Hi. Just found this forum. I'm trying to repair a Chinese 2500 watt pure sinewave inverter, 12 vdc to 120 vac, model DPP 25. Can I post the brand name ? I have not been able to get specific diagram from manufacturer. Here's the history. There was a mishap , it fell about 3 feet & now there is no ac output. The unit does turn on & displays correct input voltage. I am not an engineer, just a hobbist with adequate soldering skills. I have metered the input & output mosfets & have not found any 0 ohms faults. There are 2 IR2110S drivers mounted to the PSW module but I don't know how to test them. The large capacitor rated at 250V DC, 820 mfds is not getting voltage. Tech support stated it should have 180 VDC, I'm only getting .5V. I don't see any signs of physical damage, cracks, broken components, burns. I did detect a possible fault, short at C3 capacitor, removed but 0 ohms short not cleared. Also removed the PSW module, no change. There are no repair shops in my area, interested in working on this, not feasable. I am not detecting any other faults. What is the opinion of the community of components sensitive to trauma which may be causing the issue ? Advice and tips on troubleshooting and opinions on what to remove or replace will be appreciated.

 

looking at that pdf collection of snippets, it seems that the scheme is producing a high DC voltage and then creating the AC output by using an H-Bridge output stage.
Since there is no high DC voltage produced the first section to check is the oscillator to drive all of those mosfet power transistors.

That collection of little details is an extremely poor substitute for a circuit drawing that is useful for servicing a piece of equipment.
So the challenge now is to locate that oscillator, and then the drivers. The other possibility is that the input power to the mosfet section has an open circuit. So you can check for the supply voltage presence in the inverter section.

REALLY THOUGH, that drawing is as stupid as they come. Much more like a netlist for an autorouter program.

 

After a fall, I'd look for cracked circuit board or cold solder joints or lifted/broken pads on the leads of heavy components. Look at it with magnification, and with backlighting of the board if possible (or reasonable; backlighting won't be much use with double-sided board with big areas of copper, or any use at all if it's multilayer with ground or power planes).

 

OK,the comment about the drop did not get thru to me at first.Certainly a connection has broken. My sad experience with broken connections points toward transformers on circuit boards having moved and having broken fine wires. I see three transformers as the high voltage supply, so it seems that there may be a break in that string of secondary connections. A power-off resistance check will identify any breaks in that string of connections, which may be either solder joint failures that are easy to fix, or wire breaks, much harder to fix.
resistance checks will reveal open circuits, reducing the number of connections that must be examined.

 

OK,the comment about the drop did not get thru to me at first.Certainly a connection has broken. My sad experience with broken connections points toward transformers on circuit boards having moved and having broken fine wires. I see three transformers as the high voltage supply, so it seems that there may be a break in that string of secondary connections. A power-off resistance check will identify any breaks in that string of connections, which may be either solder joint failures that are easy to fix, or wire breaks, much harder to fix.
resistance checks will reveal open circuits, reducing the number of connections that must be examined.

Thanks to the both of you who replied. I’ve been staring at this thing for days looking for physical damage, no luck yet. I’ll keep looking & continue to monitor this thread.

 

Consider that a hard impact will have a greater effect on the heavy items held to the PCB by their soldered connections. so resistance checks between the connections that are supposed to have connections between them can reveal an open circuit.
If the capacitor that is supposed to have 180 volts across it has only 5 volts, that tells that the section with the high frequency inverter is not getting power to the diode bridge. This points toward the three transformers, which were probably only attached by their terminals. But start the resistance checks with the DC power input end.

 

I see a dozen fuses. Hope those were checked

 

First thing I checked. Thanks for your input

 

Does the inverter draw any current when it is switched on??
This system uses an oscilator to drive a big power stage to develop 180volts DC that feeds an "H Bridge" used to create a sine wave,or some approximation of one. But the drawing is such an inferior piece that diagnostic evaluation is thwarted to a large extent. And yet I see similar drawing presented as OK. What value is the collection of snippets posted in a random arrangement?? What is the use for such documentation?? Does anyone have an explanation??

 

Does the inverter draw any current when it is switched on??
This system uses an oscilator to drive a big power stage to develop 180volts DC that feeds an "H Bridge" used to create a sine wave,or some approximation of one. But the drawing is such an inferior piece that diagnostic evaluation is thwarted to a large extent. And yet I see similar drawing presented as OK. What value is the collection of snippets posted in a random arrangement?? What is the use for such documentation?? Does anyone have an explanation??

Maybe they just want me to buy a new one. There is no ac output , no current draw. The manufacturer is Chinese. I’m thinking the problem may be in the Ir2110 drivers on the pure sine wave module. I’m trying to get a new module, easy to replace. Have not found evidence yet of broken joints, pads, components, cracks, nothing loose or broken found yet. Transformers are in solid. I’m waiting for Chinese support. I requested schematics & that is what they offered. Stay tuned.

 

Probably the failure is a mechanically broken electrical connection in one or more locations.So if the break can be located then it will probably be repairable if the needed skill set is held by the repair person. The exception being the instance of leads being ripped off of components.

 

According to the current information, you can do the following:

Check with DVM low value SMD resistors on the board incircuit. Sometimes manufacturers uses resistors <50 Ohm as a fuses. It is hard to detect a faulty resistor visually.

Second, I see a dozen SMD electrolytical capacitors on the module. These components are known to have low reliability . If you have an incircuit ESR checker, check those first.

Third, try to identify a circuit which elevates 12VDC to 180VDC. Take in mind high current ( 2500W/12V= 108A), so a wide conductors used in this circuit, and a dozen transistors in TO-220 package in parallel

 

It is not likely for a fuse to pop from a mechanical shock while not operating. Certainly a lead of a bigger capacitor could be ripped loose by the impact, though.Probably following the 12 volt path through the PCB would lead to an open connection.
But visualizing the operation from that miserable excuse of a circuit schematic would be a daunting task.
Possibly a closer examination to see what has moved as a result of the impact will uncover the failed connection. It might even be as simple as damage to the power input connection point, or even the power switch itself having something inside dislodged.. Many things can be checked by means of a simple continuity test, starting at the power plug.
Since the fault was caused by a physical impact, at least that is the claim, there should be some visible evidence of what moved during the impact. That would most probably be a poorly anchored component that was heavier, although I have seen a 2-watt resistor with a broken off lead.

 

I'd get a magnifying glass and a good light source and inspect every nook and cranny of the circuit. It's amazing what you can miss with unaided eyes that become obvious in a close-up view.

 

The most effective way to fix a failure in a device is to understand how it works, and then see waht is not working, which will quickly point toward the failure. The least effective way to attempt to fix a device is to randomly check components and connections in the hope of finding one that has failed.
THIS is why I have suggested checking the items, which are in the earlier part of the circuit, which is not working. Just inspecting will not often show an item damaged internally. Thus my suggestion of resistance checks on the transformer windings.