HP WG8-5624 PhotoInterrupter for HP LaserJet Printers.

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HP Part WG8-5624 is a photo-sensor, photo-interrupter, optical detector or sometimes just "opto". It is used in many HP, Canon and other printers, HP Partsurfer lists more than 200 uses. This page was compiled as part of the documentation for the P4014 etc where the sensor is used to detect output bin full, for instance.

A photointerrupter is a small electronic component in black plastic. The black plastic helps keep ambient light from causing problems The working part is something like a "U" shape. One arm contains a GaAs infrared LED whilst the other has a silicon photo-transistor in it.

Ordinarily the LED shines across the 5mm gap at the photo-transistor, turning it on. The beam interrupter is something like a plastic flag, shutter or paper-dog that moves in and out of the gap. Making and breaking the beam of light turns the photo transistor on and off so that the device acts as a highly reliable switch.

paper-flag-principle

Mechanical switches can be used to sense paper movement but since paper sheets are not very heavy or rigid the switches need to be very lightly contructed with easily bendable contacts. This means the contacts don't self-clean very well if they get contaminated by tarnish, oil or paper dust. Alternatives include magnetic reed switches and various kinds of proximity switch. Photo-interrupters are the preferred solution; easy to implement, compatible with electronic logic and usually very reliable. There is a bit more about their role in paper movement sensing here.

Back in the days when band-printer and dot-matrix machines ruled printers had only one "paper out" sensor. This stopped the printer before it got ink all over the platen and sent a signal to the computer so that data wasn't lost.

Cut-sheet paper requires a bit more. The roller that sets the paper in motion might slip a bit and if that happens the paper will arrive late and print might partly miss the page. A sensor just after the paper tray moves as the leading edge of the paper hits it and tells the printer logic where the paper is. There might be another sensor to ensure paper does reach the output tray - otherwise a horrible mess of compacted sheets could build up around the fuser. Cheap printers tend to just have a couple of sensors - there is some expense in using them. More professional machines can have a dozen or more sensors looking at paper width and the exact position in the paper path so they can report problems accurately and even attempt to recover automatically.

This part was designed by Toshiba specifically for copiers and printers but it is also used in heaters and air conditioners to sense airflow and in games machines to sense movement. Toshiba call it TLP1241. It is a black black plastic module with a white 3 pin "CT" connector on one side. The device is the same in all these applications, except that there are variations in the connector.

WG8-5624

Problems and Faults

The main problems for an optical sensor are dust and bright light. Dust can usually be blown away. The device lense blocks visible light with a wavelength of 700nm or less. The infra-red component in sunlight can interfere with operation forcing the signal on when it should be off. The device should be mounted where this is unlikely to be an issue. Certain kinds of oil may be incompatible with the polycarbonate(UL94V−2,black) or connector material polybutylene terephthalate(UL94V−0,white).

Toshiba recommend handling the device by its body, not by the connector or attached wire. They also recommend connecting and disconnecting the CT plug and socket by pushing and pulling straight in and straight out, otherwise the connector may become unreliable.

All optical emitters ultimately lose brightness and at some point that will innevitably be a problem with these. In practice many of these devices last in excess of ten or even 20 years - printers made in 1993 are still going.

WG8-5624

Devices like this aren't regarded as repairable. Some photo-interrupters have a visible slot which can gather paper dust so a clean with a fine brush might restore operation. The device is in a snap-in mounting and is connected via a plug so it can be easy to change - although getting to it is not always easy.

More sophisticated printers like the P4014 and M601 series have a diagnostic mode which can report the action of sensors like the photo interrupters. Otherwise tracking down faults caused by this kind of part can be quite difficult. We suspect the difficulty of identifying faults caused by photo-interrupters leads a lot of printers to landfill  !

To see WG8-5624 in context in the P4014 engineering diagrams click here. It's not a big part but essential.

HP Information

HWP-WG8-5624-000CN Photo-Interrupter WG8-5624-000CN Photo-sensor (TLP1241) - Sensor flag activated

WG8-5624-000CN Photo-sensor (TLP1241) - Sensor flag activated Part number WG8-5624-000CN is used in more than 200 HP products.

HP clearly use the code prefix "WG8" for some or all of the opto-electronic switching devices for instance WG8-5362-000CN = Photo-sensor (TLP1241) - Sensor flag activated and WG8-5382-000CN = PHOTO-INTERRUPTER TLP1242

Icecat says WG8-5624-000CN is GTIN (EAN/UPC) 5705965522363

Distribution suggests Kyocera 02-013 Sensor TLP1241 SO-30 5SNSP0012749 has EAN/UPC 5705965578674.

HP tend to call this part WG8-5624-000CN. Canon use WG8-5624-000. As already suggested the part is made by Toshiba who call it TLP1241. Ricoh apparently call the same thing B6021501 and Kyocera 02-013 whilst Xerox have it as 137E16140.


WG8-5624 TLP1241

Web Research

Research began with a Google search which gave About 209,000 results; a lot for a component people tend to overlook. There were a lot of offers to sell the printer part as WG8-5624 and a lot of datasheets for TLP1241 - but few offers of sale in quantities less than 20,000.

Tradebin suggests a dozen vendors selling WG85624, mostly refurbed. How exactly you could "refurbish" a photo-interrupter beggars my imagination but presumably they are clean devices pulled from working printers. We suggest a test circuit above.

Other Research

Partlists and pricelists suggest a small family of photo-interrupters are used in HP printers with this being a favourite.

  • WG8-5624 = TLP1241
  • WG8-5645 = GP1SQ73P
  • WG8-5696 = TLP1243
  • WG8-5849 =
  • WG8-5935 = Fuser output sensor (SR5) used in ent 500 series

Supply Situation

These parts are sold as electrical components in large quantity.

As new spares WG8-5624 don't seem too common, despite the enormous number of web-sites offering them. The part is listed by three UK distributors but only one has any new stock. Demand for the part will probably be quite low.

Second-use stock ought to be quite common - many printers contain one or more of these. However it may be difficult for brokers to identify the part. There might also be issues trusting a re-used part.

We can usually provide these parts when required. The price will probably be under £5 which largely reflects the logistics of obtaining one. The suggested price and availability is just a guideline, our prices change with distribution lists - see the catalog. Stock numbers in distribution suggest there is not great call for the part but that might be because engineers don't regularly identify faults, perhaps because the parts are inaccessible or possibly because supplier pricing is so erratic.

Since the part is widely used, easy to stock and to test we are considering holding local stock. That will cut costs to people who only need one or two as part of their spares kit.


WG8-5624 TLP1241WG8-5624 TLP1241WG8-5624 TLP1241WG8-5624 TLP1241WG8-5624 TLP1241