# Generac 7550EXL no power output



## jkane6 (Aug 30, 2015)

Hello I have a rather common problem, my generator stopped producing voltage.

It is a Generac 7550EXL Gas generator. 

so far I have replaced the AVR, but no success, the part is assembly power regulator, 84132, the brushes are good, and ohm readings are ok for the brushes

but I did get come ohm and voltage readings, they are

OHM readings:

Brushes 8.6 ohms
Red:Blue 0.6 ohms
Red:Grey 0.6 ohms
Red:Blue on the AVR 2.5 OHMS

I did a field flash (using a 12 volt DC battery)

90Volts from the 110 outlet

170v from the Red and Blue off the disconnected AVR lines when in Field flash

To me it looks like the AVR, but I replaced it so I'm going to replace the Diode rectifier 65795. 

one other thing, when I was field flashing, when I connected the battery for 10 seconds, It put a strain on the motor, like I had a tools or something hooked up to the outlets, but I didn't, so I didn't understand where the load was coming from. 

If you have any insight into what is wrong I can test it and get back to you

additional info:

I found the info on testing the voltage regulator to see if it is bad, I'll do that to validate if the new voltage regulator I received is ok, if that proves ok, I'll move on to the control board. seems the transistors are usually what go when the regulator dies, if they are bad, I'll replace them and retest. 

I will also go back and check the stator for ground fault, which I didn't check the first time around, also the rotor should be checked for ground, I'll update when I get the info. 

regards

Jeff


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## KRE (Nov 29, 2011)

I assume you have checked all fuses. If so Remove the brush holder and ohm the exciter rotor via the two brush slip rings. Then both rings to ground.


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## jkane6 (Aug 30, 2015)

*Ohms for the rotor*

, 
KRE

between the two is 8.2 Ohms

no short (open) on either one when tested to ground 

the (AVR) regulator tested ok. I will test it to the control board next

regards

jeff


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## KRE (Nov 29, 2011)

The system you have is a closed loop, which means it takes power to make power. Check the connections between the AVR an main stator. The Residual magnetic field in the exciter rotor starts the build up of voltage in the main stator which supply's the AVR which supply's the brushes, which supply's the main rotor and around and around it goes until the target voltage is reached. Any defective connection in the loop will stop voltage production. Test the voltage everywhere while running and somewhere you will find the issue. Make sure the engine is running up to speed, as some units have voltage roll off to assist in starting reactive loads. HTH Kenneth


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## jkane6 (Aug 30, 2015)

*control board issues*

KRE,

I tested the board, it should be 118 K ohms, but is 68 K ohms, I then removed the control board and there is a burn spot at the moset and the input capacitor C6 and Q1, I'll repair it and retest all the connections. the board is a revision 6, 83970GS

regards

jeff


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## KRE (Nov 29, 2011)

Glad you found it.


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## jkane6 (Aug 30, 2015)

*Transisitor KSC945YTA Control Board 83970GS*

well, 

I removed all the broken parts from the board, and ordered a new transistor, the transistor had a burn spot, and you could tell it was damaged, so the part should be here in a few days then I'll put things back together and retest, hopefully this is what is wrong, the transistor is KSC945YTA, there are two on the board. 

regards

Jeff


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## jkane6 (Aug 30, 2015)

*Generator Now Works*

Hello, 

thought I should update this, the generator now works, the two issues were

1) AVR was dead (replaced)
2) Transistor on the Control board was dead (replaced with KSC945YTA)

Now the generator now works fine. 

regards

Jeff


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## mulla (Jun 29, 2020)

jkane6 said:


> *Transisitor KSC945YTA Control Board 83970GS*
> 
> well,
> 
> ...


may i ask where you order the parts from


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## iowagold (Jan 22, 2020)

mulla said:


> may i ask where you order the parts from


newark has them in stock $0.22 usd each.
https://www.newark.com/on-semicondu...CMP=KNC-BUSA-GEN-SKU-Semiconductors-Discretes


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