alone expect his trusty Antex to reach between the connections.


It is the same with Vaillant’s PCB – only 130mm by 250mm but with hundreds of tiny SMD resistors, diodes, inductors etc on one side, as well as a myriad of larger electrolytics, etc. On the back, hundreds more solder connections.


And so, PCBs are regularily thrown out because on-site repair would be too difficult. I understood the diagnosis my repair man made on looking at the still unopened boiler, “dry joint”, to be a generic modern version of, “Something’s broken on the PCB”. It may well have been an aged electrolytic, dying IC or, indeed, a dry joint.


His solution - Vaillant’s solution - was to replace the board. It solved the problem and that’s what he and I wanted.


Yes, it seems wasteful that the old PCB was scrapped but that is how it is these days. We no longer recut or retread tyres, re-lead big end bearings. Even Maplin couldn’t make a business selling electronic components.

 

[rbranco]

Some people at one time would put the boards in the oven to reflow them (without proper reflow ovens you can kill the board completely) with play stations etc hit and miss , but does not work well with double sided boards.
Main thing is to get it above the temp to make the solder flow but not too high/long to damage board or components. But some components are added after normal reflow due to temp issues, ie plastics, all depends on how they are made, wave soldered etc.

 

[ScottishGasMan]

I would be very surprised if a modern Vaillant pcb had a dry joint. I've removed various components on these boards and the leaded components are a very tight fit (almost a press fit) and the holes are plated through.
Broken joints are very rare nowdays. Pcb manufacturers of the past like Enertec almost designed the boards to fail with undersized solder pads/single sided boards/over heated components/uncompliant wiring.

Changed hundreds and never seen a dry joint on one, think its the caps that go on them in most cases but I'm not an electronics guy

 

[bernardgreen]

I would be very surprised if a modern Vaillant pcb had a dry joint

If a joint fails it is more likely ( in a boiler PCB ) to be a fractured joint where mechanical stress has caused the solder to break. The break would be hard to find by a visible inspection as it would be a very fine crack.

The complexity of a modern boiler PCB is far beyond an "on site" repair. A workshop repair would need specific test equipment and test routines to locate the fault. If the "abuse" (*) was enough to crack one joint it is likely that other joints will have been compromised.

Replacing a PCB that has a known function fault with a new fully tested PCB is a better option than to try and diagnose and repair the fault(s) on the PCB

(*) thermal cycling, vibration, corrosive atmosphere,