Electronic Machinery for PCB Repairs

What kind/type of repairs are you doing?

I have perfected a machine that will break circuits boards, you can run it backwards...

Never, Never Repair a circuit board! in gets taken to a remote site by a service engineer, appears to run OK but by the time he has got back to base it has failed again.

Result, upset customer, expence of second trip, customer buys replacement machine from a different company next time.

However obvious and trivial the circuit board fault is TRASH IT repaired circuit boards can cost you a small fortune

I tend to agree with Murpheys. I spent around 20 years as a field engineer and have seen exactly this happen. Another problem is that if you repair boards the ones that contain intermittent faults will all migrate towards you spare parts reserve leaving you with nothing but faulty boards. When you use these boards to repair equipment or diagnose faults you end up introducing additional faults and this makes the field engineers job impossible. If you do go ahead with board repair the only way you have the slightest chance of making it work is to have an impeccable record keeping system that tracks the history of every board of that type in existence, where it's been, how it was used, why it was replaced, what has been done to it and its association with other boards.

Another problem is with multi layer boards and surface mount technology you can end up doing more damage than you fix when you attempt to replace a component. You will also find that many boards contain proprietary components that you will most likely find impossible to source unless you are the manufacturer.

All this makes it very expensive to do properly and that means unless the boards are very expensive or hard to get it then they are general uneconomic to repair. Plus don't forget the hit your reputation is going to take when you start circulating faulty boards.

Although it probably difficult to implement I think this would be the best way to service machines in the field ( I am assuming the machines are fairly new, are valuable and are making money for the owners).

The visiting technician should discuss with the owner before traveling and take with him appropriate VIRGIN boards, as these are probably not avaiable he should take repaired boards that have been well tested, the machine should be got working with these repaired boards and the technician stays on site while brand new ones are obtained from the manufacturer, this may seem an expencive way of fixing things but it would be the best in the long run.

If the plant has a resident technician it may be possible to leave and arrange for him to fit fit the spare when it arrives but this may be a little risky unless he is very honest and trustworthy

I'm saddened to read such negative comments on PCB repairs. I learned my trade many years ago in the Royal Navy and we were taught to repair or re-manufacture anything - can't always get spare parts in the middle of the ocean during a war! The equipment included avionics and guided weapons. I eventually ran a repair worshop supplying boards to 80 service engineers throughout the UK. We kept simple records for each repair and any 'returns' were closely examined to find out the reason and it was a matter of personal pride to keep this to an absolute minimum. We are talking about electronic equipment/PCBs for major supermarkets and 25 years later they are still happy customers. In many cases PCBs are returned by engineers with no fault but you still have to test the board fully before returning it to the loop - you'd soon be bankrupt if you didn't do this!

One great advantage of repairing equipment in-house is you can identify and modify poor design or fit more reliable components during the repair, we once cleared a long running keyboard problem by fitting PCBs with a 16 pin DIL socket during the repair and issuing engineers with replacement ICs, (the IC was blowing apart whenever the keyboard light/switch failed) - this saved us thousands, delighted the customer and gave engineers a welcome quick-fix. A properly repaired PCB should be more reliable than the original because you can also carry out modifications which the OEM has introduced over the life of the equipment - this is vital where the OEM is a direct competitor to your own Company and your service contract includes such 3rd party systems. We used to buy a few 'new' spares each year, identify and analyse any modifications and then include these into our repair - in many cases the modification cured the fault for good!

I now run my own small profitable PCB repair business and have received only 5 'returns' from over 3000 repairs in 6 years. Many of my customers operate older electronic systems in the back of beyond, including some in Africa where second-user equipment tends to end up so I hope I'm providing a useful service which will continue until I can no longer aim a soldering iron!

Well said Tom!!!

Of course you should repair PCB assemblies...

How else will you learn of the design flaws and component changes which have made the PCB's fail!?

In my business I've done exactly that over the 23 years, I've found that a manufacturer has changed a component to a cheaper version to save money, without realising that the operation of the assembly would be affected, until it fails! So I've built a healthy respect from customers, so much so in cases, that they would rather have me fix their PCBs than send them to the manufacturers to be replaced!!

John.

Component density and small size have made most electronic devices impossible to repair economically. At the same time, low parts costs and automated assembly make whole boards very low in cost.

