I am new to electronics but I do fix appliances to earn $$ on the side which is why I'd like to take this up to the next level. I come across customers who need their PCB or PCBs repaired. I've been successful with many but I have no way of testing them other than to re install back into appliance (refridge, dryer, washer, etc...). Do I need a power supply and if so, how does one test a PCB with it? I Probably can't do so which leads me to asking ya all "what can I use?" Thanks in advance for everyone's help!!!!!

 

There is not simple answer to your question.
Every appliance is different. It depends on the specific appliance.
One solution is to have another appliance that is in working order which allows you to swap boards as well as to compare voltages.

 

To test a board you need a detailed listing of all the inputs and outputs, and the board operating characteristics and functions. Since that information is normally not obtainable, the best test is usually to put it back in the appliance and see if it works, as you have been doing.

 

One solution is to have another appliance that is in working order which allows you to swap boards as well as to compare voltages.

Way too obvious but not so obvious.

Good reminder!

 

To test a board you need a detailed listing of all the inputs and outputs, and the board operating characteristics and functions. Since that information is normally not obtainable, the best test is usually to put it back in the appliance and see if it works, as you have been doing.

Even insiders seem to have access to service manuals that do not go into many details nowadays.

Last I checked were service manuals of Epson printers. Recent ones stop at board level.

 

Even insiders seem to have access to service manuals that do not go into many details nowadays.

Last I checked were service manuals of Epson printers. Recent ones stop at board level.

Modern electronics require quite a large operation to make board servicing cost efficient. That is the result of smaller and denser electronic packaging. The use of custom chips and ASICSs also adds to this. It is hard to replace ICs with funny numbers/markings that are not public available.
As in your example with the printer. The bean counters may have found it may cost less to just scarp a defective board than repair it. For the service tech it may not be required to go beyond board level anymore. In cases there refurbishing will be cost effective the boards are sent back to the factory or centralized locations

 

Take for example attempting to repair a PC motherboard. You never see a circuit schematic for those.

The last time I saw one was for an Apple Macintosh in 1984, and it wasn't even drawn or published by Apple. I still have mine.

 

Modern micro-controllers have reduced repairmen to, "black box" changers.
There is no way anybody is going to give you the programming for the chips, so you just have to replace the board.

I have spent most of my professional life trying to protect my customers from intentionally unrepairable components. I am failing.

 

There is not simple answer to your question.
Every appliance is different. It depends on the specific appliance.
One solution is to have another appliance that is in working order which allows you to swap boards as well as to compare voltages.

But it is possible? The problem is, we don't always have access to a working board. What if I were to use a low amount of current and a thermal thermometer to check the failing chips?

Thanks!

 

What if I were to use a low amount of current using a power supply as well as a thermal thermometer to check the failing chips?

 

You're grasping at straws.
First, a lot of brain boards work on 5 volts. A, "low" amount of current from the AC power line will blow them up instantly. Second, a lot of failures are open circuit...no power is flowing so temperature sensing will get you nothing.

 

@Pane77
If you feel you can make a living out of doing this. Just go for it. It may very well be that you can create your niche service product and get money out of it. A problem I may see. Is that the use of programable logic (microcontrollers etc.) is very popular in almost all types of electronic products. The problem with such logic is that it is preprogrammed from the factory. So just replacing them will not fix the problem at all. The solution to this may be to have a stock of scrapped boards and cannibalism them for parts.

 

What if I were to use a low amount of current using a power supply as well as a thermal thermometer to check the failing chips?

No. It would not work.

There is no low voltage test for checking circuit board.

 

I tried that...once. I figured out a compressor protection board from Carrier. Replaced a transistor and asked for half the wholesale price of the board ($37.50). The guy I fixed it for wanted to pay me 10 cents for the transistor.

 

I tried that...once. I figured out a compressor protection board from Carrier. Replaced a transistor and asked for half the wholesale price of the board ($37.50). The guy I fixed it for wanted to pay me 10 cents for the transistor.

Customers are like small kids and must be handled that way. Give them an option they can not resist. And they will take that bait. You should have said, I can offer you two options. A using a brand new board, or B a refurbished one for half the price

 

The guy I fixed it for wanted to pay me 10 cents for the transistor.

You can remind him that a swing of a hammer is very inexpensive. Knowing what to hit with the hammer is the expensive part.

 

@Pane77
If you feel you can make a living out of doing this. Just go for it. It may very well be that you can create your niche service product and get money out of it. A problem I may see. Is that the use of programable logic (microcontrollers etc.) is very popular in almost all types of electronic products. The problem with such logic is that it is preprogrammed from the factory. So just replacing them will not fix the problem at all. The solution to this may be to have a stock of scrapped boards and cannibalism them for parts.

Thing is, I was going to program those chips...

 

Thing is, I was going to program those chips...

Program them with what exactly? No manufacturer will give you the binaries or source code for their products.

 

Program them with what exactly? No manufacturer will give you the binaries or source code for their products.

And the code inside the chip will almost for sure be protected. So it will not help to have a working controller unit and use the "code" from that. Yes I know it may seem unfair. But this it how it is

 

You've been given good advice. Don't try to second-guess it.