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albertofenini · 11-10-2020, 10:37 AM

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