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Dimensions Sensata power inverter repair Help

I have a 8000watt- 48 volt power inverter made by dimensions sensata. Model No.48/8000. It was working fine the last time used. It refuses to power on now. No visible signs of anything burnt. The inverter board has a 7812 voltage regulator that seems to power the other circuits on this board. With the switch on there is 27.8 volts on pin 1 and zero volts on pin 3. When I shut the inverter off voltage gradually returns to zero on pin 1 and still zero on pin 3. Does this indicate the voltage regulator is bad?

Thanks for any help.
 
I have a 8000watt- 48 volt power inverter made by dimensions sensata. Model No.48/8000. It was working fine the last time used. It refuses to power on now. No visible signs of anything burnt. The inverter board has a 7812 voltage regulator that seems to power the other circuits on this board. With the switch on there is 27.8 volts on pin 1 and zero volts on pin 3. When I shut the inverter off voltage gradually returns to zero on pin 1 and still zero on pin 3. Does this indicate the voltage regulator is bad?

Thanks for any help.
Just to confirm, you are measuring DC, 27.8V on the input for the 7812 and nothing on the output.
Sure sounds like that's the culprit so far. What was your reference when you measured that voltage? Where was the black lead? I want to confirm as well that the input should be 27V, as I am under the understanding that its a 48V system.

The gradual return to 0 could just the capacitors draining.
 
yes,
looking 7812 from top, measure voltage with black tester probe on central pin (gnd), and red (+) on left pin. This is the input. Then measure from right pin (red +) and central (black). This is the output. Let us know.
 
Measurement was taken from center pin to pin 1@ 27.8 DC and from center pin to pin 3 @ zero volts DC. Supply voltage to board is @ DC 50.6 Volts. Here is part of the schematic.
 

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Well, I'd replace the 7812, and once I have it out, I'd measure resistance from the pin3 pad to ground to make sure there is not short.
Anyone else have ideas?
 
Yes, it has to be replaced, but there can be other issues on his load. Check by tester as said Gryd3 on the load circuit, once it is removed,(pad 3 and gnd). Take a look by eye to the electrolytic capacitors after it, diodes and so on, and you can briefly test them all for shorts. Send us a picture eventually.
 
I checked resistance from pin 3 to ground with the regulator still in place. I believe it read 537 k ohms. I have some pictures but tough to get a clear shot. I will remove board later tonight. The capacitors do not look swelled or leaking. One does look slightly swelled in one picture but I think its a shadow.
 

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(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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The 7812 is ion a substantial heatsink with a number of other devices, it is possible that (since they are all electrically insulated from the heatsink) that one or more of the insulating bushes has failed and that there is a short through the heatsink. Before you disconnect anything from the heatsink, see if there is any continuity between the tab of the devices and the bolt that fixes them to the heatsink and/or to the heatsink itself (normally the bolts are in fairly good electrical contact with the heatsink). This is not very likely, but well worth checking. If, when you do remove the device from the heatsink, you find any of the plastic parts are damaged, cracked, or have metal shards on or near them, replace them!

Oh, and if any of the bolts seem loose, they may have shaken loose or they may have stripped threads -- replace them and use shakeproof washers and/or locktite (etc) and DO NOT over-tighten them.

But back to our regular scheduled program...

12V regulators are cheap and should be fairly well protected against overload.

You don't mention that it is hot, so I will assume that it's not, and that means it hasn't shut down due to overload, and nor is is shorted out.

Given that, I'd replace it. It may not fix the problem, but it might help diagnose it.

If the problem is caused by a shorted output, the device will last long enough to get hot, and probably go through several (probably indeterminately many) shutdown cycles before it finally expires. However if this had been happening I think you would have seen symptoms different to "it suddenly not powering up one day"
 
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