NMB PC 122 Controller Issues

TheInverseKey · 19 Jul 2018, 22:55

Hi All,

Here again with another NMB board that I have been keeping around and now have come to seek your guys help.

I have a NMB PC 122 using HD listen and a XT to USB soarer's converter I get nothing from the board. Now it has been confirmed to my knowledge that the NMB PC 122 use the XT protocol.

I think that the controller is not getting enough power and that the voltage regulator might be at fault. I measured the input to ground and saw 4.86 volts but the output to ground was only 1.8 volts.

Based on the datasheet that I could find on the Zilog z8614 IC the controller needs 4.75 to 5.25 volts. Therefore, am I correct that the voltage regulator needs replacing?

Datasheet: https://html.alldatasheet.com/html-pdf/ ... Z8614.html

Control Board top:

Bottom:

Any ideas about if I am on the right track would be amazing.

snacksthecat · 19 Jul 2018, 22:57

Can you show your wiring? I'll compare to the one that I converted with Soarers

TheInverseKey · 19 Jul 2018, 22:59

snacksthecat wrote: Can you show your wiring? I'll compare to the one that I converted with Soarers

The wiring of the cable you mean?

Engicoder · 19 Jul 2018, 23:03

Most if not all terminal boards with a regulator will require a supply of more than 5V as the regulator (usually some form of a 7805) will drop the voltage around 1.5V - 2V. Many terminals supplied 12V to the keyboard. Often you can remove the voltage regulator and place a jumper wire from pin 1 to pin 3. You want to trace the power path and ensure that nothing else relies on the voltage level before the regulator.

TheInverseKey · 19 Jul 2018, 23:05

TheInverseKey wrote:
snacksthecat wrote: Can you show your wiring? I'll compare to the one that I converted with Soarers
The wiring of the cable you mean?

snacksthecat · 19 Jul 2018, 23:13

Ah interesting, mine has no voltage regulator

For a different conversion project, I used a step up regulator to get the input voltage up to 12V and only then could I get any output from the board.

TheInverseKey · 19 Jul 2018, 23:34

snacksthecat wrote: Ah interesting, mine has no voltage regulator

For a different conversion project, I used a step up regulator to get the input voltage up to 12V and only then could I get any output from the board.

Interesting is there no voltage regulator for each of your 122's or just this one?

TheInverseKey · 20 Jul 2018, 00:07

Engicoder wrote: Most if not all terminal boards with a regulator will require a supply of more than 5V as the regulator (usually some form of a 7805) will drop the voltage around 1.5V - 2V. Many terminals supplied 12V to the keyboard. Often you can remove the voltage regulator and place a jumper wire from pin 1 to pin 3. You want to trace the power path and ensure that nothing else relies on the voltage level before the regulator.

Here is some more information that I was able to gather.

I will be referencing the following image:

I traced out the entire VCC line that has to deal with the rest of the keyboard pass the controller. After it is done powering the daughter-board that houses the rest of the switches the line terminates hence on the right of the picture there is a red line that ends.

After capacitor on the left the voltage is the same as the when it is coming out of the voltage regulator on right. This can bee seen with the light blue lines of where the voltage was calculated at.

The only spot that the voltage was higher than 1.8 was before the capacitor on the left and the voltage regulator on the right with their respected values marked.

Therefore, I think that removing the voltage regulator would be fine but I would like your opinion.