kenwood dso wont keep its time

[m3vuv]

Hi all,ive a kenwood DCS-8200 50mhz dso,when i brought it it said low batt during the self test,i removed a soldered in lithium battery that was dead(not leaking tho!),i put a holer in with a new cr2030 coin cell in,now the low bat message has gone but every time i set the clock and power cycle the scope,it looses its time on the clock,any ideas where to look,its not realy an issue as the scope works fine,it just niggles me,cheers in advance m3vuv 73.

[TheMG]

I would identify the RTC IC and check to see if power from the battery is getting to it. Sometimes there's a diode and possibly other components in the path between the battery and the RTC, so it's possible there might be a fault there.

[m3vuv]

any idea what the rtc would look like in this?,ive seen them on old pc motherboards but didnt see anything like that in this,the ones ive seen have been a black block about  30mm long by 15mm wide and about 10mm tall.

[m3vuv]

heres some pics of the board.

[m3vuv]

and another pic

[PA0PBZ]

The clock crystal is just left of the battery in the first picture (X2), see where that is connected. The pics are too blurred to find out.

[m3vuv]

well ive found the rtc and datasheet,should the battery feed pin 24 vdd of the rtc?

[m3vuv]

i measure 2.3v between pins 12 and 24,i asuume thats to low?,the battery i fitted is 3v.

[TheMG]

The datasheet says the voltage for standby can be between 2 to 6V, so 2.3V should be fine in theory. There's probably a diode between the battery and the IC to prevent the battery from being charged when the circuit is powered on.

It might be possible that the voltage is 2.3V at steady state, but drops very briefly below 2V at some point, resetting the RTC.

What was the part number of the original battery? The datasheet does seem to mention a 3.9V lithium cell. Probably Li-SOCl2 chemistry or something. Maybe a CR2030 with its 3V nominal voltage is not quite enough for some reason.

[m3vuv]

i couldnt find a part number on the original battery,and since threw it out,maybe i should try 2x cr batterys on it?

[m3vuv]

Well ive piggybacked a schotty diode ontop of the diode feeding the rtc,its now getting 2.4v,still not holding the time etc tho,does that mean the rtc is us or maybe the xtal,i can still set the time etc but it gets lost on a power cycle.

[m3vuv]

if the xtal clock wasnt running,would it cause this?,thinking of replacing the xtal and the caps that go with it.

[m3vuv]

well i replaced the xtal also the 2x 22pf disc ceramics associated with it and its fixed,cheers guys,i now have a fully working 50mhz dso!,still prefer my old tek 453 tho tbh! lol,73 m3vuv.