HP-65 1603S03504 - display not working at all

[albertofenini]

Hello everyone
From this unit we had recovered the logic board to fix another unit
but the led board has never worked
Basically no sign of life on the leds
We have used a working logic board to check the basics :
Vgg, Vbsw, Vss and Vcc are all there and correct
The coils are all closed
On the anode driver Vbsw is present and correct
On the cathode driver Vbsw and Vcc are present and correct
We have then checked the following waves both at the logic board and on the anode or cathode driver where needed
Disp0 : flat at 0 volt
Disp1 : flat at 6 volts
Disp2 : flat at 0 volts
Disp3 : flat at 0 volts
Disp4 : flat at 6 volts
RCD : flat at 0 volts
Step is equal at anode and at cathode and is flat at 6 volts
On the anode driver all the pins for the segments are flat at Vbsw

What could it possibly be ? And what could be possibly check ?
Pictures, not much to be seen can be found here : HP-65 1603S03504 display not working at all
Thanks for any help or suggestions you may want to share !

[teenix]

(11-12-2020 11:33 PM)albertofenini Wrote:  Hello everyone
From this unit we had recovered the logic board to fix another unit
but the led board has never worked
Basically no sign of life on the leds
We have used a working logic board to check the basics :
Vgg, Vbsw, Vss and Vcc are all there and correct
The coils are all closed
On the anode driver Vbsw is present and correct
On the cathode driver Vbsw and Vcc are present and correct
We have then checked the following waves both at the logic board and on the anode or cathode driver where needed
Disp0 : flat at 0 volt
Disp1 : flat at 6 volts
Disp2 : flat at 0 volts
Disp3 : flat at 0 volts
Disp4 : flat at 6 volts
RCD : flat at 0 volts
Step is equal at anode and at cathode and is flat at 6 volts
On the anode driver all the pins for the segments are flat at Vbsw

What could it possibly be ? And what could be possibly check ?
Pictures, not much to be seen can be found here : HP-65 1603S03504 display not working at all
Thanks for any help or suggestions you may want to share !

Not sure I understood, but did the logic board work in a different calculator?

If so, then maybe the anode driver is faulty and is upsetting the CPU operation.

cheers

Tony

[albertofenini]

Hi Tony
You are right, the logic board works perfectly when put in another unit
Or to say it right we used a logic board coming from a working unit and we tested that after these measurements it still works when put in it’s own unit

It may be the anode driver but shouldn’t at least work the rcd signal ?
That is coming from the cathode driver right ?

Also I was expecting to see good display waves at the cpu side or the faulty anode driver may silent these ?

Thanks !!!!

[teenix]

(11-13-2020 07:30 AM)albertofenini Wrote:  Hi Tony
You are right, the logic board works perfectly when put in another unit
Or to say it right we used a logic board coming from a working unit and we tested that after these measurements it still works when put in it’s own unit

It may be the anode driver but shouldn’t at least work the rcd signal ?
That is coming from the cathode driver right ?

Also I was expecting to see good display waves at the cpu side or the faulty anode driver may silent these ?

Thanks !!!!

I cannot say for sure, but it "seems" like the CPU board fails when connected to the anode driver and (maybe) cathode driver. It is possible over the years of driving the coils, that the chip internals have failed and have shorts inside which load up the CPU board to the point that it stops.

The only way to test is to remove the anode driver and see if the signals reappear from the CPU board.

You might have to be careful with the signals to the anode driver as anything that upsets the relationship between the anode/cathode drivers may damage the chips. This is because the coils need to have a path to discharge which is usually through the LEDs and transistor switches in the cathode driver. If the coils get charged and cannot discharge properly, that voltage may build up and break down the junctions in the driver transistors. This is explained on page 3 of the Classic Notes PDF. In an older engine, an extreme example is where a spark jumps the gap in the spark plug when the coil primary current is disconnected by the points.

If the anode driver is removed, then the coils cannot charge and therefore not damage the cathode driver or the LEDs. The cathode driver cannot step without the anode driver, but should not matter as no LEDs will be lighting.

cheers

Tony

[albertofenini]

Hi Tony, thanks !

we'll take the anode driver out, and see what happens
at this point RCD should be working
as it should be Disp0 -> Disp4, since these are produced from the Hybrid, right ?

I may have asked this already, but how complicated is to engineer a replacement
for these chips, anode driver, cathode driver, card reader sense amplifier or roms
and rams ? Is there anything compatible that can be used nowadays ?

Thanks again !

(11-13-2020 10:35 AM)teenix Wrote:  

(11-13-2020 07:30 AM)albertofenini Wrote:  Hi Tony
You are right, the logic board works perfectly when put in another unit
Or to say it right we used a logic board coming from a working unit and we tested that after these measurements it still works when put in it’s own unit

It may be the anode driver but shouldn’t at least work the rcd signal ?
That is coming from the cathode driver right ?

Also I was expecting to see good display waves at the cpu side or the faulty anode driver may silent these ?

Thanks !!!!

I cannot say for sure, but it "seems" like the CPU board fails when connected to the anode driver and (maybe) cathode driver. It is possible over the years of driving the coils, that the chip internals have failed and have shorts inside which load up the CPU board to the point that it stops.

The only way to test is to remove the anode driver and see if the signals reappear from the CPU board.

