HP 97 calculator printer issues

[isanchez]

Dear all,


I am repairing an HP97 printer. I have replaced the paper tracking rolls. I also have replaced the gearwheel, for a metallic one.

The printer prints with high quality and the interspacing is perfect..nearly 10 over 10 of quality.

The thing is that the noise has been increased a little bit. It is more noisy now. I have oiled and reviewed all the parts. I do not know what cause this noise. Maybe the metallic gear? apparently no.
The noise is present when the header goes back to the stand by position, in the more left side. When moves left for printing seems ok, but it is when reurns back whe i find this noise appears.

can you give me any idea how to proceed? is is not really annoying, but I would like to reduce it, if possible.

On the other hand, I have seen that a couple os resistors(?) have been connected to the board. I do not know what is the purpose...I enclose a picture

thanks and kind regards

Ignacio

[teenix]

Those resistors were originally on the other side of the circuit board.

I imagine that someone has changed the motor speed and print intensity but put the resistors on the other side of the board. It may have been easier to solder them there if experimenting with the values.

The motor is driven at full speed when the head moves to the home position. It may cause more gear noise during this time.

cheers

Tony

[Paul Berger (Canada)]

My experience with my two 97s is that they are noisier with a metal idler both of mine have a distinctive wheeze on return.

[isanchez]

Thanks Tony and Paul!!!

now it is clear. Seems a good idea to make this gears in plastic.

I have another 97 with dim and irregular printing. Not a big issue but obvious. Do you think I can increase the printing intensity implementing (replacing) these resistors? Which are the specs? Do you have any idea? I only need to improve the printing quality, not speed.

I have checked with two different printing headers+boards and the same issue: dim not regular printing.

Thanks and kind regards

Ignacio

[teenix]

Old paper?

Irregular printing could mean spacing, intensity, missing characters etc so not sure.

cheers

Tony

[isanchez]

Hello

Checked with new paper. Even I changed the combo (board + ribbon + header) with more or less the same result.

This afternoon I will upload an example.

Again: thanks and kind regards.

Ignacio

[AndiGer]

(03-08-2022 07:04 AM)isanchez Wrote:  Do you think I can increase the printing intensity implementing (replacing) these resistors? Which are the specs? Do you have any idea? I only need to improve the printing quality, not speed.

Refer to the service manual. Table 4-7 contains selectable resistors R7 and R8.
According to the figure 4-20 R7 is for adjusting motor speed, R8 for print intensity. (Pls. don't ask me, whether lower value will increase or decrease intensity :-).

HTH
Andi

[Dreato]

I believe that someone on the forums here was selling 3D printed plastic idler gears. They ARE quieter. Also, that brass gear will eventually tear up the Delrin gear that rotates the print head shaft, and then you're in much bigger trouble. That's why the original HP gear was a softer plastic. It was made to wear out first. My high school friend (age 70) was an HP repairman for many years and has shared many tips about these old machines. I believe the 3D printer STL files are available on this forum, too. I've printed a few myself, and they work extremely well.

Best Regards,
Dave

[isanchez]

Dear all,

Thanks a lot!!!. Very useful information. I shall try to get the plastic parts
Regards


Ignacio

[isanchez]

(03-08-2022 04:20 PM)AndiGer Wrote:  

(03-08-2022 07:04 AM)isanchez Wrote:  Do you think I can increase the printing intensity implementing (replacing) these resistors? Which are the specs? Do you have any idea? I only need to improve the printing quality, not speed.

Refer to the service manual. Table 4-7 contains selectable resistors R7 and R8.
According to the figure 4-20 R7 is for adjusting motor speed, R8 for print intensity. (Pls. don't ask me, whether lower value will increase or decrease intensity :-).

HTH
Andi

thanks||

[isanchez]

(03-09-2022 05:43 PM)isanchez Wrote:  

(03-08-2022 04:20 PM)AndiGer Wrote:  Refer to the service manual. Table 4-7 contains selectable resistors R7 and R8.
According to the figure 4-20 R7 is for adjusting motor speed, R8 for print intensity. (Pls. don't ask me, whether lower value will increase or decrease intensity :-).

HTH
Andi

thanks||

For darker print, increase
resistance.(Refer to table 4-7)
For lighter print, decrease
resistance. Then go to step
14,

[Duane Hess]

(03-08-2022 05:20 PM)Dreato Wrote:  I believe that someone on the forums here was selling 3D printed plastic idler gears. They ARE quieter. Also, that brass gear will eventually tear up the Delrin gear that rotates the print head shaft, and then you're in much bigger trouble. That's why the original HP gear was a softer plastic. It was made to wear out first. My high school friend (age 70) was an HP repairman for many years and has shared many tips about these old machines. I believe the 3D printer STL files are available on this forum, too. I've printed a few myself, and they work extremely well.

Best Regards,
Dave

My sentiments EXACTLY, this gear and the "dual" gear in 46's and 81's obviously was designed with the same idea in mind. Sacrificial failure to protect other parts.

Has anyone 3D printed the idle gear for the 46's & 81's? I know you can fabricate one by combining 2 different gears. However, I've always wondered if the thrust angle on the 46 & 81 printers was 20 degrees, such as most gears are made. Maybe everything I have is worn so they seem to be different (closer to 28-30).

[Dreato]

There's a gear design plugin (GF Gear Generator) for the Fusion 360 3D design program. Give it a shot. You'll have to get familiar with the figures of merit for spur gears: # teeth, gear height, pressure angle, and others I can't recall.

Regards,
Dave