Re: in the adjustment menu i can not get the driver idle current down to the 1 amp setting


davebb123456
 
Edited

Hi Steve
All the bands are now set to output power as specified, But as I could not set the 430mhz final Ideal current to 2.5amp above the 00 setting, as I could only get 400ma over, but I am now getting 35w out at 13.8v ,
As I could only set to 400ma final Ideal current on 430mhz ,do you think it is not in the right class for SSB, it does sound good on another Rx, 
What do you think would do this, would it be the ALC setting,, I might look at this tomorrow, thanks again for your help, 
Thanks Dave 2E0DMB
 

On Sun, 24 Apr 2022, 17:52 Steve W3AHL, <w3ahl@...> wrote:
Dave,

Set the Driver Idle Current adjustment reading to "00", then note the current draw.  Rotate the  dial to INCREASE the current draw by 1.0 amp above the previous reading.  That establishes the proper Driver Idle Current, assuming the adjustment circuits are working correctly.

This only sets the Class A Driver idle current -- it has nothing to do with the output FET's operating points, which are fixed.

The UHF PA FET is often weakened by excessive (>35 VDC) voltage spikes on the 12 VDC power input when operating mobile, due to counter EMF spikes from the engine's starter motor.  In my experience though this usually results in the UHF power output dropping to 5-10 watts or zero.

I would do the complete Transmitter adjustment procedures before attempting any troubleshooting of varying transmitter power output by band.   It may bring all the bands close to specification.  If not, it may lend more insight to where the problem is.  If multiple bands are below the specified output level after correct adjustments, then the Driver (Q504) may be at fault.

It is important to verify that the "12 VDC" input supply is 13.8 volts at full TX PO output and capable of supplying 25+ amps before doing TX adjustments.  More importantly, verify that the supply voltage seen by the circuits inside the unit are > 13.3 VDC under full load by measuring across the TUNER port pins 3-4.  A common problem is excessive voltage drop across the factory supplied fuse holders on the input power cable.  These fuse holders are a poor design and should be replaced with 30 amp automotive style fuse holders.

Steve, W3AHL

 

 

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