[GCARC] FTDX3000 info

[Ken Bozarth]

Hey gang, here is some technical info on the Yaesu FTDX3000 that is not
obvious in their manuals. The Tuner interface connector, a mini-DIN, can
supply up to 1.5A reliably to an external tuner. The MFJ998 has a current
requirement of 1.5A. These ratings are always worst-case peak ratings. The
fuse inside the FTDX3000 is a resettable Polyswitch device rated at 1.5A
continuous hold current and a trip current of 2.9A. These devices should
trip when subjected to over current and return to normal after the over
stress has been fixed. So I feel safe operating the tuner with only the
rig's power. Used in this way, there are no timing issues when turning of
the tuner then the rig.

 

Yaesu Service has confirmed that there has never been a theory of operation
written for this rig. Has Yaesu ever written one for there other rigs?

 

Yaesu Service has mentioned the signal on the Tuner interface labeled
"TXINH" and stated that some tuners can invoke this Transmit Inhibit
condition, but they do not know when it is used. They said it could be the
reason for the strange "NO TX" condition I have been complaining about.

 

Yaesu Service also confirmed that there is no thermal regulation of output
device quiescent current (some call it idle current). Compared to older rigs
using bipolar devices, the idle current in the FTDX3000 is set surprisingly
high, at 2.5A per FET. There may be two reasons for this high quiescence,
both of which seem valid to me. (1) With higher quiescence, linearity is
improved, coming close to class-A. (2) All MOSFETS have a quiescent current
at which the current is stable over a wide temperature range. The FTDX 3000
finals are operated below this current and so, quiescence will rise with
case temperature, but not to the point of runaway. Yaesu engineering was
smart to see this and use it to advantage.

 

Yaesu Service personnel I spoke with do not know in depth how the fan
controls in the service menu work, so they advise to leave the two values at
the default values. If we could get to the design group we may find out, but
fat chance of that happening. I have played with the values and found that I
can make the fan run faster and if I work with them some more, perhaps I can
make the fan come on at a different temperature or run indefinitely. 

 

The other night during the 10m net my intermittent No-TX issue came back
after a month of operating flawlessly  in a normal mode. I started using an
abnormal mode (External tuner selected but with it turned off). I think I am
on to something here. Back to normal for another month. Stay tuned.

73,

Ken