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HP48G Hardware Troubleshooting Questions/Tips
10-11-2019, 04:07 PM (This post was last modified: 10-11-2019 08:49 PM by Phenixg.)
Post: #1
HP48G Hardware Troubleshooting Questions/Tips
Hello Guys,

I would like to know if any of you have some tips to determine if a processor is dead. My HP48G stopped working a few weeks ago and I tried all the well know tips to revive it but none of them worked for me.
Here are what I have done so far :
* The keyboard foam have been replaced and the connector cleaned with isopropyl alcohol
* Zebra connectors cleaned
* Tried the warm reset, the pinhole reset, the capacitor short and the battery connectors short.
* I left it without battery for 2 weeks.

Here are what I can see:
* There is no sign of life on the display. Nothing when I just connect the batteries, nothing when the "ON" button is pressed and after.
* The "ON" key seems to work: I measured voltage between ground and the ''ON" connector, I get 4.x volts when the on button is pressed; I get 0.0 volt when released. I also measured the resistance, when the on is pressed; the value seems to vary.

Q1: Is there any specific voltage or resistance(or whatever parameter) in some specific spots on the board that would confirm that the processor cannot wake-up or being prevented to wake-up by some other components failure?

Q2: Is there a way to test that display is receiving signals from the processor.

Q3: What are your thoughts?

Thank you Guys.
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10-12-2019, 01:24 AM
Post: #2
RE: HP48G Hardware Troubleshooting Questions/Tips
A crude approach I applied recently is to swap cpu boards with a known good 48s|g calculator. You can also find schematics here at hpcalc.org:

https://www.hpcalc.org/details/3543

Those may provide help finding a clock signal, address line, etc. to see if the cpu is functioning.

Who decides?
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10-16-2019, 03:54 PM
Post: #3
RE: HP48G Hardware Troubleshooting Questions/Tips
Thank you mfleming. I am working on it.
I wish there were as much detailed information about this landmark device as there are about the venerable 41. I really envy the 41 people; It is such a regrettable thing that some of us discarded our beloved toy just because a banal resistor become open or common transistor shorted.
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10-17-2019, 04:14 PM (This post was last modified: 10-17-2019 04:27 PM by TomC.)
Post: #4
RE: HP48G Hardware Troubleshooting Questions/Tips
I too am very interested in having better 48G documentation beyond the commonly available schematics (by Marcel Flipse).

Perhaps some day when I have some extra time in my life, I will open a normally operating 48G and take some voltage and oscilloscope measurements.

By the way, if memory serves me correctly, the referenced 48 schematic by (by Marcel Flipse)has incorrect wiring of the serial port. I wish we could a hold of an editable copy of that schematic!

Cheers,
TomC
(10-16-2019 03:54 PM)Phenixg Wrote:  Thank you mfleming. I am working on it.
I wish there were as much detailed information about this landmark device as there are about the venerable 41. I really envy the 41 people; It is such a regrettable thing that some of us discarded our beloved toy just because a banal resistor become open or common transistor shorted.
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10-17-2019, 04:34 PM
Post: #5
RE: HP48G Hardware Troubleshooting Questions/Tips
(10-17-2019 04:14 PM)TomC Wrote:  By the way, if memory serves me correctly, the referenced 48 schematic by (by Marcel Flipse)has incorrect wiring of the serial port. I wish we could a hold of an editable copy of that schematic!

The pin-out shown in this schematic is of the 48 DEVICE itself, while the pin-out shown in the Technical Interfacing Guide is of the CABLE, so they appear to be opposite, but are in fact, in-sync with each other.

Unless you mean the circuit itself is incorrect; can't help with that.

--Bob Prosperi
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10-17-2019, 04:46 PM
Post: #6
RE: HP48G Hardware Troubleshooting Questions/Tips
Compare the Flipse chematic with the diagram in the HPJournal 6/91 which shows the connector on the calculator - they do NOT agree)

(10-17-2019 04:34 PM)rprosperi Wrote:  
(10-17-2019 04:14 PM)TomC Wrote:  By the way, if memory serves me correctly, the referenced 48 schematic by (by Marcel Flipse)has incorrect wiring of the serial port. I wish we could a hold of an editable copy of that schematic!

The pin-out shown in this schematic is of the 48 DEVICE itself, while the pin-out shown in the Technical Interfacing Guide is of the CABLE, so they appear to be opposite, but are in fact, in-sync with each other.

Unless you mean the circuit itself is incorrect; can't help with that.
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10-17-2019, 04:50 PM
Post: #7
RE: HP48G Hardware Troubleshooting Questions/Tips
See attachment; both show the calculator view. HP Journal is correct:


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10-17-2019, 06:34 PM
Post: #8
RE: HP48G Hardware Troubleshooting Questions/Tips
(10-11-2019 04:07 PM)Phenixg Wrote:  Here are what I can see:
* There is no sign of life on the display. Nothing when I just connect the batteries, nothing when the "ON" button is pressed and after.
* The "ON" key seems to work: I measured voltage between ground and the ''ON" connector, I get 4.x volts when the on button is pressed; I get 0.0 volt when released. I also measured the resistance, when the on is pressed; the value seems to vary.

