HP-19C Repair Odysee

[PANAMATIK]

The newPIK chip is printing to the HP82240B printer!

I made the first successful print lines to the HP82240B printer. The output is the same as the HP-19C thermo printhead would produce. The print line data is assembled by the original HP-19C ROM code in the ACT c register and sent from the ACT to the newPIK prototype. Last week I used the PIC serial interface and had to make some extra cable connections between the two chips, now I use the original communication lines. The communication is preliminary done through the ISA (Instruction/Address) line. When I receive the PIC16F18877 processor next week with 2xSPI interface I can use the DATA line for communication, which is then like the original.



The prototype setup, left the HP-19C hardware with newACT, right the newPIK



Some prototype print lines (with some hickups for now)

The partially corrupted print lines are timing errors, which will be no problem to correct. This was just my first try of testing IR printing, which I started today, and to verify, that the Data is sent correctly from the ACT to the PIK.

Bernhard

[AndiGer]

Although I don't own a 19C - very cool job, Bernhard

[PANAMATIK]

The "newPIK" schematic is ready!

As always there was a tradeoff between possibilities and reality.

The disadvantages:

1.) The newPIK will not be working standalone with the original ACT chip. For now it is only usable for repair of an HP-19C together with the newACT. The newACT repair kit hardware is unchanged when programmed as HP-19E. Using the newPIK in an HP-97 requires to use also a newACT for the HP-97, which I still have to develop.
2.) The newPIK relies on the original display driver chips, therefore there is no alphanumeric LED display possible.

But there are some advantages:

1.) Very easy to install. Just remove the original ACT and PIK chip and insert the new circuits.
2.) There will be a Real Time Clock which can display time, date, day, alarm time, stopwatch.
3.) There is a Low Power mode. When you switch OFF the calculator the state of all registers and programs will be retained.
4.) You can store many user programs in flash memory. The original HP-19C/29C application programs are preprogrammed.
5.) There is a beeper for alarm time and stopwatch countdown alarm.
6.) Display of battery voltage and temperature



Why did I not develop a PIK chip, which can be used in any HP-19C and HP-9X calculator with the original ACT?

In my opinion this is impossible with any of the 5V PIC or ATMEL devices available. The reason is the timing of the synchrounous ISA and DATA signals of the ACT. These signals are synchrounous bidirectional communication lines between ACT and PIK, where the ACT is master and PIK is slave. If a PIK instruction is output on the ISA line, the PIK has to decode the instruction and react before the next clock arrives. This is only 5,5us. No way with 4-8MIPS interrupt driven software. This can be done by a FPGA but not with a small processor.

But why then did I not go for a FPGA solution?

I would really like to program a PIK with a FPGA, but the available FPGAs with the necessary amount of cells are rather big, with many pins and they have 3,3V or 1,8V signals. They would not tolerante the 6,4V power of the HP calculators. And even if the inputs are 5V tolerant, all output signals must be converted to 5V level. I cannot see a minimalistic solution which finds place on the small area of a 28-pin package.

Bernhard

[Harald]

The original ACT can still be used in another calculator if it is still good. So this is not really a problem in my opinion.
Do you need a 19c for your prototype? I still have one in a box I could send over to you

[PANAMATIK]

(06-04-2021 11:12 AM)Harald Wrote:  The original ACT can still be used in another calculator if it is still good. So this is not really a problem in my opinion.
Do you need a 19c for your prototype? I still have one in a box I could send over to you

Hallo Harald,

I remember thankfully, that you sent me your HP-19C years ago for extracting the ROM code for the first time.

PM sent!

Bernhard

[PANAMATIK]

During my HP-19C PIK development it happended to me, that I received a bunch of HP-19C calculators for future repair or investigation.

I want therefore present two images of this unusual ensemble of rare calculators.



I received also the final PIC processor for the new PIK some days ago. The third prototype is going to be built next. This prototype will be able to print on paper then.

Bernhard

[rprosperi]

Amazing photos Bernhard, thanks for sharing these! Rare gatherings like this must be documented, for who would otherwise believe it could happen.

Probably there has never been such a gathering of Clydes (and one KISS) in one place, with the possible exception of the factory where they were made.

