Bizhub 250/350 eating drums

**wagon** · 05-21-2008

OK... I used to rebuild hundreds of di250, etc. IU's a year and since they are mostly the same as all the later stuff you will need :

1) The dev spacer rollers (at each end of the mag roller).. started in Di183. The one at the drive end wears the most, so you can often just change that one. Put a (tiny) amount of grease on the shaft before installing the rollers.

2) Inspect CAREFULLY the mylars at each end of the mag roller. They get worn and holes develop, causing dev to come out. This happens most on units with stuffed spacer rollers. If the spacer rollers are kept good you may never need to change the mylars. These, once again, are a Di183 part. You may need to glue the mylars in... I think they sometimes come with a self adhesive stuff, but I can't remember. Take care with their alignment when installing.

3) Superglue, into the dev unit casing (after cleaning), the shaft the drive gear that is driven by the machine runs on. Then lightly grease the shaft.

I apologise for not posting part numbers - I don't work on these anymore, so I am going by memory. Hopefully this will help. In actual fact, these tips apply to every model 'based on' the Di250/350 engine - so, Di350, 351, Biz350, 3510, etc.

Wagon.

**ni311** · 05-24-2008

For Bizhub 1611/2011 the part number is 4163-5298-01 and it's called ROLL

**fixthecopier** · 05-24-2008

Thanks for all of your help. I love this site.

**kingarthur** · 08-12-2008

Originally Posted by fixthecopier

I just became aware of this problem as I was leaving the shop. The service manager has a 250 and a 350 with same problem, machines are in different locations. The 250 has 260,000 copies. The drum and developer were changed at 200,000. It lasted 42,000. Changed it and it lasted 7,000. Changed it and it lasted 7000. Dave says it is sucking developer to make copies and killing the drum. Drum charge, hv parts, and all the usual have been changed. Has anyone seen this?

The "official" answer from Km in the uk is to tape paper over the mylars when emptying the dv units, as, apparently, when you tip over the units to empty them you are contaminating the collars. What we do is hoover out the units without tipping them up, this way the dv units seem to be lasting.

View Profile · 08-19-2008

KM's fix: In the BH 250, I think they are now sending a plastic sheet with the new developing unit so you can cover the rollers etc. while doing the dev change.. . DO be very gentle when lifting the top cover of the d/u and flipping it over.. this is a weak spot and as questionable a design as i have seen in my 27 years in this biz.. if the cover moves more than a half an inch side to side, the control mylars just come off.. And I HAVE had this problem with a 2510 & a 3010.. I thought I'd be smart and just do a d/c in these just like in the BH250.. It tested my & the customers patience until I found out what I'd done

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**Dave10** · 11-25-2009

The stuff about being careful with developer is crap. I know this is what they say at KM, but we are ALWAYS careful about this. We use the mylar covers included with the drum and are very careful when adding developer, and we still get this problem over and over. There is something else going on.

**Hansoon** · 11-25-2009

Some observations I made for another panel some time ago. Perhaps of any use for you though slightly out of context since this was a very long thread overthere:

.......the "nub" on the transferroller is sliding on the drumsurface. Its doing that since the days of the Di-250/350 series and was never causing problems. Old machines with transferrollers over 300K even have the nub being "dug" out by the drums without new drums suffering. The nub is there to keep the distance drum-transferguide constant.

Beside the nub is a small circular disc like roller with a very fine edge. A mark of this edge can be found on the drumsurface but until now never damaged the drum. This disc roller (or collar) keeps the distance transferroller-drum constant.

The distance drum-mag roller however is regulated (or kept) by another disc like roller or collar as Minolta calls them. This roller is sitting on the end shaft of the mag roller and runs also on the drum surface. If worn it can cause drum jitter (most of the larger Minolta's) or in case of the smaller digitals, Di-152/183/250/350/200/251/351 and Bizhubs 200/250/350 will cause ripping of the mylar at the end of the mag roller. Strangely enough almost exclusively the rear one, the driven side, never the front one. The momentum from the gears may be the reason this happens only at the rear of the unit.

