In Need of Soldering Tips

Hi, I wonder does anybody have any tips on a soldering issue I am having! I am replacing a couple of diodes in an amplifier.

There are two wires and a diode soldered to the same joint. I am replacing the diode so is there a way to unsolder it without unsoldering the other wires at the same time?

JG

 

Go to YouTube... lots of videos... best way to learn and practice.

 

Thanks for the response, I have checked YouTube and I have watched loads of videos, but none showing the problem I have!

JG

 

I'd have to see a picture of it to be 100% sure, but I can say with some certainty that you'll likely end up unsoldering all three things and re-soldering them all afterwards. It can be a bit tricky, but practice makes perfect. Be careful not to overheat stuff (i.e., leaving the iron on the joint for a long time) - diodes can be killed by overheating.

 

Unsoldering the others is not an issue, in fact it would be best to remove most of the old solder from the connection before you start, with a solder sucker or solder wick. You want the wires touching and the solder to coat the connection like glue.

If you can't do that, just clip the old one off at that end before you solder in the new one. There may be a little turn of the wire from the original diode left in the original clump of solder, but it won't hurt anything. Wrap the new one around the ends of the leads of the other two and solder. Or if they are insulated right up to the junction, cut the old diode out leaving 1/2 inch or so and solder the new one to that lead.

 

That is what I was thinking of doing, just clipping the old one off at that end. So you reckon it is ok to do that. Here is a pic of what I was talking about. It has a pair of diodes (twisted) and they connect to the same joint as the pink cable and also a connection from the red capacitor(??) above.



JG

 

Here you go. There is a twisted pair of diodes soldered to the same joint as the pink cable.



JG

 

Yes, I think it would be ok to cut out the old diodes and carefully solder to the remaining leads if you can't remove the old solder. Get good metal to metal contact between the old and new leads before soldering.

Those diodes don't look burnt or anything, are you sure they are bad?

 

Thanks for the tips. The amplifier is 29 years old and it went dead last week. Sent an email to the guy that built it and explained what was happening. He suggested changing those diodes.

It could also be a diode on one of the ht supplies that has gone short circuit.

These might not be the diodes that have gone. There are four twisted pairs in total. I just took a pic of these.

JG

 

Where would it show if a diode is burnt?

JG

 

Looks like a textbook full wave rectifier in a power supply. Are those 1n4007's? Replacing all four should be cheap. make sure you have those white lines in the correct direction after replacement.

If you have a multi-meter you should be able to measure AC voltage where the wires come out of the step down transformer and goes into that rectifier. If you don't have voltage there then the transformer has failed. You should be able to measure DC voltage over those electrolytic capacitors. They're there to take out ripple after rectification. If you have voltage there the transformer and diodes are probably good.

I'm shocked that there isn't any heat shrink over those solder connections.

 

Often once the smoke comes out they are literally burnt to a crisp. @Drew just above is right. Do you have or can you borrow a multi meter?

 

It was working fine one day and the next day when I turned it on the 5Amp fuse blew. I tried a couple of fuses but no joy.

So with no power where do i connect the positive and negative of a multimeter to check the AC or DC voltage?

JG

 

Absolutely no burning smell from amplifier,anywhere.

 

The suggested You Tube tutorial would be a good start, however be aware some of these are kitchen sink surgeons, teaching others how to become kitchen sink butcher surgeons. I am a tech, musician, audiophile, who started out as a professional solderer in manufacturing. One clue on the right tutorial is the time it takes to solder. On a PC, the operation should take no more than 0.5 seconds (very fast) and a terminal strip about 2 seconds.... any longer than that, the solder begins to oxidize, and you have cold solder.

The iron should be 25 watt for the work you are doing. The tip should be chisel type NOT round. The tip should be cleaned and tinned.

It is (usually) best to remove the component leads, however this is more easily done by clipping the leads before de-soldering. This way, the lead is more easily removed with needle nose pliers.

