[SOLVED] Debugging printing to HP82240B

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grsbanks
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Re: [SOLVED] Debugging printing to HP82240B

Post by grsbanks »

There is no polarity. The original PSU provides AC to the printer. That is then rectified and filtered inside the printe.
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rprosperi
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Re: [SOLVED] Debugging printing to HP82240B

Post by rprosperi »

The printer works with multiple HP chargers; The intended charger is seen at the bottom of this page:

https://www.keesvandersanden.nl/calcula ... argers.php

This is an AC charger so polarity doesn't matter.

However the printer power specs (in the manual) are stated as:

9 - 12 V AC or DC, 500-1500mA.

One recommend DC charger is the HP F1011A, introduced for use with the 95LX/100LX/200LX, and this adapter's specs are:

12V DC, 0.75A, center tip negative (just verified with one here).
--bob p

DM42: β00071 & 00282, DM41X: β00071 & 00656, DM10L: 071/100
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moonwalker
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Re: [SOLVED] Debugging printing to HP82240B

Post by moonwalker »

The restorative surgery was a success.

After disassembling the printer (four screws under the rubber feet, two in the battery bay; two connectors in the big prominent socket in the middle, one of which is battery connector; one ribbon cable that's kinda hard to pull out; two smaller screws holding printing mechanism and mainboard in place) I soaked the hot glue holding IR receiver inside some plastic piece in 91% isopropyl alcohol to soften it, then carefully tore it apart, releasing the IR receiver soldered to the wires. Desoldered the IR receiver, removed the wires from the board, plugged the IR receiver into the through-holes where wires were soldered on the board facing numbers back towards the board, soldered it in place. Next was remove the power connector leftover wires, replace them with new wires long enough to reach the opening on the back of the case. Solder the power connector, polarity doesn't matter. I used https://www.amazon.com/gp/product/B07D4BK8W4/, which has two PSU contacts in the center, and the side contact is for sensing whether PSU is plugged in or not. I cut off the side contact, and bent both center pole and barrel contact at 90 degrees so they face towards the back of socket - without doing so the printer case won't close during reassembly. The socket stays snug enough facing round side downward. Reassembled everything - put mainboard in place, routed all the wires, plugged the battery connector (should be marked clearly on the board), put the printing mechanism in place with the small screws, plugged the big socket and the flat ribbon cable (even more difficult to plug it in, had to wiggle it back and forth for it to go in), finally put all the buttons and top cover back in place, replaced the six big screws and rubber feet.

With this the printer works fine, gets IR signal from calculator facing the original IR receiver window as intended, and gets power from a standard 12V DC power supply I use for external IDE/SATA to USB HDD adapter. Haven't tried experimenting with rechargeable batteries, would be cool if they were to charge while I have external PSU connected to the printer.
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rprosperi
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Re: [SOLVED] Debugging printing to HP82240B

Post by rprosperi »

moonwalker wrote:
Sun Jun 27, 2021 8:02 pm
With this the printer works fine, gets IR signal from calculator facing the original IR receiver window as intended, and gets power from a standard 12V DC power supply I use for external IDE/SATA to USB HDD adapter. Haven't tried experimenting with rechargeable batteries, would be cool if they were to charge while I have external PSU connected to the printer.
Just to be clear, the printer has no charging circuit. It uses only non-rechargeable batteries, or it can be powered by the external supply, but there (likely) is no direct connection between them (other than connecting to the same board), so it's unlikely they could be charged properly. After all the work to fix it, seems it's not worth experimenting with something that really "shouldn't" work....
--bob p

DM42: β00071 & 00282, DM41X: β00071 & 00656, DM10L: 071/100
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moonwalker
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Re: [SOLVED] Debugging printing to HP82240B

Post by moonwalker »

rprosperi wrote:
Mon Jun 28, 2021 3:04 am
Just to be clear, the printer has no charging circuit. It uses only non-rechargeable batteries, or it can be powered by the external supply, but there (likely) is no direct connection between them (other than connecting to the same board), so it's unlikely they could be charged properly. After all the work to fix it, seems it's not worth experimenting with something that really "shouldn't" work....
Granted, I'm no electrical engineer, mere programmer, but if I understand correctly, if I plug the AC adapter while battery bay is full of NiMH cells then the worst case scenario - the batteries are charging, but since there is no overcharge protection circuit I gotta watch 'em like a hawk to make sure they don't overcharge, potentially resulting in overheating or even explosion. And if they are not charging at all - it's good to know that I can safely plug the AC long term with no risk of batteries blowing up in my face or setting my home on fire.
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Guenter
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Re: [SOLVED] Debugging printing to HP82240B

