Tektronix TDS540 repair help please.....

Hi all...

I have acquired a scrapped TDS540 which has become a bit of a restoration
project.



It originally failed Acq/Proc Interface, Acquisition and Attn/Acq Interface.

Opening it up there was evidence of electrolyte leakage from and subsequent
corrosion around the SMT electrolytic caps.

Replacing the SMT electrolytic caps on every board plus a thorough degrease
and clean reduced the power on errors to just Fail ++ Acquisition.

The trigger threshold was not adjustable - always triggered at 0V.

This I traced to an open circuit via under a resistor (U1550 Pin 7 to U1552
pin 16)

I have repaired the via and the scope now appears to work correctly but
still has the Fail ++ Acquisition fault at power on.



The entry in the error log is as follows:

181890:23:59 ERROR: diagnostic test failure

ctlConfidencDiag, **2.50e-9<=exp<=1.20e-8 actual=4



I know that this scope is no longer supported and that schematics are not
available but If anyone here has experience working on them and knows what
this error message means I would greatly appreciate a hint as to which area
of the PCB I should be looking at.



My reply email address is corrupt to stop the spambots. Please respond here
or mail r o b i n b o w d e n (a-t) d i e 4 l a s e r (d-o-t) c o m



Thanks & regards,

Robin Bowden


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