Agilent 54622 - 4 channels on digital acquisition stuck on low

[gkmaia]

I got a Agilent 54622 that has an issue with the digital acquisition.

Digital channels 2, 5, 6 and 7 are stuck in low.

The acquisition circuit of each channel starts with a cap, then a resistor then the acquisition ASIC.

Then probing these channels on the node between the capacitor and resistor or between the resistor and the ASIC the signal is killed and pulled to -4.5v.

Has anyone come across this issue before or has some experience with these Agilent MSOs?

[SilverSolder]

I have the same scope (but haven't seen the issue you are having).

Suspect the ASIC is blown, as some of the inputs seem to be acting more like an output on your unit.

Maybe swap the ASIC on the bad channels with its neighbour to prove the theory?

[MarkL]

The 1NB4-5036 is an 8-channel comparator.  Before concluding it's dead, I would try lifting a leg on the chip of one of the dead input channels to make sure the -4.5V is coming from it, maybe with a small load of 1k to ground.

Someone is selling 1NB4-5036 on ebay for USD $6.95.  It's also used on many of the 167xx logic analyzer modules if you know anyone with a dead module for salvage.

[gkmaia]

Thanks guys. I just bought the ebay ASIC as it was just 6 bucks.

I will let you know when it arrives is that was the issue.