Post by Guenter »

moonwalker wrote:
Mon Jun 28, 2021 5:01 pm
Granted, I'm no electrical engineer, mere programmer, but if I understand correctly, if I plug the AC adapter while battery bay is full of NiMH cells then the worst case scenario - the batteries are charging, but since there is no overcharge protection circuit I gotta watch 'em like a hawk to make sure they don't overcharge, potentially resulting in overheating or even explosion. And if they are not charging at all - it's good to know that I can safely plug the AC long term with no risk of batteries blowing up in my face or setting my home on fire.
The manual states "Do not use the AC adapter without batteries installed..."
Because it mentions an AC adapter in this sentence its also important to also note the specs in the manual for the power adapter which are 9-12V AC or DC; 500-1500mA

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moonwalker
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Re: [SOLVED] Debugging printing to HP82240B

Post by moonwalker »

Guenter wrote:
Mon Jun 28, 2021 11:56 pm
The manual states "Do not use the AC adapter without batteries installed..."
Because it mentions an AC adapter in this sentence its also important to also note the specs in the manual for the power adapter which are 9-12V AC or DC; 500-1500mA
Well, then that sounds like I have no choice but keep those NiMH cells in there while I connect it to AC power!

I don't have original HP 82240B manual, and I cannot find the schematics for it, but a similar wording is used in the original manual for TI-59 I have. There the adapter is DC, but there is still a rectifying bridge just like in HP 82240B. In TI-59 the output of that bridge is connected to the battery pack over a resistor, and the rest of the calculator is powered from the contacts of the battery pack. So if the PSU is the primary source of the power there is a bit of a voltage drop on that resistor, and then the rest of the calculator and the battery pack are connected in parallel. My understanding is if the voltage/current is sufficiently high the battery pack will be consuming extra power, if not - supplying extra power to keep the calculator working, helping regulate the voltage/current going through the machine. There is still a separate power supply module that further regulates the voltages/currents though. I assume (but don't have the schematics to confirm, and haven't yet tested the voltages/currents) that HP 82240B has a very similar arrangement when it comes to power.
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Thomas_ER
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Re: [SOLVED] Debugging printing to HP82240B

Post by Thomas_ER »

moonwalker wrote:
Tue Jun 29, 2021 12:40 am
.. I don't have original HP 82240B manual, and I cannot find the schematics for it, ..
Please find the schematics attached.
Attachments
HP82240B_Schematic_part1.pdf
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HP82240B_Schematic_part2.pdf
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[ HP48/49/50/42S/WP34/HP Prime/ DM42 (#00185+00318) ]
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moonwalker
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Re: [SOLVED] Debugging printing to HP82240B

Post by moonwalker »

Thomas_ER wrote:
Tue Jun 29, 2021 12:43 pm
Please find the schematics attached.
Thank you very much!

From the quick look at it the power switch is after either PSU or battery pack, so batteries are connected to PSU when the printer is turned off, but they should not be charging ever unless the Schottky diode reverse leakage current is high enough for at least trickle charging. The PSU voltage first passes through the voltage regulator (I assume that's what U1 on the schematic is), then there is a transistor that I guess is also used to further regulate the power but I'll need to do some reading to understand how, and finally the batteries are connected, before all of that going through something that looks to me like yet another, more complex, power regulating circuit.

So at a first glance, it looks to me like the requirement of a battery pack is there mostly to protect PSU from being overloaded, but of course I will need to do more reading to better understand the circuits shown in this schematic.
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rprosperi
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Re: [SOLVED] Debugging printing to HP82240B

Post by rprosperi »

moonwalker wrote:
Tue Jun 29, 2021 3:52 pm
So at a first glance, it looks to me like the requirement of a battery pack is there mostly to protect PSU from being overloaded, but of course I will need to do more reading to better understand the circuits shown in this schematic.
That's exactly the reason. All of HP's (and other mfr's) portable printers suggest/require keeping batteries installed as the current drain imposed by moving the mechanisms can exceed power available from the low-current power supplies; the batteries supply the high in-rush current needed to get the parts moving.

It seems highly unlikely your batteries will be charged for the same reason (low current available on the charger) but it will be interesting to see if that happens, so please report the results when you can.
--bob p

DM42: β00071 & 00282, DM41X: β00071 & 00656, DM10L: 071/100
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