Have you tried to adjust the contrast?
It happened to me a "dead" HP48, but for some reasons the contrast defaulted to minimum.
Pressing some times ON+ solved
:-)
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10-17-2019, 06:42 PM
Post: #9
RE: HP48G Hardware Troubleshooting Questions/Tips
(10-17-2019 04:14 PM)TomC Wrote:  By the way, if memory serves me correctly, the referenced 48 schematic by (by Marcel Flipse)has incorrect wiring of the serial port. I wish we could a hold of an editable copy of that schematic!

Cheers,

Exactly what needs to be changed? I can edit PDF files.

Tom L
I think therefore I am-Descartes
I think therefore you are-Gorgias
You're not here to think-Army Sergeant
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10-17-2019, 06:53 PM
Post: #10
RE: HP48G Hardware Troubleshooting Questions/Tips
(10-17-2019 06:42 PM)toml_12953 Wrote:  
(10-17-2019 04:14 PM)TomC Wrote:  By the way, if memory serves me correctly, the referenced 48 schematic by (by Marcel Flipse)has incorrect wiring of the serial port. I wish we could a hold of an editable copy of that schematic!

Cheers,

Exactly what needs to be changed? I can edit PDF files.

The connections to the middle two terminals of the connector are the wrong way round.

— Ian Abbott
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10-17-2019, 07:15 PM
Post: #11
RE: HP48G Hardware Troubleshooting Questions/Tips
(10-17-2019 06:34 PM)Marco Polo Wrote:  
(10-11-2019 04:07 PM)Phenixg Wrote:  Here are what I can see:
* There is no sign of life on the display. Nothing when I just connect the batteries, nothing when the "ON" button is pressed and after.
* The "ON" key seems to work: I measured voltage between ground and the ''ON" connector, I get 4.x volts when the on button is pressed; I get 0.0 volt when released. I also measured the resistance, when the on is pressed; the value seems to vary.

Have you tried to adjust the contrast?
It happened to me a "dead" HP48, but for some reasons the contrast defaulted to minimum.
Pressing some times ON+ solved
:-)


Yes, I did try to adjust the contrast.
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10-17-2019, 07:38 PM
Post: #12
RE: HP48G Hardware Troubleshooting Questions/Tips
I edited the PDF. Is this correct? If so, I'll update the version on my site with this new file:

https://www.hpcalc.org/temp/HP48sch16.PDF
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10-17-2019, 07:57 PM
Post: #13
RE: HP48G Hardware Troubleshooting Questions/Tips
The wiring looks correct, HOWEVER, it would be nice if the pin names matches what HP had used in their document (see my attachment).

TomC

(10-17-2019 07:38 PM)Eric Rechlin Wrote:  I edited the PDF. Is this correct? If so, I'll update the version on my site with this new file:

https://www.hpcalc.org/temp/HP48sch16.PDF


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10-17-2019, 08:04 PM
Post: #14
RE: HP48G Hardware Troubleshooting Questions/Tips
(10-17-2019 07:38 PM)Eric Rechlin Wrote:  I edited the PDF. Is this correct? If so, I'll update the version on my site with this new file:

https://www.hpcalc.org/temp/HP48sch16.PDF

It appears this change does indeed correct the diagram. The I/F Doc shows pins in this order:

Shield
HP48 TX (matches with PC_RX)
HP48 RX (matches with PC_TX)
Signal Ground

--Bob Prosperi
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10-17-2019, 08:12 PM
Post: #15
RE: HP48G Hardware Troubleshooting Questions/Tips
I updated the file. Is this pin labeling better?

(10-17-2019 07:57 PM)TomC Wrote:  The wiring looks correct, HOWEVER, it would be nice if the pin names matches what HP had used in their document (see my attachment).

TomC

(10-17-2019 07:38 PM)Eric Rechlin Wrote:  https://www.hpcalc.org/temp/HP48sch16.PDF
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10-17-2019, 08:44 PM
Post: #16
RE: HP48G Hardware Troubleshooting Questions/Tips
Eric:

I think that's perfect!

[Finally, it's annoyed me for all these years!!!]

TomC

(10-17-2019 08:12 PM)Eric Rechlin Wrote:  I updated the file. Is this pin labeling better?

(10-17-2019 07:57 PM)TomC Wrote:  The wiring looks correct, HOWEVER, it would be nice if the pin names matches what HP had used in their document (see my attachment).

TomC
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10-17-2019, 09:17 PM
Post: #17
RE: HP48G Hardware Troubleshooting Questions/Tips
Shouldn’t the title block/version number be updated?

Tnx again,
TomC

(10-17-2019 08:12 PM)Eric Rechlin Wrote:  I updated the file. Is this pin labeling better?

(10-17-2019 07:57 PM)TomC Wrote:  The wiring looks correct, HOWEVER, it would be nice if the pin names matches what HP had used in their document (see my attachment).

TomC
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10-17-2019, 11:46 PM
Post: #18
RE: HP48G Hardware Troubleshooting Questions/Tips
(10-17-2019 09:17 PM)TomC Wrote:  Shouldn’t the title block/version number be updated?

I did update it, to version 1.6. I also fixed a few spelling errors. I chose not to change the date.
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10-18-2019, 02:59 PM
Post: #19
RE: HP48G Hardware Troubleshooting Questions/Tips
Excellent! Awesome!

Thanks very much!

TomC
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