803a lost all output?

[Coonass77]

Well... I was load testing my new to me 803a today and everything was going great - had it loaded to about 85% of rated load and she was chugging along just fine for about 15 minutes. All of a sudden it jumped to about 100% load and the engine really started laboring. Within the 15-20 seconds it took me to get over to it and start investigating, the load went to 0%, I lost all output voltage and the engine returned to idle and kept purring along. I had it set to 120/240 1PH and no warning lights or tripped breakers before, during or after the failure event. I'm now not getting any voltage on the L1 or L3 output.

I have the TM's and will start methodically working through them to troubleshoot, but thought I'd ask if some of the experts had any suggestions of likely culprits or places to start looking based on the symptoms I experienced.

I appreciate any insight anyone could provide. This, and the HMMWV forum are fantastic resources with some great folks! Thanks!

 

[kloppk]

If the set has the Fuse Mod (fuse on left side of the VR) see if it's blown. If it is it's likely the VR failed.
If the fuse is good then start the set and hold S1 in START. You should get AC st the sets meter and the outlet.
Do youget AC there with S1 in START while running?

If your set does not have the fuse mod installed do not attempt to start the set until you get the mod installed.

 

[Guyfang]

So, the set starts and runs. No output. Right? Is there 120 volts on the 120 volt outlets? Yes? Good. No, well, we need to dig deeper. Will the S5 switch, (AC output contactor switch) close the CB1, (Output contactor)? And will the DS7, (Output contactor light) come on, when you flip up S5?

 

[Guyfang]

If the set has the Fuse Mod (fuse on left side of the VR) see if it's blown. If it is it's likely the VR failed.
If the fuse is good then start the set and hold S1 in START. You should get AC st the sets meter and the outlet.
Do youget AC there with S1 in START while running?

If your set does not have the fuse mod installed do not attempt to start the set until you get the mod installed.

This is VERY IMPORTANT!!

Open to read comment!

 

[Coonass77]

Thanks for the replies! I'll try to answer all the questions below...

Yes, it has the fuse mod - no, the fuse is not blown. Note: This set does not have the MOV installed (I have one on order but it isn't here yet. Hopefully this isn't my problem - I knew about the fuse mod, but if I wasn't supposed to run it without the MOV, I wasn't aware of that....)

Yes, holding SI in Start w/ the engine running produces 120/240 volts on L1/L3 and I have 120 at the convenience outlet. When I return S1 to Run, voltage drops to 23/46 on L1/L3 and 23 on convenience outlet.

Yes, DS7 turns on when I flip up S5, and when I push to test it.

I've been staring at the schematic, but I'm not seeing how S5 closes CB1?? Regarding CB1: with CB1 pushed in, the engine runs, with it popped out, the engine will not crank and dies if running when popped out.

I assume that because I'm getting voltage with S1 held in Start, that means it's still capable of producing power, but the problem could be on the control/excite part of the system?

 

[kloppk]

CB1 is the circuit breaker for the 24 volt power.
S5 controls K1 the contactor.
It's good that the set produces power with S1 in Start. That rules out a bunch of stuff.
You should perform the AC Voltage regulator test per the -24 TM and see if the VR is toast.

 

[Guyfang]

My bad. Wrote CB1 instead of K1. Getting old. Yep. Getting old.

 

[Coonass77]

Because of the fact that I do not have power at the convenience outlet (except with S1 held in Start), I'm guessing it's the VR and not something to do with K1 (if I understand the power flow correctly....) I'll run the AC VR test per -24 TM tomorrow and see what I find out. Thank you for the guidance, guys!

 

[kloppk]

You are correct. K1 has nothing to do with getting power to the outlet.

 

[Coonass77]

I ran the AC VR tests this morning. Step "j" failed - I got zero volts across 7 and 8. Everything else passed as indicated. Bad AC VR?



Should step "o" read "If steps h, j, l and n AREN'T as indicated...."? Or am I somehow misinterpreting the context of that comment???

 

[kloppk]

It means that if all the above tests pass then the VR is bad.
When you did test j did you have your meter set to AC volts an the meters leads connected to terminals 7 & 8 while holding S1 in START?

 

[kloppk]

Getting no voltage at step j indicates the Quad winding in the get head isn't working or there is a wiring or connection issue from the Quad winding to the VR.
Check for a broken wire where the wires exit the gen head. Next disconnect cable P5 from the bottom of the control cube and inspect the pins in P5 and J5 for corrosion. Clean if present and then reconnect. Then try test j again.

 

[Coonass77]

Yes, "j" failed (0v) w/ meter set to AC, measuring across 7 & 8 with S1 in Start position - I just went out and triple checked.

Inspected and found nothing that looked like a broken or loose wire coming out of the gen head (or anywhere else leading up to the VR).

Inspected P5 and J5. Didn't find any corrosion, funky looking pins or anything else that seemed to indicate something was amiss.

Put it back together and retested - still getting 0v between 7 & 8.

Resistance between F1-F2 Exciter Leads matched TM: ~12ohm. (Measured at P5)

Resistance between Q1-Q2 leads matched TM: ~1ohm. (Measured at P5)

I'm off to check resistance on Q1 & Q2 from J5 to VR 7 & 8. If that checks out, I'm at a loss...

 

[Coonass77]

Between fighting the flu, Thanksgiving holidays and the rest of normal life, it took me a while to get back to this one, but I did want to close the loop on my issue...

I found my AC VR had failed, and in doing so, blew the fuse mod fuse - thus the reason for step "j" of the AC VR test failing. Replaced the AC VR and my 803a is back to making power exactly as she should be.

On a related note... my replacement AC VR came from Kurt Klopp (kloppk) and it's great quality. Kurt was also a tremendous help in troubleshooting and very professional. He's highly recommended!