Samsung multifunction: scanner error

[SparkyGuy]

Lightly used Samsung SCX-4100 multi.

When powering on, LCD display says "Warming Up Please Wait" while the fuser
heats up. Meanwhile the scanner carriage does a quick "zero" just out a few
mm's and back, but continues to run the carriage motor endlessly, banging
against the zero stop until it gives up and puts up "Scanner Error" on the
LCD.

I got one good copy from it when it didn't do the "infinite zeroing" thing,
so I know it can work.

The scanner carriage is just a piece of tin with the plastic bulb/camera
holder, riding on a single rod. A toothed belt runs around the motor drive
gear and a spring-loaded tension gear at the end of the run. The belt is
simply "pinched" in a groove in the plastic bulb holder. When the carriage is
run up against the zero stop, the motor keeps going and the belt slips
through this groove.

I presume that this is the way it was designed to zero the carriage, just
running the motor long enough to run the full length of the bed and stop. But
it doesn't stop until it gives up.

There is no "home" sensor. No magnet, no opto, nada. Just a metal tab on the
carriage that bangs against another at the top of the run.

I tried holding the belt still, thinking that maybe the motor current is
monitored and when it goes high, that's zero. But the motor (a stepper) just
skips sync, and tries to keep going.

The under side of the glass has no marks that might be used for zero
indication by the camera.

I checked ground (it's tight) and for routing of the data cable from the
scanner carriage (it goes through its huge ferrite bead).

How do these el-cheapo models determine zero position?

Where might I look for a problem?

Yes, I know it's cheap. But if I can keep it out of the landfill and have a
simple document scanner, that would be great.

Thanks.

 

[webpa]

Lightly used Samsung SCX-4100 multi.

When powering on, LCD display says "Warming Up Please Wait" while the fuser
heats up. Meanwhile the scanner carriage does a quick "zero" just out a few
mm's and back, but continues to run the carriage motor endlessly, banging
against the zero stop until it gives up and puts up "Scanner Error" on the
LCD.

I got one good copy from it when it didn't do the "infinite zeroing" thing,
so I know it can work.

The scanner carriage is just a piece of tin with the plastic bulb/camera
holder, riding on a single rod. A toothed belt runs around the motor drive
gear and a spring-loaded tension gear at the end of the run. The belt is
simply "pinched" in a groove in the plastic bulb holder. When the carriage is
run up against the zero stop, the motor keeps going and the belt slips
through this groove.

I presume that this is the way it was designed to zero the carriage, just
running the motor long enough to run the full length of the bed and stop. But
it doesn't stop until it gives up.

There is no "home" sensor. No magnet, no opto, nada. Just a metal tab on the
carriage that bangs against another at the top of the run.

I tried holding the belt still, thinking that maybe the motor current is
monitored and when it goes high, that's zero. But the motor (a stepper) just
skips sync, and tries to keep going.

The under side of the glass has no marks that might be used for zero
indication by the camera.

I checked ground (it's tight) and for routing of the data cable from the
scanner carriage (it goes through its huge ferrite bead).

How do these el-cheapo models determine zero position?

Where might I look for a problem?

Yes, I know it's cheap. But if I can keep it out of the landfill and have a
simple document scanner, that would be great.

Thanks.

On cheap and expensive machines, zero position is usually determed by
a led-pt (phototransistor) pair or assembly. These sometimes have
tiny aperatures that become blocked by ambient hair (pet-human-etc).
Find your sensor pair and clean it. If still no joy, look at the
assembly with a video camera or still camera...their sensors can "see"
IR emitters very clearly (verify this with any working TV remote
control). If you don't see the emitter shining: Fix it.

 

[SparkyGuy]

On cheap and expensive machines, zero position is usually determed by

a led-pt (phototransistor) pair or assembly.

I've disassembled the scanner completely. There's no place for an opto (if it
existed) to be "interrupted" (by a tab or such). There's nothing but a long
rectangular plastic holder that has a long pcb glued on the bottom and the
lamp and camera elements within. (Surprise! When I removed it and turned it
over, there was a label: "Canon". The flex cable connects to the pcb.

Used a digicam as you suggested. Nothing other than the exposure lamp.

It's still a puzzle how it registers ("zeros") let alone what's
malfunctioning.

Thanks.

 

[Lionel]

I've disassembled the scanner completely. There's no place for an opto (if it
existed) to be "interrupted" (by a tab or such). There's nothing but a long
rectangular plastic holder that has a long pcb glued on the bottom and the
lamp and camera elements within. (Surprise! When I removed it and turned it
over, there was a label: "Canon". The flex cable connects to the pcb.

Used a digicam as you suggested. Nothing other than the exposure lamp.

It's still a puzzle how it registers ("zeros") let alone what's
malfunctioning.

Could be using the CCD itself to detect a pattern underneath the lid
of the unit, just before the start of the glass sheet. That's how a
lot of them do their lamp check. Try looking for patterns or black
marks on the underside of the housing that surrounds the glass.

 

[SparkyGuy]

Could be using the CCD itself to detect a pattern underneath the lid

of the unit, just before the start of the glass sheet. That's how a
lot of them do their lamp check. Try looking for patterns or black
marks on the underside of the housing that surrounds the glass.

I thought that might be the case. Just beyond the clear glass area (in the
"home" end of the glass) is this pattern of white and black (view in
mono-space font). Area within lines is white:

__________ ___________ ___________
| |__________| |__________| |
|___________________________________________________|

I cleaned the glass. What else to do? If it's not "reading" this pattern,
could indeed be the reason its not "zeroing".

I'm guessing the ccd is toast. Or one of the traces on the ribbon cable (one
of those mylar PC affairs) broke.