However, what seems to happen is that the hole in the collar wears out by the time and becomes larger and at the same time the circumference of the collar wears off too. This wear in total allows the mag roller to come nearer to the drum surface with the mylar inbetween. Eventually the surface of the drum will grab the mylar and rip it off in the direction of the drum rotation. That's the beginning of the end. Re-attaching the mylar with tape doesn't work. The distance between collar-mylar-drumsurface and the strain working on the mylar seems too strong to keep it in place.

The only solution is replacing the collars or at least flip their place from front to rear.

It seems that the new toner/developer of the Bizhub series is more abrasive and that's probably why the Bizhub's are obviously having more often problems than the older Minolta digitals though this very same construction is in use since many years.

The abrasiveness of the toner/developer might explain why Minolta wants the collars being covered when doing the developer change. Hence the mylar strips supplied with a new drumunit to cover the collars avoiding toner or developer particles coming near the collars.

As I mentioned before do I take out the mag roller anyway for cleaning the developer unit and this gives me the opportunity to clean everything well, collars and the shafts, and also allows me to change the collars from front to rear of the mag roller. Measuring the hole and circumference of the collars with a micrometer show a significant difference between of new and old one and also the collar running in front and rear.

and:

A) The drum is fixed and steady in its position by the two metal pins molded in the plastic side covers who in turn are fixed to the developer unit base. Later units have unfortunately a plastic pin which breaks easily.

B) The nubs on the transferroller bushings ride on the drum surface and are there to keep the distance of the spring loaded movable guide of the transferroller constant to the fixed drum.

C) The thin sharp edged collars sitting beside the transferroller bushings ride on the drum surface and are there to keep the distance of the spring loaded movable transferroller itself constant to the fixed drum.

D) The collars sitting on the end of the mag roller ride on the drum surface and are there to keep the distance of the spring loaded movable mag roller constant to the fixed drum.

H) Between the surface of the fixed drum and the surface of the spring loaded movable mag roller are two mylar seals (or guides). The seals are fixed to the base of the developing unit in the cavity under the mag roller. The seals are than led from under over the surface of the mag roller and are attached to the doctor blade with another adhesive piece of seal.

I) The distance drum surface to the mag roller surface is critical not only for the copy quality but also for providing enough space for both seals.
The distance drum surface to the mag roller is determined only by the size of the collars at both mag roller shafts. This distance decreases, especially that of the rear collar, because of excessive wear (probably caused by abrasive toner/developer particles). At a certain point the collar(s) are weared down so much that the gap between the drum and mag roller is not sufficient to keep the seal from being touched by the turning drum. When the drum surface grabs the seal it will be ripped off in the direction the drum turns, in this case downwards.

and:

We manufacture now ourselves collars with an integrated bearing to avoid early wear.

This is a preliminary version, I think to reduce the outside diameter of the ball bearing to 10mm instead of 13mm to have more plastic "meat" around it to avoid cracking of the plastic when getting old.

Hans

**fixthecopier** · 11-25-2009

You are correct. The last few I changed were because the small piece of mylar that is on each end of the mag roller, tucked up under the cover. This strip is coming out from under the cover, on the right side, and bunching up and digging into the drum, pealing the finish off.

**srvctec** · 12-15-2009

Originally Posted by Dave10

The stuff about being careful with developer is crap. I know this is what they say at KM, but we are ALWAYS careful about this. We use the mylar covers included with the drum and are very careful when adding developer, and we still get this problem over and over. There is something else going on.

Yeah, I know it's CRAP since I'm the one who initially started a ticket on this with KM shortly after the BH250/350 series came out. KM came to the conclusion that we were making a mess of things when that is absolutely not the case. Something changed between the 3510 to bh350 series since we NEVER had a single failure of ds collars on 2010-3510 series machines. We even had a developer unit last over 600k which is impossible with the bh350 series. We've tried everything we can think of- removing the stupid sponge spacer, trimming off the mylar that goes the full length of the doctor blade, moving the thin white ptfe washer that comes installed on the front side of mag roller near the ds collar to the inside between the seal and frame. Nothing has worked. What we really need is to have a source for ball bearing ds collars that are of correct diameter as shown in the above post. I bet the developer units will go to 400k like they are supposed to with ball bearing ds collars!

So, where can we buy these collars Hansoon?