basic printed circuit boards

tuckermot

tuckermot

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Hi all

I am interested in going back to basic,s involving pcb,s..My object is to be able to do basic simple repaire,s to radios, monitors ect. I know the world of pcbs is vast and i want to start at the begining,i am finding it hard to find what ref books to buy or where on the internet to find this information like how to read a pcb wiring diagram properly and understand the markings of the components ect.I have items at home that have stopped working and i would like to have a go at repaire.give me a house and i will bash it but give me a radio thats stopped working apart from confirming a supply to pcb i have not got a clue please if any one can point me in the right direction please private message me

cheers

Rich
 
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hi rich. My mentor from when i was training, was not only a spark, but a qualified video, TV, radio and microwave repair engineer. He said that he spent a lot of time and money going to college at night to learn (back when VHS and betamax was still about),. he quit his business repairng these items as it was becoming unprofitable, as its far easier to buy a new PCB, than to fault find and then repair it.
If your interested in this for academic/hobby reasons, then go for it, but not for financial gain
 
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Hi john boy
i want to do this for non financial gain just get frustrated that i can do Installations and test with ease but when it comes to making a non working telly work i am at a lost .i understand most pcb,s are throw aways due to the llabour cost ect to repaire it just seems its a skill that is dieing andtis a real shame because the old school boys & girls who could fault find pcb,s are very clever and i respect what they do they are allways under rated in my eyes
 
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just want to repaire my own stuff ect hence no labour cost,s just finding it really hard to find the information i need to help me achieve this john .someof the components are pennies to replace so it is some times cost affective to repaire allso satisfaction in making a non working item work again is priceless
 
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tuckermot,
I suggest that if you are not familiar with the components used, you first study these, and how to recognise them.
There used to be paper cross reference books, these days the web is easier.
I had a breakdown before Xmas on a customer pcb.
Maker gone.
Needed it up and running before Xmas as it was a standby pollution control system.
I had never worked on the board or the system before.
You just need to understand what the I/O does then find out what it is not doing and work backwards.
Identifying each component and its function to be correct before moving on.
You'll need a good scope, good high input impedance a.c. & d.c. DMM, good soldering irons and de-soldering tool, some solder wick, tweezers of assorted kinds, and a good magnifying glass if your eyes are approaching anything like mine!!!
That is without the signal generation kit, an LCR meter is useful, as is an earth free work zone and "safety isolated" supply.

Before anyone says replace it with a new one, it is part of a system, which was custom built, so lead times on a replacement system would be 12-16 wks!
Costs would be well in excess of my couple of hours tracing and rectifying the board fault.
 
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With multi layer boards it’s not really viable.

I had a nice little sideline repairing photographic studio equipment. It got very difficult sourcing components without going to the OEM, they would rob you blind.
 
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one of the problems you face is that you can't test a component in situ, due to parallel paths. also, it is very easy to destroy modern pcb tracks when desoldering components. 40 years ago you could use a poker heated in the fire, but modern pcb's are designed to be throw away. most of the time it's only worth it if you can identify the fault quickly and replacement components are cheap and easily obtained. apart from your wanting to be able to do a repair for your own satisfaction, that's about it, really.
 
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There is an electronics forum here: Forum for Electronics They do have various eBooks available but you'll need a number of points in order to access them. Failing that you could try working your way through this (not sure it's that compreshensive, but looks to cover the (very) basics): A Rough Guide to Electronics so would be a start.

About the only thing I fix these days is power supplies (and only some of them). As already said, not commercially viable though.

Edit: just checked and it looks like the eBooks have been removed from the edaboard forum.
 
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I can understand where you are coming from Tucker......i have come from an engineering background..(heavy industries)....and enjoy repairing mechanical stuff that i have stashed away that you always promised yourself that you would "get up n running"....i know that the world of PCBs is a but different from vintage lawnmowers and old power tools n all that lot.....but still good fun to watch how it all comes apart and how it was constructed though isn`t it.....and then when you put some power....(or petrol) in it ..and it fires up...sometimes for the first time in many years........
 
