Graham wrote:
Anyone worked on Racal MA 1723 HF exciter synth board ?

If you know the set, you will know the board ....

I do not know the set. However, I have a 1255 HF transceiver synth unit
sitting here that needs to be repaired and I'd love someone who is more
familiar with the technology to peek at it for me. Some previous tech
appears to have butchered some things in the process of trying to fix it.
It does not lock up and from the look of it someone has attempted to
swap chips in the divider chain.

I can only get the varactor control line voltage up to 13 V , that's
2
V short of the
spec in the handbook ..

But by reducing L17 , you can get the synth to lock at 29.9999 with
a line voltage of 13.2 V .. ae output signal is on freq and
stable ..


Is this a fault or was it not allways possible to reach 15 v on a
'older' synth board ?

If it is like the 1255, the varactor voltage is controlled by a charge
pump that involves some tantalum caps. I would check the caps for leakage
before doing anything else. If you crank L17 down and the thing will
lock at 29.9, does it ALSO lock stably at the bottom of the range?

If it's like the 1255, it should actually go down to some outrageously
low frequency and stay locked.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."