kenwood dso wont keep its time - Page 1
Forum section: electronics / repair

author: m3vuv
author_rank: Super Contributor
timestamp: August 22, 2020, 11:05:31 am
content: 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.

author: TheMG
author_rank: Frequent Contributor
timestamp: August 22, 2020, 03:07:18 pm
content: 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.

author: m3vuv
author_rank: Super Contributor
timestamp: August 22, 2020, 05:05:51 pm
content: 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.

author: m3vuv
author_rank: Super Contributor
timestamp: August 22, 2020, 07:07:07 pm
content: heres some pics of the board.

author: m3vuv
author_rank: Super Contributor
timestamp: August 22, 2020, 07:11:22 pm
content: and another pic

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 22, 2020, 07:20:12 pm
content: 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.

author: m3vuv
author_rank: Super Contributor
timestamp: August 22, 2020, 09:46:43 pm
content: well ive found the rtc and datasheet,should the battery feed pin 24 vdd of the rtc?

author: m3vuv
author_rank: Super Contributor
timestamp: August 22, 2020, 09:48:14 pm
content: i measure 2.3v between pins 12 and 24,i asuume thats to low?,the battery i fitted is 3v.

author: TheMG
author_rank: Frequent Contributor
timestamp: August 22, 2020, 11:09:58 pm
content: 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.

author: m3vuv
author_rank: Super Contributor
timestamp: August 23, 2020, 05:27:10 am
content: i couldnt find a part number on the original battery,and since threw it out,maybe i should try 2x cr batterys on it?

author: m3vuv
author_rank: Super Contributor
timestamp: August 23, 2020, 05:53:58 am
content: 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.

author: m3vuv
author_rank: Super Contributor
timestamp: August 23, 2020, 06:15:11 am
content: if the xtal clock wasnt running,would it cause this?,thinking of replacing the xtal and the caps that go with it.

author: m3vuv
author_rank: Super Contributor
timestamp: August 23, 2020, 07:38:01 am
content: 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.