For example, a tech here in Canada gets $25/hour. A mother board worth $75 fails. This board is a 4 layer board covered with surface mount parts on both sides = non repairable.

What we do is send them back to the manufacturer. They have an Automated Test Machine, a bed of nails tester they use which isolates the fault and they decide if they will fix it or not. Often they scrap them.

The good old days if 1/2 watt resistors are gone forever.

In truth, every case needs to be judged separately, and many things are scrapped by the economics.

Hi Tom,

I was told to buy a new controller box and it will cost me over $2,000.00. I am repairing this small 12V. circuit board myself. The board contained 2 small relays, relay timer, 6 different capacitors and resistors, AC rectifier, solid state relay and mosfet resistor. I hopes it will works after replacing all these items on the same board. All component are from the same manufacturer and some are newer versions. I would like to know of what you think? Look forward to hearing from you.

Thank you,

Thada

You should be ok doing that although I wouldn't change all the components at the same time - very expensive! I always replace components with exactly the same type and manufacturer - You sometimes get microprocessor components which will only work properly with others from the same manufacturer, (Hitachi is one example).

When repairing/fault finding always replace components one at a time, (unless obviously damaged) and keep a note of where you've got to so you can pick up the fault trail after an interuption, (I tie a label on the PCB and write on it all the tests).

When you find the defective component open it up to find out what failed - this is very important in the case of EM Relays where you can check contact wear. Repeated failures of one component could suggest a more robust type or investigation of the associated circuit, (input and load).

Keep a note of the fault with the circuit diagram to help you on the next one. It also helps if you can find a known good PCB to write down the resistances, voltages and waveforms at key points in the circuit so that you check the next defective board more easily.

Whenever possible carry out fault finding:-

a) Physical inspection of solder joints and components using an eye-glass and good light.

b) Out-of-circuit electrical resistance checks at key points in the circuit.

c) In-circuit tests ,(hopefully the first two procedures will have spotted any short circuits which would cause further damage).

I am not sure whether or not this has been covered yet but it's important so I will go over it again.

Over the last decade of so and to a lesser extent prior to that there has been an ever increasing use of microcontrollers. The problem with microcontrollers is that you can't just plug a new one in as they need the appropriate program to be loaded onto them before they will operate. The program is usually proprietary software so even if you manage to get a copy of it chances are that you will be breaking the law by reproducing it loading it onto another microcontroller.

You are going to see more and more of these as they are becoming cheaper more powerful and simpler to use so be prepared.

Another hassle you will come across is PROMS that again contain software that you may or may not be able to get a copy of and again copying it may be a copyright infringement to reproduce.

Modern electronics is becoming more and more digitally based and microcontroller driven so trying to repair these is going to be difficult and may even be illegal so tread wearily as the field is littered with traps and pitfalls.

A worthy attemp to try and save $2000 but I hope for your sake you do not change all the components and then find the fault lies in the print circuit.

Tom,

Thank you for your input. I did just that, by replacing one component at a time. I am still stuck on an output to operate a dc motor. I think my problem is: "NEC Photocoupler" and "NTE Silicon Controlled Rectifier". Perhaps you know more about these 2 item. In the mean time, I will check on Hitachi products.

Thanks,

Thada

You are speaking more of failure analysis rather than outright repair. Failure analysis is of course important and should be carried out whenever needed.

As to repairing the boards it depends on the cost and availability of a replacement. If at all possible I would prefer to use a new board over a repaired one. With many of the mass produced boards out there at the moment it's just not worth repairing them. Don't get me wrong there is a place for the repair of boards especially when we talk of expensive small production hard to obtain ones.

If you have boards that are being used by field engineers to carry out both repairs and fault diagnosis then there are several things to consider. Many of these boards may come back as only suspect rather than actually being faulty but they may contain an intermittent fault. I have on many occasions had a board returned from a repair facility with No Fault Found only to have it fail within 24 hours. The problem is you have no way of knowing which board has an intermittent fault and which is actually OK unless you can replicate the fault. Over time this can lead the to migration of any boards with intermittent faults to the stock a spare boards making the field engineers job so much harder. You may replace a board as a diagnosis step only to end up introducing a new intermittent fault to the equipment you are trying to trouble shoot.

