I got involved in the latter stages of this diagnosis. By the time I arrived there was a nice list of 10 loads that are routed through fuse 7 on the power supply which blows. It's had lots of parts including an interlock switch, power supply, and 6 or 7 fuses along the way.
The first thing we did was roam around the machine and unplug various 24vdc motors on our list. I don't remember the whole list but it included new toner motor, recycle toner motor, used toner motor, cleaning unit motor, transfer cam motor, primary cleaner motor, web motor, etc. With the power Off and VOM set to resistance, we measured the load side of the fuse holder to ground: 0.00 ohms. Oops! That's a problem.
Next we started pulling connectors on the Logic PWB. The two connectors that seemed to make a big difference were the LCF optional paper deck (resistance changed to 1K), and the HVT (changed to infinity).
Next we re-connected all the motors, and all the logic PWB connectors excepting the LCF and HVT (gradually settles around 39K ohms). This time the LCF made no difference, not sure why. Maybe a pinched wire or damaged pigtail or connector? The HVT still drags it down to 1K. With the HVT unplugged and another fuse at fuse 7, we made a bunch of perfect (blank) copies, like you might expect.
The new HVT still pulls down the resistance to 1K. So I'm not certain that the HVT was necessary. But this machine no longer lights up fuse 7. Calls like this rarely go in the direction you think it will. I just try to follow wherever the evidence leads. =^..^=
The first thing we did was roam around the machine and unplug various 24vdc motors on our list. I don't remember the whole list but it included new toner motor, recycle toner motor, used toner motor, cleaning unit motor, transfer cam motor, primary cleaner motor, web motor, etc. With the power Off and VOM set to resistance, we measured the load side of the fuse holder to ground: 0.00 ohms. Oops! That's a problem.
Next we started pulling connectors on the Logic PWB. The two connectors that seemed to make a big difference were the LCF optional paper deck (resistance changed to 1K), and the HVT (changed to infinity).
Next we re-connected all the motors, and all the logic PWB connectors excepting the LCF and HVT (gradually settles around 39K ohms). This time the LCF made no difference, not sure why. Maybe a pinched wire or damaged pigtail or connector? The HVT still drags it down to 1K. With the HVT unplugged and another fuse at fuse 7, we made a bunch of perfect (blank) copies, like you might expect.
The new HVT still pulls down the resistance to 1K. So I'm not certain that the HVT was necessary. But this machine no longer lights up fuse 7. Calls like this rarely go in the direction you think it will. I just try to follow wherever the evidence leads. =^..^=
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