Hi all,
My 58503A Option 001 GPSDO had been running 24/7 for the past several years. A few weeks ago I noticed that the same segment (segment E) in all of the digit positions was not working, although the rest of the segments were working as they should. I unsoldered and removed the Vacuum Fluorescent Display (VFD) module (which is the same as in the 53131A, 53132A , and 53181A) and found that I could not get that segment to light up with the appropriate inputs applied, although I could get the other segments to light up. "Aha!" sez I, thinking that a new VFD will do the trick. Unfortunately, it did not. The new VFD checked out just fine on the bench, but when installed in the 58503A the same segment failed to light up and all of the other segments worked properly. So then I figured that the failed display segment in the original VFD somehow damaged the output from the driver chip (HV518PJ, a 44-pin PLCC) for that segment. So I got out my SMD rework equipment and replaced the driver chip. Problem solved? Unfortunately not. The behavior is identical to the original behavior, and also to that of the new VFD with the old driver chip. Everything works properly except segment E. I've installed the display board into another 58503A and the display is still defective in the same way. So it's not a problem with the motherboard. I don't have another Option 001 display to compare this one to, so this is the point at which I'm stuck. The only other point of failure that I can think of is this: there is an instrument-specific chip on the display board, a 58503-80023, that may be some sort of decoder that turns the status messages from the motherboard into a stream of serial data to send to the driver chip (which has no decoding logic at all) to create the necessary characters for the messages on the display. Any thoughts on where to proceed from here? Any theories as to how the original VFD had the failed segment, but changing the driver chip and putting in a new display didn't fix it? It's literally a straight connection between the various output pins of the driver chip and the corresponding input pins of the VFD. I checked the traces and there is continuity between each driver chip output pin and the input pin on the VFD. If the problem is a failed 58503-80023 chip, then how could a failure in the VFD cause the chip on the input side of the driver chip to fail? Or is it just some strange coincidence? I've been referring to the CLIP for the 53132A to troubleshoot the display board, but that only goes so far. The PCB in the 58503A is p/n 58503-60010. Is there any detailed information available on this board? Anyone with a 58503A Option 001 board they'd be willing to part with? Thanks for any help or suggestions, Stan _______________________________________________ time-nuts mailing list -- [email protected] -- To unsubscribe send an email to [email protected] To unsubscribe, go to and follow the instructions there.
