Hello All,
I'm new to the board. I have a HP 4192A LF Impedance Analyzer with a tricky problem (at least for me) that I haven't been able to troubleshoot. The HP service manual is written around troubleshooting procedures using a HP 16343A Logic Test Box and two test ROMs which I don't have and seem to be unavailable on the surplus market.
When I power up, the unit passes all the self-tests (P-01 through P-06) and says "PASS" on Display "A", shows the Hex address for the HPIB, and then the two Displays, "A" and "B", go blank. The manual self-test (blue-key & 6) also passes. The default internal trigger doesn't work (i.e., the trigger light doesn't flash in auto and no auto triggers on any internal test point). A manual trigger from the front keyboard or external trigger input will flash the trigger light once, but no display of data on "A" or "B". If the "average" function is selected on the front panel (blue-key & 4) the trigger light will stay on 4x longer with a manual trigger, as with a normal functioning 4192A. All display elements and LEDs light up stable and solid on the manual self-test. All front panel key entries appear correct and panel LEDs respond as they should. I replaced A6-U33 as suggested in the Service Manual under Timing Notes on page 8-36, but no change. I can send commands and receive output from the HPIB interface (measurements are not correct -- probably residual noise). I'm pretty sure (but not positive) that the A6 Computer board and the A5 Display/Key board are working normally. The oscillator is stable and accurate and can be commanded from both the front panel and HPIB. The DC bias also responds to commands. I've checked the outputs from the fractional N chip with a data probe and there's data being output (no logic analyzer to test it further). The Frequency display on the upper right responds normally to all inputs (frequency, bias, oscillator levels). It appears the unit is not able to complete a measurement sequence (in any mode), get its data to the displays, and initiate another trigger. Any ideas on how to progress from here would be greatly appreciated. Is there a definitive test that can be done to verify correct operation of the A6 computer board and the other digital boards (without the Test Box and test ROMs) before I dive into the analog section?
One of the power-on Self-Tests which the analyzer passes is a CRC check of the system ROMs. There are discrete Error Codes for each System ROM which appear on Display "A" with a failure, but no Error codes show. I can introduce errors by disconnecting certain internal coax cables, and the self-monitor immediately picks them up and displays the proper Error Codes on the otherwise blank Display "A". I think the self-monitor is working properly.
Larry
