Problems with 640G sensor charger,oh yes, sensors too!


New Member
Relationship to Diabetes
Type 1
I've used the Medtronic 640G for well over 3 years now. Many moons ago, the charger started messing around. I have to replace the sensor on the charger 2/3 times each charge because, although the 30 mins charging time has passed and the light stops flashing, it hasn't actually charged. ThMedtronic team told me I could buy a new charger (£200) so I've carried on using it. I've just had a couple of days break after putting in a new sensor and then being told not to calibrate while the thing updated. This resulted in a costly sensor fail. As evening became middle of the night, I cursed and cried and risked being without cgm. I re-charged the transmitter tonight. 2 minutes green flashing light, then red. I replaced the sensor battery, then same again. I timed these episodes. Each lasted 2 minutes. I can't face 15 of these sessions, and then a few more. It seems obvious to me that the charger's duff. Who do these things always happen out of hours.
I wonder if anyone else has had this problem?
I've had so many problems with the 640G. The sensor shoots in with such power that I'm surprised whenever it works.
I've said it before and I'll say it again. I DO NOT want to play this game any more
Thanks for listening


Relationship to Diabetes
Type 1
This doesn't sound right and sounds like you may have a faulty transmitter/charger. Do you get funded the sensors?


Well-Known Member
Relationship to Diabetes
Type 1
Hi @susieclew , how old is your transmitter? I’ve just had a replacement transmitter after 18 months use as I was facing similar problems. I think the transmitter is guaranteed for 12 months? but they do last longer. I was getting lost connections, calibrations not received, sensor updating messages. The transmitter would charge or so I thought - the flashing light on the charger went out but when I removed the transmitter I didn't get the flashing green lights and on re inserting it to the charger it started charging up again. Have you tried putting the green test sensor into the transmitter to see if that helps to reset it?

Did Medtronic suggest it might be the transmitter rather than the charger? Have they said the wasted sensors will be replaced?

It can be a challenge to establish which bit isn't working correctly. I hope you can get things sorted out.


Staff member
Relationship to Diabetes
Type 1
Sorry to hear about your tech woes @susieclew :(

It can be very unsettling to have the tech you are used to helping with your diabetes have a wobble and become unavailable can’t it :(

How long have you been using the MM640G? How far through your contract are you? My enlite/G3 sensors always seemed to take at least 45 minutes to charge before the light went out.

Like @Flower I am wondering how old your transmitter is... sometimes they seem to meekly fade away with just a slightly shortening charge-life after a year, while others find their flagging transmitter misbehaves much more significantly :(

Particularly difficult where you are self-funding this expensive tech!