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HP 46 repair - Printable Version

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RE: HP 46 repair - Geoff Quickfall - 04-28-2019 05:43 PM

As I stated I have not had time to document the calculator internals.

Is the cap electrolytic? If so i would recap that circuit. Did you remove it for a capacitance test? Also they can reform but why try, just replace it. Before you try how about bridging it with a cap via clips to see if that actually is the problem.

I am in the process of restoring an already working Hammarlund 129x and will of course be recapping the entire radio wax and paper caps. No silver mica disease yet but that should not be a problem in any case.


RE: HP 46 repair - AndiGer - 04-28-2019 06:11 PM

Didn't remove the cap for test purposes ...

Alex Knight's repair tip is here:

Duane Hess posted similar problems concerning the printer here (no final solution posted):

My idea is to disassemble the 81 and try the 46's printer in that one. So maybe I can isolate the problem to the printer or the board.
So if it is the board I will try replacing the cap.

RE: HP 46 repair - vassilisprevelakis - 05-02-2019 11:03 PM

(04-15-2019 08:27 PM)AndiGer Wrote:  What is the best material for lubrication?
What do you use for those old machines?

Perhaps an equally relevant question is which parts need lubrication?

I looked at the "HP-46 HP-81 HP 9805 Updating Revision Repair of Printer Assembly" (46urep.pdf) manual, but there is no diagram to indicate the location of the parts.

Best Regards


RE: HP 46 repair - AndiGer - 05-03-2019 08:54 AM

So I connected the 46 printer inside my 81 with the same result. Printer motor doesn't spin.
Even with PRT OFF at startup the 81 printer spins for a while - 46 printer doesn't move at all.
Didn't try the other way round - 81 printer connected to the 46 board. Suppose this will be alright but who knows.

I conclude the problem is the printer itself.
Have no idea how to proceed as I don't know and didn't find anything how the printer motor (mounted "PCB thru") works or what to check.
On the printer's PCB is a 22 uF 10V cap. Not easy to go to the solder joints to desolder. Seems one has to remove some screws that also hold the motor in place. But to get it back to the right orientation together with the print drum and the solenoid sensors will be complicated. Just now don't dare ...

RE: HP 46 repair - vassilisprevelakis - 05-04-2019 12:53 AM

(05-03-2019 08:54 AM)AndiGer Wrote:  But to get it back to the right orientation together with the print drum and the solenoid sensors will be complicated. Just now don't dare ...

Hi Andi,

I fully agree with you. That printer totally intimidates me. I've looked and looked for assembly-disassembly drawings on the net and did not find any, so when my HP-46 developed a printing problem I knew that if it was the printer itself I'd be in deep trouble.

The problem is that the last two columns print intermittently (rightmost hammers 17 and 18 have a problem).

I looked at the printer connector and was very happy to discover that the printer is not receiving a signal to fire these hammers, so the problem is with the motherboard electronics.

My next suspect were the transistors that drive the hammers, but these turned out to be OK.

So the most likely suspect is the U8 CMOS quad two input NOR gate IC (4001). Of the 4 gates two are used to drive the transistors for hammers 17 and 18. The other two are linked together as two inverters in series driving the 4th display line. (I am not sure why, as the other 3 lines are sent directly.

So now I am waiting for some 4001s so that I can go ahead with the repair.




RE: HP 46 repair - AndiGer - 05-05-2019 04:37 PM

@Vassilis: Wish you success when replacing U8. Diidn't know you still can get those old chips. Maybe used from a donor machine only?

Yesterday received a Casio R-1 calculator that also has the Shinshu Seiki EP102 inside. 3 teeth from the 17/68 double gear are missing but still printing.

Removed it from the R-1 and connected to the HP-46. As expected the printer also works inside the HP-46. But of course the characters on the print drum are different.

So one step could be to interchange the print drum between those two printers. No easy step ... (and steal the double gear from the other printer).

The printer from the R-1 is a different design. I attached images of the R-1 printer. Motor side and electronics are different design, right side drum gear is pure metal with a marking hole instead of plastic-metal mix with a marker in the plastic.
The design of that one coming from the HP-46 is identically to that in the link in post #17.
Hoped I could compare the two printers directly.

I measured the resistance when detached from the calculator between red and black wires:
The one coming from the HP-46 measures 1,300 Ohms continuously.
The other from the R-1 starts at nearly infinity and drops to 480 kOhms. When I turn the motor manually resistance rises to infinity to come back after some seconds to 480 kOhms.

What can I look after in the original HP-46 printer's electronics? Still hope I can get it back running ...

