Orion 4100gx 3.3 amps at idle

One side of the board is puling 3.3 amps at idle (with power connected to only that side of the board). Also found a few of the PS Fets getting hot one side of the board. This would typically indicate a shorted driver, PS Fet or output transistor.

I pulled all of the drivers and they check good. I pulled the PS fets that where getting hot and they all checked good (replaced them anyway as seen in photo). Ohm checked the opposite side PS Fets and found and they all checked good.

I pulled all of the output transistors on the side same with the overheating PS Fets and they checked good.

I lifted the legs on the resistors for the output transistors on the other side and the amp is still pulling 3.3 amps at idle.

I pulled all of the caps and lifted one wire of the heat sensor and it amp is pulling 2.0 amps at idle (see attached photo for current state of amp pulling 2.0 amps). PS fets still getting hot (circled in photo). I could find no solder traces.

Would greatly appreciate any help on this one...


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Removing the caps dropped the voltage to 2.5 amps. Lifting one wire of the thermal switch dropped it to 2.0 amps.

No, the PS is not operating after the thermal switch is disconnected. However, my bench power supply is set at 12.5v DC and the DC voltage on the center legs of the PS Fet's is 8.13v.

Only the one 6488 circled in the attached photo is getting hot with the wire lifted on the thermal switch.


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Perry Babin

Paid Member
2003-11-20 11:01 am
The non-494 amps won't start through a limiter. They just pull about 5 amps without starting.

You can measure the DC voltage across the emitter resistors to see if current is flowing through them. You don't need to desolder them.

The circled transistor isn't a PS transistor. It's the transistor that controls the rest of the transistors. It should not be passing current with the thermal removed. It may be leaky. If it's not, what's the DC voltage with the black on the emitter and the red on the base?
I hadn't realized the non-494 amps won't start through a limiter. Thank you for that info.

The reason I desoldered the emitter resistors was to take the 6488 output transistors out of circuit.

I did realize the circled 6488 wasn't a PS transistor and likely was functioning as a regulator or controller. The DC voltage across its base and emitter is +0.320v.