DamianInRochester
Lifetime Supporting Member
It looks as though you definitely had an arc between those two traces. Can't see much from the top though.
DIY Repairing a PLC?
- Thread starter gedds1993
- Start date
Gil47
Member
On the power supply board, the one with the large capacitor, is a device that has the numbers 220n K on it, just above the number 220, is a black 12mm (half inch) round device, that I believe is a fuse that is on the 24V DC.
(In the photo the number 220 is upside down In the picture it is at the bottom of Photo)
I know the ML1000 have a fuse that looks like that one, check the numbers and details written on its top.
(In the photo the number 220 is upside down In the picture it is at the bottom of Photo)
I know the ML1000 have a fuse that looks like that one, check the numbers and details written on its top.
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This is a switch-mode power supply (SMPS).
That's not burn marks. Just flux. Don't worry about it.
Starting at the lower left of image 34 is the power in connector.
Fuse is round black device. Check for open.
Blue device is MOV or cap. Check for short.
Q1 mounted on heat sink. Should be switching transistor for primary of transformer. Check for short - Collector to Emitter.
C1, 220n K is dual cap. Noise filter. Rarely fail. Check for short.
LF1, 615160 is dual coil. Line filter. Doubt it has a problem.
Next is orange device. TNR1. Transient Noise Reducer? MOV. Check for short.
Thin black rectangle is full wave bridge. Check for short.
Large cap is main filter. About 200 uF, 200-400 volts. Check for short.
Check other diodes. I see D8 and D6.
I expect blown fuse. In addition Q1 or main cap shorted.
If all of that checks okay, power up and measure voltage across main cap. Should be about 200 VDC. If so, then all of the above is probably okay.
To the right of main filter cap is 2 heat sinks. Should be diodes. Check for short.
Heat sink to the right of transformer is probably a SCR for overvoltage protection. Check for short.
If all of that checks out, then replace all capacitors. Use low ESR type. Panasonic FC series from Mouser.
If it still doesn't work, the last 2 items are the IC's. The 8 pin device is the regulator. Replace.
PC1, the 4 pin device is an optoisolator. This provides a feedback signal to the regulator IC. That's how it measures and regulates to 24DC. Replace.
Following is my SOP for a quick SMPS checkout.
Power up and measure voltage at main cap. Should be at least 170 volts.
Check all diodes.
Replace all caps.
That fixes 95% of them.
When testing, make sure it has some kind of load, or it won't run. Some supplies, including this one (I expect), have a resistor across the output to give it a minimum load.
That's not burn marks. Just flux. Don't worry about it.
Starting at the lower left of image 34 is the power in connector.
Fuse is round black device. Check for open.
Blue device is MOV or cap. Check for short.
Q1 mounted on heat sink. Should be switching transistor for primary of transformer. Check for short - Collector to Emitter.
C1, 220n K is dual cap. Noise filter. Rarely fail. Check for short.
LF1, 615160 is dual coil. Line filter. Doubt it has a problem.
Next is orange device. TNR1. Transient Noise Reducer? MOV. Check for short.
Thin black rectangle is full wave bridge. Check for short.
Large cap is main filter. About 200 uF, 200-400 volts. Check for short.
Check other diodes. I see D8 and D6.
I expect blown fuse. In addition Q1 or main cap shorted.
If all of that checks okay, power up and measure voltage across main cap. Should be about 200 VDC. If so, then all of the above is probably okay.
To the right of main filter cap is 2 heat sinks. Should be diodes. Check for short.
Heat sink to the right of transformer is probably a SCR for overvoltage protection. Check for short.
If all of that checks out, then replace all capacitors. Use low ESR type. Panasonic FC series from Mouser.
If it still doesn't work, the last 2 items are the IC's. The 8 pin device is the regulator. Replace.
PC1, the 4 pin device is an optoisolator. This provides a feedback signal to the regulator IC. That's how it measures and regulates to 24DC. Replace.
Following is my SOP for a quick SMPS checkout.
Power up and measure voltage at main cap. Should be at least 170 volts.
Check all diodes.
Replace all caps.
That fixes 95% of them.
When testing, make sure it has some kind of load, or it won't run. Some supplies, including this one (I expect), have a resistor across the output to give it a minimum load.
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I don't think I heard the term PLC used in my entire time i was an undergrad. It was all theory, circuit analysis, math, math, math and more math.
Yes, it was the same in my EE courses - never heard PLCs mentioned. Of course it could be because that was before PLCs were invented . . .
In any case there was too much emphasis on proving some old dead guy's Theory of This or Theory of That, and not enough practical hands-on training.Yes, it was the same in my EE courses - never heard PLCs mentioned. Of course it could be because that was before PLCs were invented . . .
...how long ago was that? Lol
[email protected]
Member
PLC Reapiar
I thought I put in my two cents worth about repair of PLCs. Several good point made above about it not being worth it repair them. I will agree that often they are not worth repairing and with many of the newer ones it is not even possible because they are so small and mostly surface mount components. Replacements are often less expensive than the time and parts to maybe fix the problem. The other side of that is there are a lot of old and very old PLCs out there still in use today. When one of them breaks you may not be able to find a drop in replacement at any cost. They you are faced with the choice going to a current production PLC model and recreating the wheel. I am sure several of the people on this forum make a good part of their living making these switch overs. It that won't work because of cost or time repair might be necessary. If you have this skill it can be very handy and save your company a lot of money.
On the specific problem with the power supply. My coworker always says to replace all of those big electrolytic caps first. The score marks are to let out pressure in a severe failure (which did not happen in this case). Sometimes you will get some brown leakage on the board near the caps. If that does not fix the problem then try the voltage regulators.
Extra knowledge is always an asset for you and your employers.
I thought I put in my two cents worth about repair of PLCs. Several good point made above about it not being worth it repair them. I will agree that often they are not worth repairing and with many of the newer ones it is not even possible because they are so small and mostly surface mount components. Replacements are often less expensive than the time and parts to maybe fix the problem. The other side of that is there are a lot of old and very old PLCs out there still in use today. When one of them breaks you may not be able to find a drop in replacement at any cost. They you are faced with the choice going to a current production PLC model and recreating the wheel. I am sure several of the people on this forum make a good part of their living making these switch overs. It that won't work because of cost or time repair might be necessary. If you have this skill it can be very handy and save your company a lot of money.
On the specific problem with the power supply. My coworker always says to replace all of those big electrolytic caps first. The score marks are to let out pressure in a severe failure (which did not happen in this case). Sometimes you will get some brown leakage on the board near the caps. If that does not fix the problem then try the voltage regulators.
Extra knowledge is always an asset for you and your employers.
Peter Nachtwey
Member
Actually, gedds1003 may have a chance with a power supply. The components are usually big enough to handle easily.
We design our boards so that the input and output circuitry can be easily repaired. It is a real shame to throw away a whole board when one can replace a resistor or output transistor. However, it is more and more difficult to do this now that one can only get small surface mounted parts. One doesn't have a chance if not trained and the right tools for surface mounted part removal and replacement aren't available.
We design our boards so that the input and output circuitry can be easily repaired. It is a real shame to throw away a whole board when one can replace a resistor or output transistor. However, it is more and more difficult to do this now that one can only get small surface mounted parts. One doesn't have a chance if not trained and the right tools for surface mounted part removal and replacement aren't available.
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