[Jonas Sandstedt]

Bernhard, I have to agree that it is an awesome collection. I hope that you one day have time to share how these HP-19c units work and what measures that have to be done to fix possible malfunctions.
Regarding printheads, I ordered a couple of TH102-E printheads which were received today. The TH102-E is used in the Seiko printer MTP-102 that is adapted for 38mm paper width, the printhead TH201-E used in the Seiko printer MTP-201 that is adapted for 57mm paper width was unavailable. I guess the only difference is the length of the flex cable. As mentioned previously, MTP-201 is used in for example the HP-82240A/B.
I enclose some pictures of the printhead, unfortunately it is glued to a plastic holder, and the flex cable is shorter than the one used for the HP-19c. As you can see, the printhead is not as wide as the one used for the HP-19c. I have not figured out how to use the printhead, or even if it can be used, but wanted to share the pictures for information purposes.
Best regards Jonas
           

[Artur - Brasil]

(03-01-2021 12:31 PM)PANAMATIK Wrote:  Hi All,

I want to present you a small HP-19C repair story here in the forum, which I and a friend had experienced recently. I have provided it as .pdf file with images for download.

I hope you enjoy the text while reading. In any case we had a lot of fun at "one of the best birthday workshops ever".

Bernhard

Hi! Congrastulations for your great work!
I'm with a deffective 19C here too and your article is being ot great help in my work! Thanks!
I was reading all comments in the thread, but they go away to other topics and I would like to go one step back and ask:
You said:"After removing the printer from the circuit and simulating the ON/OFF switch, MAN/TRACE/NORM and the home switch" -well, I did the connections for ON state: connecting S1c – S1d – S1e (12-9-2) togheter. But, what to do with HOME and MAN/TRACE/NORM? Could them be left open just for simple tests?
Best regards
Artur

[PANAMATIK]

(07-05-2021 12:47 PM)Artur - Brasil Wrote:  You said:"After removing the printer from the circuit and simulating the ON/OFF switch, MAN/TRACE/NORM and the home switch" -well, I did the connections for ON state: connecting S1c – S1d – S1e (12-9-2) togheter. But, what to do with HOME and MAN/TRACE/NORM? Could them be left open just for simple tests?

The MAN/TRACE/NORM switch is connected to pin 2,3,6 of the 25-pin keyboard connector. when 2-3-6 open this is TRACE mode, 2-3 connected NORM, 3-6 connected MAN mode.
If HOME is open at power up, the motor moves endlessly until HOME connects to GND, indicating the motor home position.


Bernhard

[[kby]]

The plastic holder doesn’t look all that different from the one the 19c printhead actually is in (not glued). Of course I realize the devil is in the details…

(06-30-2021 04:11 PM)Jonas Sandstedt Wrote:  Bernhard, I have to agree that it is an awesome collection. I hope that you one day have time to share how these HP-19c units work and what measures that have to be done to fix possible malfunctions.
Regarding printheads, I ordered a couple of TH102-E printheads which were received today. The TH102-E is used in the Seiko printer MTP-102 that is adapted for 38mm paper width, the printhead TH201-E used in the Seiko printer MTP-201 that is adapted for 57mm paper width was unavailable. I guess the only difference is the length of the flex cable. As mentioned previously, MTP-201 is used in for example the HP-82240A/B.
I enclose some pictures of the printhead, unfortunately it is glued to a plastic holder, and the flex cable is shorter than the one used for the HP-19c. As you can see, the printhead is not as wide as the one used for the HP-19c. I have not figured out how to use the printhead, or even if it can be used, but wanted to share the pictures for information purposes.
Best regards Jonas

[Artur - Brasil]

Many thanks for your kindly reply!

I will let it in trace, as it is easier. The calculator, in ON mode, and having all parts (except keyboard front part) attached moves the head printer to right position, but none on display. As you did, I changed the two transistors in power circuit and this restored voltage levels but nothing on display. I tested the display with a multimeter and LED segments are working.

It's sad to see a beautifull machine stoped like this one.

Best regards,
Artur!

[PANAMATIK]

(07-05-2021 05:34 PM)Artur - Brasil Wrote:  Many thanks for your kindly reply!

I will let it in trace, as it is easier. The calculator, in ON mode, and having all parts (except keyboard front part) attached moves the head printer to right position, but none on display. As you did, I changed the two transistors in power circuit and this restored voltage levels but nothing on display. I tested the display with a multimeter and LED segments are working.

It's sad to see a beautifull machine stoped like this one.

Best regards,
Artur!

