Samsung multifunction: scanner error

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.

Reply to
SparkyGuy
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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.

Reply to
webpa

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.

Reply to
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.

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Reply to
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:

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

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.

Reply to
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.

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.

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Reply to
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: )

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

Reply to
SparkyGuy

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.

From the connector, or from the ribbon itself?

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

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Reply to
Lionel

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.

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

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

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

Thanks again,

Sparky

Reply to
SparkyGuy

Exactly.

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.

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Reply to
Lionel

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