OK.
For starters, let's look at the power situation of the printer.
NOTE!!:
LETHAL VOLTAGES EXIST in the printer, especially in the areas you will be testing. Take
extreme caution when performing these tests!!
If you cannot read a schematic or are at all unsure or uncomfortable about performing these tests, STOP and seek professional assistance!
If you are unclear about the locations I desribe below, please submit
in focus pictures of the WHOLE PCB and then close-ups of quadrants showing the SMPS chip and surrounding components.
This is a preliminary group of tests for basic power to the SMPS chip. Others may need to be performed.
1. Check which SMPS chip you have, i.e., the M51977P (16 pin)
View attachment 69143 or
View attachment 69144 (20 pin)
2. Note chip orientation markers.
View attachment 69145
Using schematic above, taken from the Datasheet for the M51977P (check point 2 is in two locations - they are identical):
Your particular circuit may vary, especially in the Mains to transformer area!
3. Check for
DC values on pins marked
1 (Vcc) and
2 (Gnd).
4. If DC value between 12 and 30VDC, STOP!
(At this point my best guess would be that the SMPS chip, or some other component associated with it, is defective.)
5. If not, check for
AC value between
2 and
1AC. If present, the diode to the left of the check point is defective.
If DC values thus far are all very low or zero, continue with 6. below:
Again,
NOTE!!:
LETHAL VOLTAGES EXIST in the printer, especially in the areas you will be testing. Take
extreme caution when performing these tests!!
6. Using schematic above, check for DC values
across points
3 and
4 for a DC value in excess of 100VDC. There may be an AC component.
7. If present, check for value across points
4 and
5. If similar to step 6. above, then quite possibly the transformer is defective.
Let us know what you find.