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Hi Tom,

Really nice to get your message.
Know doubt you will remember me and the confusion I caused about a Varactor being on the on the Control Board on the Power Supply of the HP 8591E.
As it turns out I miss-read the Code for the Diode.

I thank you for your message because I completely agree that the probability of so many resistors (3) changing value is very unlikely.
Normally I would never undertake uncontrolled behavior or measuring very many resistors in circuit.
But I explained how this came about. There are a huge number of 10K resistors in this circuit and most of them measure 10K +-5%
Once 20 years ago I would have done this and by a process of elimination it did help find the fault.
But say 9 times out of 10 (I do no know what the real probability is) once the component was lifted out of circuit it turned out to to have its specified value which was quite different to the in circuit measured value. Hence the in circuit measurement was a useless waste of time.

However if you look at the circuit following the measurement and if the resistor measured has a simple termination this in circuit can help find a faulty complement.
Same as the diode test which usually give 0.5 0.7 volts in one direction and an extremely variable higher value voltage in the other direction.

Any way I have found even more more resistors (measured in circuit) that have very low values and are on input circuit to input pins 2,4,5 to U2408 and so likely do effect the MUX channels #5, 6, 7 values.

Later today I will carefully write up what I have found.
I will process the findings by marking up circuits and putting these online. That way the others reading here will be able to focus on contributing from their significant knowledge their significant observations.
Yours sincerely
Jeff King

On Mon, Apr 1, 2024 at 08:05 PM, JD wrote:

Do you have any specific recommendations for where to begin debugging this
problem?

Did you follow up on Satbeginner's post (#203616)?

Raymond

Do you have any specific recommendations for where to begin debugging this problem?
I've read through that forum post and don't know where to start.
I've already checked components for shorts and haven't found any so far.

My main question involves how I can follow the "Inverter Troubleshooting Procedure" from the service manual.
I believe this is the problem.
From what I understand, I'm supposed to test the PSU outside of the oscilloscope with the dummy load.
Is this correct?
And if so, this means I'm supposed to attach the PSU to mains voltage too?

On Mon, Apr 1, 2024 at 1:26?PM Raymond Domp Frank <hewpatek@...>
wrote:

On Mon, Apr 1, 2024 at 07:09 PM, Raymond Domp Frank wrote:

Maybe the option has an interaction with the triggering.

Answering my own question: Of course there's at least one interaction, and
with the sequencer; the -01 (DVM) displays on-screen, so interleaving!
Do any of the -01's displays work?

I've never seen a 2465DVM, but according to Jeff it has the CTT, which
does route triggers through the option.

On Mon, Apr 1, 2024 at 07:09 PM, Raymond Domp Frank wrote:

Maybe the option has an interaction with the triggering.

Answering my own question: Of course there's at least one interaction, and with the sequencer; the -01 (DVM) displays on-screen, so interleaving!
Do any of the -01's displays work?

Raymond

The right part of the new error message contains info that ISTR is associated with options. Since you have an -option 01, did you try to tun the Options tests/exerciser?
Maybe the option has an interaction with the triggering. Does the option support gated measurements? I'm not at all familiar with the -01.

Raymond

Did you check DC values at outputs of control MUXes (in response to operating their associated knobs), as I think Siggi suggested?
A nonsense voltage could drive an input signal to a fly-by-wire control out of any sensible value, although I'm not sure if it could result in no-trigger on Auto, except if there's a silly AC on it instead of DC (because the S/H cap. is open)... Yes, a very wild guess.

Raymond

On Sun, Mar 31, 2024 at 10:53?PM <jking2603@...> wrote:

Hi Siggi

Have now marked each and swapped U700 for U900. All photos taken here are
with hybrids swapped.
Nothing has changed and there are NO sweeps occurring with any triggering
condition setup at 0.2 mSec or 100 mSec

I have prepared photos to show the instrument settings because that is
probably easier for you to interpret.

