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HP-46/81 Case, Power Supply - Printable Version

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HP-46/81 Case, Power Supply - Duane Hess - 10-10-2017 03:04 PM

Wish to ask some advice, just to ensure I don't get into a non-recoverable situation (i.e. things get damaged).

The service manual for the 46 & 81 seems to state the units use the same power supply. Certainly seems that way. I have all the parts for an 81 except for the case bottom, top and power supply. Pretty sure all the 81 parts work.

Own an extra 46 which is fully operable. Don't recall the values, but the 3 (4?) voltage test/check points in the 46 match the service manual. Before swapping the parts wanted to ask has anyone done this or is sure the power supply for the 2 units is the same?


RE: HP-46/81 Case, Power Supply - AndiGer - 10-11-2017 01:33 PM

Dear Duane,

Maybe this repair report and the contained link from Dave to Tony Duell's schematics for the 81 can help you? http://www.hpmuseum.org/forum/thread-5847.html
On the same site there is also a schematic drawing for the 46 by Tony: http://www.hpmuseum.net/exhibit.php?hwdoc=214
If you compare both schematics maybe gives the answer(s).

RE: HP-46/81 Case, Power Supply - AndiGer - 10-24-2017 03:24 PM

Just because of curiosty reasons:
Did you rebuild the 81 with the 46 power supply?
Due to Tony's schematics for both calcs should be identical.

RE: HP-46/81 Case, Power Supply - Duane Hess - 10-25-2017 05:33 AM

I have not, but that is the plan. Was hoping for a post "Yes! I've done exactly that."

Been messing with other stuff around the house,... just because. Have a 1-day trip to take & probably will get on it this weekend. The schematics were quite conclusive, in my opinion, there is no difference at all between the 46/81 supply.

Will update the thread after trying it. Plan on giving my spare 45 to my brother, so someday will need a case, power supply. Hopefully with a top-case that says "Hewlett Packard 81".

RE: HP-46/81 Case, Power Supply - Duane Hess - 10-30-2017 12:49 PM

Swapped all the 46 keyboard, display card, printer, mother board from the unit and installed the 81 stuff (buffered keyboard). Turned the unit on, the busy LED went on solid & nothing would happen other than the printer motor would turn accordingly to the PRINT OFF key.

Both the 46 and 81 cards have the BUSY LED and the full numeric digit display. ... think its Option 1 on the 46 and Option 3 on the 81.

Installed the 46 display card, same results, coincidentally noticed if powered off unit & turned in back on in about 1/2 second it would operate. Reinstalled the 81 buffered keyboard display, had issues, memory recalls would not work right. Printing was spazzy. Seemed to randomly work OK, overprint, omit positions, etc. Reinstalled the 46 display card as it seemed to work better. But I'm quite sure that was coincidence.

Would need to go check my notes. The +6, -12 and +15 VDC test points were within the voltage variations on the 46. After swapping in the 81 parts those were OK, except for the +15VDC was 13.somethingVDC.
[EDIT] The voltage tolerance values were from the 9805 service manual as I didn't noticed reference to tolerance levels in the 46/81 manual.

Noticed the HP46 Printer Repair Tip on the museum which describes spastic printing behavior. However, nothing it seems to describe the LED lockup upon power on. Also it seemed when the buffered keyboard display was installed recall of memory registers intermittently would fail with flashing 9.99999999E99.

Any suggestions would be welcome. Definately will be some time before repair should the problem be the capacity mentioned in the Printer Repair Tip article.

RE: HP-46/81 Case, Power Supply - Duane Hess - 10-30-2017 04:16 PM

Should mention, always (or almost always, forget) when the printer was shut off the unit worked OK; unless the buffered-keyboard display was installed.

Seems like the longer the printer ran, the worse it was.

All the 81 parts (motherboard, printer, keyboard, display/buffer) were from an HP service kit. In the original boxes, bags were all factory heat sealed. 100% sure all parts have never been used.

Obtained them from a former HP employee who obtained them at interal to HP yearly surplus sales. Think it was obtained about '73-'74. So unless the parts are powered on during manufacturing for testing all electrolytic capacitors have never been powered on for over 40 years.

That being said likely all caps have ripple in them. Don't have an oscilloscope, so who knows.