Correct PCB Pad Restoration

[GasMask52]

This last month I've successfully finished repairing a couple of Marshall amps , a VS65 & a VS100R - two more to go , today I'm attempting to fix another VS100 that has crackling issues (had this before on a different amp)

Got a couple of questions :

**In the Pot image - the pins that have the red circles , are they grounds?? Would poor soldering with lifted pads cause noise issues with these pins?



**Clearly the 4 middle pads are all slightly lifted (should I leave them?) , and the external ones are missing - What's your take on fixing this?

[Jon Snell]

Not much will restore the damaged tracks on the board. Always use a hot air system or de-solder the large lands with a hot iron and speed is the essence, then use a soldering bit the correct width to heat all four pins up at once and then remove the control.
I use these pcb land repair stencils. I select the size required, place the transfer on the board and heat it with a soldering iron that has an aluminium bit (to avoid sticking) and the heat softens the adhesive on the transfer that fixes itself to the pcb. Solder and flux joins the new pad to the remaining good tracks on the board
Using de-solder braid with a warm iron just damages the lands.
At this point I would clean the board and holes, fit the new component and wire wrap the legs and solder to good track that has been prepared with a fibre glass pen.

[Jon Snell]

The large pins are fixing points and can be used as a ground. They will not cause noise problems unless the track on the board runs a ground through them.
Fit the pot and cross your fingers or wire wrap as described earlier.

[GasMask52]

The large pins are fixing points and can be used as a ground. They will not cause noise problems unless the track on the board runs a ground through them.
Fit the pot and cross your fingers or wire wrap as described earlier.

Thanks for the reply! ok , so I guess in this case those fixing point pins are not grounds , due to the fact that those holes are not in the lighter green pcb layer (that is grounded) and i see no tracers around.

I get your point about repairing it with wires , though I presume to be successful on the middle 2 holes (far right) because I can actually see tracers leaving the hole , which brings me to consider exposing the copper of the pcb and soldering it with wire - but what am I supposed to do this with holes that don't present tracers? where would I attach and solder the wire?

[Jon Snell]

If you look very closely, pin 1 has no connection. Pin 2 connects to pin 3. Pin 4 is on its own, so if you install the pot and solder it in, wrap two turns of thin tinned copper wire around each ground lug to give you something to solder to and provide some sort of strength to support the pot. A single strand from some flex works well.

[Kevina]

PACE do thremal PCB pad and track repair systems; very comprehensive and accurate, but they are not cheap

[nevetslab]

This last month I've successfully finished repairing a couple of Marshall amps , a VS65 & a VS100R - two more to go , today I'm attempting to fix another VS100 that has crackling issues (had this before on a different amp)

Got a couple of questions :

**In the Pot image - the pins that have the red circles , are they grounds?? Would poor soldering with lifted pads cause noise issues with these pins?



**Clearly the 4 middle pads are all slightly lifted (should I leave them?) , and the external ones are missing - What's your take on fixing this?

I've had to make the same repairs on these Marshall front panel PCB's. Even using a Pace MBT / SX-70 Desoldering Iron with well-maintained desoldering tips, moderate temperature, I find the bloody pads lift off the PCB. And, the woefully too small support bracket pads nearly always lift off, just as they do on Fender's Hot Rod Series boards. It's a PCB Quality issue more than anything else, I'm afraid to say. I'll normally make repairs using 26AWG or 28AWG Solid wire, with the usual scraping away the solder mask on traces that have broken away from the solder pads, tinning and then tack-soldering the wire into place on the traces, while wrapping the wire around the pot terminals.

[nickb]

It's something I've noticed over the years. As PCB manufacturing tolerances and process have improved so the width of tracks and size of pads has decreased. The PCB designer appears focused on density rather than mechanical strength. Why should they care? They only have to make the board once and not repair it.

For these little so and so's, I use a desolder gun to suck the solder off the the primary connection terminals so they are free. I then do the same for the mounting pads but they almost never release. The problem is aside from the ridiculous size of the pad, that you have to apply a lot of heat due to the metal bracket so to solve that I then use chip qwik low temperature solder on the mounting posts so I can melt the solder on both posts and pull the pot free of the boards. Finally suck the mounting pads clean. Even with all that a mounting pad casualty is not unusual.