A good friend of mine saved this nice arbitrary function/waveform generator from the dumpster. He mentioned that presumably the output was overloaded with 230V line voltage.
Upon powering it up it issued output overload. But allowing to activate the output. An executed self test showed the following error codes:
| Error Code | Description |
|---|---|
| 625 | Self-test failed; amplitude DAC These errors indicate a malfunctioning system DAC(U801), or failed DAC multiplexer (U803) channels. |
| 630 | Self-test failed; internal ADC over-range condition This error indicates a probable ADC failure. The failure could be of the system ADC (U703)), the ADC input multiplexer (U701), or the ADC input buffer amplifier (U702). |
| 626 627 628 | – Self-test failed; waveform filter path select relay – Self-test failed; -10 dB attenuator path – Self-test failed; -20 dB attenuator path These errors indicate that the specified relay is not being properly switched or the attenuator/amplifier is not providing the expected amplification or gain. These self-tests use the internal ADC to verify that attenuators are operating properly. |
All those errors have to do with the self test feature where the controller reads back set voltages and amplifications with an onboard ADC. With the knowledge about an higher voltage overload on the ouput I looked out for the input protection circuitry.
After opening up the unit and doing a close optical inspection –
a BAV99 protection diode suffered death probably saving other components. But this wasn’t the only issue.
Upon powering the unit back up and touching different parts (lacking a proper thermal camera) I detected a pretty hot area where four parallel amplifiers are used in a 20db gain stage. One of them died. Due to the parallel nature of the circuit I just tested the device without the dead ic and it works and passes the self test.
Those amplifier ICs cost about 15 Euro. If I don’t use those high gain settings I don’t need to replace the part.
