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Onur ILKORUR · 03-06-2014, 06:05 PM

Hello,

I had this 29C for a long time and I was using it with great care, charging the batteries out of the calculator, using the correct type of rechargeable batteries with correct current rating.

Last weekend, when I was in the middle of my calculations, it displayed a "0" at the far right hand side of the display and stopped responding to any key press. This "0" was brighter than anything it has displayed so far. I turned it off and on again but there was a blank screen. Hoping that this may be caused because of the flat batteries, I replaced them with freshly recharged ones. The moment I placed them in, I have noticed that I have left the calculator on, and it immediately displayed that "0" again. Turning it off and on gave the same blank screen.

I made sure that the calculator was off, and took the batteries out, waited for a couple hours, and placed the batteries back in. When I turned it on, I had flickering "0"s and when I pressed a key, some segments of some digits were lit and the key-digit combinations were consistent.

After reading the posts regarding 25/25C/29C repairs, I have decided to write my experience here, because I couldn't made any resemblance with any article that I have read so far.

I would appreciate any input that may shed a light to what is going on with this 29C. I have another 29C which was serviced by the previous owner, therefore I am not sure which components are salvageable. Besides, that one has a daughter board, but this one does not. Also I have a 25C and a 25 willing to donate their parts if needed.

Thanks in advance,
Onur

Massimo Gnerucci · 03-06-2014, 07:10 PM

A fried ACT I fear... Sad

Onur ILKORUR · 03-06-2014, 09:53 PM

Well, I have several ACT chips lying around. I guess the best way is to buy a low profile socket and start testing.

Is there something that I need to pay attention to while doing this?
like: iron temperature, wrong ACT causing other failures...

/Onur

Mark Hardman · 03-06-2014, 10:25 PM

(03-06-2014 09:53 PM)Onur ILKORUR Wrote: Well, I have several ACT chips lying around. I guess the best way is to buy a low profile socket and start testing.

Is there something that I need to pay attention to while doing this?
like: iron temperature, wrong ACT causing other failures...

/Onur

Based on Eric Smith's invaluable "HP Calculator Chips" site, the donor ACT will need to be either P/N 1820-1596 or 1820-1741.

I weep for your loss.

Mark Hardman

Onur ILKORUR · 03-06-2014, 10:48 PM

That is a very good list indeed. I am so surprised how I missed it till now.

I think lady luck has changed her mind. I have an AMI 1820-1741 lying around. I don't recall for how long or from where I have it but I think I know already what I am going to do this Sunday afternoon.

Mark and Massimo, thank you for your valuable time and input. I will share the result here.

/Onur

Onur ILKORUR · 03-06-2014, 10:54 PM

One last thing ...

I am usually punished after replacing some ICs by the power supply. Meaning that, I sometimes replace some ICs on a circuit board, but later I realize that the IC is being blown away because of a faulty power supply.

I think I need to check the voltage levels of the power supply before I replace the ACT?

/Onur