Making Standard SIMM s Work / Memory Upgrade on the HP LaserJet 6MP / 5MP

*** I am not responsible if you ruin perfectly good 72 pin SIMMs or your HP LaserJet printer. Proceed with CAUTION and NOTE: This procedure worked on my 6MP and MAY NOT WORK FOR YOU AND COULD DAMAGE YOUR EQUIPMENT.  Read these instructions in entirety before beginning work.***

I am a bit of a computer and electronics junkie and recently had the opportunity to purchase a close to new HP LaserJet 6MP at auction for next to nothing. Being the curious chap that I am, I wondered how much RAM the thing had and if I could possibly upgrade it cheaply (ie: not have to buy the HP-approved upgrade modules). I found that the unit had the standard 3 Megabytes installed and that it also sports two empty 72 pin SIMM slots, much like those found on older 486 motherboards. This really peaked my interest because I have a bag of totally worthless SIMMs laying around that I figured I could use. After doing a little research, I found that:

The following HP LaserJet printers seem to use the same type of RAM: 5, 5M, C3100A, 6MP, 5Si MOPIER, 5Si MX, 5Si, 5Si NX, 5M, 5, 5N, 5se, 4+, 6P, 6Pxi, 6Pse, 5P, 5MP, 4MV, 4P, 4MP, DesignJet: 750C, 750C Plus, 700, 330, 350C, DeskJet: 1600CM, 1600C, 1600CN, PaintJet XL300

Depending on your printer, you may have a different maximum capacity. The memory capacity on the 6MP is 35 Megs (Two 16 MB sticks + PostScript card RAM + Internal RAM).

HP used a technology called “presence detection” that essentially jumpers unused pins on SIMM memory modules together in certain sequences to tell the printer how much RAM is installed and what type it is.

Any 72 pin RAM SIMM can be used on the 6MP so long as it is 70ns or slower speed and is equipped with “presence detection” or jumpered pins.

*Most of this information I obtained from a newsgroup posting titled “SIMM Identification for LaserJets”, Author Unknown and eBay auctions for SIMM modules for the HP printers.

Being that I had a whole bag of RAM that I could sacrifice and some free time on a boring Sunday afternoon, I decided to try to make my SIMMS work in my 6MP LaserJet printer. The first attempts worked on a 4 meg SIMM, but I wanted to max out the RAM, so I perfected my technique on a second set of RAM. This process is detailed below.

Required Supplies & Tools

You will need a few tools to operate on your RAM and make it compatible with your LaserJet, DesignJet, DeskJet, or PaintJet printer. They are pictured below (click the picture to enlarge in a popup):

The needed tools are:

  • 15 watt (or lower) soldering iron – too hot an iron will burn your memory components
  • Multimeter – digital or analog doesn’t matter so long as you can detect continuity (use the OHM setting)
  • Stranded wire to use for jumpers (one strand per jumper) – speaker wire works well
  • Needle-nosed pliers help hold the hot wire while you solder
  • Solder wire, of course
  • Wire cutters
  • Grounding strap (optional, but highly recommended) to discharge static electricity

Identifying your RAM

More than likely you will have the same situation that I did. I tested the RAM for continuity between pin 72 and pins 67-70; none of my pins had continuity (were connected to each other). If you find that pin 72 is connected to any other of the pins 67-70 on your RAM module, then you may just have “presence detect” enabled RAM that will work out of the box in your Hewlett Packard printer. Before you start soldering jumpers, test the RAM in the printer and see if it’s recognized.

If you don’t have continuity between pin 72 of your SIMM and any of the pins 67-70, then you will need to solder jumpers onto the RAM. I found the following chart online in a newsgroup post titled “SIMM Identification for LaserJets”:

“I” indicates infinite resistance to pin 72.
“G” indicates pin     pin     pin     pin     size    speed
70      69      68      67

I       I       I       I       not a valid SIMM (possible ROM SIMM)
I       I       I       G       not a valid SIMM (”               “)
I       I       G       I       not a valid SIMM (”               “)
I       I       G       G       not a valid SIMM (”               “)
I       G       I       I       8 MB        70 ns
I       G       I       G       1/16 MB     70 ns
I       G       G       I       2/32 MB     70 ns
I       G       G       G       4 MB        70 ns
G       I       I       I       8 MB        80 ns
G       I       I       G       1/16 MB     80 ns
G       I       G       I       2/32 MB     80 ns
G       I       G       G       4 MB        80 ns
G       G       I       I       8 MB       100 ns
G       G       I       G       1/16 MB    100 ns
G       G       G       I       2/32 MB    100 ns
G       G       G       G       4 MB       100 ns

This chart tells you what pins should be shorted on your RAM module to work with the HP printer you have. I knew that the SIMMs I had were either 8meg or 16 meg modules and so started by eliminating any other sizes from the list of possible jumper configurations. NOTE: 70ns or SLOWER RAM is required. Also, using the wrong type of RAM in your printer should not damage it, but might.

