The repair on an HP LaserJet 4 printer.

[Skywave]

Having received a good deal of helpful advice and suggestions at this Forum about the repair of this item, which has finally reached a satisfactory conclusion, it seems appropriate to give a brief summary of what happened.

Originally, the printer flagged a Service Fault code and by reference to the Service Manual, several culprits were listed as 'possibles'. Normally, having many 'possibles' is O.K if you are in a service depot with a plentiful stock of 'known good' spares: not in my case. But I do own two HP LJ4 printers, so by carefully swapping modules around, I was able to narrow the search.

Initially, the d.c. controller was proven to be faulty. A replacement was purchased, but the fault remained. At that point, only one module was left as the 'possible culprit': the main motor pcb ass'y. The HP part number is RH7-1151. However, it soon became apparent that trying to obtain that part was going to be difficult - if at all. That pcb consists of the motor itself and its accompanying electronics: the heart of those electronics is a 3-phase motor controller chip made by Sanyo. Apart from the fact that it was not mechanically possible to divorce the motor from the electronics (so I couldn't test the motor in isolation), the Sanyo chip appears to be obsolete: 'unobtainium'. Hence, a repair to component level was out of the question.

However, a bit of research revealed another HP part number, RH7-1152, with the description 'motor pcb ass'y. for a LaserJet 4'. Since I have some experience with HP part numbers, that part number, being the 'RH7-1151' 'plus 1', to me, sounded very much like a 'mark 2 version' of the '1151: I decided to take the gamble: found a source and bought one. When that item arrived, I promptly fitted it: printer restored to normal working order. (Phew!)

Now upon an exam. of the '1152 part, I discovered that the motor controller chip was different to the type fitted on the '1151: ah-ha! - as I suspected. However, during this entire repair procedure, care was needed in identifying parts, since there are several variants on the 'HP LJ4' theme: and some parts are not interchangeable amongst them.

So, all-in-all, quite a challenge, but thanks to all the help and suggestions made by members here - plus an application of my '3Ps' - success was eventually achieved. However, without a second LJ4 available, I suspect I would have been forced to abandon this printer.

And the final cost to me: just under £30; I'm happy with that.

Al.

[paulsherwin]

Glad you got it sorted.

[G8UWM-MildMartin]

I'm also glad you resurrected it very cheaply compared to its original price without killing the other one.
They're an ideal companion to Paul Stennings's service data DVD:
Genuine but old stock 92298X cartridges can be had for under £25 and will do over 8000 pages and, used with, say, Tesco Basics paper, gives a total page cost of well under a penny.

[Nymrod121]

"Three of the most useful items in any fixer's toolbox: Patience, Persistence and Perseverance."

Q.E.D. - !

Guy

[julie_m]

If I remember rightly, the LJ4 was about the last of the tank-like-built HP laser printers (I'm sure we had one at my last place of employment up to late 2002), so well done for keeping it going.

[Skywave]

Originally Posted by G8UWM-MildMartin

Genuine but old stock 92298X cartridges can be had for under £25 and will do over 8000 pages and, used with, say, Tesco Basics paper, gives a total page cost of well under a penny.

Quite: those old stock cartridges and that paper is exactly what I have been using for ages.
These printers may be heavy, a bit clunky and (relatively) old tech., but they're built like a battleship, reasonably easily to dismantle (being of a modular form of construction), and, moreover, they provide my wife and me all we need for our simple computer printing needs. Now add to that that the initial acquisition cost of these printers was zero and as long as I can get parts for repair (when necessary), I shall keep using them. The OSs in use here are Windows_2k and Win_XP SP3.

Al.

[mole42uk]

I now wish that I hadn't ditched mine when it died last year. I had the double-sided sheet feeder on it too. Probably the best printer I ever had.

[Andrew B]

Have you dismembered the old board/motor assembly ?

I like to identify and collect the component from whatever I am repairing, I then put it in my "black museum" of Hunts, Waxes, thermal intermittent LED's, OC resistors and "YES" I have an open circuit 1N5408

[Skywave]

Originally Posted by Andrew B

Have you dismembered the old board/motor assembly ?

No. In essence, there are two sub-assy's.: the motor itself and the pcb (to which the motor is attached), with the motor drive electronics on it. The motor cannot be removed from the pcb; the motor cannot be dismantled. Most of the parts on the pcb are tiny SMT devices. The controller i.c - which is also SMT - appears to be an obsolete item.
It is quite clear that from HP's viewpoint, this ass'y. is the LRU (lowest replaceable unit).

Al.

[Jim - G4MEZ]

That's a great fix Well done!

Originally Posted by julie_m

If I remember rightly, the LJ4 was about the last of the tank-like-built HP laser printers (I'm sure we had one at my last place of employment up to late 2002), so well done for keeping it going.

Not quite, I think the LJ5 (just an update to the LJ4) carries that honour.. Last HP Mono printer with a proper steel chassis before the LJ4000 series came in with its cheap plastic chassis that would break at the drop of a hat... Good electronics though...

The LJ5 chassis might have bent but a hammer would sort that out... Nothing known to man would make a successful repair to a LJ4000 plastic chassis...

I still use an LJ4000 as my main mono printer... Consumables are just as cheap as for the LJ4...

For colour I run the last HP battleship, the Colour LaserJet 4500... Apart from taking a while to warm up and calibrate it is a great machine. Consumables for that too are now plentiful and cheap...

It's interesting to note that every generation of HP laser printer since the LJ5 has got flimsier and more fragile... They have also got faster too.

[julie_m]

Originally Posted by Jim - G4MEZ

It's interesting to note that every generation of HP laser printer since the LJ5 has got flimsier and more fragile... They have also got faster too.

I think we have witnessed the evolution of the printer from precision instrument to consumer cp built down to a price and with performance barely an afterthought.

I suppose they only get away with it because most people don't remember the days when printers were built do do a job well, and be maintained in the field. They just see how many pages it can print per minute (on a good day, with the wind behind it) and the initial purchase price.

[Paul Stenning]

Printers also tend to be one per desk or shared by just a few people rather than one per office now, so size and price (along with ease of replacing toner etc) are more important that heavy duty construction.

My main client uses Brother mono laser printers on a one per desk basis for printing delivery notes and invoices etc, probably 100 or so pages per printer per day. They normally get about 3 years use before they start becoming temperamental and are replaced. At under £100 each the cost is negligible to them.

[mole42uk]

Originally Posted by julie_m

most people don't remember the days when printers were built do do a job well, and be maintained in the field.

Most people don't remember the term "paperless office" which was heralded in the early 70's as the Next Big Thing, once we all had computers on our desk.

[Paul Stenning]

Very true. Computers have just allowed people to create even more paperwork easily themselves...