HP-65 1333A02242 display missing all the decimal dots

[albertofenini]

Hi everyone
this is a more challenging work ...
The unit is working in the meaning that it turns on but all of the decimal dots are missing
We have given the unit a good clean and thinking of a cold joint on the pin that control
the decimal dot anode segment (I believe is the h segment)
we have refreshed that soldered pin of the 1820-1029 anode driver
However it didn't fix the problem
What could we possibly check to troubleshoot the problem ?
Thanks in advance for any idea you may want to share with us
Take care !!
HP-65 1333A02242 display missing all the decimal dots

[teenix]

(11-08-2020 11:39 PM)albertofenini Wrote:  Hi everyone
this is a more challenging work ...
The unit is working in the meaning that it turns on but all of the decimal dots are missing
We have given the unit a good clean and thinking of a cold joint on the pin that control
the decimal dot anode segment (I believe is the h segment)
we have refreshed that soldered pin of the 1820-1029 anode driver
However it didn't fix the problem
What could we possibly check to troubleshoot the problem ?
Thanks in advance for any idea you may want to share with us
Take care !!
HP-65 1333A02242 display missing all the decimal dots

I would check that the decimal point data is being generated with an oscilloscope and exits from the hybrid chip pins 11 to 15 and that they appear on the anode driver pins 1 to 5.

Page 9 of my Classic Notes PDF show the waveforms for 0.00 being displayed.

http://teenix.org/ClassicNotes.pdf

If they are appearing correctly then perhaps the anode driver is faulty as it decodes these signals to provide the digits and decimal point.

I would also check that the correct signals are appearing from pin 18 from the anode driver for the decimal point. Perhaps the corresponding coil is open circuit or has a bad connection.

cheers

Tony

[AndiGer]

Maybe this link can help? See the last entry. It is posted for the HP-67 but maybe also hits the situation in the HP-65?
Good luck!

[teenix]

(11-09-2020 09:30 AM)AndiGer Wrote:  Maybe this link can help? See the last entry. It is posted for the HP-67 but maybe also hits the situation in the HP-65?
Good luck!

Good link.

However, the display drivers in the 65 are a more complicated concept to the 67. The 65 anode driver consists of a decoder to sort out the 5 input display lines to 7 segment outputs and additional processing for the decimal point and then energizes the coils, and with the help of the cathode driver, discharge into the LEDs. It also has synchronizing circuitry to the hybrid ARC chip. A driver transistor in the mentioned 67 configuration would not work in this case.

cheers

Tony

[albertofenini]

Thanks Tony, will try this evening and will post ...
Can we take these values and these waves from the logic board connector as well ?
I think it may be easier since the Hybrid does not have pins connections accessible from the top ....

(11-09-2020 03:06 AM)teenix Wrote:  

(11-08-2020 11:39 PM)albertofenini Wrote:  Hi everyone
this is a more challenging work ...
The unit is working in the meaning that it turns on but all of the decimal dots are missing
We have given the unit a good clean and thinking of a cold joint on the pin that control
the decimal dot anode segment (I believe is the h segment)
we have refreshed that soldered pin of the 1820-1029 anode driver
However it didn't fix the problem
What could we possibly check to troubleshoot the problem ?
Thanks in advance for any idea you may want to share with us
Take care !!
HP-65 1333A02242 display missing all the decimal dots

I would check that the decimal point data is being generated with an oscilloscope and exits from the hybrid chip pins 11 to 15 and that they appear on the anode driver pins 1 to 5.

Page 9 of my Classic Notes PDF show the waveforms for 0.00 being displayed.

http://teenix.org/ClassicNotes.pdf

If they are appearing correctly then perhaps the anode driver is faulty as it decodes these signals to provide the digits and decimal point.

I would also check that the correct signals are appearing from pin 18 from the anode driver for the decimal point. Perhaps the corresponding coil is open circuit or has a bad connection.

cheers

Tony

[albertofenini]

Thank you very much !
However, as Tony has stated, the way an HP65 handles the display is different from how it is handled in a HP67 ...

(11-09-2020 09:30 AM)AndiGer Wrote:  Maybe this link can help? See the last entry. It is posted for the HP-67 but maybe also hits the situation in the HP-65?
Good luck!

[teenix]

(11-09-2020 11:37 AM)albertofenini Wrote:  Thanks Tony, will try this evening and will post ...
Can we take these values and these waves from the logic board connector as well ?
I think it may be easier since the Hybrid does not have pins connections accessible from the top ....