It could very well be that you have RAM that is so old you have idea how many megabytes it is or how fast it is. If this is the case, you only have a limited number of possibilities in soldering jumpers on. GO FOR IT!

The operation begins

The first step that you should take it to verify how much RAM your printer already has. To do so, plug in your printer, load paper and turn it on. After the printer warms up and the lights stop flashing, depress both the test print and resume buttons on the left top of the 6MP to print a status report page. This page tells you what modules you have installed in the printer, the printer’s pagecount and how much RAM is installed in the printer. If you have less than 35 megabytes total in your printer, then you have room to expand! If you have only 3 megabytes, you are at the standard level of RAM. Anything in between means that there is already a memory upgrade in the printer, but that shouldn’t stop you from maximizing it! 72 pin SIMMs are so cheap nowadays that there is no reason not to. You will be surprised how much faster your printer spools and prints because spool times are drastically reduced with more RAM.

The first thing I did was to remove the printer’s side panel where the RAM is hidden. On the 6MP LaserJet, the RAM is located under a removable cover on the left front of the printer. You can see a picture of where the release is below. You need to raise the top cover where the toner goes and the power cable cover on the left rear before removing the side panel. To remove the side panel, raise the toner cover, depress the side panel release button and slide the panel toward the front of the printer.

After you have removed the side panel, you should see three SIMM slots. On of the slots is most likely filled with a PostScript SIMM if you have a PS enabled printer. The other two slots are where we will install our modded RAM. A picture of the slots and the PostScript SIMM on my laser printer is below:

After you have the covers off, you can start soldering your SIMMs. This is a bit of a trial and error process, especially if you are not sure what type of RAM you have or if you have little experience soldering. Hopefully you do have experience soldering or things might get a little hairy. Using the chart above with the Ground / Infinite designations, solder the jumpers to match your configuration. I would recommend the following:

  • Cut the wire strand / jumper long to solder the first point – this makes it easier to hold
  • Tin the jumper ends before soldering. Tin the RAM pin contacts before soldering also.
  • Don’t rest the soldering iron on the RAM too much or you may damage your SIMM from heat.
  • Hold the wire with pliers (it gets HOTTT!).
  • I soldered my jumpers on the back of my single-side RAM modules to make maneuvering my hands easier.
  • Solder as high on the RAM contact point as possible to prevent interference when installing in the SIMM slots.
  • Use as little solder as possible and make a good contact.
  • Check for bridges between RAM contacts before installing. Use your multimeter to make sure only the pins you soldered register a short or continuity.
  • If you are soldering more than 2-3 jumpers on the SIMM, I would recommend jumpering the pins in series and not all on pin 72. This will make the soldering easier.
  • Wear your static strap to prevent damaging the sensitive RAM.

Once you have soldered the SIMM with a configuration referenced in the chart above, carefully place the RAM in the printer one SIMM at a time and print a test page. If the test lights go through their sequence and finish illuminated as normal (with only the ready light lit), AND your total RAM shows up correctly on the printer test report, you were successful! If not, try another jumper configuration after you have turned the printer off and carefully removed the SIMM.

Finishing up

After you have soldered your SIMMs, you should have something that looks like the following:

When you have successfully tested your RAM and everything is working as expected, close up the printer and go about your business! The installed SIMMs look like this in my printer:

Credits / Restrictions
Credit for the chart featured, titled “SIMM Identification for LaserJets” goes to Author Unknown. It could very well be that this document is from HP, but I could not find it on their site or find a posting online with the original author intact. If you wrote this or have a copyright, please let me know and I will post it accordingly.

Dennis Little is the author of this document and images. Use and reproduction is permitted so long as this document remains intact in its entirety and references and Dennis Little as the source.

A PDF of this document is available here: PDF document

Pictures were taken with my new FujiFilm S3000 3 megapixel digital camera if you are interested. I am an amateur photographer and it takes great pictures and lets me play with SLR-like functions. Good deal for little money, this one is. It also takes a variety of filters and lenses readily available in all major brands.

