Lousy electronic servicing job...

[Mini-Me]

Hi all.
:)

I collected a Toshiba radio-cassette unit from a client who said that they had already taken it to another service shop for repair, and paid 60 bucks to have it fixed, but the same problem still exists.

The problem was that the volume would cut in and out completely as you touched the volume control.

When returned as fixed, it had the same problem.
The client could have taken it back to the fella, but he told me that he thought the guy was a bit of a con-man to him, so decided not to.

The first thing I checked, was the volume control and it's connections to the circuit board.

Check out this image of the "Repaired" radio, as I have just now come across it:

http://img90.imageshack.us/img90/1958/dryjointspl0.jpg

This is the PCB where the volume control is soldered.
The two rows of 3 pads are the volume control connections(it's a stereo radio).

See anything interesting?
Like the dry-joints on all the pins?

No self-respecting "Technician" worth his or her salt, would ever miss something like this.

Amazing what you come across in your career sometimes...

[PrntRhd]

Yeah, we call that a cold solder joint, but same difference, it becomes a switch instead of a conductor. Wrong temperature when the board was soldered.

[mjc]

I remember my first electronics lab...if that prof had seen that kind of solder job, the lab would have been an F (minus...if the scale went that low).

[Paleo Pete]

Are all the solder joints on the entire board that dull? They don't look shiny enough to me to be decent, anything that dull looking would be a big red flag to me. Solder should be bright, smooth and shiny. Everything I see in that pic is fairly smooth, but dull and gray, not shiny and silver. I'd check every solder joint on the board, those might not be the only loose ones.

Makes me wonder about QC in most electronics manufacturers these days, I fixed a Dean Markley bass practice amp not long ago, same problem but on two pins of a transistor. Dan Electro effects pedals and Zoom effects both have a long time reputation for cold solder joints, my RMS practice amp had the same on the input jack, which is why I got it free, fixed a friend's practice amp by simply resoldering a couple of contacts...Most any electronics tech will agree that the first thing to do in troubleshooting any repair job these days is look for bad solder joints. And I'm nowhere close to an electronics tech, I Just know how to solder...quite well, in fact, and how to test a few components. Seems to me an incredibly expensive machine designed to solder an entire circuit board at one time lots quicker than a person could should at least be able to do a proper job of it.

So why is it my 30 year old Fender amps both had no cold solder joints and still don't, even after being subjected to years of road trips in trailers, being dropped and beat around by people in a hurry to get the night over with? Ditto for both my Peavey amps...Manual soldering done by PEOPLE who can look at the thing and tell it's right before moving on to the next solder point. And at least half decent QC. Since they have been subjescted to such abuse, I went ahead and resoldered everything in both Fender amps, as a preventative measure, solder joints working loose is a common problem, but due to the nature of their use, not shoddy workmanship or quality control. That kind of vibration would probably rattle anything loose after 30 years...but both my amps were still in great shape when I checked them out. One had a broken leg on one capacitor, but actually broken, not bad solder. Every capacitor in the other one was dried out after 30 years, normal for electrolytics. But the solder joints were all in better shape than anything I've seen new. For that matter I have patch cables I made myself over 10 years ago that still have solid connections, even after being stepped on, yanked out of amp jacks, you name it for 10-15 years. But a billion dollar corporation can't make a radio that will hold up half that long...

And they call this progress? These things are made of cheap plastic, cheap labor, bad QC, cost more, anything with a remote control is more than a lot of people can handle to set up, and they hand you this kind of garbage for twice the price it was 10 years ago...I can't believe people still hand over their hard earned money for such complete trash.

This is what we get for letting huge corporations turn us into a disposable society.

Yeah I have an attitude... :D

[yawningdog]

Those aren't bad solder solder connections, those are OLD solder connections. In other words, they probably looked fine (or at least better) when the machine was new.

Turning a device on causes the current to heat it up. Turning it off causes it to cool. This heating/cooling cycle causes expansion and contraction in the joint which causes the fillet to harden and eventually break. A well engineered circuit will draw less current through its soldered connections, but other than that it's very hard to stop this kind of thing. It almost certainly has nothing to do with vibration.

This problem seems obvious when you zoom in on it and snap a shot, but on a circuit board with hundreds of these things on it, I wonder how many of you could have found it. And in my experience, customers aren't always so eloquent as to say "The volume would cut in and out completely as you touched the volume control." A more likely description would be "Something is wrong with the sound" which is a good deal tougher to diagnose.

Sorry Pete, but I couldn't disagree with you more. A machine is infinitely more capable than a person at producing high quality solder work. They don't come in drunk on Friday afternoon or hung over on Monday morning. And my first troubleshooting step was never to check the solder joints. It was to try and reproduce the problem. Problems like this are very often intermittent in nature which again makes them hard to diagnose.

This is a cassette player anyway. I have this cool new machine called a CD player, and it sounds a lot better than an old cassette, and the media lasts a lot longer.

[Mini-Me]

This is the original wave-soldered board.
The fella that my client took the unit to, never delved deep enough into the unit, to discover the dry-joints in the first place.

A volume control has practically no current flow at all - it is only used as a potential divider for the input to the power-amplifier, and although there is a current flow, it is negligible - in the order of a few microamps.

While it is certainly true that current flow heats up connections - especially badly done ones, this is not one of those cases, as there would never be enough current to cause connections on a volume or other sound control like this to fail due to heat.

It's very common to see most PCB's(printed circuit boards) with this dull type solder, as the solder mixture contains more lead then tin, in order to keep the melting point lower then a solder with a higher tin content, and to keep the heat-stress to a minimum as the board passes through the solder wave at the factory.

You must be having bad luck, yawningdog, as I have always been able to get satisfactory explanations from my clients as to the fault symptoms.
If they only say "Something is wrong with the sound", then I would be asking them what it was, or to describe it in their own words.
:D

It almost certainly has nothing to do with vibration.

I 40% agree with you.
True - heat will generally cause these kinds of dry-joints, but it is also very easy to break these connections on headphone sockets, power sockets, RCA line-in's or outs, Video RCA's, Mic sockets, PCB-mounted push-buttons, rotary pots or sliders - anything which is wave-soldered at the factory, which is pretty much everything...

It's not always heat - people can be rough with things, and this force is transmitted down to the connections and can cause them to break.

I have fixed God-only knows how many iPOD's headphones sockets with dry-joints like these, as people tend to ram and yank the headphone plug in and out, and it ends up breaking the SMD headphone socket connections from the PCB - heat not the problem here, it's rough handling!!!
:D

And my first troubleshooting step was never to check the solder joints. It was to try and reproduce the problem. Problems like this are very often intermittent in nature which again makes them hard to diagnose.

True. I spoke to the client when I went to look at it, and wiggled the knob and reproduced the fault, so knew that the back had to come off it to see why. I've got so used to tinkering with things to see if I can get it to misbehave, that I totally forgot to mention that this should be the first step - but you usually have to take it to bits anyway! :D Intermittent faults are sometimes a big pain in the posterior - I totally agree - I chased one in a TV once for about 3 weeks - it kept coming back with the same problem - Grrrrrr.

This is a cassette player anyway. I have this cool new machine called a CD player, and it sounds a lot better than an old cassette, and the media lasts a lot longer.

Owwwwwwww
Sarcasm.
:D

Yep, it is a cassette unit, but many older folk are still very sentimental about their old radios or stereos, and so long as it is not a write off, there is money to be made servicing it - even old fossils of technology like this.
:p