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HP32E Power Supply (Or equivelent Spice) Voltages - Printable Version

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HP32E Power Supply (Or equivelent Spice) Voltages - joey - 12-28-2021 11:35 PM

Hello All,

I was given a non working HP32E for Christmas by a dear friend. He found it somewhere, with the battery all corroded, and figured it would be an easy fix. Knowing I am a EE, he figured the solder less design would be interesting to me (Which it is!).

So the battery was carefully removed and it became clear the ribbon cable on the battery end was eaten up, which based on searching the internet is pretty standard. What is not standard is that the battery (I will say chemistry to be safe) migrated into the power supply board. The flex that went onto the back plane was not damaged, however when trying to remove the flex to assess the damage (and it is great), a number of the tacks on the PCB lifted off (and all the pads are highly corroded, I have never seen a circuit board in such bad shape). I have done some reverse engineering and made a new flex by hand using copper tape, and tested it and that is ready to go. However, I do not have the voltages for the power supply.

When looking online I did find a schematic for the 32E, a couple actually, and they did not consistently provide a reference point. However, after some reverse work of my own, I know everything that I need except for the turns ratios for the transformer. I would like to construct a "novel" board that provides stable voltages to system. While I feel comfortable in moving forward (to a degree), I really do not want to blow out some amazing and irreplaceable chips and ruin a piece of history by guessing or getting "kinda close".

Therefore, if someone would be willing to measure all of the voltages from within their spice calculator, specifically on the flex/ribbon that goes onto the backplane, I would feel comfortable safely moving forward in working on the device and trying to bring some life into this amazing calculator.

Thank you in advance,

RE: HP32E Power Supply (Or equivelent Spice) Voltages - teenix - 12-29-2021 06:27 PM

I wish I could help out but I don't have access to one of the Spice models.

The logic of the day was about 6V, but this circuitry must have changed slightly with only a single rail power supply, so not sure. The other output, as you probably surmised, is for a constant current source for the LED displays of which only one LED segment is on at any one time.

The coil is probably still ok, unless the battery acid got to the wires. Maybe it is worthwhile just re-creating the power supply board with a new PCB. The transistors and zener may still be serviceable and the rest are common parts.

The turns ratio may be a matter of carefully unpacking it and trying to figure it out. You never know, but I doubt if that info is floating around.



RE: HP32E Power Supply (Or equivelent Spice) Voltages - Jlouis - 12-29-2021 09:27 PM

I don't know if you intention is to run the calculator in a power supply or a charger, but if I recall correctly ( I have a 33C), the safest way to use a Spice in on batteries.

Many here have lost their spices by using a charger and for a reason that I can't remember, the charger fried the calculator.

Someone here in a non Alzheimer's state like me can explain better.

Good luck and welcome.



RE: HP32E Power Supply (Or equivelent Spice) Voltages - wbvreeuwijk - 01-05-2022 05:04 PM

Hi Joey,

I have repaired a few Spice models with corroded batteries.

I found the following helpful page to determine the function of the PSU. https://www.keesvandersanden.nl/calculators/powersupply.php

Here are pictures from one of these PSU boards (I think it's from an HP-33E). You'll notice that there is a trace missing on the left.