HP Color LaserJet 5500 Fuser - C9736A

This outline of how the fuser works in the Color Laserjet 5500 series largely applies to the Color LaserJet 5550 as well. The 5550 fuser is a different part code and has some improvements such as the ability to speed up more quickly for heavy media but otherwise they are very similar.

Replacing the Fuser - Quick Guide.

The fuser in the Color LaserJet 5500 and CLJ 5550 is user replaceable. This is one of the benefits that tend to be found on professional printers as against cheap little mono machines.

The printer will give a message "REPLACE FUSER KIT" when its firmware detects that the fuser needs to be changed.

The fuser is in the top of the CLJ 5500 / CLJ 5550 printer under the hinged lid and just behind the control panel. The printer should be turned off before handling it as several electrical connections are partly exposed. It may also be helpful to leave the printer turned off with the lid open for a while - immediately after use the fuser is hot.

The fuser is held in place with two big blue thumb screws which need to be unscrewed; it should just lift out by handles on either side. The big block of connectors on the right hand as you look at the machine makes this side more difficult to lift, so ease the fuser straight up.

The replacement fuser eases into place where the old one was removed. Secure it with the thumbscrews and turn the power on. Having given the message the printer should be watching for the change and will prompt with: "NEW FUSER KIT=" select YES and the job is done, the printer should start up normally. There is more information below on what do do if that isn't what happens.

The old fuser should have a value. Unfortunately the price usually paid won't cover courier fees. One refurbisher is offering £1 per unit in April 2011. If you re-pack the fuser in the box it came in and put it with recyclable cartridges most of the recyclers will take it. We will, of course, accept the old fuser if you buy a new one from us.

What Fusers Do

Fusers in laser printers adhere the toner to the page using a combination of heat and pressure. In ordinary fusers this is done by having a heated roller spring loaded against a rubber roller so that paper is squeezed between them. The temperature of the heater is typically in the range 150 to 300 centigrade so that the paper and toner are quickly raised to an adequate temperature. The printer will vary the fusers temperature and operating speed to suit the print media. Heavy paper might travel slowly through a hot fuser. Transparencies tend to be handled slowly through a cool fuser. Ordinary office paper will be handled quickly through a fairly hot fuser. A laser printer will typically match its "headline" speed when ordinary office paper is used.

Fuser temperature is maintained by a thermostatic feedback loop between the fuser, power supply and the DC controller. A thermistor on the fuser senses it's temperature and feeds that to the DC controller. If the fuser is too cool the DC controller tells the power supply to turn on the fuser heater. When the temperature is just above correct the heater goes off.

The Color LaserJet 5500 and CLJ 5550 fuser is typical of HP and Canon recent designs in replacing the hot roller with a foil sleeve wrapped round a heater. The heater comes to temperature rapidly, and this allows the printer to operate from power-save in a short time and return to power-save quickly without unduly delaying the next print-job. HP sometimes refer to this as "Instant On" technology but don't use the term for this printer. The HP CLJ 4600 and CLJ 5500 use a rather different kind of heater.

The service manual says this fuser uses an induction heater type. A circuit board behind the fuser provides the power for oscillating coils. The circuit diagrams show the wires connecting from the fuser PSU but doesn't go into details. It would be nice to have the details but they probably aren't needed, the fuser PSU seems reliable.

The entry on fusers is identical to that for the Laserjet 4600 confirming that the machines are closely related.

"REPLACE FUSER KIT" Message

Normally the fuser only needs replacing when the printer explicitly asks for it with the message "REPLACE FUSER KIT". The main reason for fusers failing is that the non-stick working surface loses its qualities and the image degrades until something sticks permanently and the image gets a mark in it. Software makes an estimate of when this will happen from usage figures and then gives the "replace fuser" prompt.

The printer tries to detect a new fuser at power up and after a short wait prompts with "NEW FUSER KIT=". The user needs to press downarrow to highlight "YES" and then press the tick key to accept and reset the fuser count.

Fuser Failure Without Message

Fusers can also fail before their time. Quite often this will lead to a paper jam in or just before the fuser. In these cases the foil on the hot roller has often ripped and the problem can be seen by looking into the fuser mechanism - bits of ragged foil are visible.

Resetting the Fuser.

If the fuser does degenerate before it's time it will need replacing and the rest then has to be done through the control panel. Steps are:

Mucky Print.

One surface of the fuser is heated, in the CLJ 5500 series this is the rear /lower surface because that is the side of the page with the toner on it. The toner part-melts in the fuser so that it sticks to the paper and the colours blend. Toner would stick to the fuser hot surface as well but that should not happen because:

• Fuser foil is made from (or coated with) non-stick material.
• Modern colour toners contain lubricant material that makes them less likely to adhere to the fuser.

A potential problem with "compatible" toners is that their colour quality is OK but the temperature or non stick qualities are not so good. For instance a toner with an incorrect melting point might build up on the rollers giving dirty print. A toner with inadequate release properties is likely to build up on both fuser surfaces giving dirty print and shortening the life of the fuser.

Life Shortening Events for a Fuser

A critical event for a fuser is something like a staple passing through it. This might seem unlikely but paper will pickup and feed with a staple in the corner, it just won't pass through the fuser without damaging it.

Transparencies and envelopes pose particular problems. The CLJ 5500 has a sensor that detects OHT supplies and adjusts accordingly but it can't deal with inappropriate material. People sometimes put inappropriate transparencies through a printer and it melts in the fuser. It is difficult to remove the mess and the cheapest repair is to replace the fuser. Envelopes have sticky material on their flaps and it may tend to leave a deposit in the fuser which leads to marks on the page. Printer manufacturers sometimes give stern warnings in the user manual about using only approved brands of transparency and envelopes - and indeed their own paper.