Your machine can be restored somehow, I'm sure. If the motor moves to HOME position at power up, this proves that at least ACT and PIK and ROM chips are working, because moving the motor is an active software part. Did you check the Display Enable signal VDISP ? 1818-0432 U7/pin 5 must be High

Bernhard

[teenix]

In this case, the PIK chip automatically does the print carriage home as the printer home test instruction (PIK1120) does not execute by the ACT on the HP-19C or HP-97 at switch on.

This was also confirmed on my 97 CPU board.

cheers

Tony

(07-05-2021 08:43 PM)PANAMATIK Wrote:  Your machine can be restored somehow, I'm sure. If the motor moves to HOME position at power up, this proves that at least ACT and PIK and ROM chips are working, because moving the motor is an active software part. Did you check the Display Enable signal VDISP ? 1818-0432 U7/pin 5 must be High

Bernhard

[Artur - Brasil]

Your machine can be restored somehow, I'm sure. If the motor moves to HOME position at power up, this proves that at least ACT and PIK and ROM chips are working, because moving the motor is an active software part. Did you check the Display Enable signal VDISP ? 1818-0432 U7/pin 5 must be High

Bernhard
[/quote]

Yes, there is 5V on it, but I had to remove the display for taking such measure, as IC is under it.
Well, if you don't mind, here my measures for top board (without keyboard and display), taking pin 1 of 12 pins connector as 0V reference:
1 0V (reference)
2 5vdc
3 0
4 -12.3
5 0
6 square signal 5V 10.42kHz
7 6.20V - some little ripple (100mV)
8 5V
9,10,11,12 5V

The 1818-0432 IC (also pin 1 of 12 pins connector as reference)
123468 sawtooth 3.289kHz signal, 3.19V
5 5vdc
7 9 0vdc
10 6,16vdc
11 thin-pulse 3,289kHz
12 0
13 thin pulses
14 0
15 183,8kHz, 19,8vpp, 7,08v rms
16 same as 15
17 -12Vdc
18 0

DISPLAY PINS (display installed) - from left to right
1 2 3 4 5 7 sawtooh from 3V to 5V - 3,289kHz
6 8 0Vdc
9 ... 21 3,79vdc

And the other IC - 1820-1629?
I tested the display inserting + probe to holes on the left (1-9) and - probe on holes 10 - 21
The left ones controls the segment on each digit; the right ones the digit.
Comparing the voltages present on its pins, it will not turn on, as the left ones are above 3V and the right ones at 3,8V - only 1,2Vmax of difference...

Again, I move the printer head by hand, turning the axe, and when the power is applyed, the head goes full left and goes full right and stop.
Best regards and many thanks for your precious knowledge!
Artur

[teenix]

Quote:1 0V (reference)
2 5vdc
3 0
4 -12.3
5 0
6 square signal 5V 10.42kHz >>> Printer Strobe
7 6.20V - some little ripple (100mV) >>> Typical supply noise
8 5V
9,10,11,12 5V

These seem OK

Quote:The 1818-0432 IC (also pin 1 of 12 pins connector as reference)
123468 sawtooth 3.289kHz signal, 3.19V >>> Display segment a b c d e f
5 5vdc >>> Vcc
7 9 0vdc - Display segs h and g, will be 0V for "0" display, but [h] on briefly for a decimal point
10 6,16vdc >>> Vss
11 thin-pulse 3,289kHz >>>> Display strobe
12 0 >>> GND
13 thin pulses >>> ISA bus
14 0 >>> No connection
15 183,8kHz, 19,8vpp, 7,08v rms >>>> 2 Phase clock
16 same as 15
17 -12Vdc >>> Vgg
18 0

These seem ok - and would indicate a "0" on the display, if pin 7 is not showing anything then maybe no decimal point.

Quote:DISPLAY PINS (display installed) - from left to right
1 2 3 4 5 7 sawtooh from 3V to 5V - 3,289kHz
6 8 0Vdc
9 ... 21 3,79vdc

And the other IC - 1820-1629?
I tested the display inserting + probe to holes on the left (1-9) and - probe on holes 10 - 21
The left ones controls the segment on each digit; the right ones the digit.
Comparing the voltages present on its pins, it will not turn on, as the left ones are above 3V and the right ones at 3,8V - only 1,2Vmax of difference...

This is the cathode driver and makes sure only 1 display digit is turned on at any time, otherwise you will either get no display or digits bleeding into the following digits. (Display strobe mentioned above) The full display is refreshed during a single instruction cycle, then a pulse will appear on the RCD pin to reset the driver back to digit 1 for a new display refresh.

