HP-67 failed main board?

[naznerd]

Hello all,

I have a nice HP-67 that was working fine including the card reader. I set it down for a couple of hours and when I tried to use it again, it displays "-00000000000 00" as soon as it is powered on. This unit is in great physical shape, and has zero corrosion in it. I checked the main logic board for bad solder joints and found none. I've tried using with and without the original HP charger, and it makes no difference. I used a multi-meter and probed voltages on various chips. Most the of the chips shows ~6v, however the large AMI chip has ~17v, which seems wrong? I'd appreciate any insight into what the issue might be and how to correct it.

Thanks!

Larry

[Geoff Quickfall]

Hard to diagnose over the phone (internet :-) but looks like an ACT failure at first glance.

Questions:

1. Is this repeatable or does the display change at every on / off cycle?

2. When keys are pressed, do you see a momentary flicker in the LED display?

3. How are you supplying voltage for testing, regulated bench supply at 3.6v ~ 4v?

4. Are all pins contacting, examine closely at the pin via interface.

That’s to start!

[teenix]

(10-15-2024 02:24 AM)naznerd Wrote:  I have a nice HP-67 that was working fine including the card reader. I set it down for a couple of hours and when I tried to use it again, it displays "-00000000000 00"

This is usually caused by a ROM failure, where the HP program is stuck in a continuous loop at start up. As the display registers (A and B) are reset to zero at this point, the display shows all zeros. The fact that this is happening shows that the calculator otherwise is functional.

The attachment shows the same from my emulator

cheers

Tony

[Dave1947]

My HP-67 did exactly the same thing about 6 months ago. I bought a Teenix motherboard and couldn’t be happier. Continuously memory and increased storage are great. I have several hundred programs stored on the calculator. The upgrade maintains functionality of the card reader also, but it is somewhat redundant since you can also connect to your pc and use remote storage.

[naznerd]

(10-15-2024 08:44 PM)Geoff Quickfall Wrote:  Hard to diagnose over the phone (internet :-) but looks like an ACT failure at first glance.

Questions:

1. Is this repeatable or does the display change at every on / off cycle?

2. When keys are pressed, do you see a momentary flicker in the LED display?

3. How are you supplying voltage for testing, regulated bench supply at 3.6v ~ 4v?

4. Are all pins contacting, examine closely at the pin via interface.

That’s to start!

1. It happens every time.
2. No indication of a key press
3. Battery pack with and without the HP power supply.
4. I've checked and reseated the boards with no change in behavior.


Thanks for the reply!

[naznerd]

(10-15-2024 10:16 PM)teenix Wrote:  

(10-15-2024 02:24 AM)naznerd Wrote:  I have a nice HP-67 that was working fine including the card reader. I set it down for a couple of hours and when I tried to use it again, it displays "-00000000000 00"

This is usually caused by a ROM failure, where the HP program is stuck in a continuous loop at start up. As the display registers (A and B) are reset to zero at this point, the display shows all zeros. The fact that this is happening shows that the calculator otherwise is functional.

The attachment shows the same from my emulator

cheers

Tony

Thanks Tony.

[naznerd]

(10-16-2024 11:49 PM)Dave1947 Wrote:  My HP-67 did exactly the same thing about 6 months ago. I bought a Teenix motherboard and couldn’t be happier. Continuously memory and increased storage are great. I have several hundred programs stored on the calculator. The upgrade maintains functionality of the card reader also, but it is somewhat redundant since you can also connect to your pc and use remote storage.

I became convinced that this was a failure that I would be unable to fix without a donor calculator, so I ended up ordering the Teenix board also.