You can tap the connections between the CPU board and keyboard.

cheers

Tony

[albertofenini]

Thx Tony,
looking at the keyboard from the keys side it should be first, second, third, fifth and sixth from the left, right ?

(11-09-2020 12:06 PM)teenix Wrote:  

(11-09-2020 11:37 AM)albertofenini Wrote:  Thanks Tony, will try this evening and will post ...
Can we take these values and these waves from the logic board connector as well ?
I think it may be easier since the Hybrid does not have pins connections accessible from the top ....

You can tap the connections between the CPU board and keyboard.

cheers

Tony

[teenix]

(11-09-2020 12:12 PM)albertofenini Wrote:  Thx Tony,
looking at the keyboard from the keys side it should be first, second, third, fifth and sixth from the left, right ?

The "Step" output is anode driver pin 6.

cheers

Tony

[albertofenini]

what is the "Step" output ?

(11-09-2020 12:32 PM)teenix Wrote:  

(11-09-2020 12:12 PM)albertofenini Wrote:  Thx Tony,
looking at the keyboard from the keys side it should be first, second, third, fifth and sixth from the left, right ?

The "Step" output is anode driver pin 6.

cheers

Tony

[teenix]

(11-09-2020 12:42 PM)albertofenini Wrote:  what is the "Step" output ?

This is the signal from the anode driver to step the cathode driver to the next display digit.

cheers

Tony

[albertofenini]

Thanks Tony,
I understand that I'm missing some basic knowledge, and I should go back to study the documents ...
What is the purpose of each of disp0, disp1, disp2, disp3, disp4 ?
Is disp4 wat you call "step" ?
I know that it may be not easy to summarize these concepts so I will appreciate
any hints that will help to better understand the working scheme ...
For instance, with reference to the PDF you mentioned at the beginning of this post
can we say Disp0 = A, Disp1 = B, Disp2 = C, Disp3 = D, Disp 4 = E ?

(11-09-2020 01:22 PM)teenix Wrote:  

(11-09-2020 12:42 PM)albertofenini Wrote:  what is the "Step" output ?

This is the signal from the anode driver to step the cathode driver to the next display digit.

cheers

Tony

[teenix]

(11-09-2020 01:32 PM)albertofenini Wrote:  Thanks Tony,
I understand that I'm missing some basic knowledge, and I should go back to study the documents ...
What is the purpose of each of disp0, disp1, disp2, disp3, disp4 ?
Is disp4 wat you call "step" ?
I know that it may be not easy to summarize these concepts so I will appreciate
any hints that will help to better understand the working scheme ...
For instance, with reference to the PDF you mentioned at the beginning of this post
can we say Disp0 = A, Disp1 = B, Disp2 = C, Disp3 = D, Disp 4 = E ?

Hi Alberto,

The display for the Classics looks simple but is quite a complex setup. The Classic Notes PDF document link that I provided earlier explains how it all works with images from my oscilloscope and there is more information available in the HP-45 patent document which is available on the web or I can email if you like.

Re: Disp0=A etc., yes, that is correct.

In simple terms, the 5 lines have partially decoded display information on them and is fed to the anode driver which fully decodes that into 7 segment display control.

This data (very quickly - in 20uS time slots) charges and discharges the coils to turn on the appropriate LEDs for each digit.

After all 8 LED segments are either turned on or off depending on the digit to display, the "step" signal from the anode driver tells the cathode driver to move to the next digit and the anode information (lines 1-5) continues.

However, before the "step" occurs, if there is a decimal point to display (segment H) then the anode drives issues an extra "step" signal and the next digit shows a decimal point only. This functionality is explained and shown in diagrams in both the mentioned PDF files.

Happy to help further if I can :-)

cheers

Tony

[albertofenini]

Hi Tony
We have uploaded all the waves for the segments captured with the faulty units
Also we have moved this cpu board in a known working unit and the decimal point was working
I think the fault could possibly be in the anode driver
The waves are visible at the initial link
What do you think ?
Take care and thanks for help !!

[albertofenini]

We have also uploaded the waves for disp0, disp1, disp2, disp3, disp4 and step at the anode driver ...

[teenix]

(11-09-2020 09:49 PM)albertofenini Wrote:  We have also uploaded the waves for disp0, disp1, disp2, disp3, disp4 and step at the anode driver ...

