HP 8550 Service Manual - Page 534

Document tray 4 paper sensor (S1) Registration 5 sensor (S3) Measure the voltage between YES connectors J5-8 and J5-9 of the DADF controller PCB. Is the NO reading 1.5 V or less when paper is in the document tray and 4 V or more when there is no paper in the document tray. Measure the voltage between YES connectors J9-B12 and J9-B11 of the DADF controller PCB. Is the NO reading 4.5 V or more when paper is in the document tray and 1.3 V or less when there is no paper in the document tray. Replace the document tray paper sensor (S1). Replace the DADF controller PCB. Replace the registration sensor (S1). Replace the DADF controller PCB. E712 The communications IC on the ADF side is faulty. This error occurs when communication with the printer is disrupted for five seconds or more. Cause Wiring Step 1 2 DADF controller 2 PCB Checks Yes/No Action Turn the power switch off and then YES on. Is the problem corrected? Check the wiring from the printer's dc controller PCB and the DADF controller PCB. Set the meter range to 200 V dc. NO Connect a + probe to connector J2-1 and a - probe to connector J2-2. Measure the voltage. Connect a + probe to connector J1-6 and a - probe to connector J2-2. Is the reading 24 V in both cases? Make sure the ADF is receiving power from the printer. Replace the DADF controller PCB. YES Is the problem corrected? NO End. Replace the printer's dc controller PCB. 532 Chapter 7 - Troubleshooting EN