Excellent - I see no problem with your instrument settings, you should be

getting sweeps in AUTO and AUTO LVL trigger modes.

On each photo I have annotated the intended information setup state.



Shows a new error message that occurred yesterday when i was probing A5 to
verify operating TPs 1, 2, 3

It appears that you've somehow wiped or invalidated the scope's
calibration. The dots on the operational OSD also signify this AFAIK.

In AUTO, yes, have you verified that the OSD displays AUTO trig?

I cannot answer this because I do not know what I am looking to see.

That is why I sent you the pictures. can you see the Display of Auto trig?

Yeah, turns out the sweep mode and the trigger level are displayed on the
OSD, but not the trigger mode. That's indicated by the FP LEDs.

I await your feedback as to what you think is not working?

I'm baffled to be honest. In your shoes I'd be looking at the signals from
the display sequencer to the trigger and A sweep hybrid. The one problem
that comes to mind is if the holdoff circuit is busted and you're in
infinite holdoff.
Maybe take a look at everything in front of HRR on the display sequencer
(U650). IIRC there's a reasonably good description of the holdoff timer
current source in the service manual
This would however only explain the no sweep condition, I don't see how
it'd cause the 05 POST error, unless perhaps if the POST relies on the
sweep state machine to run.

On Mon, Apr 1, 2024 at 04:53 AM, <jking2603@...> wrote:

Shows a new error message that occurred yesterday when i was probing A5 to
verify operating TPs 1, 2, 3

That indicates a checksum error in the EAROM. The dots on the bottom of the screen usually indicate calibration is lost. I didn't see the dots in your earlier video, so that matches.

Nothing to worry about while searching for your main problem.

Raymond

On Mon, Apr 1, 2024 at 06:40 PM, Raymond Domp Frank wrote:

between 5V (Vd) and inputs of U2465

That'd be U2456.

Raymond

On Mon, Apr 1, 2024 at 08:00 AM, <jking2603@...> wrote:

R2230 measures 0.62K compared to 10K spec. This is on Circuit 2 Front Panel
Scanning

R2230 is not part of general, periodic front panel scanning. It is one of two pullup resistors for P501, the calibration jumper (at location J501), on A5 near the front panel. It determines whether the instrument should start up for normal operation or in calibration mode.
I guess you measured in-circuit, which would be meaningless as to their resistance value, as Tom suggests. P501 normally should be in the No-Cal position while you're working on the 'scope. R2224 and R2230 both are connected between 5V (Vd) and inputs of U2465, an 8-channel digital multiplexer. Their resistance value is not important.
I suggest temporarily pulling P501 and comparing the resistance of R2240 and R2230. Both then should be about equal R-value. If they deviate significantly (more than say 20%), it may indicate a problem with U2456, which is part of the front panel scanner. I don't think front panel scanning is (related to) your problem, though.

I don't think chasing for resistor problems in that area is useful with the problem you have.

Raymond

On Sun, Mar 31, 2024 at 10:59?PM <jking2603@...> wrote:

the traces with POS controls about mid-range, then select SINGLE trigger.
Each time you toggle the mode control down, you should get a sweep.

as you see in the photo

It turns out I misremembered how this works, and/or conflated with my
digital scopes. SGL SEQ mode requires a trigger to start the sweep or
sweeps. I was able to cause a sweep on my 2467 by arming SGL SEQ, then
wiggling the trigger level control around until the trigger condition was
met. LINE trigger should work as well, though of course there does seem to
be something not right with your triggers or sweeps.

On Apr 1, 2024, at 00:14 , Ozan via groups.io <ozan_g@...> wrote:

Base of Q326 will only show a signal if sweeps are running.

If you set 7B70 as described in test conditions, and with a 1V/1kHz sine wave at External input:

Yes, and I verified 1Vpp 1kHz sine on my 2465A.

- Do you see any sweeps?

No. My assumption has been that it's sweeping too fast to see.

- Do you see sharp pulses (not a sine wave) at base of Q309? What amplitude?