The waveform for your "step" looks like it is the "E" waveform on my diagram. The others look ok.

I would expect the step trace to show 14 pulses spaced 20uS apart and one spaced 5uS apart, all over a 280uS period. These pulses step the cathode driver to the next digit on the display.

Interesting stuff follows - maybe not :-)

The cathode driver is essentially a 15 stage counter which activates each output in sequence with the step pulse. Normally these type of counters would reset to the first output after the maximum pulse count is received and scan again, but this approach will only work in the Classics if the anode driver was synchronized to this event, but it isn't.

It is the job of the cathode driver RCD input to reset the counter back to the initial output. This pulse comes from the ARC chip and is synchronized to the 5 display data pins between the ARC and anode driver and in this way, each digit will receive the correct segment information.

It takes the CPU 280uS (nominal) to execute 1 instruction and the 15 display digits are fully updated during this time with 20uS available to update each display digit. Timing is critical with this setup as the display could show garbage or information could bleed into following digits, or the driver transistors in the IC's could be damaged.

Now those with a mathematical mind might say something is wrong here.
15 digits x 20uS = 300uS, not 280uS.

The answer lies with the final decoding circuits inside the anode driver. When a decimal point is to be displayed, the anode driver issues an extra step pulse and excites the decimal point coil in the last 5uS of the 20uS time slot. The decimal point is small compared to the other LED segments, so it requires less energy to appear at the same brightness. The coil for the decimal point LED is energized and disharges over a smaller time and also has about half the inductance as the others (130uH vs 68uH).

The display 7 segments are controlled by the data in the A register while digit blanking and the decimal point are controlled by the data in the B register. Each register has 56 bits split up into 14 x 4 bit nibbles. These can hold binary values from b0000 to b1111 (0 - 15) with bit 3 on the left down to bit 0 on the right.

The ARC normally sends the required 5 bit data to tell the anode driver to step the cathode driver and display the digit from the corresponding A register nibble.

If the B register nibble [bit 1] is set to 1 (ie. 0010) then extra data is encoded into the 5 bits so that after the digit is displayed, the anode driver steps the cathode driver again and lights the decimal point. Any number in a B register nibble with bit 1 set would work, ie 2 3 6 etc., however bit 3 cannot be 1 or no LED segments in the digit will light.

Because multiple decimal points can be displayed, the final digit count could well exceed the 15 digits available. If the cathode driver reset itself after the 15th digit, these decimal points would cause other digits to be displayed starting from the beginning of the display scan resulting in garbage being shown.

The logic in the cathode driver stops this happening by not resetting itself if more than 15 step pulses are received before a reset pulse.

This is shown in the Classic Notes on page 12 which has a HP-65 running a small program that places some 2's in the B register which then shows multiple decimal points while the display is active during running programs. You can see all the double stepping occurring in the oscilloscope image.

cheers

Tony

[albertofenini]

Hi Tony
Thank you very much for the interesting explanation.

Let me ask you, are RCD and STEP the same ?

At this point what’s your diagnosis ?

The cpu board proved itself working when put in another unit so I
would assume something is wrong on this keyboard pcb

Is the wave for the h segment (the decimal point) correct ?

Could the anode driver or the cathode driver possibly defective ?

By the way We have also another unit , which we posted about this summer, with all the g segment missing, would it possibly be a similar problem ?

Take care and thanks again!!!

[teenix]

(11-10-2020 06:49 AM)albertofenini Wrote:  Hi Tony
Thank you very much for the interesting explanation.

Let me ask you, are RCD and STEP the same ?

At this point what’s your diagnosis ?

The cpu board proved itself working when put in another unit so I
would assume something is wrong on this keyboard pcb

Is the wave for the h segment (the decimal point) correct ?

Could the anode driver or the cathode driver possibly defective ?

By the way We have also another unit , which we posted about this summer, with all the g segment missing, would it possibly be a similar problem ?

Take care and thanks again!!!

Hi Alberto,

The step and RCD are different signals. The step advances the cathode driver to the next digit. The RCD resets the cathode driver to start the digit scan again.

I would say the RCD is working if you see digits on the display.

If you look at the signal on the step pin of the cathode driver (pin 9) you should see 15 pulses that repeat every 280uS. 14 of these will be spaced 20uS apart and one of these pulses will be spaced about 5uS. This one is the decimal point digit.

