Burnt damage on pcb after transistor blew.

Thread Starter

mick5621

Joined Apr 23, 2023
23
I've just taken a Roberts R9993 radio in which isn't working, the normal suspect is a B772 power transistor (Q3) has blown. Anyway I've opened this one up and found the transistor (Q3) has blown and taken the pcb with it uderneath all the way down to the fiberglass and has lifted it up around the immediate area.
Diode D3 on the board has blown too, some of the tracks are still there but my question is what can I use to make the pcb good again and replace the transistor (Q3). I know I can repair the track going to R9 on the board and R19 too but I just need advice what to use to repair the damage board. Any advice and help appreciated
 

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Ya’akov

Joined Jan 27, 2019
9,069
Welcome to AAC.

You can use copper foil tape, like this. Keep in mind, this is pretty thin so you may be better off doubling it. It can be soldered to, the adhesive can tolerate soldering temperatures.

You will need to clean the surface well, and possibly seal it with some UV solder mask to get a good surface to work on.
 

Thread Starter

mick5621

Joined Apr 23, 2023
23
Welcome to AAC.

You can use copper foil tape, like this. Keep in mind, this is pretty thin so you may be better off doubling it. It can be soldered to, the adhesive can tolerate soldering temperatures.

You will need to clean the surface well, and possibly seal it with some UV solder mask to get a good surface to work on.
Cheers for your reply,
So I can fill the 'hole' with solder mask and then copper tape on top to replace missing tracks then?
Obviously I'm new to this hobby so wasn't sure, I've never come across damage to this extent before.
 

Ya’akov

Joined Jan 27, 2019
9,069
Cheers for your reply,
So I can fill the 'hole' with solder mask and then copper tape on top to replace missing tracks then?
Obviously I'm new to this hobby so wasn't sure, I've never come across damage to this extent before.
Yes, you should be able to level the area with solder mask, then use the copper tape to rebuild the traces. You’ll want to solder across the old and new trace, so you may have to remove some original solder mask to do it.
 

Thread Starter

mick5621

Joined Apr 23, 2023
23
Yes, you should be able to level the area with solder mask, then use the copper tape to rebuild the traces. You’ll want to solder across the old and new trace, so you may have to remove some original solder mask to do it.
That's brilliant information, I didn't realise I could use solder mask to fill a hole like the one shown in the pictures. I've seen YouTube videos of people using epoxy so I was going to get some in but if solder mask is a substitute then I've already got that in. Thanks so much for up help
 

Ya’akov

Joined Jan 27, 2019
9,069
That's brilliant information, I didn't realise I could use solder mask to fill a hole like the one shown in the pictures. I've seen YouTube videos of people using epoxy so I was going to get some in but if solder mask is a substitute then I've already got that in. Thanks so much for up help
Solder mask is resin, like epoxy. It’s just easier to use since it is UV cured so can be worked indefinitely until you cure it. It’s best to build layers rather than try to fill deep defects so it is easy to cure.

@MaxHeadroom’s suggestion of solder braid is a good one too.
 

Thread Starter

mick5621

Joined Apr 23, 2023
23
I forgot to mention that you should work from the bottom out. Layer from the lowest point like you were filling the hole.
So when I first got your reply I started to pour the solder mask into the hole, feeling good about my effort I put it under my uv lamp for 15 mins, had a look at the result and the crust gave way and it was still wet underneath. So I sucked it all out (with a tissue and not my mouth )then decided to layer it up but by bit, and it's amazing stuff is that solder mask. I will give it a finish level course tomorrow and I should be good to go.
Thanks everyone for your help, advice and tips on solving my problem, I'm 52 now and still learning everyday, I do love my new hobby.
 

Ya’akov

Joined Jan 27, 2019
9,069
So when I first got your reply I started to pour the solder mask into the hole, feeling good about my effort I put it under my uv lamp for 15 mins, had a look at the result and the crust gave way and it was still wet underneath. So I sucked it all out (with a tissue and not my mouth )then decided to layer it up but by bit, and it's amazing stuff is that solder mask. I will give it a finish level course tomorrow and I should be good to go.
Thanks everyone for your help, advice and tips on solving my problem, I'm 52 now and still learning everyday, I do love my new hobby.
Sorry I didn’t mention It earlier. Please let us know how it works out.
 
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