[Graham]

Anyone worked on Racal MA 1723 HF exciter synth board ?

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


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 ?


Tnx - G ..

[Scott Dorsey]

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."

[Graham]

On May 21, 3:27 pm, (Scott Dorsey) wrote:
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."

Ok Scott,

Well , since the post ive had a few other things go on it as well ,
new fault every time i powered it up .even one of the chips that drive
the led's on the front panel failed .. took a while to realise the
function was still working and the lamp had died .. ..
however ....after a few new bits ... so far so good ....

The lock voltage has risen slightly upto about 13.6 max now after a 48
hour run , then it refused to lock when cold .. finally after
'exercising' the chips on the synth board in there holders ..locks at
switch on ..and holds down past 100 khz ..as it ground equipment ,
everything is plugged in .. if it was airborne would be 100 p/c
soldered

dont know if i'm really going to get the extra volt by fitting new
caps .. full out of lock is 14 v .

.. fed it some audio the other day and it actually sounds quite good ..
there are a set of control lines , that feed the amp, one named 'tx' i
have found closed to ground on tx, so thats a handy feed for the tx/
rx ae switch, next step air test , be about 25 watts from the linea
drive drive amp so should do ok .. cannot mute the rx , so have to
use a short agc

G ..