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tuckermot said:
Hi all

I am interested in going back to basic,s involving pcb,s..My object is to be able to do basic simple repaire,s to radios, monitors ect. I know the world of pcbs is vast and i want to start at the begining,i am finding it hard to find what ref books to buy or where on the internet to find this information like how to read a pcb wiring diagram properly and understand the markings of the components ect.I have items at home that have stopped working and i would like to have a go at repaire.give me a house and i will bash it but give me a radio thats stopped working apart from confirming a supply to pcb i have not got a clue please if any one can point me in the right direction please private message me

cheers

Rich
Click to expand...

Hi Rich: Take a look at www.electronicrepairguide.com you should find everything you want on there. Also an addition to Pauls earlier list is a Capacitor ESR meter, available from the above site. I put off buying 1 for a long time prefering to do things the old fashioned way, but since buying 1 I would'nt part with it.
 
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No problem mate, my Daughter just reminded me that I bought her an Electronics training course on CD ROM a couple of months ago.
If it's any good to you then I can do you a copy of it.
 
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I will sort you out with a load of material at the start of the new year, with multi layer boards its not much more of a problem than with single or double sided boards with plate through hole, the only real problem with multi layer boards is either heat damage(over current through tracks) or manufacturing defects/water or chemical ingress and corrosion, both of which can only be seen with specialist thermal imaging or x-ray testing equipment, and only the manufacturers have that......if a multi layer circuit board has a board fault (the actual sheet of fiber glass and printed tracks) such as a broken or burnt through track, then that can never be repaired even by the manufacturer, and they will have it shredded and recycled and just manufacture a nice shiny new PCB to replace it...as the boards are bonded sandwich construction.... You should use what is referred to as the "half split method" when fault finding circuit boards.....then there is learning about the relationship between components, Logic Element components, microprocessor/micro controller input and output signals and anything that can interfere with them and cause the microchip to shut off/power down or give out a non-useful output signal that may make other components power down or malfunction etc... You should be keen to work on de-soldering / reworking small sized surface mount components and be willing to make up a number of small selection boxes of components as well as a small tool kit of good quality electronics tools, I would say that you can build a very good tool kit for about £200-£220.00 ($300) and a good shop-available multimeter should do for your purposes....if you would want to buy an oscilloscope and it is only for hobby use, then don't worry about buying a big expensive benchtop oscilloscope or an expensive handheld Fluke one......a good hobby use one would be a Velleman HPS-10 or HPS-20 (10 Megahertz or 20 Megahertz) which is single channel (single input probe) and these are available in Europe, the UK and the USA for about £130.00 ($200.00) I am not sure where you stay so that's why I mention Dollars...
 
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I've repaired loads, started off with electronics at primary school.
I've always found household items with blown capacitors in the PSU the most.
Remember though that a blown capacitor or resistor is usually caused by something else, could be overvoltage, another faulty component, lightning strike or user error!
 
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Yep, I'd agree about the failed caps being a common problem. Electrolytics have a shelf life and will fail in time anyway, so not always caused by another problem. Although they don't always fail completely, sometimes just their spec will change, which is often enough to cause problems.
 
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Hi Tuckermot,

Repairs of complex electronic items such as radios, TV's and Hi-Fi's etc, especially down to component level is really something you would do as an experienced electronics engineer. I don't mean to sound like I'm throwing cold water on your ambitions but it's not a skill you're going to pick up in a few months of spare time and a couple of reference books.

If you seriously would like to learn about electronics I would suggest you first become a Radio Amateur. This is a fairly short, cheap and simple course that is obviously aimed at basic radio competency but there is a certain amount of theory thrown in. More importantly is that it will introduce you to people who are into amateur electronics and are enthusiastic about passing on their knowledge. It will also give you access to a world of free information and support from like minded guys all over the world and one of the best starting places there is for learning electronics.

After becoming a Radio Amateur you could also then do a night-school City and Guilds course (ONC) or a correspondence course in electronics at a local college or at home. This kind of course would be a whole lot easier with some support from other enthusiasts.

