OMG it's a 999 board - then it's only a 4 pin - oh geeZ - I thought it was an XL...
The DX uses 4 pin - shieesh!
Ok too many things on my desk today ...this whole week...
Sigh...Sorry NZ8N...you're right...
Well, look into it when you're ever come across a 5-Pin Grant ...
Then that goes back to the 4558 chip...and follow NZ8N's lead on this - it's the keying circuit he's taking you to.
Here's some help from Graphics I've done up myself...
For overview...
The 4558 serves two functions,
In Galaxy, Connex, Uniden - President... a Mic amp and a RX/TX switch
The RX/TX switch side
- - designed to look at 3 things - Power Good, PLL LOCK signal and if you want TX or RX - the pins 5-8 dose just that; using a resistor feedback principle of "threshold" to make the amp work more like a switch but with reservations
- - I will toggle to this state, if these two are met first - kind of logic so it's kinda treated like an AND gate
- - but the AND is for a looking at a change of state as well as Power and LOCK remaining in their original condition..
So if the thing wants to start TXing, then the Resistor divider network that parses the signals arriving - make sure the diodes that route the RX/TX sides to the INPUT are working - AS WELL AS THE OUTPUT.
This isn't for the Grant 999 board,
but it is a good flowchart of things going on in there...
Sorry about identifying the WRONG radio...
This (I hope) should help...
The above graphics give different VALUES for the RESISTORS used, but their pinout functions are still pretty much the same.
So with the above graphics, find a resistor network that works for you - they did different values of the types of outputs the PLL chips they served with and the functions of how their lock functions were checked.
While you're there, look for C173 - a 10uF cap - looks at the PA switch - see if that's gone, shorted or issues with the WIRING of the PA switch...