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