TDS540 -diagnostic test failure Dac Range Test ** DAC system failure

Hi,

I'm in the process of repairing a TDS540 acq board and have been making good progress but have got stuck on faulting the 'diagnostic test failure Dac Range Test
** DAC system failure' error - I've traced out the DAC signal path through the buffer and the multiplexers out to the various hold capacitors and op amps. replaced one bad op amp and a multiplexer. but still keep getting this.

Two questions:
- is this an error message in of itself, i.e. its not a summary related to a prior error message
- now does the circuit determine the fault?

Thank you

Hello,

I couldn't find any more info in our old databases so I can only speculate based on current products. Most DAC circuits have an ADC hanging off the output to form a feedback loop. Perhaps the "DAC System Failure" indicates the TDS commanded one of the DACs to put out a Voltage and the feedback ADC did not detect any change.

Just a guess, sorry.