I have acquired a TDS540C scope with the following problem. Although the startup tests are Passed, and the Diagnostic tests are Passed, it will not pass SPC. Here is what I discovered so far. Even thought the Start Up Tests are Passed, if one looks at the Error Log it has the following message tagged with the start up time and date:
Warning: VariGain Setting beyon (not displayed)
Ch 4 1.0957 > 1.080
The same message is received if one runs the Diagnostic Tests. Now, as far as the scope working, everything appears normal, all four channels show signal. The offsets on all four channels are zero, or very close to it. The signal gain on all four channels appears the same, the same signal on all four inputs will appear as a single trace, indicating very close gain match. All channels trigger just fine. So, the scope appears to be operating in a completely normal fashion.
However, it always fails SPC with the following Error Message:
ERROR: Internal Adjustment Range
(3@ 5001): 1.0111 = > Balance dac #4 (ID # 147)
It would appear that something in the Channel 4 signal path is preventing the scope from passing SPC even though the signal from it matches all other channels. I did replace the op amp (072) feeding the balance input to the channel 4 acq. Chip, just because I had one. It did not help. I am sure the messages probably narrow the problem down if I understood what they mean.
Wondering if anyone has any ideals as to what the problem might be, or where I can get information on the meaning of the error messages. I have the schematics for this scope, the TDS540B schematics appear to be the same as the TDS540C. This model does not have the 'Electrolytic' problem of some other 540 models, so that is not the problem.
I have had very good luck at getting the answers to problems on this Thread, hope that is the case with this problem.