Ranger SS 158 EDX dimming frequency counter

[timrim]

I have a ranger SS 158 EDX and I need to dim the frequency counter on it.
The frequency counter board is EPT900043Z. There is an unused pin called "DIM", do I simply ground this pin to dim the frequency counter or is there a resistor I need to add?


By the way, I emailed Ranger Tech Support and this was their response:

Hello,

Sorry, we cannot modify components of the radio.
We are only after factory specifications and we
cannot suggest technically as it may affect the
radio performance or it may damage other parts
of the radio.

Regards.
Charlie F. Almazan
Ranger Communications Inc.

Personally I found this to be shameful on their part, I have lost all faith in Ranger now. I have always been able to get companies to offer simple changes to make my customers happy, however, Ranger don't seem to care much about its customers. I won't forget that.
Sorry for the rant...

[Rick]

Not all EPT900043Z are fully populated with all the components required to make the Dimmer work that is why Ranger Tech Support gave you the answer they did.

I know it not helpful but that Ranger for you.

If you checkout the Galaxy DX2547 which uses the EPT900043Z counter module.
http://www.cbtricks.com/radios/galaxy/d ... h_main.pdf
http://www.cbtricks.com/radios/galaxy/d ... 3z_pcb.htm
If you can read diagrams you will see how it works.
Hope this is of some help.

[timrim]

Thats what I was afraid of. Apparently there are missing parts, because grounding the Dim pin has no effect on the display. I have successfully dimmed the channel LED and the meter, its just the darn counter that wants to be difficult. I guess my only option is to offer customer the ability to turn off frequency counter all together.

[Rick]

You do not ground the DIM to make work, look at the Galaxy DX2547 Sch diagram and you will see now it works.

[timrim]

The schematic shows a pull up resistor to the 5 volt supply. I put in a 20k pot and tied one leg to ground and the center I soldered to the DIM pin and it works very well. Apparently the first time I tried it, the probe must not have made actual contact with the pin or the display would have dimmed totally dark. All is well now thanks for pointing me back to the schematic!

[Rick]

It is not just a simple case of using a pot as the dimmer control.
I do not know which Galaxy diagram you look at but none just use a pot to the 5 volt supply as there is no 5 volt supply in any case.

The dimmer control is used in conjunction with a NPN transistor Q403 that has a limit resistor in the emitter.

The reason for Q403 is to give good control to the dimmer and help in protecting frequency counter Modula, and stops the main regulator from going to ground.

You can just do it you own way, but this may cause trouble and burn out track on the PCB.

[timrim]

It is not just a simple case of using a pot as the dimmer control.
I do not know which Galaxy diagram you look at but none just use a pot to the 5 volt supply as there is no 5 volt supply in any case.

Thanks for the heads up Rick, I will do some careful testing and scrutinize it more carefully, and if need be, I will simply duplicate the transistor dimmer circuit that Galaxy uses. Transistor and parts won't amount to much more than a few pennies anyway.
The 10k ohm pullup resistor was found on the frequency counter board schematic on this page. http://www.cbtricks.com/radios/galaxy/d ... er_sch.pdf

NOTE: I should have mentioned that I did place a 1K ohm resistor from the pot to ground to keep from grounding out the system, and, according to the factory schematic, there is a 4K resistor already in series with the dim line, so it can never be pulled completely to ground.