Fluke 5502A Calibrator with strange problem

[CrazyTiger]

Hi All.

I have this Fluke 5502A calibrator, upon turn on, "Starting Up" Shows up and then it keeps cycling and rebooting to "Start Up". However leaving it be, it does boots into the calibrator sometimes and everything works perfectly, outputs are bang on.

To eliminate the problem, I tried removing all modules, leaving on the bare minimum of Processor, Front Display, and Power Supply. Its still the same. Power Supply test points are on the dot. So my suspect is the Processor A9 Module itself. Suspect is SRAM

I also noticed something weird, I went and checked the clock setting, it was not moving. Can someone help me to check on their 5500A/5502A/57xxA, if the clock setting is just setting feature without readback. I have checked all of Flukes 55xx service manual, they never mentioned anything about their RTC battery replacement. Anyone done this before?

Remarks:
57xxA stated on their service manual, its a simple replacement, but the architecture of 55xxA and 57xxA is different

[ddrl46]

Recently we had two Fluke 5520A calibrators develop a problem where they would lock up and reset when saving their calibration coefficients after a zero routine and also started losing information such as their serials numbers etc. Changes to the GPIB address and other settings also resulted in a lock up / reset.
This fault turns out to have been caused by bad flash memory ICs on the A9 CPU assembly. Funnily enough these ICs read / programmed perfectly fine using a programmer, but caused trouble in the calibrator.

Since the Fluke 5520A and 5502A share pretty much the same A9 CPU board design this might be worth checking out.

We replaced these flash ICs with MT28F004B1VG-6B. Luckily enough the data we read from the old ICs using our programmer turned out to be still in tact.
The originals were MT28F004B5VG-8BF but these appear to be pretty much unobtainium, and the ones we managed to find turned out to be fake remarked ICs (top boot block instead of bottom boot block).
We also noticed that the cheap chinese programmers such as the Xgecu T56 do not program these memories correctly, however a proper Dataman Pro48 programmer did the job.

Something odd we noticed is that the Vpp pin of the flash ICs was connected to +12V, which is kind of strange since the datasheet we were able to find for the MT28F004B5 indicated that this pin should not exceed 5V, this datasheet however does not include the -8BF variant of this IC so maybe this is allowed. This is at least something to keep in mind when replacing these ICs since the MT28F004B1VG variant we replaced it with is compatible with both 5 and 12V.

Replacement of the RTC battery on the A9 CPU board requires no special actions besides setting the time/date after replacement.

[service]

Dear CrazyTiger.
Did you manage to replace the battery?
Did this solve the calibrator problem?

[Louis_C]

Our 5500A has the same issue. It also showed an error on screen that said it "Lost sync with in-guard". Any idea's?