Without option 130, the last resBW is 1kHz.

With option 130: 300,200,100, and 30 Hz

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There a problem with standard resBW.

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Marco,

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Obviously, it seems that it is the LOG section that is lacking, since the LIN mode works with the correct RF level.

It may be one of the gain controls in module A.

I will look at the behavior according to the level of the control signals.

But before touching an adjustment, it is necessary to have analyzed the circuit, because the alignment of a LOG amplifier is very complex.

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It is necessary to check the gains of the stages according to the signals IFG4,5 and 6, VLOG12 and3 and finally VLIN and VLOG.

Maybe one of the potentiometers has a bad contact.

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Yves

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Marco,

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Indeed, removing option 130 removes a variable.

You will have to put jumper A14W1 back if you do this. But I don't know if it will change much, because the signals are not mixed, it is a multiplexer that chooses to take the signal coming from option 130, or that of the LIN/LOG output A14.

Option 130 has its own LIN/LOG amplifier with an IF of 8.56kHz instead of 21.4MHz.

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If you vary the level of the external RF signal by 10dB jumps, if the jumps also appear by 10dB jumps on the 8591E screen (without changing the REF level), then the log amplifier curve is normal.

Now if the level is too high, there is an offset.

According to the tests, this offset only affects the LOG mode and not the LIN mode.

So, is this offset created by digital compensation (after ADC), or does it appear in the A14 module.

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What I will do: there are test points, so I will measure them all in LIN and LOG mode from the calibrator @ -20dBm, and you can compare.

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I have already repaired a log amplifier for an 8562A.

There were three defective potentiometers.

Adjusting all that was quite painful (several hours), but I managed it. The problem is that each adjustment affected all the other stages.

Here, all the stages are DC coupled except the first one.

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Yves

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Marco,

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PRESET

CF 300MHz

SPAN 1MHz

ZERO SPAN

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For TP1 to TP 4

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For TP 5 to 10, there is the signal at 21.4MHz.

I measured this signal with the oscilloscope at first, but for the last stages we can easily measure, but after a few stages, the signals are too weak.

Still using the oscilloscope probe, but connected to another Spectrum at 21.4 MHz, even if the readings are not valid in absolute value, it is possible in relative mode to see the difference between LOG mode and LIN mode.

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The most important TP for the moment is TP5, which is stage 7:

I measure 1.975Vpp on the oscilloscope in LOG mode, and 142mVpp for LIN mode.

By calculation I would have 22.9dB, the measurement on the Spectrum also gave me 22.9dB.

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So do an oscilloscope measurement at TP5 to know the absolute value for LOG and LIN, and by calculation, you will know the ratio in dB.

If your values ??are compatible with mine, then the problem is not on A14.

The detector and video driver are the same for both modes.

So, if there was a problem there, both modes would be affected.

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Yves

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I Have no modifications on my PCB A14

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Marco,

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Comparison between your board, my board and part list version E

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Part list E version

For R93 ??5.62k 1%?

For R101 5.62k 1%

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Your board without modif (8591E)

For R93 ??5.62k 1%?

For R101 5.62k 1%

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My board (8595E)

For R93 ??4.22k 1%?

For R101 4.22k 1%

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On schematic version E, R93 and R101 are 5.62K

On schematic version A, R93 and R101 are 4.64K

But I think that these values are pre-selected.

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Part list E version

For R24 1.21k 1%?

For R25 1.21k 1%

For R26 1.21k 1%

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Your board without modif (8591E)

For R24 1.21k 1%?

For R25 1.21k 1%

For R26 1.21k 1%

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My board ?(8595E)

For R24 1.21k 1%?

For R25 1.21k 1%

For R26 1.21k 1%

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Resetting to its original state is the obvious thing to do.

After your series of tests, you will be able to better understand if there is a problem.

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Yves

The RF signal goes through the 3 converters and then goes to the A11 filter module, then to A12 Amplitude control, A13 filter.