One possibility: Cut the leg of the 22 uF 10 V capacitor and measure that one? If ok I could reconnect soldering a short piece of wire?

RE: HP 46 repair - Geoff Quickfall - 05-07-2019 07:26 PM

I haven’t seen the cap yet, is it electrolytic? The disc caps rarely fail but 50 year old electrolytic can.

Yes, clip to remove from circuit and try a resistance check while in circuit to see if it leaks as well as a cap check.


RE: HP 46 repair - AndiGer - 05-07-2019 07:40 PM

Hi Geoff,
Thank you for your reply. In the link in post #17 -> picture #5 you can see it. As in mine. Electrolytic. Only one - blue mantle. Diode check in my DMM gave constant result in circuit (DMM + on cap -). Will clip and measure. Have LCR-T4 tester.

RE: HP 46 repair - AndiGer - 05-12-2019 11:16 AM

Before I go to clip the capacitor here are some results compared to the working printer in my HP-81:

Printers detached from main board.
HP-81 printer (power) red to (power) black gives 875 Ohms constantly.

HP-46 printer on the first refresh of DMM most of the time gives around 300 Ohms (sometimes also around 200 or around 600 to 800), second refresh gives 1230 Ohms, 3rd refresh 1270/1280 Ohms and then goes up in steps to be stable at 1300 Ohms.

Is it possible to derive the problematic part from that behaviour? Capacitor or diode or transistor?

RE: HP 46 repair - vassilisprevelakis - 05-15-2019 10:43 PM

(05-05-2019 04:37 PM)AndiGer Wrote:  @Vassilis: Wish you success when replacing U8. Diidn't know you still can get those old chips. Maybe used from a donor machine only?

Hi again,

I got a box of 50 (!) RCA CD4001BE chips, NOS parts. They were just thrown in the box without any kind of static protection, but at least the ones I tested survived the ordeal.

So I changed U8. Initially I intended to add an IC socket, but the chip is under the base of the printer and there isn't enough clearance. Its amazing in a box that big to have tightly packed components.

Anyway I soldered the 4001 directly on the PCB and now the printer works fine.

I am attaching a picture of my new and fully working HP-46!!![Image: HP46-LR.jpg]

All the best


RE: HP 46 repair - Geoff Quickfall - 05-16-2019 05:56 AM


Good work!

RE: HP 46 repair - BobVA - 05-16-2019 09:45 PM

Fantastic job! Thanks for saving that nice calculator from the scrap heap!

RE: HP 46 printer repair - AndiGer - 05-26-2019 04:38 PM

Today I cut the leg of the 22 µF / 10 V rated cap and measured. The cap gave about 48 µF (VLoss 5.2%, ESR 2.2 Ohms). I by-passed it with a 22 µF 25 V (22.5 µF, VLoss 4.5%, ESR 7.6 Ohms) but motor still not spinning.

More findings:
If I switch on the calculator (only works with PRT OFF) and switch the printer on the motor spindle is attracted by a magnetic field and trembles in it but doesn't spin.

Another weird thing I found: The solenoids of the right-most 7 hammers (inside printer housing, not directy visible 4, outside at the bottom 3) attract and fire the hammers when the motor is turn by hand.
So I isolated the connector pins of these solenoids inside the connector with paper but the motor still not spinning.

As the printer from the Casio is printing I suspect no problem on the main board itself.

Edit: all diodes of the solenoids measure the same value. With my DMM 105 +/- 1. On the Casio I read 100 +/- 1.

Any ideas? Thank you

RE: HP 46 repair - AndiGer - 04-30-2020 01:48 PM

In several steps I did it ... :-)

The printer seams to be a "version 2" compared to the printer repair manual contained on the museum DVD as it contains a Hall generator, only 2 solenoids (or is inductors the right word?) and one single PCB.

I removed the PCB from the printer and examined it. As the PCB is built symmetric in some parts the values the both (mounted) C945 transistors gave were suspicious.
After I replaced those 2 transistors I got the printer back spinning! :-) - Although the original transistors measure good values.
The motor has 6 different positions when in rest. Sometimes it doesn't start from one of the 6 positions. In this case I must help the motor to start by slightly rotating the print drum below the paper. As I know that I can always get the calculator working.

RE: HP 46 repair - tsb - 05-16-2020 03:15 PM

I recently picked up an HP 46 that only powers on the printer. No response from the keyboard or display. Where do I even start troubleshooting this? I have searched, but was unsuccessful finding any guidance. Thanks.

RE: HP 46 repair - AndiGer - 05-16-2020 08:07 PM

Did you check the voltage test points? They are written on the main PCB - thank you HP
If voltages not ok - I can't but sure here are some guys can