You might have to be careful with the signals to the anode driver as anything that upsets the relationship between the anode/cathode drivers may damage the chips. This is because the coils need to have a path to discharge which is usually through the LEDs and transistor switches in the cathode driver. If the coils get charged and cannot discharge properly, that voltage may build up and break down the junctions in the driver transistors. This is explained on page 3 of the Classic Notes PDF. In an older engine, an extreme example is where a spark jumps the gap in the spark plug when the coil primary current is disconnected by the points.

If the anode driver is removed, then the coils cannot charge and therefore not damage the cathode driver or the LEDs. The cathode driver cannot step without the anode driver, but should not matter as no LEDs will be lighting.

cheers

Tony

[teenix]

(11-13-2020 10:41 AM)albertofenini Wrote:  Hi Tony, thanks !

we'll take the anode driver out, and see what happens
at this point RCD should be working
as it should be Disp0 -> Disp4, since these are produced from the Hybrid, right ?

I may have asked this already, but how complicated is to engineer a replacement
for these chips, anode driver, cathode driver, card reader sense amplifier or roms
and rams ? Is there anything compatible that can be used nowadays ?

Thanks again !

Yes. The ARC chip in the hybrid normally generates the signals.

Replacements are all doable. I am looking into a few things now, but not being able to get home has stopped the works.

Not sure except for the good gear that Bernhard has created and the CPU replacement boards from me and Harald.

cheers

Tony

[albertofenini]

Hi Tony
No way ! We removed at first the anode driver and took all the measures
Voltages all around are correct and in the right places
However RCD and all of the Disp* are flat and at zero value
Then we removed also the cathode driver and measured everything again
Same as above
Should we try to remove the coils as well ?
What are the chances the all of the leds are burnt ?
We have uploaded couple of pictures of the pcb without the drivers and there are no signs of short circuit whatsoever
Thanks again for all the support
Take care !!

[teenix]

(11-13-2020 09:46 PM)albertofenini Wrote:  Hi Tony
No way ! We removed at first the anode driver and took all the measures
Voltages all around are correct and in the right places
However RCD and all of the Disp* are flat and at zero value
Then we removed also the cathode driver and measured everything again
Same as above
Should we try to remove the coils as well ?
What are the chances the all of the leds are burnt ?
We have uploaded couple of pictures of the pcb without the drivers and there are no signs of short circuit whatsoever
Thanks again for all the support
Take care !!

It seems that the oscillator may be faulty then. This is the 330uH inductor and the 150pF capacitor under the displays and these form an LC oscillator.

I would replace both drivers and measure the 01 and 02 input signals on pins 7 and 8 of the anode drive which also appear on pins 40 and 41 of the hybrid. Pins 38 and 39 are the 01 and 02 out signals that feed the ROM chips.

If these are flat then it is possible that those LC components are faulty, bad connections, bad PCB trace or the anode driver is faulty.

cheers

Tony

[albertofenini]

Hi Tony
thanks for the reply
I can confirm that both Ø1 and Ø2 are flat, with and without the drivers installed

Is the capacitor the one mounted close to the battery cable on the led board ?
Is the inductor the one close to the resistor just under the PRGM switch ?

Should we change capacitor and inductor, will we be able to see Ø1 and Ø2 even without the anode and cathode driver in place ?

thanks for help !

(11-14-2020 12:29 AM)teenix Wrote:  

(11-13-2020 09:46 PM)albertofenini Wrote:  Hi Tony
No way ! We removed at first the anode driver and took all the measures
Voltages all around are correct and in the right places
However RCD and all of the Disp* are flat and at zero value
Then we removed also the cathode driver and measured everything again
Same as above
Should we try to remove the coils as well ?
What are the chances the all of the leds are burnt ?
We have uploaded couple of pictures of the pcb without the drivers and there are no signs of short circuit whatsoever
Thanks again for all the support
Take care !!

It seems that the oscillator may be faulty then. This is the 330uH inductor and the 150pF capacitor under the displays and these form an LC oscillator.

I would replace both drivers and measure the 01 and 02 input signals on pins 7 and 8 of the anode drive which also appear on pins 40 and 41 of the hybrid. Pins 38 and 39 are the 01 and 02 out signals that feed the ROM chips.

If these are flat then it is possible that those LC components are faulty, bad connections, bad PCB trace or the anode driver is faulty.

cheers

Tony

[teenix]

(11-14-2020 12:52 AM)albertofenini Wrote:  Hi Tony
thanks for the reply
I can confirm that both Ø1 and Ø2 are flat, with and without the drivers installed

Is the capacitor the one mounted close to the battery cable on the led board ?
Is the inductor the one close to the resistor just under the PRGM switch ?

Should we change capacitor and inductor, will we be able to see Ø1 and Ø2 even without the anode and cathode driver in place ?

thanks for help !

I cant help much there as I don't have a board handy. It will likely be one or the other, but both may be faulty

If you have good spares of the components, then try changing them. I think there are only three passive components on the display board, the 220K ohm resistor should be easy to spot which leaves the other two as the oscillator.

cheers

Tony

[albertofenini]

We’ll sure try !
Thanks for all the support !
Take care !

[albertofenini]

We have added a picture with the components of the LC
The resistor has a different value, brown, black yellow
Will try to find a right one
We don’t have a way to measure inductances
And will check the capacitor
Then will check LC and post the results ...