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HP15c runs slow
12-18-2015, 09:22 PM
Post: #1
HP15c runs slow
Hello

I have two hp15c calculators, one made in Brazil 1988 and one made in USA 1985

But I have a small problem with my Brazil one, it runs much slower than my USA made one and I cant figure out why.

Sometimes when I try to start my Brazil one the ON button does not work, it does not react at all.
I have to press ON and ÷ to start the keyboard test, then I can press Enter to abort it with error 9 and the calculator works again, and sometimes when I press f and clear ∑ the screen goes blank for a long time before I can use it again.

The same sometimes when I press a number and SIN COS TAN the screen goes blank for a long time before presenting the results.

I know that HP15C is a slow calculator in general but I dont have these problems with my USA calculator at all, and its irritating when I use it and things take longer than expected.

but its not always like this, many times it works as normal.

It performs the ON X selftest with no errors and I have tried to replace the batteries.

what could cause the calculator to run slower than normal?

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12-19-2015, 10:03 AM
Post: #2
RE: HP15c runs slow
My two cents: by the time calculators were slow and there was no cristal but a simple RC circuit to set the clock. Condensators are known for not aging well; also passive components have a tolerance and you may just have been unlucky with the Brazilian on. A solution could be to replace the condensator.
Those are guesses, I haven't checked the 15C hardware.
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12-19-2015, 11:29 AM
Post: #3
RE: HP15c runs slow
Hi Adalin, welcome! Nice collection, by the way!

As you reported intermittent problems, I don't think it is bad condensators, maybe a bad soldering?

I have two Brazilians ones and although I don't have an American to compare, I think their slowness is typical for any 15c, although in those days I didn't think they were slow.

There's a recurrent solution that I have learned in this forum that is to remove batteries and shortcut the batteries contacts. If that don't resolve the issue, I think it's better to disassembly the unit for inspection and repair, but let's see if there are some better suggestion from people in this forum.

Good luck

Cheers

Jlouis
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12-19-2015, 01:44 PM
Post: #4
RE: HP15c runs slow
I agree with Jlouis, start by removing the batteries and shorting the battery contact together briefly to see if that helps. If not, open the calculator and inspect the inductor and capacitor that form the oscillator (it's an LC circuit not an RC circuit, at least on the US versions, and I'm pretty sure on all versions from that time period). Just reflow the solder on those components.

If that still doesn't work try replacing the capacitor with a 180pf ceramic one or something close to that value. The inductor is around 180 uH, BTW.

FYI using a smaller value inductor and/or capacitor you can speed up the calculator by a factor of 2 or more. This comes at the expense of higher current drain of course.

-katie

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12-19-2015, 02:32 PM
Post: #5
RE: HP15c runs slow
Hello

Yes I have tried to short the battery terminals together, no results except the reset

One thing I did not mention is that its often the first time I start it for some time that it struggles, after that its fine for a couple of hours, runs just fine.

I did not think about the LC oscillator but now that some of you mention it it makes sense, perhaps the capacitor has drifted or is leaky in some way and needs a jump start to work.

I found the posts about increasing the speed of the calculator in the forum and I will try to replace the capacitor and the inductor to a slightly smaller value, I dont want to increase the power drain to much but increased speed is always nice.

My board seems to be a slightly different type than the pictures I found online, the orientation of the components are different and only SMD. But the values are the same.

I will change the 22µF capacitor also just in case

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12-19-2015, 07:15 PM
Post: #6
RE: HP15c runs slow
Out of curiosity, how long and how often have you been using it?
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12-19-2015, 09:20 PM
Post: #7
RE: HP15c runs slow
I mostly use it at work to calculate electrical parameters in field once or twice a week, I bought this unit as a spare to my older one maybe 16 months ago but I started to use it in my everyday work because its a little more beat up than my older one, so more fit for field use one can say.

But it has been slow since I bought it, before that I dont know how it was used.

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12-23-2015, 12:49 PM
Post: #8
RE: HP15c runs slow
I replaced the inductor and the capacitor and it seems to run fine now, I made it run a bit faster in the process.

mystery solved!

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12-23-2015, 12:52 PM
Post: #9
RE: HP15c runs slow
Congratulations.

I wish I knew how to boost my 15c too.
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12-25-2015, 11:36 PM
Post: #10
RE: HP15c runs slow
(12-23-2015 12:49 PM)Adalin Wrote:  I replaced the inductor and the capacitor and it seems to run fine now, I made it run a bit faster in the process.

mystery solved!
Nice. Batteries will drain faster though. Alas it may now last for only 15 years instead 20.
This being said, it is always better than the reedition that drains in ... 2 months.
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12-26-2015, 12:24 AM
Post: #11
RE: HP15c runs slow
(12-25-2015 11:36 PM)Tugdual Wrote:  ... it is always better than the reedition that drains in ... 2 months.

Is this an exaggeration or is the LE really that much power-hungry?
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12-26-2015, 02:22 AM
Post: #12
RE: HP15c runs slow
(12-26-2015 12:24 AM)Marcio Wrote:  
(12-25-2015 11:36 PM)Tugdual Wrote:  ... it is always better than the reedition that drains in ... 2 months.

Is this an exaggeration or is the LE really that much power-hungry?

A lot depends on how often you press the buttons. Battery life will be much better if you don't use itSmile

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