My amp has a board that is a royal pita to remove, literally a 2 hour job and i need to replace one slightly burnt resistor.. i was thinking that i could snip the offending resistor out leaving as much of the legs as possible, and solder the new one (quickly!) To the leads of the old one..
If i ever do pull the board again, id plan on a proper replacement...
Hate doing things that make me feel like im doing a hack job, figured I'd check here to see if this is generally an accepted repair method..
If i ever do pull the board again, id plan on a proper replacement...
Hate doing things that make me feel like im doing a hack job, figured I'd check here to see if this is generally an accepted repair method..
But if you can snip the leads from the top, why not just removing the R from the top?
Then replace with a new one from the top with very short leads that just go into th holes and solder from the top?
Jan
Then replace with a new one from the top with very short leads that just go into th holes and solder from the top?
Jan
If this is an old school board with no copper on the top side, I can see why it would be better to just snip off the resistor.
With a "normal" PCB that has copper on both sides and regular vias, I would do like Jan suggests, but be careful. If you can't remove all solder from the holes (hard if you don't have a good solder sucker), heat up and carefully push the new resistor into place. Do not force it, or you might end up damaging/pushing out the trace on the other side (happened to me on prototype boards).
With a "normal" PCB that has copper on both sides and regular vias, I would do like Jan suggests, but be careful. If you can't remove all solder from the holes (hard if you don't have a good solder sucker), heat up and carefully push the new resistor into place. Do not force it, or you might end up damaging/pushing out the trace on the other side (happened to me on prototype boards).
Just make sure and have the existing leads well tinned prior to hacking out, er snipping out the resistor. That way it should only take a quick hit with the iron to reattach the new part.
My fear whenever faced with something like that is that the tiny leads will fall through or pull out during soldering.
Sometimes it is just better to take the time also, vs risk of damage, or loss of sleep…
My fear whenever faced with something like that is that the tiny leads will fall through or pull out during soldering.
Sometimes it is just better to take the time also, vs risk of damage, or loss of sleep…
One possibility, if there is room, solder the new resistor on top of the old, or on the side. Then carefully snip the old off.
I think you can do exactly what you planned. Is this a low wattage resistor? If so, then certainly.
Here’s how things like this usually go: you try to do the right thing by pulling the board then something stupid happens and something else gets damaged in the process!
K.I.S.S. principal.
Here’s how things like this usually go: you try to do the right thing by pulling the board then something stupid happens and something else gets damaged in the process!
K.I.S.S. principal.
It is, but some people want to journey over the top.
#8 advice concerning low power is ok.
If medium power, make sure things will stay fixed.
If high power, elaborate.
Snip off old body and solder new resistor to those stumps, least damage to the board and guaranteed good soldering on the invisible side, since it will be the factory original.
Who cares about "ugly"? ... a solid electrical/mechanical connection is the main point, the rest is just aesthetics.
PS: before resoldering scratch stumps bright clean, and use a hot soldering iron, good solder or if available add a tiny flux drop, so as to quickly soldering on top without melting bottom too much.
I have done it countless times, to avoid removing nightmare PA mixer boards with 70 pots and jacks/switches on them for access, or 15 pot Guitar preamps (plus jacks/switches/etc.)
Lots of modern equipment is designed for simple assembly but nightmare servicing.
Who cares about "ugly"? ... a solid electrical/mechanical connection is the main point, the rest is just aesthetics.
PS: before resoldering scratch stumps bright clean, and use a hot soldering iron, good solder or if available add a tiny flux drop, so as to quickly soldering on top without melting bottom too much.
I have done it countless times, to avoid removing nightmare PA mixer boards with 70 pots and jacks/switches on them for access, or 15 pot Guitar preamps (plus jacks/switches/etc.)
Lots of modern equipment is designed for simple assembly but nightmare servicing.