At this point we have the AUX IF signal available at the back of the instrument at 21.4MHz.

From this point, the signal can take two different paths: the one from A14 LOG-LIN amplifier/detector for the standard resBW from 5MHz to 1kHz, and finally the second path, option 130 which contains narrowband filters (300Hz,100Hz,30Hz...).

Option 130 has its own LOG-LIN amplifier/detector.

The output of A14 and option 130, is the AUX VIDEO signal available at the back of the instrument.

Depending on the selection of the resBW, a multiplexer will choose one or the other.

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So, the question arises, since the signal for option 130 follows the same path to the input of A14 (AUX, IF) and option 130 does not have a level problem, then logically the problem would be with A14 LOG amplifier/detector.

This would be true, if no other conditions change from the previous circuits when switching between option 130 and normal mode with A14.

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I checked all the data we took, and the data at TP5 gave us some similarities and some not.

But our probes did not have the same impact on TP5 (hot spot). I would say that TP5 may not be the best point of comparison.

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The probe effect:

Your probe

mkr level with probe on tp5 mkr level no probe

Log -14.2 -4.3

Lin -21.6 -20.2

You get 9.9 dB with or without probe for LOG mode, and 1.4 for LIN mode.

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In my case

mkr level with probe on tp5 mkr level no probe

Log -25.9 -20.0

Lin -23.1 -21.2

I get 5.9dB with or without probe for LOG mode, and 1.9dB for LIN mode.

The probe used TEK P6138 10MOhms 10pF.

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I studied your comments about the two SELFCAL videos.

On my Spectrum, the video display limiter was enabled, that's why the limiting level is different. But in the following image, I have disabled it.

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I take the example here of the 1MHz resBW, but the remarks apply to all filters between 5MHz and 1kHz. During the amplitude calibration, the filters are aligned to have the correct filter width.

We see that the signal is limited at the top of the screen, but this is not the real limit, by putting a marker we can find the limiting point. With this configuration for the 1MHz filter, in my case it is -6.57dBm. I used an external signal to find this limitation. When the 1MHz filter is aligned, the measured level is -11.63 dBm, so the filter is aligned 5dB before the compression point. The firmware searches for the peak, then the two points at -3dB. The filter is readjusted in width to have a value within the specifications, then switches to linear mode for the level adjusted to -20dBm.

With your 8591E, the level reaches -4.74dBm, it's high, but it seems that the filter is reaching an alignment.

Starting check 1.06MHz

tests#1 560kHz

tests#1 780kHz

tests#1 880kHz

tests#1 960kHz

tests#1 1.01MHz

goes to LIN mode for the level at -20dBm

So, the level at 21.4MHz would be stronger on your Spectrum, as well as the limiting point since you have -4.74dBm, without knowing where the real limiting level is.

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So, as you pointed out, is this an imbalance between LIN and LOG MODE. You start from -4.74dBm to -20dBm, or 15.3dB. But on my Spectrum, I go from -11.63 to -20dBm or 8.4dB.

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But there is no error message, and you are left with an error of 15dB after the SELFCAL, while in my case everything is correct with a level of -20dBm as expected.

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Marco,

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The gain and attenuator control lines are A1, A2, A3, A4 and A5 for the attenuators in the A12 module.

G1, G1 and G3 in the A12 module for the gains, and G4, G5 and G6 in the A14 LOG amplifier.

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Between CORR ON and OFF, in my case, there is a 6 dB difference, and it is in A12 that there was the change for 6dB.

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If the REF Level changes, then the attenuators and gains will vary in A12. For A14, nothing changes.

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The behavior of your 8591E is very strange.

If the A12 module had only a 1dB attenuator enabled in CORR mode, then in CORR=OFF mode, there would be only a 1dB difference.

But this would mean that the level arriving at A12 would be low normally, but you have -5dBm, you should have a 10dB attenuator enabled, and this does not seem to be the case.

And in no corr mode, the noise increased by 10dB...weird.

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Yves