MEP-804A Voltage Regulator Fuse (FU2) Blowing

[Echo5Bravo]

Hello. I am new to the forum, but have spent many hours reading the posts here over the last couple weeks. I must first say this forum is a wealth of knowledge and I have learned tons of useful information as well as located all the TMs for a generator I am working on. Thanks to everyone out there that has worked to share their expertise on this forum.

I recently bought a MEP-804A generator from a GP auction. It was manufactured in 2005, had a tier 2 reset in 2011, and is showing about 800 hours. Before purchasing the generator, the place I bought the generator from provided a video of a function check they performed shortly before. During the function check the generator started, and the gauges were showing that electricity was being produced. After buying the gen and getting it home I put 2 new 12V car batteries in (installed in series using the labeled cables provided in the battery compartment) and started it up. The gen started up pretty easily, but the gauges indicated no voltage or frequency except during excitation when S1 is held to start position. When S1 is released voltage and frequency drop to 0. That is when I found this forum and learned all about my generator.

After some digging I found an obvious issue that I had been overlooking, the voltage regulator fuse (FU2) was blown. I got another fuse, different brand (an ATM-3) but according to the manufacturer is equivalent to the KTK-3 that is standard, put it in and it blew right away after starting up the gen. I read a post here where someone else had a FU2 blowing right away and it was recommended that his voltage regulator was bad.

So next I performed the voltage regulator test that I found in the TM. I have a TRC (P/N 19870) voltage regulator. I performed each step to test the VR and after each test I received measurements that were in the expected range of the test. I then got to the part of the test where the TM says this -

If steps h, j, and I are as indicated above, AC voltage regulator is defective and must be replaced.

Now I've seen other people ask this question, but I've never found a definitive answer. I would assume that if the measurement I took during the test were within the specified range, that would mean my VR passed the test. Even though the wording of the above statement might make it sound like the VR is bad only if the measurement are in the specified ranges, I don't think that makes sense.

Even if my voltage regulator passed the test, I know it's just a general test and doesn't necessarily cover all scenario where it may be bad. So I have 2 questions.

1. Does the problem with the blown fuses mean that the VR must be bad or does anyone have any other suggestions? I did take a voltage measurement on terminal 1 on A1. When S1 is in the run position I get 7VDC. When S1 is in the start position it jumps to 200VDC and stays around that level until S1 is released to run and then it very slowly loses voltage until it returns to around 7VDC.

2. Does anyone know where I can get a TRC (P/N 19870) voltage regulator? I've searched the web and looked on the big auction site and found many for a MEP-805 and other models, but can't find one for the MEP-804.

I'd be glad to take more measurements or provide any further information that would help troubleshoot. Thanks for reading my long post!

 

[Guyfang]

The TRC part number 19870, (NSN 6110-01-368-7123) also has several other part numbers. 01-21501 and 01-21501-2 are also good part numbers. You may have to look for an entire TRC conversion kit. NSN 6110-01-532-9723, part numbers, 88-22560 or 88-22560-2.

If the fuse blows, it can only be the Volt reg.

Regulators show up from time to time in the auction house. Don't know what else to tell you.

 

[Echo5Bravo]

Guyfang - Thanks for the additional part numbers. I figured it had to be the voltage regulator, but I guess I needed to hear it from an expert. So far no lead on one, but I'll keep eyes out.

If anyone else out there knows where to find a 15Kw voltage regulator - TRC 19870 (NSN 61101-01-368-7123) - please let me know. Thanks!

Any chance a volt reg. can be repaired? I guess that could be risky.

 

[Suprman]

You can take the regulator off and see the components. I have not seen the 15k 60hz regulators for sale. I have a 400hz one and I have heard a component or two can be replaced and it could be used in a 60hz generator but have not done it myself.

 

[Echo5Bravo]

I took off the regulator yesterday and examined it. I then took a few screws out and got the circuit board free from the regulator box. As far as I could tell there was nothing glaringly obvious that it had been fried. There's so much lacquer on the board though it's hard to tell if a component might look a little burnt or if it's just heavily coated. I've been watching some videos on generic voltage regulator function and I may take the regulator apart again and test out various components. But that's starting to get a little over my head. I'm sure I won't be able to go too far down the self repair path.

Thanks for the hint about converting a 400Hz to 50/60Hz. I hadn't thought of that. I'll do some reading/searching and see if that seems like a viable option.

 

[Suprman]

If its blowing the fuse then chances are a component (transistor, diode) is shorted. Use a multimeter and start where the power connection terminal is and work your way along. Alot of modules will have some sort of protection like a diode across the power inputs to protect against reverse polarity. A voltage spike can cause a component to short.