Quote:Again, I move the printer head by hand, turning the axe, and when the power is applyed, the head goes full left and goes full right and stop.

Probably means the PIK and printer motor circuits are OK.



If the display is not working, perhaps look at the components around pin 5 of 1818-0432, 5K6 resistor, 6K8 resistor and a NPN transistor. These provide the common power for the display LEDs.

cheers

Tony

[PANAMATIK]

(07-05-2021 11:35 PM)teenix Wrote:  In this case, the PIK chip automatically does the print carriage home as the printer home test instruction (PIK1120) does not execute by the ACT on the HP-19C or HP-97 at switch on.

This was also confirmed on my 97 CPU board.

cheers

Tony

That is correct, but let it more precise:

At power up the ACT reads the initialization instructions from ROM. When it encounters the pik_home? test instruction, the PIK chip executes the instruction and tells the ACT if HOME switch is activated or not. If not , the ACT branches to code which invokes the pik_cr? instruction, which let the PIK start the motor until a debounced negative edge occurs on the HOME input, i.e. HOME position is arrived.

ACT and PIK and ROMs must be OK to perform the correct HOME return movement.

Bernhard

[teenix]

(07-06-2021 07:15 AM)PANAMATIK Wrote:  That is correct, but let it more precise:

At power up the ACT reads the initialization instructions from ROM. When it encounters the pik_home? test instruction, the PIK chip executes the instruction and tells the ACT if HOME switch is activated or not. If not , the ACT branches to code which invokes the pik_cr? instruction, which let the PIK start the motor until a debounced negative edge occurs on the HOME input, i.e. HOME position is arrived.

ACT and PIK and ROMs must be OK to perform the correct HOME return movement.

Bernhard

Oh ok, that is interesting, maybe there are different ROM and PIK versions.

Both my 19C and 67 emulators running standard Microcode don't show a PIK HOME? instruction getting executed on start up or during the key wait loop, only - Is there a key press available? - PIK1320.

The carriage would not home itself at switch on when running the standard HP-97 Microcode on my HP-97 CPU board which caused me to do some head scratching. My guess was the PIK chip senses the state of the carriage through it's HOM pin input and homes the carriage by itself - but this only happens at start up.

Once up and running and waiting for something to happen, if a print operation is to take place, then the Home? and Paper_Out? instructions do get executed (setting the STATUS flag [3]) before the printing takes place. If STATUS [3] flag is set, the Microcode shows error on the display and printing is stopped or not started.

Obviously the HOM pin is required on the PIK chip because it detects the head position and stops the motor when the carriage is back home. It wouldn't be wise for the Microcode to do this because it might be doing something else and unable to monitor the situation. For example, the printer HOM instruction is not executed when a program is running in MAN mode.

Under some conditions, (example: printing multiple lines), if the 97 and 19C carriage will not home, the Microcode will stay in an infinite loop.

Code:


HP-97
$38D    0 -> s3
        pik1120    // carriage home? (sets S3=1 if so)
        if s3 = 0
          then go to $38D  // no

HP-19C
$306        PIK1120
        if s3 = 0
          then go to $306

cheers

Tony

[PANAMATIK]

(07-06-2021 08:00 AM)teenix Wrote:  Both my 19C and 67 emulators running standard Microcode don't show a PIK HOME? instruction getting executed on start up or during the key wait loop, only - Is there a key press available? - PIK1320.

Hi Tony,

You are right. I checked again my interpretation of the HP-19C code. And indeed the HP-19C does use the pik home? 1120 and pik cr? 1220 instructions at startup only if "Continuous Memory" is corrupted and "Error" shall be printed. Therefore an automatic PIK induced "MovetoHome" at power up is also performed, which is not triggered by software. This escaped my attention.

Then at the moment only the PIK is confirmed to work. ACT could be damaged.

Bernhard

[Artur - Brasil]

Well, I checked again the voltages. All are there, but nothing on display.
I checked again and it seems to me that, as I tested display using + probe at left and - at right, the voltages of left should be more positive than right, but my measuring on real circuit shows the inverse!
I'll try again, but I'll give some time. I have other things to work in home...

Many thanks Tony, Teenix, Bernhard, Panamatik. I really like to have the opportunity to learn with you!

Sincelrely best wishes from Brazil !
Artur