MEP-802a Voltage regulation

[willswim15]

Hi everyone, I hope you are all staying safe
I have a MEP-802A that runs fine but has a output voltage of 148 at 55hz and when I turn the frequency up the unit shuts off with a over voltage light.
At first I thought it was the voltage regulator but after doing some checking I think the problem is elsewhere. I have these readings on the voltage regulator connector with my dvm and the unit is running.
pins 3 to 4 is 28vac pins 6 to 7 is 58 mv dc pins 7 to 8 is 19.4 vac and with the unit off and pin 1 to 2 (with pin 1 removed from the regulator) I have 0 to 5K ohms

I don't have a wiring diagram to troubleshoot it any further . Any help with this would be greatly appeached thanks in advance.

Keith

 

[kloppk]

Withe the set running and no load applied you should see the following approximate voltages at the regulators terminals.
1 to 2. 1.07 vac
3 to 4 120 vac
5 to 6 5 vDC
7 to 8 69 vac

I suspect the issue with your set is that the 120 vac that's suppose to go to the regulator on terminals 4 & 4 isn't getting there. You said you are only getting 28 vac. Because the regulator is only seeing 28 vac it's trying to dramatically increase the sets output voltage.
The voltage across 7 and 8 on your se is really low too. Those are the AC input from the Quad winding in the gen head.
Does your set have the Fuse Mod? It's a fuse mounted just to the left of the voltage regulator.

The schematics can be found in the -24 TM in the TM section at the top right of the forum.

 

[willswim15]

Withe the set running and no load applied you should see the following approximate voltages at the regulators terminals.
1 to 2. 1.07 vac
3 to 4 120 vac
5 to 6 5 vDC
7 to 8 69 vac

I suspect the issue with your set is that the 120 vac that's suppose to go to the regulator on terminals 4 & 4 isn't getting there. You said you are only getting 28 vac. Because the regulator is only seeing 28 vac it's trying to dramatically increase the sets output voltage.
The voltage across 7 and 8 on your se is really low too. Those are the AC input from the Quad winding in the gen head.
Does your set have the Fuse Mod? It's a fuse mounted just to the left of the voltage regulator.

The schematics can be found in the -24 TM in the TM section at the top right of the forum.

Thank you for your reply with the great information and I was thinking along the same lines as the regulator wasn’t getting enough voltage to even properly function I’ll look for that schematic and chase that poor connection down and I do not have that fuse mud but I am planning on putting that in the MOV mod in across pin seven and eight thanks again I’ll keep you updated
Keith

 

[Daybreak]

Thank you for your reply with the great information and I was thinking along the same lines as the regulator wasn’t getting enough voltage to even properly function I’ll look for that schematic and chase that poor connection down and I do not have that fuse mud but I am planning on putting that in the MOV mod in across pin seven and eight thanks again I’ll keep you updated
Keith

Howdy,
STOP.
IMHO do not run it any more until the quad fuse is in place. It's easier to wait, and get that done, that tearing the genhead apart because you blew the stator.

MEP-802A MEP-803A Filters and Parts

The 2nd post has quick links to the info you need.

 

[willswim15]

Howdy,
STOP.
IMHO do not run it any more until the quad fuse is in place. It's easier to wait, and get that done, that tearing the genhead apart because you blew the stator.

MEP-802A MEP-803A Filters and Parts

The 2nd post has quick links to the info you need.

Thank you for your reply
I will get that quad views install tomorrow and then continue to troubleshoot the unit

 

[willswim15]

Thanks everyone for your help I was able to get this unit running I traced the wires down to the quad windings and noticed that at the voltage regulator connector pins 4 and 5 The wires have been reversed from whoever worked on it the last time so I swap those back and I got 120 V at the regular pins 3 and 4 but the output of the generator still was 155 and the regulator wasn’t able to adjust it at all from the front panel voltage knob . so I pulled a regulator unit apart and noticed that the two MOSFETs we’re shorted drain to source I replace those and the quad op amp Chip and the unit is working great now thanks again everyone for your help
Keith