Re: "Sampler??"

On a sunny day (Fri, 2 Aug 2024 10:09:24 -0000 (UTC)) it happened
Cursitor Doom <cd999666@notformail.com> wrote in
<v8ib8k$2p2d8$1@dont-email.me>:
 

On Fri, 02 Aug 2024 05:11:43 GMT, Jan Panteltje wrote:
>

On a sunny day (Thu, 1 Aug 2024 08:27:16 -0000 (UTC)) it happened
Cursitor Doom <cd999666@notformail.com> wrote in
<v8fgt4$231a4$1@dont-email.me>:
 

...
I moved overseas and couldn't hold on to everything, sadly. Didn't
have time to find a museum either.

 
 
As to repair / fault finding of that thing we were talking about,
I dunno what the symptoms are?
But after letting the 100 pages or so sink in in my brain:
Like somebody mentioned, check power supply (caps) for ripple with a
scope,
supply voltages.

>
Yes, first thing I did. And replaced any suspect caps.
>

Likely source of damage is the input stage (may have been overloaded,
manual shows strict limits)

>
No, the input stage is fine. I can see all the local FM stations at
their expected strength levels - but they appear to be about 20Mhz lower
than they are!

 
The 'about' 20 MHz is susicous, as the IF is 21.4 MHz.
Looks almost like a problem with the calibration On page 12 of the
manual I see an internal reference output,
is that 10 MHz correct?
What happens when yu feed in 10 MHz from an other source?
 quote from that page:
  To lock the spectrum analyzer to an external frequency reference, set
  the FREQ REFERENCE Analyzer performance will be degraded unless
  frequency reference phase noise and spurious sign dBc single sideband
  (1 Hz) referred to 10 MHz at a 100 Hz to 10 kHz offset. To lock
  another spect the spectrum analyzer internal frequency reference, set
  the FREQ REFERENCE switch to INT
 
 
 

So, put some 100 MHz or so signal on the input, check with a scope if
it reaches the first mixer stage check if something comes out of that
mixer stage.
If not check if the local oscillator signal is present at the mixer
stage if all OK go for the next mixer,
If all OK check if the sweep generator works so the local oscillator
is actually sweeped,
check if any signal in the (20 MHz or so?) first IF stages,
basically follow the signal path.
With all the boat anchors you have 'floating??' about those
measurements should be easy.
All OK so far and display scope working at least you should see a
trace with something on it
 
Need more info on what the problem is, should not take more than a
hour that way.
If something with the other electronics.. have not looked at it much.

>
Self-diagnostics have localised the fault to within the YTO loop and my
subsequent investigations have narrowed down this issue with the
'greater "sampler" stage' putting out garbage. As I said further up the
thread, either there's an issue with the 'sampler' itself or it's just
doing its best with faulty input signals: garbage in/garbage out.
There are 3 inputs to the section: fM/N, f20/30 and fYTO. All those
signals are present and their power levels are fine. But I need to
ensure their frequencies correspond to the charts provided in the manual
and the relevant derivation formulas. If not, the loop has no chance to
lock.
My biggest problem is finding the time to fit it in!

 
OK, we will wait and see.
If all else fails, this was fun to create:
 https://panteltje.nl/panteltje/pic/scope_pic/
 https://panteltje.nl/panteltje/pic/scope_pic/screen_dump2.txt