Mep-804 over voltage

[Todd1]

2007 Mep 804a was missing quad fuse ( the fuse at the left of the VR ktk-3 ? In assuming). Had under voltage. 25 v no freq. So, far I diagnosed and replaced bad voltage pot R1 and installed ktk-3 fuse. Fired it up when holding in start voltage went 300 on meter. When I let off start it died and has over voltage. I have a parts machine was thinking of replacing VR but am afraid to ruin it. I would love some feedback. Thx

 

[Ray70]

Have you tried this more than once? On the 804 I believe it should stay running after an overvoltage fault. Maybe you didn't hold it long enough for the oil pressure switch to close. I think first you should ( if you haven't already ) is make sure it will start, stay running and that it trips over voltage again.
I once had an 804 tripping for overvoltage ( as well as having magic smoke leaking inside the control panel ) and the cause was a wire had chaffed against the back right corner of the watt transducer, and causing something inside the transducer to heat up severely ( and burn the potting material ).
However, mine was not shutting down, it stayed running with the fault indicator illuminated.

 

[Guyfang]

I do not think its possible to "ruin" an A1. The A1 is what is in charge of AC volt production. So yes, go ahead and put your spare A1 in and see if that cures the problem. ho do you KNOW your spare A1 is good? Ever see it installed in a gen set that works right?

 

[Todd1]

I do not think its possible to "ruin" an A1. The A1 is what is in charge of AC volt production. So yes, go ahead and put your spare A1 in and see if that cures the problem. ho do you KNOW your spare A1 is good? Ever see it installed in a gen set that works right?

First thx for reply I’ve been ready all 804 related and both of you guys are amazing. I bought genset off GP. They said it made voltage. It didn’t . They didn’t show under voltage light on and the quad fuse was missing so the gen would stay running. But impossible to make voltage. The courtesy outlet not producing voltage or 25v. Made drill hum when I plugged it in to test. This is prior to testing VR. I got 10v dc between 141 wire and terminal 3. I got 158 volts ac between terms 10 and 11. Then measured resistance from Terminal 5. 0 with 50 or 60 hertz. So replaced the pot with good used one. Got overvoltage light and shut down after I let off start. So I replaced VR from one machine to machine I’m working on. (Unverified VR) Now I’m back to low voltage fault. However, I had 50 hz and 50 volts at gauges. Tried starting and holding start for couple seconds not long and am ready 52 hertz but zero volts on machine gauges. So I did VR tests again 10v term 3 , zero volts ac between terms 10 and 11, however resistance between term 5 is within spec 3k and 18k but reads the same between 50 hz and 60 hz switched. recap 0 volts on meter 52 hz. Thx guys

 

[Guyfang]

Did you know that there are two different types of volt regulation systems? And that you can not mix and match them?. The total of 4 parts, MUST all be from the same manufacturer.

Do you have all the TM's downloaded for this machine?

 

[Todd1]

I appreciate all advice. I’ll bone up on the manual. I’ll look for chaffed wires as ray70 suggested.……I’ll make sure all 4 component match. As guyfang suggests. Many thx…… I had the s5 in between spots so when I moved it the voltage on the meter went to back to 50v with freq 52hz . I replaced R1 and A1 with parts from another machine that I have never seen run. I went from 25v on meter to 50v. I’ll keep you posted.

 

[Guyfang]

Might help

 

[Todd1]

Guyfang, You Sir are the man!!! Thanks I’ll keep you updated.

 

[Todd1]

Guyfang, you are the man. Many thx. I’ll keep you posted.

 

[Todd1]

Finally got it making voltage. Haven’t load tested yet.……here’s a recap. I initially had under voltage. I was missing quad resistor. Put resistor in and when I let of start it stopped running And got overvoltage. I checked VR as per guyfang posted in a similar post. checking A5 for resistance I noticed the voltage pot was bad. I also got 158 vac between pins 10 and 11. swapped VR and basically didn’t change anything. I then rechecked VR . I noticed 0v on pins 10 And 11 . So I isolated the wires 10 and 11 which run from the VR to the potential Transformer. I had an open on the wire between 11 vr to pin 7 on T1. Made a jumper and fixed problem. Many thx to everyone. With special thx to Guyfang. You help many folks.