HP15C displays gibberish. Is it broken?

[sebi]

Dear community,
I have the opportunity to buy a HP15C that displays gibberish.

Can you tell by looking at this image if its broken?
Can it be fixed?
Thanks,

[Maximilian Hohmann]

Hello!

Hard to tell. Maybe it just needs a reset (remove the batteries overnight and short the battery terminals) and new batteries.

Good luck
Max

[sebi]

(10-03-2020 04:34 PM)Maximilian Hohmann Wrote:  Hard to tell. Maybe it just needs a reset (remove the batteries overnight and short the battery terminals) and new batteries.

Indeed but I would like to be more confident I can fix it before buying it online...

Isn't this gibberish pattern something known among the HP calculator community?

[rprosperi]

You can also use the built-in self-test, described here:

http://www.rskey.org/~mwsebastian/selfte...tm#voyager

[Valentin Albillo]

(10-03-2020 05:08 PM)rprosperi Wrote:  You can also use the built-in self-test, described here:

This person says that he/she has "the opportunity to buy" the calc so I take it he/she doesn't have the calc available to perform the manipulations you and Maximilian suggest.

Perhaps asking the seller to perform them could be attempted.

Regards.
V.

[sebi]

(10-03-2020 05:16 PM)Valentin Albillo Wrote:  This person says that he/she has "the opportunity to buy" the calc so I take it he/she doesn't have the calc available to perform the manipulations you and Maximilian suggest.

Indeed, I have to possibility to buy it "as it is" based on this picture only, without having the possibility to test it first.
I doubt the vendor wants to make any manipulations for me as he is a secondhand goods dealer...
I might ask but depending on the result I won't be able to negotiate the price anymore.

BTW: I am a "he", I am Sébastien. Nice to meet you.

I would like to know my chances of being capable of fixing it.
I am not that bad at fixing electronics stuff but I have no experience with such calculators.

[Maximilian Hohmann]

Hello!

(10-03-2020 05:35 PM)sebi Wrote:  I would like to know my chances of being capable of fixing it.

If it is really broken: The chances are zero. Here is a thread about repairing an HP15C that has some pictures: https://archived.hpcalc.org/museumforum/...75694.html
As you can see, it contains two integrated circuits only. None of them can be replaced by a new one, because there have been no new ones since thirty years. And I strongly doubt that anything mechanical/electrical (like a key pressed constantly or a poor connection beween PCB and display) will result in the pattern shown in your picture.

Bying that calculator is like buying a lottery ticket: If it can be fixed by resetting and putting in new batteries you will have made a great bargain. Otherwise you will get a pretty paperweight for your money, which is a lot more than a non-winning lottery ticket :-)

Regards
Max

NB: If I were you I would still ask the seller (by mail or phone) to remove the batteries overnight. If that is already too much effort for him he can keep his crap. After all, he wants to sell his items, not you.

[rprosperi]

Valentin and Max's suggestions to ask the seller to do the test and/or remove batteries make sense IF the seller will do them; the results will remove most doubts.

Otherwise, I agree with Max; if the seller will not accommodate these reasonable requests, I'd let the seller keep it, unless he's selling it for a very cheap amount, (< 10 EU) then it may be worth taking a gamble.

[bernouilli92]

I suppose this is the same hp15c I offered 50€ for a few months ago but the seller refused my offer. He wants 70€.
As written, this is a gamble and even 50€ is too much to take a chance.

This hp15c is listed since february and I doubt he’ll ever sell it.

[Marcovecchio]

I just saw this same pattern on a 15C I was fixing yesterday!

The calculator was working, but some LCD segments were failing, so I dismantled it to clean and reassemble. However, I use a bench power supply to work on my calculator repairs, and I accidentally inverted the power supply terminals when trying to power up the 15c!

I went into despair, because the calculator drew 2 amps from the PSU, with the wiring inverted! I quickly unmade the inversion, connecting the terminals correctly, and this is the moment I saw this very same pattern you posted.

I went into despair a second time, I thought the calculator was fried forever, but miraculously, after 10 or 15 minutes, it started working ok again, and I noticed a big resistor-like component was hot. I think it's not a resistor, but an inductor, used to generate calculator clock.

So, I suspect this pattern happens when the calculator has no clock on the processor. In my case, perhaps the voltage inversion made the oscillator circuitry overheat / fail temporarily, but after some minutes, it went to nominal temperatures again and operation was restored.