I think the shape is correct, and amplitude is a bit over 200 mVpp. Photos here; GND reference set at centerline.





The manual shows ~10x lower, I think due to the note about 10x probe? All waveforms I measured through the trigger amplifier were 10x larger than shown on the schematic. The PDF scan is missing some of the detail, though.

If signal at Q309 base doesn't have sharp edges, and because you ruled out a bad VR304, bias point of VR304 could be wrong.
- Is +15V correct?
- What voltages do you see at the bases of Q309 and Q317?
- What voltages do you see left sides of R300 and R306?

+15 is 15.01 at the test point.

Base of Q309 and Q317 is the same, +3.8 from chassis ground.
Emitter of Q317 is 4.46, collector is 0.

Left side of R300 is 3.54; other is 3.96.

R306 I measure 3.49 at one end (physically the top), and 3.54 at the other end. I can't see the foil trace, so not sure which is left vs. right in schematic.

thanks,
Adam

Base of Q326 will only show a signal if sweeps are running.

If you set 7B70 as described in test conditions, and with a 1V/1kHz sine wave at External input:
- Do you see any sweeps?
- Do you see sharp pulses (not a sine wave) at base of Q309? What amplitude?

If signal at Q309 base doesn't have sharp edges, and because you ruled out a bad VR304, bias point of VR304 could be wrong.
- Is +15V correct?
- What voltages do you see at the bases of Q309 and Q317?
- What voltages do you see left sides of R300 and R306?

Ozan

Are you measuring these resistors in circuit? If so, those measurements may be largely meaningless. It is rare (though not impossible) for a resistor to go down in value. It is very rare for three resistors to go down in value.

--Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
420 Via Palou Mall
Stanford University
Stanford, CA 94305-4070

Finally I found something that maybe faulty parts.

Because I was searching for conductivity on MUX S&H circuits i happened to measure some 10K resistors on A5 to understand how much voltage drop might occur.

R2650 measures 8.3K compared to 10K spec. This is on Circuit 1 Reset Control

R2735 measures 3.4K compared to 10K spec. This is on Circuit 2 Delay Ref 0

R2230 measures 0.62K compared to 10K spec. This is on Circuit 2 Front Panel Scanning

I am optimistic these maybe causes of malfunction.

Next Steps
finish the measuring MUX channels and DC Voltage change from adjusting front panel controls,

measure resistance on all resistors on A5, because there maybe other resistors with changed values that contribute more faults.

Yours sincerely
Jeff King

Sorry that I haven't been following this thread too closely, so I apologize if you've already gone through and checked the various adjustments in the TD circuits. If not, do that first. TDs tend to exhibit long-term drift, which you can compensate to a degree by tweaking the adjustments.

Good luck!

-- Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
420 Via Palou Mall
Stanford University
Stanford, CA 94305-4070

On Mar 31, 2024, at 16:52 , n4buq via groups.io <n4buq@...> wrote:

Glad it isn't the TD. Yes, I've pulled side panel to get to the right-hand side of the time-bases. Getting to the left-hand side is a bit more of a challenge.

Did you also look at the other TD?

VR322 and VR358 both look OK on the curve tracer, or at least what I think a 4.7 mA TD should look like. I started tracing things out with the side panel off, and things looked reasonable until the Trigger Generator <4> of the manual from tekwiki.

A waveform was present at Q309 and Q317, but not at the base of Q326, so I'll look at that area more closely and take better notes. The triggered holdoff stage description in the manual is over my head, as usual.

thanks,
Adam

Have you tried playing with the FP while
measuring the MUX outputs?

Not Yet.

I will do that next and provide a range of DC voltages together with any front panel change causing the range of voltage.

Your sincerely
Jeff King

the traces with POS controls about mid-range, then select SINGLE trigger.
Each time you toggle the mode control down, you should get a sweep.

as you see in the photo


The LED says ready
the screen goes blank and
no scan occurs.