***UPDATE 2015/07/10***

karusisemus has a terrific blog post with more details and a clearer explanation of what we are trying to accomplish, here:

32 Responses to “Making Standard SIMM s Work / Memory Upgrade on the HP LaserJet 6MP / 5MP”

  1. Thanks for this useful tip!
    I successfully added 40Mb to my LaserJet 5p
    1x8Mb + 2x16Mb
    Graphics print improved drasticaly


  2. It’s working! I added 8MB to LaserJet 6P nad works perfect! 😀 thanks a lot!

  3. You’re welcome and that is awesome news! Thanks for letting me know. 🙂

  4. Hi! I’ve just put 2x32MB SIMMs in my 6MP and it works, wow! Thanks for the instructions!

  5. Hi,

    I just upgrade mine to 34MB with two sticks of 16MB/60ns (8 x Siemens HYB3117405). So far everything is ok. The self test reports 34Mb so all looks ok.
    However i don’t see any improvements in printing. Can you direct me to something I could print with and without the extra memory so that the difference would be visible.


  6. Hi nea_caisa,

    The additional RAM in the printer will not make the printer print faster, it only helps speed up the process known as “spooling”. Spooling is the process of your computer offloading a print job to the printer’s memory for processing.

    For instance, consider the situation where you have a document with a lot of graphics or a document with many, many pages and a printer with little memory. If your printer only has 4 MB of RAM and your document is 16 MB, your computer will have to split the job up into multiple parts (less than 4 MB each) and spool each part to the printer. Your computer will then have to wait until each part completes in order to send the next part.

    If you upgrade your printer to 32 MB and try to print the same large or graphics-heavy document, your computer should send the job much more quickly and with less processing involved; your computer no longer has to split up the job into multiple parts.

    I do not have a specific document for you, but you could try this test:

    1) Print a document that is larger than the original amount of RAM you had in the printer. You might be able to do this by creating a new document and inserting a bunch of photographs into it.

    2) Observe the amount of time the job takes to finish spooling (i.e. when the job disappears from your print queue). When you have the print queue open, also observe the size of the job as reported by the queue to make sure that the document is sufficiently large to justify the test; the size must exceed the amount of RAM.

    3) Now turn off the printer and remove the new RAM

    4) Perform the same print and observe the spooling time now. Your spooling time will be extended.

    That is not a very scientific test, but it should demonstrate to you the spooling time reduction that the new memory facilitates.

    I hope that this helps and thanks for writing! -Dennis

  7. Hi, I’m looking for a postscript SIMM like the one you have on your 6MP. You have one kicking around that you’d be willing to part with for a cheap price? Thanks!

  8. Hi Corvus, I am afraid I got rid of that stuff long ago. Maybe you can find something on eBay or Craigslist? Good luck with your project!

  9. Thanks for letting me know, Dennis. One guy has them on eBay for $30 each; I’m just trying to go even cheaper than that!

  10. lol I did that more than 10 years ago on my 6P and I’m still using it without any problem ! Nice to see people still interrested by that trick

  11. Hello, I’ve made two 4MB modules with the above trick and they work well in a LJ 4 plus printer. Oddly though I cannot make a plain LJ 4 printer accept any memory. I’ve read elsewhere it needs a parity memory and I happen to have one 16MB 70ns module with presence detect from the factory that I think has parity. At least it has 6 chips per side like the C2065a. It is recognized as 1MB by the printer (I think LJ4 does support only 8MB modules).
    I tried to make it as 8MB module but unfortunately printer rejects the module with “Failed RAM test”. It is not “parity error” though. And I think the module is healthy as I took it off an old PC that was working… Any ideas?

    Not that I really need more memory but it’s interesting to make the thing working…

  12. Hi Alex,

    I am not sure of the resolution to your problem, but perhaps someone else will chime in at some time with a hint. I do know that if parity memory is required, you will not be able to get non-parity to work.

    I also know that I have had the same experience in the past as you have now… putting in a larger than supported RAM stick often results in a system only recognizing a fraction of the overall size. Not sure exactly why that is, but probably has to do with memory registers and the system being able to access only a small portion. Glad to hear that you find this kind of this as interesting as I do!

    Good luck on the LJ 4.


  13. I have HP-6MP and I bought new 16Mb SIMM RAM, installed it as recomended, but my printer not see added memory modul.
    What can I need to do.

  14. Thank you, thank you, thank you. You saved me $700.00. The memory just went bad on my HP Laserjet 5Si and after purchasing 3 different 72-pin SIMMs (none of them worked), I was about to throw the printer out and go buy another one. After hours of searching I ran across this article, jumpered the pins and WOW!!! it works!! Thanks a million!

