MEP-805B no power to fuel pump = won’t start

[Dogger]

Anytime a circuit board trace gets hot enough to melt and cause an open there is a problem in that circuit...dead short or faulty component on that circuit or wiring harness issue, etc. They may have repaired the open circuit trace but fault has to be located to prevent a reoccurrence or additional issues in that circuit might occur.

Also, in the pictures you posted above it looks like the P24 connector has scorch marks on it near the capacitor. Wonder if that capacitor ever blew and was replaced earlier...?

Another observation, in post #16 above photo, the mounting standoff just above P24 looks a bit funky on circuit board like it got hot around the mounting screw that attaches standoff to circuit board. If you notice the standoff on the right, it attaches to the green sheet metal behind it and there is no annular paint relief where it attaches, however on the left one that looks like it may have gotten hot, there is what appears to be an annular paint relief where its mounted to sheet metal making me think that is an "intentional grounding point" with perhaps a star washer on opposite side. Anyway, it looks like perhaps something might have shorted through it to that ground point. But hard to tell from photos and no hands on examination.

I’m definitely looking for what could have caused the problem to correct and prevent any reoccurrence. I appreciate the comments and will look closely at the standoffs. Additionally P24 definitely has some char on it but didn’t last long enough for the plastic to melt so must have been a quick flash, likely the capacitor but not 100% sure.

 

[Dogger]

I traced wires this afternoon and found two disconnected from TB8 (Exciter Field Terminal Board), I reconnected and now have/see generator producing power. Problem now is unit cranks but shuts down due to high voltage. I attempted to lower from toggle switch as well as set screw on A4 (Voltage Regulator) all attempts were unsuccessful. I did notice A4’s LED light for field voltage indicator is not lit. However, tested and confirmed field voltage which was high. Hertz appears ok. Unless I’m missing something else it appears AVR-100, A4 Voltage Regulator isn’t doing its job.

 

[Guyfang]

I don't suppose you have access to another VR, so you can try it out?

 

[Dogger]

I don't suppose you have access to another VR, so you can try it out?

Unfortunately I do not, I am gonna see if I can locate one to purchase. Something tells me they are hard to find and they definitely don’t give em away. If the price is thru the roof, I’ll purchase another non-operational 805B and have all sorts of spare parts.

 

[Guyfang]

Are these lights on IAW the TM?


Are the I&O dip switches set right?

 

[Dogger]

Are these lights on IAW the TM?
View attachment 812521

Are the I&O dip switches set right?
View attachment 812522

#33 & #34 are lit, #35 “Field Voltage” is NOT. All dip switches are set correctly.
I tested per procedure (pic attached) this morning and step 9 reading was 192 VDC so definitely a problem somewhere. I’m hoping to identify vs replacing complete module and it doesn’t resolve issue.

 

[mep805b]

I am happy to see you got it going. I agree with CB. Something serious went wrong at some point. I am going to guess water damage to one or more boards. Its dry and patched now and may last a lifetime. The boards and coating are very rugged. It should be traced back though if it fails again. Tracing is not too hard on these vintage boards. I am used to working with BGA. These boards are massive and easy to work with. Possibly pull and do a quick visual on the other two boards. I think the power problem will be on one of the other two boards or backplane. @Dogger. It may be easier to swap boards with a working machine to find the problem board. You are welcome to send them here for testing on our machine. You have my contact details arriving via fedex on Monday. Good luck and please keep everyone posted as the fleet of MEP805 units are aging in the private sector. If anyone has one or more dead boards i would love to purchase them so we can create a bank of spare working and tested boards. I am also working on and adapter to retrofit the ESD5550 board to the military units. this will reduce the replacement cost from $1100 to about $50. I am pretty sure this will simply involve reversing the pinout and manually connecting the wires. I have a test ESD5550 on order.

