A small 15W or 20W non-temperature-regulated soldering iron is just ok for getting started. The problem is that it's too hot sitting idle and starts to cool down once you start using it.

You will find a temperature-regulated soldering iron does a much better job.

As you have found out, a 15W or 20W iron may not be hot enough to solder large components. You may need to go to a 25W or 35W iron.

For very large components or large ground planes that sucks away the heat I sometimes have to resort to a Weller 200W/260W Soldering Gun.

 

yes i have been looking at the temperature regulated ones not to long ago... i will have to invest in one at some point because like you said its hot when not using and then cools a lot when touching the solder joint... the only way i could get the big cap off with the 20W was to hold the iron straight up and put the board/joint above the tip it worked so i guess i was just on the edge of being to cool. i will have a look on ebay and see what i can pick up

Thanks for your input

Cheers

jayjay

 

Definitely look for a "temperature controlled" soldering iron.

You can buy in the handheld type, I have a toolbox one with a little trimpot and LED on the handle to set the temperature.

The benefit of temperature controlled irons is they have more heat power available, and will use as much power as needed (or as little) to get the job done. So they are gentle on tiny parts and have good power for larger parts and thick tracks.

Another benefit is the tips last longer and stay clean longer, because oxidation gets worse as temperature rises and they only have as much temperature as you dialled in. Crude irons get hotter and hotter as they sit, so they oxidise the tips badly.

 

I use a 33 watt soldering iron for circuit boards, but It's a little too hot. 30 watts or 27 watts would be better, especially now that the leads on resistors and capacitors are thinner than they were 20 years ago. I have a 140 watt gun and a 250 watt gun and a propane torch with a soldering tip

It depends on what you're doing. A Weller 250 is great for soldering a ground to the chassis. Get out the propane if you're doing battery cables or arc welding cables.

I did the study on poly caps. They are all the same if they start with, "poly". It's just that they are way better than the paper caps from the 1950's.

The ceramic caps are basically bullet proof. I've never seen a bad ceramic cap in 50 years, unless it was cracked. The difficulty is that low quality ceramics are available, like stuff that is rated as +80%, -20%
If I remember correctly, the NPO types and the ones with a 7 in them (like X7R) are the good ones.

What else...adding flux is never bad. You can only get it wrong with too little flux. And, don't paint the board with water base flux and let it dry. It doesn't work if you let it dry. Pre-coating the parts and the pads with solder is called, "tinning". It will get you a good solder joint in the worst of conditions because all you're doing is re-melting when you install the part. All the fuss about getting the solder to, "take" has been done before you assemble it.

Repeating MrChips...trying to carry flux on the tip is a mistake. Just a small drop of solder on the tip to get the heat flowing and add the rosin core solder at the joint so the internal flux is fresh at the point you're soldering.

I'm sure I missed a few things, but it was nice rambling on about this.

 

...
The ceramic caps are basically bullet proof. I've never seen a bad ceramic cap in 50 years, unless it was cracked.
...

I agree completely when ceramic caps are in low voltage circuits.

But in higher voltage circuits (like CRT TV h-out stages) they fail all the time. I've replaced heaps, they fail short circuited and open circuited, and a lot just blow themselves to smithereens and you find bits of them floating around inside the TV.

 

The last time I did 2 TV's in the same year was in the 1970's.
My experience might be told to be valid now.

 

I've done enough to have boxes of 1kV, 2kV and 3kV ceramic caps in stocks.

But then my TV fixing days are too old to be valid now too!

Why are TV's so skinny now? Where do they fit the CRT neck and electron gun???

 

I think the Bose sound engineering people got into that. CRT's are now using the folded horn design. The electron guns are at the bottom of the screen and a metalized mylar sheet with thousands of tiny reflectors bounce the electrons from going vertical into going horizontal onto the display plate which is printed with electro-luminescent red, green, and blue emitters.

 

Hi everyone... i need a little help to identify a voltage regulator and possibly a replacement part as i cannot find the exact one that is on the board... nor can i find the manufacturer's marking in many list's i have looked through from google.

this board is an amplifier from a Logitech z5500 and one of the channels is quieter than the rest (front left) so i opened it up and had a look... i have been checking capacitors to make sure everything is ok... then i came across a bad 36 ohm resistor (see pic) the resistor still reads ok at 35.7 ohms but it has bits missing from it so i shall replace it... also a capacitor that is in the same area is reading funny... should be 47uF but when tested it constantly jumps from 40uF to 37uF ... given the +/-20 it is still in tolerance range but i will change it also as i it seems funny that it is jumping such a great range all the time.

i have been reading some posts in the Logitech forum about this amp... someone said if the resistor has gone (which mine hasnt i dont think, just looks burt) then i should check/change the voltage regulator thats with it... the regulator is a 78m18a which supplies +18v... but thats all i know and i would like to get replacements anyway for both regulators... one is +18V and the other is -18V ... but i dont know what current rating they are or anything else other than that they are +&- 18v any help would be aprreciated.... Cheers.

theres two pics for each regulator... in one pic you can see the codes/markings for what regulator it is... and in the other pic you can see the manufacturer's logo

(Had to put it here as i cannot for some reason start a new thread... i keep getting internal system error)

 

so... i have been looking around and i see that these regulators are the to-252... will it be possible for me to change these to a to-220 if i use a heatsink? if so how would this be done? just solder the middle leg to the board where the old regulator was and attach the heatsink?

