Agilent E3633A, Gain out of range for gain error correction

[somlioy]

Hi, My E3633A started to act weird (error 632 and 718). I got a tip from free_electron on the forums that one of the op-apms in the adc-circuit would be defect and suggested me to replace all four (U25, U28, U35, U41). So I did. After reassembled the unit and tried to power it on. I immediately knew something was wrong when it took a few seconds for the display to turn on so I turned it off again quickly. I smelt magic smoke and saw a burnt resistor. R148. See the attached schematic on page 22 (129).

Does anyone know why I smoked this resistor and possible other stuff? And maybe explain the circuitry around R148?

Finally got around and replace those parts and everything seems alright except that I still got the err 718 (Gain out of range for gain error correction) when turning on the output. Display shows -0.014V/0.055A. DMM shows a climbing voltage. Output is climbing whether its on or off. It has been powered for a while now and its outputting about 22volts atm.

No errors when I'm doing a self test at boot.

Are there still some faulty components or do I just need an calibration?

Schematics attached.

[amspire]

Without wading through the full circuit, it looks like something tripped the overvoltage crowbar thyristor that should short the output, but it looks like something is still providing considerable power to the output.

There is a good chance that the Optocoupler (U46) is now damaged, and the crowbar thyristor (CR39) could be fused.

I would remove R148 until the supply is fully working again, and then put it back and check that the crowbar circuit is working.

Read the manual on how to configure the crowbar - a wrongly set crowbar can easily give the impression that a supply does not work.

[somlioy]

Thanks for your response.

I think I found the fault. When replacing those op-amp I managed to get a bridge beneath U25 (pin 6 and 7) and U35 (3 and 4). Also found two other chips that I fried (visually); CR24 BAV99 diode and U24 74HC4051 mux/demuxer. Muxer died because its output was shorted to the -17.4V rail. CR27 I dont know why. U25 could be damaged aswell since its output was shorted to the 15V rail if I'm not misstaken.

Hopefully I didnt kill too much due to my stupidity.

[somlioy]

Finally got around and replace those parts and everything seems alright except that I still got the err 718 (Gain out of range for gain error correction) when turning on the output. Display shows -0.014V/0.055A. DMM shows a climbing voltage. Output is climbing whether its on or off. It has been powered for a while now and its outputting about 22volts atm.

No errors when I'm doing a self test at boot.

Are there still some faulty components or do I just need an calibration?