If the above waveform is not correct I would suspect the anode driver. The attached image is the 5 data lines and RCD pin with only a decimal point on the display. This happens when after CLx you press the decimal point button.

If you see correct waveforms then I would suspect the keyboard PCB. Corroded open circuit traces for the DP output of the anode driver (pin 17) and soldering, to the LED displays. (bottom of display chips nearest switches, 3rd from right)

The DP coil might be open circuit as well.

For the G segment, I would suspect the anode chip soldering, keyboard traces and G segment coil.

cheers

Tony

[albertofenini]

Hi Tony,
this helps a lot, I will comment below between the line
Thanks again !!

(11-10-2020 09:56 AM)teenix Wrote:  

(11-10-2020 06:49 AM)albertofenini Wrote:  Hi Tony
Thank you very much for the interesting explanation.

Let me ask you, are RCD and STEP the same ?

At this point what’s your diagnosis ?

The cpu board proved itself working when put in another unit so I
would assume something is wrong on this keyboard pcb

Is the wave for the h segment (the decimal point) correct ?

Could the anode driver or the cathode driver possibly defective ?

By the way We have also another unit , which we posted about this summer, with all the g segment missing, would it possibly be a similar problem ?

Take care and thanks again!!!

Hi Alberto,

The step and RCD are different signals. The step advances the cathode driver to the next digit. The RCD resets the cathode driver to start the digit scan again.

I would say the RCD is working if you see digits on the display.

Thank you, now this is clear, we have not uploaded the RCD wave but we will do it today,
I agree that RCD is probably working since the display is lit

If you look at the signal on the step pin of the cathode driver (pin 9) you should see 15 pulses that repeat every 280uS. 14 of these will be spaced 20uS apart and one of these pulses will be spaced about 5uS. This one is the decimal point digit.

If the above waveform is not correct I would suspect the anode driver. The attached image is the 5 data lines and RCD pin with only a decimal point on the display. This happens when after CLx you press the decimal point button.

To which attached image are you referring ?
The STEP image we posted was captured on the Anode Driver and with the display showing 0.00 (obviously the . was not lit)
We didn't press CLX if this can be of help in troubleshooting

If you see correct waveforms then I would suspect the keyboard PCB. Corroded open circuit traces for the DP output of the anode driver (pin 17) and soldering, to the LED displays. (bottom of display chips nearest switches, 3rd from right)

You meant the 18th pin right ?

We are in difficulties comparing our waveforms with yours and understand if ours are correct or not
What scale for the time and volt you suggest ?
You say that we should see 15 pulses ... in the STEP image we uploaded we see 4 square waves and noise in between
The first square wave is a little more distant of the following three, is this what you mean ?
Four is because 0.00 in theory is 4 digit ? (the 3 zeroes and the digital point ?)
Should we lit all the display digits to see the 15 pulses ?


The DP coil might be open circuit as well.
Any way we can check that too ?

For the G segment, I would suspect the anode chip soldering, keyboard traces and G segment coil.
Thanks, for this issue we will re-open its own post, just to not get this too confusing

cheers

Tony

[teenix]

To which attached image are you referring ?

It should be at bottom of last post.

CLx just clears the display and allows a new number entry, then pressing the DP button should result in just the decimal point showing.

You meant the 18th pin right ?
My applogies, yes.

We are in difficulties comparing our waveforms with yours and understand if ours are correct or not. What scale for the time and volt you suggest ?

For viewing a full display refresh, 2V per Div and say 40uS per div should be ok, triggered on the RCD pulse if you can, so you can see everything in a display refresh.

You say that we should see 15 pulses ... in the STEP image we uploaded we see 4 square waves and noise in between
The first square wave is a little more distant of the following three, is this what you mean ?
Four is because 0.00 in theory is 4 digit ? (the 3 zeroes and the digital point ?)
Should we lit all the display digits to see the 15 pulses ?

I was pretty sure that all 15 pulses should be there regardless of how many digits are being displayed. Have a look at page 15 of the Classic Notes, it shows a HP-65 waveform.

(The DP coil might be open circuit as well.)
Any way we can check that too ?
From the common coil terminal to the DP coil terminal should measure low ohms. I think this should be between VBsw and pin 18 of the anode driver. VBsw is the switched side of the battery, 12th pin in from right of cpu to keyboard connector

cheers

Tony