I was thinking of something like this....
http://www.ebay.co.uk/itm/TO-220-L7...mponents_Supplies_ET&var=&hash=item257b961691

or i have found these...

http://www.alibaba.com/product-detail/78M18A-new-original_574496459.html
http://www.alibaba.com/product-detail/79M18A-new-original_574497036.html

but on the 78m18a in the bottom left corner... mine says 6a and the website says 3a... should i have to worry about this? will the items from alibaba.com replace the components i have on the board? or should i buy the ones that will take 1.5A TO-220 and use a heatsink on them?

Cheers

 

The "M" is the designator, not the 3a or 6a.
Adding a heat sink will not change the internal current rating.
Those alibaba's look right.

 

Hi... thanks for the help... i just thought that if i changed it for a TO-220 then it would be stood up... i thought it might need a heat sink.

i will have to get some of the alibaba's then, just wanted to be sure of the right part.

the lcd display on the control pod is also very dimm (like it mite aswell be off) i will have to check some voltages just to be sure.

Thanks for the help and confirmation.

Cheers

 

You can do it as a TO-220 if you want to. The part numbers will still be 78M18 and 79M18. I am most familiar with LM78M18 and LM79M18, but this is a very common chip, made be a lot of manufacturers.
It couldn't hurt to add a little, bolt-on heat sink, but you might get your chips hurt if you don't attach them to some kind of heat helper.
I'd just put it back the way it was.

 

Why replace the regulator? What voltage is it making on it's output? Where does the resistor connect in relation to the regulator?

The burnt resistor is more likely a symptom of excessive current dwnstream, ie something blown in the amp that is drawing too much current.

A 36 ohm metal film resistor is a pretty simple thing, and if it still measures 36 ohms it is probably still working fine even though the burnt paint has fallen off.

Of course it needs replacing, but I doubt that replacing the resistor or the regulator will fix anything (unless the regulator is not reading 18v).

 

Also, I forgot to say, "Watch out for the pins being in the right order".
One of the best reasons to put it back the way it was is to avoid finding out whether the TO-220 chip has the pins placed differently.

 

@THE_RB ... i checked the regulator yesterday and it is giving out 17.5 volts, but i did not know this before i took it apart to the point where it took time to put it back together and check the voltage. i do not know where the resistor leads to... i will check this a little later on. the sound on the left channel is alot quieter than the rest... i am trying to find and fix this problem. thanks for your input

@#12 ... if i ended up changing the regulator like you said i would just use direct replacements to save possible problems.

the unit actually works ok.. the sub works ok... and the other channels work ok... just one is quieter and the display on the control pod is dimm... i am currently looking into that... see what i can find... thanks for both your help and input.

Cheers

 

Hi... so i just got some new capacitors in today... they are polypropylene wima 100pF/0.1nF

heres the link....
http://www.ebay.co.uk/itm/300965126212?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

i bought them (only wanted one but came in a pack of 5) to replace a ceramic disc capacitor i thought was wrong... as the ceramic disc capacitor reads as 0.220nF when the marking is 101j which from online should be 0.100nF with 5% tolerance... that would mean the capacitor was out of the tolerance range.

the new ones turned up today... and all five read the same value @ 0.220nF ... is there something i am missing here?

Any help would be appreciated because if this is correct then the old capacitor is not bad but i wonder why it reads double on all the caps i have... the 101j's i checked the kenwood graphic did read as 0.100nF so why do these new WIMA's read double?

Cheers

 

...
the new ones turned up today... and all five read the same value @ 0.220nF ... is there something i am missing here?
...

Yep! Your cap meter is faulty!

A cap marked 101 is 100pF, which is too low for many cheap multimeter style cap meters to read properly.

Also your initial fault assessment was wrong, ceramic caps do not fail in a way that doubles their capacitance. They can go open circuit (reduce to very low capacitance) or maybe short circuit. And i did say earlier in the thread that the reliability of ceramic and poly caps is very good, in a low voltage circuit. There should be no need to check them for failure unless they were physically mashed or something.

If you want a good cap meter for small caps there is one here;
http://www.romanblack.com/onesec/CapMeter.htm
which measures down to fractions of a pF. Kits are available (I don't make any money from kits, they were produced by someone else.) Or you can build your own from the details on my web page.

 

ok... so i broke out the manual for my test meter which is a fluke 287 and took a screenshot of specs for capacitance... i have attached it to this post. my meter should be able to read those values... just when it is idle (not testing anything on cap mode) it jumps from -0.142 -> 0.137 and i should tare it use REL but even then... it still jumps... i guess i will get a meter that reads caps better and just use this for higher value caps... i will take a look at your link shortly... thanks for that.

i did read that you said they do not often break down in low voltage circuits and this was noted... its just because it had been bent over flush with the board both the legs had cracked and i was not sure if it was ok... so i checked it.

Thanks for your input.

Cheers

 

It would be nice if multimeters were good at reading real small caps but generally they struggle.

It could be the leads adding a lot of cpacitance, does it have the ability to zero-out the leads?

It's pretty common for ceramic caps to have broken material right where the legs enter. But they are a reliable part, consisting of a ceramic disc with a round metal coating on each side, and a leg on each side.

There's really no mechanism where they can fail to double the capacitance. I've even seen them with the top part of the disc broken off (like a "moon" shape), and the cap working perfectly but at 20% less capacitance (because the plate area was reduced).