 

[mciikurzroot]

Its really not a deathr sentence or much less that you have to replace with a TRC and from my experience a TRC will be very over priced and or expensive, Basler and several others make fully capable replacement VR units especially if you don't plan to parallel operation, then a new replacement unit can be found affordable enough.. If indeed your TRC is bad. You will need to know the F1-F2 or most commonly called the Field resistance and at the moment i forget the expected field resistance, if it get where no one else can help with that let me know and i have 3 of the 804B units, while the B units don't bring out the 10-11-12 output winding's like the A model does to my best memory the actual generator is the same and the field exciter is the same i think.. all this said the actual resistance is the magic number you want... From this its just how picky you want to be or how original you want your interior control box to look, I favor operation ability V. purist original ... From what you indicated the actual generator is getting excited from the forced field flashing on start up but when you release the start switch and the 'forcing' is stopped, it's voltage starts to decay back to just static excitation levels . You can also take a small 9v battery and rig up and jury rigged feed for the field and see how it goes, but again the resistance is you first big step to making your decisions based on facts at hand. Also a new different brand of VR will almost likely require you to change the front panel mounted VR pot but that is simple also. Polarity wont matter on the 9V supply, you will however see slight voltage different readings . As a caution i would not leave this 9V scheme in place long, you might well see higher voltage peaks and cause way ass more damage than you want or intend, your best served if you have a variable supply output you can control. As i think on this you will not be well served doing this exercise .. This is fraught with way less good accomplished V damage might be caused. Take this as a possibility and see what all the rest of our supporters chime in with. End result is you got support here from this group.. best mac/mc

 

[Guyfang]

The mep-804a and mep-804b both use the same volt regulator.

 

[Echo5Bravo]

@Suprman - I've started testing individual components on the VR circuit board. I'm probably little better than novice when it comes to this, so I've had to search the web for ways to test particular components. At this point I'm fairly certain none of the resistors are shorted and all of the diodes are testing good (found there is a diode test mode on my multimeter, pretty cool). Apparently there is a fuse hard wired on the board, at least it's labeled F1 and I assume it's a fuse. But it has continuity between both ends. I didn't test any capacitors as I don't know of an easy way to test them with the limited equipment I have. I then tested the 2 transistors, Q1 and Q2. I had to look up a specific procedure for testing transistors with a multimeter. The Q1 component failed the test, Q2 passed. Q1 also appears to have continuity between any 2 of its 3 leads, Q2 does not. I know having the components soldered onto the board can skew test results like this, so this led me to get out the solder sucker and remove Q1. I retested it and I got the same failures. All 3 leads have continuity (< 1 ohms) between each other. I don't know a lot about this component but it seems to me that this one is shot. I looked them up and it costs about $3-4 for a new one, so I ordered 2. They're supposed to be here tomorrow. I'm just worried now when I put the new transistors in that whatever fried them the first time is still out there and is just going to fry it again. At least these things are cheap enough I don't mind frying a few. I'm not sure what or where else to test in order to be sure nothing else is damaged.

 

[Echo5Bravo]

I've tried replying to this thread 3 times already. Each time the site tells me a moderator must approve my post, so this is just a test to see if it is working today.


Ah, so I just figured out that putting an 'at' sign in my post keeps it from being posted right away.

 

[Echo5Bravo]

Ok, looks like my posts might be working today. If the 3 posts I made yesterday decide to show up, my apologies ahead of time for repeating myself.

I started going through each component on the volt reg. circuit board. This is a little over my head so I had to look up a few 'how to test' guides online. At this point I'm pretty sure no resistors are shorted, and all diodes are tested good. Apparently there is a fuse hardwired to the circuit board, or at least there is a component labeled F1, which I assume is some type of fuse. It has continuity so I also assume it is functional. I didn't check any capacitors as I don't really have a tool to test them with. None of them look like they've been leaking, blown, or damaged. There are 2 transistors on the board, Q1 and Q2. Based on their model number these are MOSFETs. Using a set of instructions that detail how to use a multimeter to test transistors in general and another for testing MOSFETs specifically, I tested Q1 and Q2. Q2 passed all tests, Q1 failed without question. I also did a basic continuity test on each transistor. Q1 always has continuity between any 2 of it's 3 leads. I don't know a lot about how a transistor should behave, but this seems like sure sign of a short. Having the components on the board can skew results so I then removed Q1 and tested it all again. All test results were exactly the same even when Q1 was removed from the board. I went ahead and ordered 2 new transistors, which are IFRP450's. They cost about $3-4 each and I should have them today. I worry now that whatever fried this transistor is still out there when I hook up the new transistor it will die a quick death. At least these are cheap enough that I won't be out much if they do blow out right away.