 

[Lionel]

I thought that might be the case. Just beyond the clear glass area (in the
"home" end of the glass) is this pattern of white and black (view in
mono-space font). Area within lines is white:

__________ ___________ ___________
| |__________| |__________| |
|___________________________________________________|
Bingo.

I cleaned the glass. What else to do? If it's not "reading" this pattern,
could indeed be the reason its not "zeroing".

I'd say that's almost certainly the case. You might check of
misalignment of the sensor, or for something interfering with the
light path from the lamp to the pattern, to the sensor.

I'm guessing the ccd is toast. Or one of the traces on the ribbon cable (one
of those mylar PC affairs) broke.

I've never seen a totally bad CCD. The golden rule of electronic
equipment diagnosis is that 90% of faults are due to bad connections
of some sort, & 90% of those connection faults are in moving parts.
I'd trace the path around the flat cable, starting from the joints on
the main board ribbon connector, right through to the joints on the
corresponding connector on the CCD board.

 

[SparkyGuy]

Bingo.

I'd say that's almost certainly the case. You might check of
misalignment of the sensor, or for something interfering with the
light path from the lamp to the pattern, to the sensor.

There's no "sensor", per se, in this design, is there? I mean, the pattern on
the underside of the glass that marks the end of the "page" region is read by
the CCD and interpreted as "home", right? No sensor, cheap to do in software.
Or am I not understanding something? (always a possibility (c: )

I've never seen a totally bad CCD. The golden rule of electronic
equipment diagnosis is that 90% of faults are due to bad connections
of some sort, & 90% of those connection faults are in moving parts.
I'd trace the path around the flat cable, starting from the joints on
the main board ribbon connector, right through to the joints on the
corresponding connector on the CCD board.

I ohm'd out the cable. Tests good.

Looks like the CCD has died. Well, the printer is "ok", but not great. It'll
be fine for text (albeit single-sided). Have inkjet for image printing.

Thanks,
Dave

 

[Lionel]

There's no "sensor", per se, in this design, is there? I mean, the pattern on
the underside of the glass that marks the end of the "page" region is read by
the CCD and interpreted as "home", right? No sensor, cheap to do in software.
Or am I not understanding something? (always a possibility (c: )

By 'sensor', I meant the CCD, as we've already confirmed that the unit
doesn't have a dedicated home position sensor.
Your unit obviously uses the black & white pattern as both a home
position sensor & a white-level reference, & does both in firmware.
(And yes, back in the old days, when an 8048 CPU & a 2716 (2KB) EPROM
were the second & third most expensive chips in the scanner, it was
cheaper to use dedicated sensors to detect home position, rather than
a handful of EPROMS. ;^)
Anyway, I was referring to the possibility that the CCD might be out
of optical/mechanical alignment with the 'home position', or might
have dirt/dust on that end of the CCD, which might screw up the
pattern detection.

The latter is a very common failure mode, BTW. And those tiny clip
down connectors for the mylar film cables pop open/loose *very*
easily, especially with vibration. Back when I fixed Toshiba laptops
for a living, those bloody connectorss were the single most common
cause of screen failures (after accidental breakage), because the LCD
modules use as many as eight of those ribbons to connect the
pixel-drive controller boards to the actual glass, & when one came
loose, part of the screen would go dead. The best fix turned out to be
re-clipping the ribbon firmly & then taping across the clip & part of
the ribbon with fibreglass tape, a procedure that Toshiba eventually
started doing at the factory.

I ohm'd out the cable. Tests good.

From the connector, or from the ribbon itself?

Looks like the CCD has died. Well, the printer is "ok", but not great. It'll
be fine for text (albeit single-sided). Have inkjet for image printing.

Thanks,

My pleasure. Even if it hasn't gotten your scanner going, maybe
someone will have found the discussion educational. ;^)

 

[SparkyGuy]

Anyway, I was referring to the possibility that the CCD might be out

of optical/mechanical alignment with the 'home position', or might
have dirt/dust on that end of the CCD, which might screw up the
pattern detection.

If its out of alignment, there's little I can do; it's a plastic assembly
riding on a polished rod. Not a precision fit, and no adjustment I can see...

I never cleaned the CCD assembly, but what have I got to lose? I'll take some
alcohol to it and see what happens.

The latter is a very common failure mode, BTW. And those tiny clip
down connectors for the mylar film cables pop open/loose *very*
easily, especially with vibration. Back when I fixed Toshiba laptops
for a living, those bloody connectorss were the single most common
cause of screen failures (after accidental breakage), because the LCD
modules use as many as eight of those ribbons to connect the
pixel-drive controller boards to the actual glass, & when one came
loose, part of the screen would go dead. The best fix turned out to be
re-clipping the ribbon firmly & then taping across the clip & part of
the ribbon with fibreglass tape, a procedure that Toshiba eventually
started doing at the factory.

Did Toshiba give you credit for the fix? (c: Well, at least the world now
knows the Lionel designed it! Take note, world!!

From the connector, or from the ribbon itself?

Ribbon only. I'll attempt to test across the connectors next.

My pleasure. Even if it hasn't gotten your scanner going, maybe
someone will have found the discussion educational. ;^)

And with the added bonus of USENET's "forever" archive, your advice is
recorded for future generations (c:

Thanks again,

Sparky

 

[Lionel]

I never cleaned the CCD assembly, but what have I got to lose? I'll take some
alcohol to it and see what happens.
Exactly.


Did Toshiba give you credit for the fix?

No, because I didn't invent it. Somebody at Toshiba came up with
the idea of using glass-tape, & multiple people in the field (myself
included) tried different variations on that theme to improve the
reliability, so my contribution wasn't all that big.