  15. Hi Cory, glad you were able to get it to work!

  16. Thanks to this clear write up I just successfully installed 2x 8MB Compaq EDO SIMMs in a LJ 4 plus.

    I didn’t even have to use wires with these SIMMs. They had some “non-connected connections” between the last few pins and pin 72. So I just had to apply a drop of tin to connect pin 69 with pin 72.

  17. Purchased 32MB 70nS SIMM modules advertised as compatible with HP LaserJet printers. Sure enough, they didn’t work. Fortunately I found this site and tested the SIMMs with an ohmmeter. Pin 68 was shorted to pin 72 but pin 69 was not. A quick solder bridge later, both sticks went back in the printer and it immediately recognized them as 32MB RAM.

  18. Hi Jim, glad to hear that my information was a help to you. Enjoy and thank you for letting me know we have another successful operation out there!

  19. Hi Dennis,
    Thanks for this valuable information. I do wish to keep using my 5MP for as long as it will last mechanically. I’m a little unclear on the jumper coding in the SIMM presence detect chart above. I have two 16Mbyte SIMMs, each has the jumper pads available for pins 67-72. (They are 60nS devices, but I am not too worried about that.) Do I use the “2/32 MB 70nS” config, and solder accordingly on both of the SIMMs? I believe this to be the case, but I am not sure.

    Thank you so much.


  20. Hi Greg,

    It has been 8 years since I last did this and posted about it, but let me see if I can offer some hints. 😉

    1) I am unsure if your RAM (60 ns) is going to work. For some reason, I have noted here that only 70 ns or SLOWER RAM will work for the LaserJet; 60 ns is going to be 10 ns FASTER than 70 ns and that may be a problem.

    2) Assuming the 60 ns stuff will work though, the next step is that you need to measure for continuity on pin 72 to any of the other pins 67-70. If you do find continuity there already, you may already have presence detect RAM; stick it in the printer and see if it works.

    3) The “2/32 MB 70 ns” refers to the type and quantity of chips on the stick of RAM that you have. Figuring this out can sometimes be accomplished by looking for coding and typing in the model number printed on the RAM stick, searching Google for the specs. Then follow the chart accordingly.

    If you are not able to find you particular RAM listed online (I could not find mine, for instance), you may have to play a game of testing each possibility given in the jumper chart. If the printer does not recognize the RAM or show the full amount you have upgraded with, that is not the correct jumper setting. I know I had to do a little experimentation with mine to narrow down what memory chips I was working with.

    Best of luck!


  21. Hi Dennis
    May I add my thanks to you for this article
    Mine is a Laserjet 4 M plus (old but tough) and two sticks of 16 meg 72 pin memory from ebay.
    Sure enough it did not work just gave a 53.00.02 fault.
    By adding the correct links all now fine, printer recognises memory and works a treat.
    Thanks again.

  22. Hi Mark,

    Thanks for taking the time to write and let us know that this trick worked for your LaserJet 4M Plus. You are welcome and happy printing!


  23. Hello all, I have a HP LaserJet 6mp printer. I purchased 2 16mb 70ns fast page 72p SIMM, the website I got it from made me select from menus in terms of the printer make and model. After installing the memory and turning the printer on I get nothing but the orange lights. What I dont understand is that if this memory was specifically for this printer, do I still need to do this soldering with the pins, which I dont have a clue of how to do?


  24. Sorry to hear that the memory isn’t working out well. If they are a reputable seller, they should stand behind the RAM they told you would work (assuming a mistake was not made in selection). I am unsure what all orange lights means for that particular model, but you definitely should not have to solder
    RAM that was spec’d to work out of the box. If the seller will not replace and you do end up soldering, let us know if you have questions. Best of luck!

  25. I spoke with the seller in email exchanges they are allowing me to return the ram using a pre paid label. They said two things could be wrong 1 ram is no good and 2 something about a pin configuration jumper for the pin 3 was missing. I would assume its exactly the same thing you show here. Its the jumper, I attached a photo for them and they confirmed that as well.

  26. thanks for clear helpful info
    followed info and successfully upgraded the 5mp
    dropped 2x32mb(the only unused available with OEM ‘presence detection’)
    recognized full,showed total 67mb(32+32+3 soldered based memory)
    available memory 38mb,I think this is because 5mp max limit is 32mb
    truly helpful info,thanks

  27. This worked a treat, many thanks for the post.

    The original online purchase was supplied without the speed detection being set and Arch Memory immediately sent a replacement without requiring any return from NZ. That’s great service. With nothing to lose, I decided to give this a go and ended up with two working cards! I used resistor leads and a jump wire.