 

[Echo5Bravo]

@mac - Thank you for your thoughts. I had not considered hooking up a power source to F1 and F2. I agree any action like that should be handled with extreme caution. If I were to end up doing it I would certainly use a variable power supply and also make use of the existing 3amp fuse and fuse socket going to F1 to protect against any accidents.

I measured the resistance on the field wires and it registers 33ohms. I took a measurements on diagnostic output pins J and F and also on the wires leading to terminal 1 and 3 on A1. Both were the same as expected at 33ohms.

I'm glad to hear that using a non-TRC volt reg may be a possibility. While I would like to use original parts if possible, I certainly agree that functionality is more important!

 

[Echo5Bravo]

mac - Thank you for your thoughts. I had not considered hooking up a power source to F1 and F2. I agree any action like that should be handled with extreme caution. If I were to end up doing it I would certainly use a variable power supply and also make use of the existing 3amp fuse and fuse socket going to F1 to protect against any accidents.
I measured the resistance on the field wires and it registers 33ohms. I took a measurements on diagnostic output pins J and F and also on the wires leading to terminal 1 and 3 on A1. Both were the same as expected at 33ohms.
I'm glad to hear that using a non-TRC volt reg may be a possibility. While I would like to use original parts if possible, I certainly agree that functionality is more important!

 

[DieselAddict]

For sure take care if you do a live voltage test on the regulator. Having an isolated variable transformer is an excellent idea.

Keep us posted on the progress.

 

[Echo5Bravo]

I got the 2 IRFP450 transistors in yesterday and today I soldered them onto the volt reg. board. Only one of the transistors tested bad, but while I was at it I figured I would replace both. I've not done much soldering, but these components have pretty large pins and the board is not packed full of stuff in the way, so I actually found it pretty easy to solder the new one on. I debated about removing the capacitors from the board and testing them one by one (there's probably 10 or so) but I got impatient and decided to put the volt reg. together and put it back in the generator. After I got all the wires from the gen hooked up to it I put in a new fuse and started it up. Lo and behold if it didn't start generating electricity like a champ!!! I checked the voltage at the gen's volt gauge and also at the main output terminals, 120V and 210V are being produced. Now I haven't tested it under load yet, but I did let it run for a few minutes and stopped and started it a few times. Everything so far looks perfect.

I'd like to say a special thanks to Suprman. Once I took a look at the volt reg. board I thought there's no way I'd ever be able to troubleshoot it. But when Suprman posted to just start by checking diodes and transistors and follow the circuitry, that gave me enough encouragement to take a deeper look at it. Of course I had to google 'diode', in order to recall what those were (also had to google about 100 other things as I went along), but in the end I found it was a pretty easy task to check out most of the components and verify if they were working or not.

Thanks to Guyfang and everyone else who offered advice and encouragement.

Maybe I got lucky with it being the transistor, but if anyone else has a bad voltage regulator I'd say get out your multimeter and start checking it out!

 

[Guyfang]

Good to gooooooooooooo!

 

[mciikurzroot]

Super job man was ass super ... we need to call you like "Yoda" or such .. proud of you.. mac/mc

 

[DieselAddict]

Nice work!

 

[Echo5Bravo]

mac - Yoda? Ha! Too funny. Thanks!

 

[justinfaith]

I got the 2 IRFP450 transistors in yesterday and today I soldered them onto the volt reg. board. Only one of the transistors tested bad, but while I was at it I figured I would replace both. I've not done much soldering, but these components have pretty large pins and the board is not packed full of stuff in the way, so I actually found it pretty easy to solder the new one on. I debated about removing the capacitors from the board and testing them one by one (there's probably 10 or so) but I got impatient and decided to put the volt reg. together and put it back in the generator. After I got all the wires from the gen hooked up to it I put in a new fuse and started it up. Lo and behold if it didn't start generating electricity like a champ!!! I checked the voltage at the gen's volt gauge and also at the main output terminals, 120V and 210V are being produced. Now I haven't tested it under load yet, but I did let it run for a few minutes and stopped and started it a few times. Everything so far looks perfect.

I'd like to say a special thanks to Suprman. Once I took a look at the volt reg. board I thought there's no way I'd ever be able to troubleshoot it. But when Suprman posted to just start by checking diodes and transistors and follow the circuitry, that gave me enough encouragement to take a deeper look at it. Of course I had to google 'diode', in order to recall what those were (also had to google about 100 other things as I went along), but in the end I found it was a pretty easy task to check out most of the components and verify if they were working or not.

Thanks to Guyfang and everyone else who offered advice and encouragement.

Maybe I got lucky with it being the transistor, but if anyone else has a bad voltage regulator I'd say get out your multimeter and start checking it out!

Hello, Echo, any chance you took a pic of the circuit board? I'm needing to replace the 14 pin chip in my VR (see pic) but I don't have a part#!