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Old 01-08-2022, 09:34 AM   #12
Join Date: Jan 2022
City & State: Edmond, Oklahom
My Country: USA
I'm a: Knowledge Seeker
Posts: 20
Default Re: Need some help with Epson Printer Power Supply C655 MAIN

This was driving me crazy last night so I did some more digging. I just couldn't walk away from it. I'm a seasoned professional mechanic for a living and I know the importance of proper diagnosis. I also know you can learn a tremendous amount from failure analysis. So I kept going.

I found two transistors on the main board that appear to be shorted. I included a portion of the schematic of the main board. I'm posting this from my laptop and don't have a full copy of acrobat in it so I just did a screen shot of that portion of the schematic. I can post the full one page schematic of the main board if that would help.

The two transistors circled in red appear to be shorted. I removed them from the board and measured across the C and E, 0.3 ohms. I remeasured the +42volt input again and my short is gone.

My question is, what the hell caused these to fail? From the data sheets, they appear to be rated at 15 AMPS!! WOW! That's a lot of power.

The kicker here is, the chip associated with these transistors controls the................wait for it............PRINT HEAD!!! So looks I may have screwed something up in that during my cleaning.......DOE!!!!
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