OBI200 keeps HP MFP M477 awake

[dadbox]

I have an HP multi-function printer with fax capability. I have it  set up with my OBi200 and Google Voice, and the fax capability is working - I can send and receive faxes just fine.

My problem is that when the OBi200 is connected to the printer, the printer keeps waking up and running the fan. It doesn't print anything, it doesn't record anything in the fax log, it just makes noise.

I have the printer in my home office, so I have the printer standby setting set to 1 minute. If the OBi200 phone line is disconnected from the printer, the printer fan stops and stays off. As soon as I connect the phone line between the OBi200 and the printer, the printer keeps waking up and starting the fan.

It seems that something the OBi200 is doing on the analog line is causing the printer to wake up.

Alternatively, if I leave the phone line connected between the printer and OBi200, but unplug power from the OBi200, the printer stays quiet. This reinforces my belief that the OBi200, when powered on, is actively doing something on the analog line to cause the printer to wake up.

The only reference I was able to find suggested turning off OnHookPowerSaveMode in OBiTALK expert configuration; I tried that, but it does not stop the printer fan from starting over and over.

I have never had this printer connected to a "real" phone company analog line (I don't have one), so I can't say if this behavior is unique to the OBi200.

Any suggestions on what I might try changing in the OBi200 configuration to stop my printer from constantly waking up and making noise?

My fallback plan is to simply disconnect the printer from the OBi200 when I am not actively faxing, but I would prefer a better solution.

[zapattack]

Verify you are using a 2-wire (red/green) cable, not 4-wire(r/g/yel/blk).
Some fax machines sense control signals on extra wires.

[drgeoff]

Verify you are using a 2-wire (red/green) cable, not 4-wire(r/g/yel/blk).
Some fax machines sense control signals on extra wires.

Unlikely to be the cause in this case as only the inner two contacts of the phone socket on an OBi200 are connected to anything internally.

[dadbox]

Yes, there are only two metallic contacts in the modular connector.

Any other ideas? 

FYI, I'm electronically savvy; is there anything I can do with a voltmeter or other test equipment to diagnose this?

[SteveInWA]

I've used HP OfficeJet printer/fax/scanner machines for decades.  HP makes a big deal out of insisting you only use a two-conductor phone cord, and they supply one with the printer.  I have never read a rational, technical explanation as to why, but I just blindly follow that instruction, and I have never had a problem.

Try turning off auto-receive on the HP unit, such that it ignores inbound calls, and see what happens.