I see the 2011 version of the ARRL handbook now includes chapters on PCB layout and old equipment restoration etc so maybe start by grabbing one of the free copies that are floating around on the intertubes ;-)
 
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Get yourself a good analogue AVO (8 or similar, cue flamewar analogue V digital!)
and when you start use it, but more than the AVO use your eyes, and dont look for complex faults, because IME 80% of faulty pcb's you can see the fault. look for electrolytic capacitors with swollen cases and pointy swollen tops. browned resistors and above all cracked tracks caused by vibration, where a too rigid cable or connector joins the PCB. At the chip level I have seen many failed chips actually with a visible (tiny) hole in the body of the chip. any modem with lightning damage invariably had this! but you wouldnt notice it unless you looked carefully! Use your eyes first, then the AVO, and finally the soldering iron (or the hammer:-) Be prpared to remove components (especially diodes) from the board to test them seperately. Having given this advice , recently I have stripped many units that are so poorly and cheaply made that they are obviously BER. Components tend to fail in a current avalanche, and you would be better off repopulating the entire circuit board, or dumping it.
phil
 
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and a favorite fault on older circuit boards is the good old dry joint, where the solder has cracked around a component leg. as hermetic has said, use eyes first, coupled with a good magnifying glass. you'll be surprised at the faults you can see without any sophisticated test equipment.
 
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I was a electronics engineer but don't really bother now. As most people have said, the boards are throwaway as the time and effort is not worth it. Most circuits boards are multi-layered and with surface mounted components you will need a variable temperature solder station as well as a desolder station with very fine tips and a good magnifying glass, solder wick/braid or pump is ok for the older stuff. Use silver solder as it has a lower melting point.
Maplins catalogue have some pin outs of the most popular components and there are data sheets available if you search the net.
To fault find down to component level, the biggest hurdle would be to learn about the charactistics of the components, the difference between silicon and germanium, the difference between N-P-N and P-N-P transistors and so on.
 
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topquark said:
Yep, I'd agree about the failed caps being a common problem. Electrolytics have a shelf life and will fail in time anyway, so not always caused by another problem. Although they don't always fail completely, sometimes just their spec will change, which is often enough to cause problems.
Click to expand...
dried out capacitors happen with time if the machine/appliance is left turned on long term, such as a DVD/BLUE RAY player left on standby for months on end.....or a phone charger left plugged in all the time even when not in use with the phone just being connected and disconnected...... Dry tracks and Dry solder joints are common as well with things that are left on long term, particularly in power supply stages closest to the mains side of the appliance/unit where thermal cycling causes tracks and solder to lift and peel, vibration from mains frequency hum also adds to the damage caused by loosening solder and printed circuit tracks that may already be warm/hot and therefore softened...... Integrated circuit chips (IC'S) such as Graphics chips, micro controllers, Audio decoder chips and Amplifier chips and the heatsinks attached to them can lift up off of the tracks/pads that they are soldered/pasted onto and cause failure which is easily repaired......if a heat sink is attached with clips and /or thermal paste and works itself loose, a great deal of semiconductor devices (IC'S) will shut down due to thermal overload protection circuits designed into them to prevent irreversible damage, so some may work for a short while, shut down and latch into a power off state until the unit is swithced off and then back on again (providing the temperature has dropped enough) other IC'S might turn on and off intermittently with rising and falling temperature...
 
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For electronics repair tips, primarily TVs, take a look at eserviceinfo .com
There are lists of faults per model (I've contributed a few), plus many service manuals.

A handy hint is to use the model/chassis cross reference - a number of manufacturers "outsource" manufacturing, so you can find the same guts in a BUSH as you do in an entry-level TOSHIBA for example

My advice is to test voltage regulators first for "non-working" faults - some won't work if the voltage is just a fraction low - eg a TV stuck in standby because the 3.30V rail was just 3.15V

Simon.
 
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tuckermot

tuckermot

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