What is the most safe method of desoldering filter capacitors from fender red knob twin pcb?

[Jquijano]

Ill be doing cap job on a 1989 fender red knob twin. How should i approach the filter capacitor and powet resistor removal process without damaging the pcb traces?

[Jon Snell]

Take photographs showing details of wiring. This process assumes you are proficient at desoldering otherwise, take it to a person who is or get them round to yours for a hand.
You will render the ampifier useless with man made faults if you cannot desolder and solder proficiently.
Ensure the amplifier is disconnected from the mains supply and discharge the Grey and Blue large electrolytics.
Remove the fixing screws and lift the board to hinge out

Desolder and replace the capacitors only if they are faulty!
Do the same with the other components that are faulty.
The power resistors are ceramic wirewound and are either open circuit or OK.
NEVER replace components without the basic knowledge of how to test them correctly.

[Jquijano]

I know how to solder and desolder. I have replaced many filter caps in the past but have been warned that the PC boards in the Fender Red Knob Twins are not of great quality and there is a high risk of damaging the traces.

[TomCarlos]

It is recommended to use a solder station, one that allows you to control the amount of heat generated at the tip of the solder iron. When removing components, use only sufficient heat to "undo" the solder, to the point where you can loosen and remove the device lead from the trace. Otherwise, if you have a solder iron with "no" ability to control the heat, use it carefully and look closely to see when you reach the point of loosening the solder to remove the device lead.

I would also recommend you get yourself some type of desoldering tool, a mechanical pump type.

[Jquijano]

These are the parts i will be desoldering and soldering:

Power supply section: (2) 47uf 350v and
(2) 220uf 300v

Preamp section: (3) 22uf

Bias cap: 100uf 100v

What else should be considered for further noise reduction and perfectly working amp?

https://www.amprepairparts.com/fende...s.htm#crossref

FCK-55

[The Dude]

I'd first do a quick ESR test on the caps in circuit. Also check resistors. As Jon said, there's no reason to just wholesale replace parts. Replace only parts that are defective. To do otherwise is a waste of time and money and could make things worse if you are inexperienced.

[x-pro]

If very much itchy hands and a great desire to change by their own efforts, and in the future to confuse the polarity when installing and break the device at all, then, first the parts must be separated from the silicone glue on the circuit board. Then bite out their leads. Then you can carefully unsolder the remaining pins.

[Jquijano]

Just checking my replacement inventory and have NOS 2.7k 10 watts and 30k 10 watts power resistors. Now i need to get the complete filter cap set. Do you guys recommed F&T caps?

[The Dude]

If those resistors are bad, you need to figure out why. They wouldn't go open without some serious current draw. If they aren't bad, why on earth would you replace them?

[Jquijano]

Im buying a 35 years old amplifier which i believe will need to have a cap job at least and maybe some resistor swap. I will be receiving the amp in one month from now. I just want to order the parts that will need replacement.

[Mick Bailey]

I've worked on a lot of these amps, with numerous different faults - but problems with the power resistors haven't been one of them. I wouldn't change them unless there's a fault - you unnecessarily risk damaging the amp or making a mistake.

The PCBs are no different to any other Fender PCB of this era. I have a desoldering station, which minimizes risk. For the many years before that I just used a soldering iron and desolder pump. Much damage is done to traces by heat-soaking the pad with an iron that is too small, underpowered or not hot enough. 'Hot and fast' is the way I work. X-pro's suggestion is what I would do in your position. Slice through the glue, cut the leads off and leave enough length to grab hold of. You can then quickly heat the joint and pull the lead through from the other side of the board. If necessary, remove any surplus solder afterwards with fluxed braid or a good quality desolder pump.

F&T caps are good, but so are Miec, which are very reliable.

Evaluate the amp first. Play through it, make observations and think about it before replacing parts that may be good. Whilst the grey Illinois caps in the Hotrod/Deville series are often high ESR or leaking/bulging, the caps in these amps hold up much better.

[Jquijano]

Thanks for your kind advice. Can you point out which plate resistors must be changed if it starts to crackle and generate popcorn background noises?

[Pixel]

Ill be doing cap job on a 1989 fender red knob twin. How should i approach the filter capacitor and powet resistor removal process without damaging the pcb traces?

The questions you are asking lead me to think the best way for you to move forward is to have someone with experience do this servicing. At the very least have the amplifier at hand and do some hands-on evaluation before you try to diagnose it by using clairvoyance.

[g1]

The #1 way to avoid damaging traces is to avoid replacing parts that are not proven bad.
You already know the traces are delicate. Don't take chances on damaging the board unless absolutely necessary. Think of the board as a component that is no longer available.
If you do have to replace a bad part, it is easiest if you cut the component lead off first, as was mentioned by x-pro and Mick Bailey above.

[The Dude]

You seem determined to just start replacing parts without doing any testing or assessing what the amp actually needs or doesn't need. This is NOT an effective or recommended repair process. All too often I've seen it result in causing more problems rather than less.

Edit: In fact, crackling noises may not require any parts. You could simply have connection issues. Or, you may have a bad tube. Just at a quick glance, I already see some areas that need to be checked, including some areas that may be damaged from previous work. Start by giving the entire thing a good lookover for solder issues before just throwing parts at it.



A = Possible cold solder joint.
B&C = Possible broken traces.