Re: Continued: 2465B CTT/HPIB/WR TEST 05 fail 42, all CTT fail

Chuck Harris <cfharris@...>

Hi Jon,

I guess, but how would you get the zero crossing/trigger
points into the CTT?

Tek used a combination of features in the trigger hybrid,
and a PAL that they grafted onto the trigger hybrid to
massage the signal from the vertical trigger tapoff so that
the CTT could time it... all a reasonable thing to do.

I have some suspicion that the unfortunate problem with
the trigger hybrid when doing CTT functions is the interface
between the PAL and the trigger hybrid. Perhaps the PAL's
inputs are too heavy of a load for some trigger hybrid's

Or maybe there is a timing issue between the PAL and the

It could even be something as stupid as a failed internal
pull up resistor on one of the hybrid's input/output pins.

Some simple probing around on the PAL may be in order.

I have never found the PAL, or the PAL's socket to be the
problem, but I have found trigger hybrid swaps will make
things happy.

-Chuck Harris

Jean-Paul wrote:

Dear Chuck

The CTT option operation and self test seems to be dependent upon

1/ CTT board, EEPROM on board
2/ Trigger Hybrid U500, only certain ones work, even though they may work fine in a non CTT scope.
3/ successful CTT calibration, stored on NVRAM of A5

At the moment I have all three of these factors in question, as the original A5 board is in the hands of a friend to do the SMD leaky cap clean-up and NVRAM replacement. So, I am using another scopes A5.
I shall get the original A5 back and see if that changes anything after a CAL attempt.

The design of the CTT option seems rather flaky, to depend on unspecified U500 properties.

Kind Regards


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