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teenix · (This post was last modified: 07-06-2021 04:50 AM by 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