Yes, tin, snip close to part, tack new part on the stumps. That's how we fixed TV sets back in the day. With a little skill and luck it lasted the life of the set. Yes OCD, but you can't bill the customer 2 hours for what shouldn't take 15 minutes. The customer does not know the factory made it hard. A hack that lasts IS the right fix.
(When this PoS PCB amp becomes Collectable; someone will spend a week fixing "bad repairs". Altho I just saw worse in a Fender Custom Shop new build.....)
(When this PoS PCB amp becomes Collectable; someone will spend a week fixing "bad repairs". Altho I just saw worse in a Fender Custom Shop new build.....)
Thank you ALL for the responses!
To pull the board and fix the right way, 2 daughter boards need to be removed, and a whole host of hookups to the main board (B+ x 2, 4 5v AC connections, heater and so on) need to be removed.
I have done it once, wound up having to extend a few wires a little to be able to get the soldering iron into very tight spaces without melting anything...
Unfortunately there is no reliable way to heat the original solder - replace and know I have a good connection from the top..
I know the solder should follow the heat, but if whats under is oxidized as badly as some of what I saw id really be surprised if flux
As it is, I do know if I heat it too long, I WILL be doing it all over
Again, If I ever HAVE to go that deep again, I will but a close snip, scotch bright, liquid flux and a quick dab should do it.
Its a 20K Ohm B+ dropping resistor for the first stage of my 12AT7 , Before the 100K plate resistor...
I made the mistake of using a low impedance DMM while measuring the vdrop across the plate resistor and saw the magic smoke!
That fluke will be relegated to everything BUT reading voltage drop!!
To pull the board and fix the right way, 2 daughter boards need to be removed, and a whole host of hookups to the main board (B+ x 2, 4 5v AC connections, heater and so on) need to be removed.
I have done it once, wound up having to extend a few wires a little to be able to get the soldering iron into very tight spaces without melting anything...
Unfortunately there is no reliable way to heat the original solder - replace and know I have a good connection from the top..
I know the solder should follow the heat, but if whats under is oxidized as badly as some of what I saw id really be surprised if flux
As it is, I do know if I heat it too long, I WILL be doing it all over
Again, If I ever HAVE to go that deep again, I will but a close snip, scotch bright, liquid flux and a quick dab should do it.
Its a 20K Ohm B+ dropping resistor for the first stage of my 12AT7 , Before the 100K plate resistor...
I made the mistake of using a low impedance DMM while measuring the vdrop across the plate resistor and saw the magic smoke!
That fluke will be relegated to everything BUT reading voltage drop!!
You said this before. What is this special Fluke which violates the usual rule of voltmeters (don't load the circuit)? Want to be sure I don't get one.
I encountered open resistors in an HP 200CD oscillator and a 1955 Chevrolet radio. They both worked fine after replacing the resistors, so it may just be that the resistor power ratings were too low.
Turns out, if I use the meter in manual mode the low impedance isn't a worry...
only in the auto range does it offer very low resistance while in voltage mode...
Still, I will not reach for it on the first grab until I get more familiar with it...
Update on the OP..
Had to pull the board... wanted to fix a mistake I just found out I made with the capacitors after the tube rectifier...
supposed to be max 4uf and I'm embarrassed to say what I bought and installed.. had do do with not realizing a , is the same as a . in other parts of the world!
While I was in it, ordered better diodes and caps for the on board AC to DC 300B filament section...
Had it all back together only to realize I had a bad solid solder joint...
All back apart, and now finally getting DC to both heaters.
only in the auto range does it offer very low resistance while in voltage mode...
Still, I will not reach for it on the first grab until I get more familiar with it...
Update on the OP..
Had to pull the board... wanted to fix a mistake I just found out I made with the capacitors after the tube rectifier...
supposed to be max 4uf and I'm embarrassed to say what I bought and installed.. had do do with not realizing a , is the same as a . in other parts of the world!
While I was in it, ordered better diodes and caps for the on board AC to DC 300B filament section...
Had it all back together only to realize I had a bad solid solder joint...
All back apart, and now finally getting DC to both heaters.