 

[Dogger]

I am happy to see you got it going. I agree with CB. Something serious went wrong at some point. I am going to guess water damage to one or more boards. Its dry and patched now and may last a lifetime. The boards and coating are very rugged. It should be traced back though if it fails again. Tracing is not too hard on these vintage boards. I am used to working with BGA. These boards are massive and easy to work with. Possibly pull and do a quick visual on the other two boards. I think the power problem will be on one of the other two boards or backplane. @Dogger. It may be easier to swap boards with a working machine to find the problem board. You are welcome to send them here for testing on our machine. You have my contact details arriving via fedex on Monday. Good luck and please keep everyone posted as the fleet of MEP805 units are aging in the private sector. If anyone has one or more dead boards i would love to purchase them so we can create a bank of spare working and tested boards. I am also working on and adapter to retrofit the ESD5550 board to the military units. this will reduce the replacement cost from $1100 to about $50. I am pretty sure this will simply involve reversing the pinout and manually connecting the wires. I have a test ESD5550 on order.

Pulled the two other boards and visually they appear to be in good shape.

 

[Guyfang]

I am happy to see you got it going. I agree with CB. Something serious went wrong at some point. I am going to guess water damage to one or more boards. Its dry and patched now and may last a lifetime. The boards and coating are very rugged. It should be traced back though if it fails again. Tracing is not too hard on these vintage boards. I am used to working with BGA. These boards are massive and easy to work with. Possibly pull and do a quick visual on the other two boards. I think the power problem will be on one of the other two boards or backplane. @Dogger. It may be easier to swap boards with a working machine to find the problem board. You are welcome to send them here for testing on our machine. You have my contact details arriving via fedex on Monday. Good luck and please keep everyone posted as the fleet of MEP805 units are aging in the private sector. If anyone has one or more dead boards i would love to purchase them so we can create a bank of spare working and tested boards. I am also working on and adapter to retrofit the ESD5550 board to the military units. this will reduce the replacement cost from $1100 to about $50. I am pretty sure this will simply involve reversing the pinout and manually connecting the wires. I have a test ESD5550 on order.

That's the Army method of troubleshooting. Almost mothing is "repaired" anymore. Pluck and chuck. I understand the how and why. i worked in this field the better part of 30 years. But it still hurts me to see it so. And it caused huge problems with the Army's power generation readiness.

 

[Guyfang]

About your LED5 light. Please read the following info. I got this from about as high as you can get, from someone who is in the know.

 

[Dogger]

About your LED5 light. Please read the following info. I got this from about as high as you can get, from someone who is in the know.

Thanks, I’ll check it out, also I should receive another Voltage Regulator mid week. Hopefully it will indicate on LED #35 and take control as necessary

 

[Dogger]

Thanks, I’ll check it out, also I should receive another Voltage Regulator mid week. Hopefully it will indicate on LED #35 and take control as necessary

About your LED5 light. Please read the following info. I got this from about as high as you can get, from someone who is in the know.

About your LED5 light. Please read the following info. I got this from about as high as you can get, from someone who is in the know.

Gutted the CIM and didn’t see any battery on outer two circuit boards. Unless it’s deeper within which would be on the actual screen circuit board I’m gonna say mine is non-existent.

 

[Guyfang]

Look up this guy in the forum. Send him a PM. Ask hime where the battery is.

Peapvp

 

[Dogger]

IMG_5078.MOV
Just wanted to give an update and say thanks for all the support!! I swapped out the voltage regulator and everything is now running as it should. I still need to load test it but have confidence it will perform as expected. Additionally, it looks like I will be acquiring two more 805-B’s to troubleshoot. Hopefully they will be easier to get up and running now that I have a little familiarity with what I’m working with. Still learning but really appreciate everyone’s selfless help and time!!! May God Bless

 

[Skydive]

Does anyone know where I can get parts for mep805b? I heed a liquid transmitter.

 

[Light in the Dark]

Got a part number or NSN?

 

[Skydive]

Got a part number or NSN?

yes 127678

 

[Skydive]

the part number that I have is 127678.

 

[Skydive]

When I took the transmitter out, the ohms were within tolerance. When I checked to ohms with it installed, the reading is below the empty ohms.

 

[155mm]

I just ordered from my local parts house, nothing special about it. Ground is probably your issue, skrews are notorius for stripping, drill hole in top of sensor, then bolt ground to sensor not mounting bolts