[Dead] HP color laserjet pro M451dn dead after power surge

[barakm]

Hi everyone,


I got an HP color laserjet printer (Lasrjet pro M451dn) that went completely dead after a power surge.
I'm not a technician, but I have some knowledge in electronics, and I also have
some tools (soldering iron, multimeter, osciloscope).


I suspected the DC power board, so I took it off and discovered that the square
fuse next to the main entry was blown. I replaced it, and when I connected again -
I heard one click from a relay, and then everything went dead again. The new fuse
got blown too.


So I guess there's a short-circuit somewhere along the switching power supply,
but I don't have the schematics. In addition, the power supply is composed
of 2 boards, each of them running its own switching mechanism (if I understand correctly what I see). In addition, there's probably some standby circuit that triggers everything,
since the power button is electronic.


So what am I asking?
First, if you happen to know if the shematics for this power supply is available
somewhere. The HP part number is RM2-8024. The service manual does not provide this info.


Also, if you could give some guidelines about finding the fault, this would be great.
I know the immediate suspects are the diodes, FETs, and the capacitor, but I don't
know how to test them while in-circuit....


Any hint will be appreciated !


Thanks,


- Barak

[techie0419]

[Artefil]

Re: HP color laserjet pro M451dn dead after power surge

Hi,
On HP laserJet the PSU is divided into 2 cards. One for low voltage, one for high voltage.
Here's the circuitry for low voltage
Capture d’écran 2023-08-15 à 03.09.12.jpg
On the low voltage circuitry you have two fuses (protecting against surge). Verify CA and CC lines
The high voltage circuitry is designed for supplying : primary charge roller, Developper roller, transfer roller, pressure roller.

Here's an example of high voltage

Capture d’écran 2023-08-15 à 03.29.35.jpg

I'll check if I can find any information concerning RM2-8024 (you got it on ebay.com & on servers4less.com, on ebay it's 29$, more cheaper than the original one)
Hope it'll help
Artefil