82162A Printer contrast


I have an 82143A and 82162A printer. The 82162 printer functions OK but the print quality is not the same as my 82143 printer. The 82143 printer prints very nicely on fresh Office Max thermal paper with very dark printing in the DARK setting. The printing starts to 'bleed out' a bit at that setting so it is too dark and I usually print at about setting 3. The 82162 printer prints much lighter. When set to the highest setting, the print intensity of the 82162 is more equivalent to the #1 setting ,or less, of the 82143 printer. The physical condition of the 82162 is excellent and mechanically operates quite well with no unusual noises. Also, there is not a great deal of difference between any of the settings for intensity on the 82162. In fact, it appears to be the same intensity on settings 1, 3, and 5. It is ever so slightly lighter on settings 2 and 4 which also appear to be about the same between the two. One more thing to note is that the rightmost character position is lighter than the rest.

Is there anything to be done about print intensity of the 82162?

Can I (should I) swap the print head or mechanism form the 82143 into the other as I prefer to use the IL version? Is that terribly difficult/risky?

I searched through the archives and found some info suggesting that the platen backing up the paper might be able to be adjusted to increase the print density of the outermost characters and I was curious if this could be a fix here? I looked at that and it appears to float nicely behind the printhead much like it does on the 82143 but that is all I have to compare to I don't know if it should have more pressure.
Does anyone know of any electronic reasons for this difference? Are there any adjustments to the circuitry possible? All the pixels are present and of equal intensity.
I haven’t taken anything apart yet to look furhter. I was looking for some sage advice first.



Thre were two types of print mechanisms used in these printers. One type had the timing wheel on the left, the other on the right. The motherboards were different. If both your printers are the same type, you should be able to swap them, but most 163's were one type and 143's the other.


Are you certain that there are some 82162A units with the 82143A print mechanism? I didn't think there were any, because part of the reason for the mechanism change was that it was necessary for the improved graphics capability (reduced line spacing) of the 82162A.


I dont know for sire if there are any 163's with 143 printers, but I do know there are 143's with 163 printers.


The print intensity control switches resistors in a potential divider circuit that's part of the feedback loop in the printhead power supply.

If it doesn't work properly, you might try removing the PCB and cleaning the contacts, and then getting 'my' schematic either from the Australian Site or on the HPCC CD-ROM, and checking the switch, the connections to RP4, the resistors inside RP4, and so on. Make sure the printhead voltage (VHead on the diagram) increases as you go to higher intensity settings.


I was able to look at the sevice manual for the 143 and have deduced from the trouble shooting guides and schematic for that printer that the problem is most likely the print head power supply, assuming the switch and resistors are functioning properly. Of course, this is based on the electronics of the 143. As you have mentioned, VH should be measured to determine for sure. The voltage listed in the 143 manual is a range from 13V to 18V. Assuming the power portion of the schematic between the two are similar, I should be able to measure. However, I do not know exactly where to measure VH on the 162. I have a couple of ideas I'll look into tonight. I did disassemble the 162 and inspected the contacts. They appeared in good condition but I cleaned them anyway with no effect. The question I have now is; If the Print Head Power Supply is the problem, is there a suitable replacement to be found and could the PS from the 143 be used?

Also, can you point me to the Australian site you mention? And is the schematic availible there? OR is it only availible on the CD. I appologize that I am not familiar with all of the choice sites yet as I have just recently revived my interest in HP41 things.

Thank you very much for your help.



I'm not sure if I can mention the URL for the Australian Site here, but to get it, just change the .org in this site to .net .

And yes, there's a reverse-engineered schematic of the 82162 there, along with stuff for a lot of other larger machines.

From what I remember, the power circuitry of the 82162 and 82143 is very similar. The 82162 is more complicated because it has the ability to be turned on/off over the HPIL loop, but once you get past the power switching, the power converters, etc are much the same.


Thanks. I had found the site and your schematics last night as I searched the internet. I find it interesting that the site is not on the Links page for this site.

I measured the VH voltage and it comes up a bit short at 12.8V on settings 1,3, and 5. and right around 12.2V or so on settings 2, and 4. All of which are below the minimum stated in the service manual for the 143 at a range of 13V to 18V. What I am unsure of now is if this is a power supply problem or a problem with the control circuitry feeding into it. Namely, is it being told to be the voltage it is providing, or is it being told to control to the correct V and is unable to comply. I still need to track down the intensity control resistors and check them if possible. I guess I should have paid more attention to my EE for nonbeliever's class while I was getting my ME degree many years ago.


silly question probably, but it has to be asked

You are using a good batery, right? check the voltage level of the
batery during printing to see how low it gets when load is applied to it.



That is a reasonable question. Sometimes it's easy to overlook the obvious. I have a newly built battery that I put together for the 143 that I have been using. With the brand new cells, the battery voltage runs just over 5 volts. I should note that there is no difference in the symptoms if the charger is plugged in or not. I also used the same roll of paper in both. Having two printers really helps to trouble shoot that problem. Like I mantioned before, I wish my electronic skills were a bit better. Right now I hope to characterize the thing as best I can and try to determine the best path forward. So far the info I've gotten here has been helpful but I was hoping someone else has had a similar problem as mine that I could build from. I'll post more findings when I complete more measurments.


One thing you might try is removing the print head and gently cleaning it with alcohol.

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