One thing that I failed to mention that is becoming more important is handling procedures. Many high density low power devices are extremely sensitive to static electricity and can be damaged through improper handling. Electro Static Discharge Damage can be a real nightmare as frequently causes intermittent rather than hard on faults. Many companies make their employees sign declarations that they will use proper ESD handling techniques whenever they handle boards. If you can't be 100% sure the boards have been handled correctly at all times you could be in serious trouble.

Sockets can be useful but unless the component needs to be replaced on a regular basis I have found them to be more of a nuisance than a help. Some years back I worked on a PLC system that used sockets extensively to aid repair. In the end we ditched the sockets in favour of soldering the components in directly.

Repairing boards is possible I just don't think its economic and desirable in the majority of cases. Keep in mind though it involves a hell of a lot more than just replacing a faulty component

Well, okay if you're talking of mass produced boards for the mass market, yes! there isn't any point in trying to repair a surface mounted multilayer board that only cost a few quid to replace...

But for the instrumentation that we design and maintain, the boards are usually hard to get replacements for, also the company might have to stop production while you have the board, so waiting for a week for a replacement is unacceptable and they will happily pay the cost premium to have the board repaired... The same with the medical monitors we have designed and made... The patient can't wait for a lengthy time!!

Failure analysis is an ongoing facet of the job! As I've said in a couple of cases we suddenly had the same fault appear on boards and so I looked closely at what was causing the fault, only to find that some guy in purchasing at the manufacturers had decided to replace a component with a cheaper version causing problems... The manufacturer (Switzerland) wasn't interested in changing its board building and so companies came to me, sometimes with brand new instruments for me to replace the still working component to make it a more reliable board...

John.

Hi John,

Yes I agree, what you are talking about comes under the category of the hard to get or expensive boards so repair becomes worth looking at.

As for the Swiss affair well what can I say. When you see management making decisions like that it usually means the bean counter infection has spread so far that it is most likely fatal. You will probably get a lot more of their boards to repair in the near future due to lack of availability when they go broke.

I just get annoyed when people (not you by the way) think that replacing the faulty component is all that is involved in board repair. You cant just use an automated diagnostic unit, replace component X and think it's fixed.

Oh yes Masu..... I well remember one of my worst faultfinding jobs at Marconi Instruments in the mid 70's....

I was a designer there and had worked on the spectrum analyser (TF2370) the production department and the design departments worked together in those days, so when production had a nasty fault we would get involved...

This particular fault was caused by someone removing a PCB with the power on, unfortunatly it caused two component failures on different boards... repairing one board just caused it to fail again.... it was a long job but I found that you HAD to repair both faults at the same time before switching on or both boards would die again!!!

It really was a swine!!! But the satisfaction of having my name on a specified operations report to production for them to refer was great!!!

Those were the days before the 'bean counters' took over and tried to make the books look nice and tidy with a healthy short term balance for the investors - medium term didn't matter to them !!!

John.

Cor - that stirred things up a bit! I agree totally about the multi-layer SMD populated boards - they are best avoided like the plague, but the older though-hole components are ok if you use the correct tools and have masses of patience. The smallest component I work with is a new solid state relay, I build these using semiconductor die, this has a circuit about the size of a postage stamp, (28 x 32mm) and it switches 530Vac at 80amps, get it wrong and the whole street knows about it!

All the boards I repair are tested for days at the same temperature and loading they live with in real life - I even put power supply boards in the freezer for 24 hours before testing to simulate the temperature a petrol pump sees when it is switched on in winter. I found a design flaw by this method - the data comms relay on the PSU board was hot during the day but when it cooled at night a thin layer of lubricant settled on the contacts and it took a couple of hours before it would 'talk' to the kiosk - usually minutes before the engineer arrived to find everyting working!! Having worked as a tech support engineer I have a healthy respect for these guys working on a busy forecourt or aircraft in sub-zero temperatures one job then reprogramming a computer at the next site!

I found through long experience that faults reported to the design office on paper rarely achieved anything but once we started doing investigative fault finding we were able to submit fault reports together with hard evidence AND a suggested modification to solve the problem. It was amazing how friendly and cooperative the design lab and production became once we started doing this. We kept the engineers in the picture with good feed-back on their faulty boards and had a chuckle at their cock-ups too, builds up a good team spirit.