Desoldering requires:
1) solder-wick -or-
2) solder sucker

Tip on desoldering: When de-soldering, apply MORE solder to remove solder quickly. Old solder does not melt as easily, so adding a little new solder (not much) speeds up removal. I know this may seem counter-intuitive, but the new solder melts much more quickly which then within a second melts the old solder, and then all of it wicks more quickly and very easily -or- in one easy operation pulls into the solder sucker.

Your solder job will be better when all old component leads are removed, and almost all the old solder removed. You can just clip the leads, but this results in a "globby" looking solder joint, which could be ok electrically, but looks hideous.

You will also need:
3) Weller 25 watt iron or equivalent (Archer is ok)
4) chisel tip (not round)
5) Sponge for cleaning the tip (wet with water or dilute isopropyl)
6) .032 dia or .050 dia 60/40 electronics solder
7) Isopropyl alcohol
8) Q-tips

***Avoid premium solder*** do not attempt with silver solder, nor lead free, as these are harder to work with, do not flow as easily, and have a higher melting point.
A common mistake, Do not add more rosin, it will make a mess.

Make sure the tip is clean and tinned.... repeat ... repeat ... as this is critical.

Many self taught technicians have head knowledge of electronics, excellent troubleshooting skills ..but.. lack good soldering skill. This drives me crazy, watching some of the tutorials (for entertainment) seeing them struggle with the soldering (then "teaching" us how to do it wrong) but end up pulling my two remaining stands of hair out.

Tip on soldering: Do NOT preheat the work. The heat transfer will be slow, and then too much heat conducts down the wire or lead. Heat must be applied quickly, then removed quickly. Too much heat causes the insulation to melt, or component damage. Too much heat, for too long, also oxidizes the solder as I mentioned, and you end up with a bad solder connection. (oxidized solder appears dull and rough)

The secret to a perfect solder job: Apply heat to the work, both the terminal and the wire, then immediately feed the solder. The flat side of the chisel tip tip should contact simultaneously, the terminal, the wire, and the solder. This is the "secret" to good soldering.
The rapid melt of the solder assists in heat transfer into the work (It is bad technique and wrong to preheat the work... as wrongly "taught" by some YOU TUBERS)

A good solder connection should be smooth and shiny, good flow, no melt of wire insulation.
A bad solder connection appears dull, rough and globby, too much solder buildup, and insulation burn. (or PC board burn)

If your solder does not appear like factory, it isn't good enough.

My above advice is not an opinion.
There is no opinion to soldering skills.
Either one does it right, or wrong!

I suggest to practice on something from a thrift store, hopefully a non-working device.
Do not attempt your first solder job on a good piece of equipment.
Soldering skill takes some practice, and most of all the correct technique.

Almost everyone can solder, when using the correct technique.

Good luck,
Steve VK

 

Brilliant! Thanks for the detailed response!

JG

 

Really suggest you get a hold of a meter and make simple tests before ripping parts out.

 

I have a multimeter but i don't know where to measure it?

JG

 

I have a 40W chisel head soldering iron??

JG

 

Hi, too much for the work you're doing, I wouldn't take the chance to damage those filter caps.
I guess my best advice is to practice on something disposable first... before making any attempt on your valuable gear... or just some terminal strips and wire.... but desoldering is more challenging than soldering. A bad desolder results in a bad solder job... practice !

 

Thanks for the great advice?

I have a multimeter, where do I check which diode might be the problem?

JG
JG

 

The red guys are resistors.

 

First of all, be careful, as the caps can hold a charge. These have bleed resistors, so these should be safe to work on.. but never trust it. The caps can be discharged by shorting across the terminals.

Appears to me the way they are wired, you can test in circuit. With the multimeter set at ohms (1k setting should be fine) place the negative lead on the banded side of the diode (cathode) and the red lead on the unbanded end. The diode should conduct at near zero ohms.

Reverse the leads, you should see some resistance... depending on the characteristics of the diode. The idea is to see that all the diodes measure almost exactly the same. If they do, then I would assume they are good.

 

Yes, they are 1N4007's all right!

JG

 

Yes, and what a strange place for it flying in the wind like that? The bridge rectifier will always be chassis/ PC board mounted, or on terminal strips. I wounder what make-model amp this is?