开云体育

I have an 11302A that seems to work properly except for an odd EA problem.
It passes self test, and will successfully run and pass EA with a plugin (11A32) in the left slot, no other plugins installed. If I swap the plugin into the center slot, EA will fail with the "Mainframe Amplifier Calibration Failed" message. Calibration signals applied the the 11A32 inputs are well within spec, and appear normal.
This will occur with any plugin I have tried, the 11A32 works fine in my 11301 and 11403A.

I have tried the trick in the service manual to reload the EEPROM data to no improvement.

Would a trip through TEKCATS cal procedure fix this, or is it a latent hardware problem?

Thanks,

Bob

Bob,
Reverting to cal constants saved in flash memory without any improvement leads me to look for a hardware issue. I would need to dig into schematics for clues. There are many unique calibration paths and pickoff points that might fail while the display path is functioning properly.

Don’t mess with a TEKCATS cal yet until you check for hardware issues.

I don’t have an 11302A but I have an 11301A and early documentation for both. I shall examine what I have in the next couple of days and let you know if I have any good suggestions.

Clark,

Thanks for the help!

Bob,
Have you exercised the Extended Diagnostics for the Vertical Block?

I don’t recall if the Vertical Block has additional tests that do not run during Power-On Self Test. Most of the diagnostic blocks have more lengthy Extended tests that are not executed during Self Test.

Yes, it all passes.

I take that back, further testing with the Ext Diag set to loop, Vertical fails with M5111 error code, from the manual suspect SCLOG, MPU.

I should be able to spend a little on this today.

Please run EA with all compartments empty and verify that it completes successfully.

The graticule, vertical deflection, horizontal deflection and timebase calibration will run. You should see the graticule scanning (bright line pairs sweeping over approximately one division in four different places to find gain reference points followed the 90 second “in progress” message. The self calibration should terminate successfully with the message, “Enhanced Accuracy requires 11000 series plugin.”

If not successful, what is the displayed message?

You might also check the grey ribbon cable from Scope Logic board to the Vertical Amp board as well as the 9-pin harmonica cable from the Processor board to the Vertical Amp. These cables can be loosened or damaged if the instrument covers are not carefully installed. From what you have reported, these cables are not likely the cause but it is good to examine them.

I just performed the tests you described. It seems to pass EA without plugins, and indicates "Enhanced Accuracy requires 11000 series plugin".
Running the Vertical extended test in loop mode immediately returns multiple M5111 errors without plugins.
I double checked and re-seated all the connectors, but no change.

That is useful. Thank you.
Please repeat the EA with two known-good plugins installed; one in Left slot and one in Center slot.

The M511x message indicates a common-mode measurement failure through the Vertical Channel Switch diagnostic path. This could also be the result of one side of the plugin's diff pairs not making contact. Verify by display or other scope that the differential signals from the plugin are indeed present and the correct amplitude at the input to the Vertical Channel Switch.

OK, will do.

Correction:
Do not bother to apply a signal through the plugin to verify the common-mode path. Measure the DC voltage at the +input and -input to the Channel Switch without a plugin. The voltages should be equal. I assume that they should be the same for Left and Center compartment paths. I can verify on my unit.

With two known good plugins it won't pass EA, same "Mainframe amplifier calibration failed"

Known amplitude signals applied to the center plugin are correct in amplitude and frequency response, and appear normal.

Will do

Left Channel
L+ to sig gnd -5mv
L- to sig gnd -5mv
measured across L + to L- 0mv

Center Channel
C+ to sig gnd -6.4mv
C- to sig gnd -4.2mv
measured across C+ to C- 1.98mv
This seems suspicious.


All measurements with no plugin

I have the Preliminary Service Information manual downloaded, but the U numbers have changed so I am not sure which part is what on the board.

Two more diagnostic tests to try. If you execute the Vertical Block, it will stop to report an error without attempting the remaining tests. The remaining tests can be invoked individually from the Ext Test menu.

Try this:
UTILITY menu select Ext Test and then Run.
Select the Vertical block then select AREA at the top of the display.

At this point you should see three individual tests; Vertical Ch Sw, Amp and System.

Select Vertical Amp and Run.
Select Vertical System and Run.

Fails the Channel Switch test, others pass.

As the other tests are passing, we can eliminate the possibility of a failure in the diagnostic hardware path from the Vertical board to the Processor board.
It seems likely that the Channel Switch hybrid is the trouble. It might be failure in the interconnection to the board or internal to the hybrid. It has been in place for only 35 years or so!

I have not yet verified this by measurement but the schematic indicates a passive path between the common-mode point of the input termination through to the input to the analog switch (U660) of the diagnostic hardware. I can verify it this evening but if you don't want to wait, check with an ohmmeter the differences between the Left and Center paths.

With power=OFF and no plugins, measure continuity from:
U660 pin 2 to J34 (+Center)
U660 pin 2 to J36 (-Center)
U660 pin 1 to J32 (+Left)
U660 pin 1 to J33 (-Left)

I have the component location for the board to
/g/TekScopes/files/11301x_11302x_kodagraphs

Correction:
Measure resistance not continuity.

I have determined that the connection shown in the schematic is a simplified view. The common-mode connection is not actually as simple as shown.

At this point I think that the hybrid (U220) is the problem. There is a chance that it is U660 but I doubt it.

U220 is the same hybrid that is used in the 11301. You could swap to see if that is the trouble. As this is the channel switch, I think that you do not need to re-calibrate the scope. Try Vertical diagnostic tests and see if it is better.

Be very careful with the hybrids. Read the service manual about handling, cleaning and especially installing them. Always be very gentle when seating the hybrid and then lightly finger tighten the nuts. Use one finger. If you pinch with two fingers you might over do it. Verify that the hybrid is flat to the board and located properly in the socket BEFORE the final tightening. Tighten the nuts in a diagonal order as shown in the manual.
The beefy heatsink suggests a rugged device but the ceramic is very brittle.

I cannot think of anything else that might help. If you are not in a hurry, perhaps someone else will offer some useful advice.

Clark,

Thank you for taking the time to help me with this! I will check the resistance as you suggest, but I agree it is almost certainly the channel switch hybrid.
I did remove it and clean the pads and socket fingers to no avail. I am quite familiar with the Tek hybrids having worked on numerous 24xx scopes over the years.

Do you have an extra hybrid available? I will ask the Vintage Tek museum also.

Thanks again for the help,

Bob