I will make a test in my spare time, with a 12c in my stash: I'll remove some components from the oscillator circuitry and see if I see the same pattern. If so, my theory is correct.

Eduardo

[sebi]

(10-04-2020 08:37 PM)bernouilli92 Wrote:  I suppose this is the same hp15c I offered 50€ for a few months ago but the seller refused my offer.

Indeed I believe it is the same offer. I asked the vendor to try resetting the calculator but he stopped replying at that point...

[sebi]

(10-05-2020 07:46 PM)Marcovecchio Wrote:  I just saw this same pattern on a 15C I was fixing yesterday!
...I accidentally inverted the power supply terminals when trying to power up the 15c!

That is a very nice hint!
Can you tell me where is located the resistor/inductor that was getting hot on the calculator?

[Chr Yoko]

i know thar vendor, i bought an HP IR printer from him with a slight price decrease. he is honest and nice guy, but as he has over 500 items on sales, and maybe only one calculator, i guess he can't help you much as he may even don't know how does it works.

also that 15c looks pretty biten on the rear, no visible battery door and may have been open?
i would pass on? as keyboard may also be damaged somehow

and buy a brand new DM15L instead as i did few weeks ago ? with no regrets and leave those old used models to collectors

[ijabbott]

(10-05-2020 08:26 PM)sebi Wrote:  

(10-05-2020 07:46 PM)Marcovecchio Wrote:  I just saw this same pattern on a 15C I was fixing yesterday!
...I accidentally inverted the power supply terminals when trying to power up the 15c!

That is a very nice hint!
Can you tell me where is located the resistor/inductor that was getting hot on the calculator?

The green thing under the battery looks like an inductor to me. Either that, or a high-power resistor, but I don't think the Voyager would need a high-power resistor!

[Marcovecchio]

It's the green cylinder just below batteries. However, my 15c is the newer model, with a single pcb, but this part of the electronics shouldn't change too much.

(10-05-2020 08:26 PM)sebi Wrote:  

(10-05-2020 07:46 PM)Marcovecchio Wrote:  I just saw this same pattern on a 15C I was fixing yesterday!
...I accidentally inverted the power supply terminals when trying to power up the 15c!

That is a very nice hint!
Can you tell me where is located the resistor/inductor that was getting hot on the calculator?

[Marcovecchio]

Well, I just made a test with an old 12c, and my theory seems to be incorrect.. Removing the clock does not create this LCD pattern, so it's not possible to pinpoint it's a clock problem.

I would buy this machine with no expectations, it may serve as a parts donor, or with some luck, it may be fixed, but I wouldn't bet money on that!

Eduardo

[sebi]

(10-06-2020 02:19 PM)Marcovecchio Wrote:  Well, I just made a test with an old 12c, and my theory seems to be incorrect..

Too bad. But good to know. Thanks

[BillBee]

As the display appears to be missing segments from the LCD (for the On-X test) is it possible the LCD contact strips need cleaning or readjustment. The early display model (ribbon cable) probably allows for easier testing or a display swap.

Just thinking,
Bill

[lyuka]

(10-05-2020 07:46 PM)Marcovecchio Wrote:  or 15 minutes, it started working ok again, and I noticed a big resistor-like component was hot. I think it's not a resistor, but an inductor, used to generate calculator clock.

It was not the axial lead inductor that was hot, but the dip tantalum capacitor at the power input. It is easily broken in short mode by reverse voltage supply. In this case, it miraculously protects the processor. After that, it is presumed that the short-circuited state became open and the operation was restored because the fuse in the tantalum capacitor was blown or the solid tantalum was completely burned down.

Lyuka

[GreyUser]

No clock in a voyager results in blank display. Every time.

No clock: An open rc network is the most common cause due to battery corrosion. I’ve never seen it occur on an early flex circuit model in the black diaper, only on the rigid pc board models. It’s tough to diagnose because the failed trace is on the hidden side of the pc board. Easy to measure though if you have Tony Duell’s schematic and you figure out where to probe with an ohmmeter. Easy to fix with a bodge wire on the component side once you confirm an open trace.

The display pattern shown on the failed unit of the OP is a processor/r2d2 comms failure, any number of causes. If a reset doesn’t fix it, it’s most likely a bad r2d2.

It is not bad LCD contact. Due to the way the display is multiplexed, regardless of the differences between the original 3:1 and the later 4:1 mux schemes, you could never create that exact display with a loss of connections, it’s physically impossible as the missing segments are common with segments that are in fact displayed.