SOLVED - HP 8591E "EMPTY DLP MEM": loses cal, settings, time despite new battery - Page 1
Forum section: electronics / repair

author: the Chris
author_rank: Regular Contributor
timestamp: December 06, 2024, 03:44:54 pm
content: I took my chances on a locally available 8591E. First power-on yielded an error message about missing calibration data, but I could get it working again thanks to MatL's advices over here:https://www.eevblog.com/forum/repair/repairing-an-hp-8593e-spectrum-analyzer/msg990688/#msg990688Somehow expected, the instrument lost these settings immediately after shutdown, pointing to a depleted RAM Backup battery, supported by a sticker that noted last replacement to have happened in 2006, besides a 2nd sticker stating a preceding exchange in 1994. A quick check of the battery voltage gave a reading of 1.06V so a replacement Li-SOCl2 battery was ordered.That battery arrived today, MFD date in 2024, 3.67V ocv. Soldered it in, watched the polarity, made a voltage reading on the board contact area, again 3.67V. All fine, I guessed. Put everything back together, ran calibration, set time and date etc. Had fun for an hour, switched it off for lunch to return an hour later. Switched on again: all settings gone (again). A brief moment immediately after power-on, a single message "EMPTY DLP MEMORY" can be seen before the instruments resumes operation with the usual complain about missing calibration data.Further test show that the data is lost even when power off and on ist done within one second after the other.So my question: is the RAM known to fail? I just replaced the SRAM in one of my E3631A so I know these can go bad indeed. But have there been similar cases before?The service manual only offeres block diagrams, no schematics, so I need to remove everything above the memory section first and trace the battery voltage supply to the RAM chip to identify it and verify that there is nothing broken in between that hinders those 3.67V to reach the RAM. I could already see by using a small flashlight that my board is the newer revision with only two EPROMs instead of four.Any help is welcome.Christian

author: wkb
author_rank: Super Contributor
timestamp: December 06, 2024, 10:46:47 pm
content: There are service docs including schematics out on the internet for the HP859x series. Search for CLIP, Component Level Information Package if memory serves.Wilko

author: the Chris
author_rank: Regular Contributor
timestamp: December 07, 2024, 06:49:39 am
content: Thanks Wilko.So far, I could only find one from 1997 showing the newest version with the button cell piggy board. But at least that one seems to use the same Dallas DS1210 standby power supply regulator for the RAMs as the old board revision as I could find that IC nearby the battery. Probing shows that the battery voltage doesn't make it to this regulator. Therefore, it is no surprise that there is no voltage at the supply pin of both SRAM chips as well.Looks like I really have to take out the board and have a look at the backside if something went wrong when the last battery was replaced in 2006.

author: the Chris
author_rank: Regular Contributor
timestamp: December 08, 2024, 10:39:02 am
content: I took out the board and some probing later the failure turned out to be indeed related to a bad soldering job on the battery replacement some years ago. Instead of cutting the wires of the old battery and use these for soldering the new one in like I did, they killed the contact to the track on the positive pad when the wire was desoldered. I could see marginal improvement on the contact resistance with another soldering attempt, but far from full voltage.I decided to lay down a new wire track above the original track that is buried inside the 4-layer PCB. After soldering, I could immediately see the voltage rising slowly on the Vdd pin of the RAMs, indicating the charge up of the supercap via the 1k resistor. The voltage settled at Vbat minus a diode voltage drop (due to R109 I think it was, probably polarity protection).After everything was put back together, the 8591E now holds memory just fine