Long Fuser Life

The estimated life of the CLJ 5500 series fuser is 150,000 pages or around 50 months in normal use. This is a moderately long life for a fuser. The size of the rollers more or less gives the life, barring accidents.

Printer manufacturers usually stress the benefits of using their own brand materials. As most people realise the print agenda is partly profit. As we suggest above their are potential issues with other products. HP isn't too guilty of this and do give information in the user guide.

Identifying Fuser Problems:

The printer gives the "REPLACE FUSER KIT" message when it expects performance to degrade due to the number of pages printed. Other messages indicating a problem with the fuser are the "50" series which are normally seen if the fuser temperature isn't right. There are two likely causes for this - the fuser heater itself has failed (they say its an induction heater) or the thermistors that detect temperature aren't working properly.

• 50.1 - Low Fuser temperature - Turn the printer off, allow it to cool and try again. This error suggests the fuser heater has failed - or its power supply fuse.
• 50.2 - Fuser warmup service - Check connector J100
• 50.3 - high fuser temperature - Check the resistance of the fuser heater and thermistor terminals. This fault could relate to the DC controller or fuser PSU.
• 50.4 - faulty fuser - Check for misconnection and check resistance of the heater and thermistor.
• 50.5 - inconsistent fuser - HP service manual says replace the fuser power supply PCB. We'd suggest checking you have a fuser with the right product code first.
• 50.6 - open fuser - P service manual says replace the DC controller PCB. We'd suggest checking the resistance of the fuser heater and thermistor terminals.

Resistance checks are across

• J100LB-5 to J100LB=6 - should be 300 to 500 KOhms.
• J100LB-1 to J100LB-2 less than 1 KOhm (specifics depend on 110 or 220V model

Repetitive Image Defects

Fusers can be responsible for making a mark on the page if one of the rollers has a defect. The mark will have a characteristic interval.

• Fuser pressure roller 63 mm defect on back of paper fuser poor fusing
• Fuser sleeve (heated roller) 107 mm defect on front of paper poor fusing fuser
• Fuser delivery roller 38 mm defect on back of paper fuser

Product Codes

As with most laser printers Color Laserjet 5500 series fusers differ depending on the local line power supply. This depends on whether they are intended for use in the US/Canada/Japanese markets which have a 110-120 Volt supply or in the EU/UK/Rest of the World where the voltage is 220-240 Volts. There can be oddities in voltage: UK construction sites and quarries sometimes use 110 volts (but aren't likely to have a CLJ 5500) US datacenters sometimes use 220 Volts to reduce the current load on the cables. Almost all the printers shipped in the UK are 220 Volts and distributors only carry the 110 volt version as a special order - if at all.

CLJ 5500

The fuser used in the Color Laserjet 5500 has had several different product codes over time. The service manual gives the following codes:

• RG5-6848-000CN (110 volt, new) -> Now RG5-6848-300CN. C9735A is a kit
• C9656-69001 (110 volt, exchange) -> Now RG5-6848-300CN

• RG5-6701-000CN (220 volt, new) -> Now RG5-6701-310CN. C9736A is a kit
• C9656-69002 (220 volt, exchange) -> Now RG5-6701-310CN

C9735A and C9736A are kits with the fuser and a multi-lingual instruction guide.

C9656-69019 is an engineering name for the kit - its probably the "brown box" version

In the UK the CLJ 5500 fuser is available as C9736A and RG5-6701 with most distributors favouring the first code.

CLJ 5550

• RG5-7691-000CN (110volt, new) -> Now RG5-7691-250CN
• Q3984-69001 (110 volt, exchange) -> Recognised as Q3984A

• RG5-7692-000CN (220 volt, new) -> RG5-7692-260CN
• Q3985-69001(220 volt, exchange) -> Recognised as Q3985A

In the UK Q3985A seems to be the part number most readily recognised but its also known as Q3985-67901

Minor Code Variations:

The "-xxxCN" part of HP product codes is meaningful to their own logistics and usually represents a variation in the product in some way. A redesign of the plastics or packaging might result in a change of number and they progress upwards. The variants may be covered in service notes. Normally the first 8 digits including the hyphen are enough to get the right part. The "CN" suffix is thought to indicate Canon as manufacturer. Canon part numbers are the same if those two letters are dropped.

Codes starting "C" are HP's own, hence they cover the kits and exchange units. Exchange makes sense within an organisation that has it's own logistics and engineers capable of refurbishing broken items. If a courier has to carry goods back it is usually not economic.

The fuser in the CLJ 5500 series is more complicated than many and has a couple of associated parts - the drive assembly and power supply board.

The fuser in these printers has its own drive assembly, which differs between the 5500 and 5550. The drive assemblies are listed by UK distributors. New units don't seem to be stocked but refurbs and "pulls" may be available on request.

• Fuser drive assembly, 5500 only, RG5-6714-000CN
• Fuser drive assembly, 5550 only, RG5-7700-000CN -> Now RG5-7699-070CN

Fuser problems might relate to the fuser power supply. New units don't seem to be stocked in UK distribution but refurbs and "pulls" may be available on request.

• Fuser power supply PCB for 5500 and 5550 (100 - 127 v) RG5-6801-000CN -> Now RG5-7991-000CN
• Fuser power supply PCB for 5500 and 5550 (220 - 240 v) RG5-6802-000CN -> Now RG5-7992-000CN

Both of these parts seem to be reliable

The service manual lists the fuser paper sensor flag as available and indeed UK distributors do hold it.

Paper sensor flag in the fuser assembly for 5500 and 5550 RG5-6842-040CN