Radu -
Entirely possible, but I have (surprisingly) seen few serious problems cluse by power supply failure in HP instruments. Some but not many.
I would still take a look at the no DELTA_F problem first. Kinda speaks to a VCO problem or at least a VCO not changing frequency due to some control problem. Next best guess is a mixer malfunction (but I think this is less likely).
I would try to find out where the ~ 21 MHz signal is coming from and then see what controls that source. A likely culpert is a "stuck" VCO - and the problem becomes WHY is it stuck. A problematic VCO PLL / PLL detector seams a likely candidate.
Keep on having fun :-)
Cheers!
Bruce
Quoting Radu Bogdan Dicher <vondicher@...>:
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Bruce,
I think there are two independent issues (still) going on at the same time.
So my initial gut feeling there may be one single trouble point triggering
this eclectic set of fails we're looking at currently was probably overly
optimistic. At least as far as I can tell right now.
I wonder if the power supply event took a bunch of things offline with it.
It's the only way I can figure what seems to be two outstanding issues left
on the docket after fixing one.
Radu.
On Sun, Sep 18, 2022 at 7:24 PM Bruce <bruce@...> wrote:
I was going to point that out.
If it was the filters, the frequency would vary. The output might
drop off, particularly if no filter ws properly selected outside the
range where you see output.
I think the main symptom is that the frequency does not vary. Check
the VCO output for frequency variation, if the VCOs seem to vayr, then
I'd look at the inputs to the mixers.
Cheers!
Bruce
Quoting Radu Bogdan Dicher <vondicher@...>:
...which doesn't explain the output stuck at 21.5MHz, but at least may
point out what's going on as far as the missing output outside of 14 - <
20MHz range
Radu.
On Sun, Sep 18, 2022 at 6:44 PM Radu Bogdan Dicher via groups.io
<vondicher=
[email protected]> wrote:
I was just starting to focus on that, Ozan, as soon as I started
perusing
Service Group L, as per your earlier point here. Thanks a ton for
narrowing
down the scope of the forensics.
To check the validity of this notion, I double-checked specifically the
19-20MHz to see if I see output (a bit of a blind spot in my earlier
measurements), and what do you know... Smoking gun! There's output all
the
way to instrument limit on 19.(9)MHz.
The filtering and associated servos seem to be the culprit here.
Radu.
On Sun, Sep 18, 2022 at 5:26 PM Ozan <ozan_g@...> wrote:
It turns out dividers are followed by a bank of filters. 14MHz to
<20MHz
(exact point is not marked) is one of the filters. It is possible
control
signals to the filter bank is not functioning. TP1 on the schematic is
just
before the filter banks. If it is accessible and you could observe
TP1, it
may help debug.
Ozan
On Sun, Sep 18, 2022 at 03:29 PM, Ozan wrote:
On Sun, Sep 18, 2022 at 10:59 AM, Radu Bogdan Dicher wrote:
I got some really weird data to report.
I've been playing with adjusting the levels and frequency.
1. It seems I am able to get an output between exactly 14MHz and
19MHz. One half a MHz up or down from there, output drops to zero.
2. As long as there's output (as above), the level adjustment seems
to be working OK. I haven't looked closer at whether the value
is exactly
what it should be, but it raises and lowers as I command it from the
AMPLITUDE controls.
3. The frequency doesn't change as I adjust per #1 above. It's
always
about 21.5MHz (says my scope).
Not sure what to make of it yet, but I am going to seek to determine
whether this can be triggered by a single module, pull it out and look
for
damaged caps (first line of defense).
Thank you all.
Radu.
---
Hi Radu,
Bruce's reply is the right way to debug. Looking at service manual,
over
the band of 10MHz-20MHz signal path through dividers look same so
output
going away just below 14MHz could be something with VCO loop. Output
staying at 21.5MHz, not changing is also pointing to the VCO/PLL. I
would
look at signal coming to J-2 of A2 "divider filter" in Fig 8-L-1.
Whether
it changes and whether it goes away below 14MHz setting.
Do you see any signal out at 2x this frequency, i.e. 28MHz-38MHz range?
Ozan