    FYI – The 16MB ram lights up all the lights on the printer and it then appears to freeze, unlike the original 6MB which is ready almost immediately.

    Like others, I thought S%#@ and immediately turned it off. I reseated the card and also tried other slots and rechecked the detection modifications. Everything looked okay, but I still got the apparent lockup.

    However, further Web research found others had encountered this and reacted the same way. Turns out the printer was only checking the Ram and settles into a single ready light after 35 seconds (45 seconds with the two extra cards).

    The second gotcha – The replacement card (which had its speed and presence detection already set), did insist that it be seated in slot 1 before the printer would even fire up at all – so you may have to play around a bit.

  28. Hello!

    I could possibly give some more detailed or additional information:

    The table above is maybe not completely correct or a bit outdated. Compare here:

    and here (German only)

    You will find similar tables elsewhere on the net.

    So this explains why putting a “huge” 32MB Simm into an old printer will show up only a small memory size: Due to the lack of presence detect pins older bit combinations later have been reused for larger modules: 1, 16 and 64 MB Modules share the same bit combination, same is valid for 2, 32 and 128 MB as well as 4 and 256 MB. Very old printers (or computers) don’t know about this fact and thus 16MB will show up as 1MB only. This limits the amount of maximum memory you can use with this systems.

    Then some points concerning the old LJ4 (non plus model):

    This printer falls into above category, 32MB is the maximum upgradable memory amount, using 4 x 8MB FPM’s. This printer does not accept EDO (didn’t exist yet then). It does however *require* parity Simms (later printer do not). It can accept both double sided Simms with 8 or 2 ram chips on each side (the parity rams left aside, in sum these do result in 3, 12 or another number of chips on each module side). And it does accept FPM’s with 70ns or slower access time *only*, all others will be rejected. Nevertheless you can down-pimp faster modules to cooperate with this printer. I was able to get 60ns modules running. Simply resolder these modules to pretend to be 70ns modules and the printer will accept them without a hasle. Generally speaking, faster modules will always be able to run in a system requiering only slower modules. So you will do no harm to any component involved. This is simply a problem of an outdated printer firmware. At the time the LJ4 was build there were no 60ns FPM’s and the bit combinations later on used for these were undefined. so HP made the firmware recognize these as illegal instead of blindly assuming a certain speed and size. So, just make the printer think it were 70ns modules and everyone’s happy!

  29. Oh, I forgot one point, sorry!

    A short hit for the soldering: Lock carefully at the modules you intend to use. very often these have universal PCB’s carrying the chips. This means you have one PCB being used for different types and sizes of modules. Therefor the presence detect pins are not directly connected to GND but wires will leads to four solder pads (sometimes even marked with 1, 2, 3 and 4). If in doubt a multimeter will show up the responsible pads. I’m pretty sure that in the Simm picture above these pads are on the very right side of the front view of the Simm module. Look closely, there are 8 square pads, four of them connected to GND and the others to the PD-connectors of the module. It is very reasonable to use these!

    So, instead of trying to solder on the tightly packed connector pins you could change the configuration with these pads. This might involve removing some pads already shorted, shorting other pads not yet connected and maybe un-shorting pads that are default-shorted (by a copper strip on the PCB, not by soldering). To unshort take a small, sharp knife and afterwards test with the multimeter.

  30. Excellent page of information.
    Having just bought an old 5P and looking for info, I came across this page. The penny dropped and I remembered I still had some ancient SIMMs in a box. The LJ5P now has 42MB (37.5MB useable) in it. Thanks for that.
    True enough, it spat the dummy when they went in as 60ns modules and I simply had to follow the chart to kid the machine they were 70ns. Two solder bridges on the 16MB modules, between pads 67-72 and 69-72, and on the 8MB sticks just one needed between pads 69-72. The pads at the end of the sticks are directly linked to the edge connectors.

  31. Several years on now, and the usefulness of older blog posts is proven yet again! I think the original fix for this issue (on a Newsgroup) was posted way back in 1996.

    Anyway, now it is 2015, and the information is -still- useful and relevant. I bought some SIMMs on eBay to update 3 old (but reliable) 6P/MP printers, and this saved my day!

    I got out my Hakko soldering station and fixed the SIMMs… now all 3 printers have 50 MB of memory and a fresh life.

    THANKS for keeping these old blog/forum posts available!

  32. […] was obtained from , which, in turn, was linked from… […]

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