E3646A Voltage drifts down slowly but continuously - Page 1
Forum section: electronics / repair

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: October 02, 2019, 02:51:28 pm
content: Hi,We have an E3646A with this strange downward drift on voltage. It's on the 6 Volt output. Not sure yet if the 25 V output is doing it as well. Whatever display digit is highlighted and flashing, drifts slowly down, and the output voltage measured drifts down with it. Do not see any Agilent Service Bulletins mentioning it.Anyone see this before?

author: amspire
author_rank: Super Contributor
timestamp: October 02, 2019, 11:00:44 pm
content: You didn't say how much the output is drifting by. Is it more then 0.01%?Is the drift on the measured output or on the inbuilt meter - we do not know if you are talking about a voltage drift or a drift in the meter measurement.Is anything attached to the rear voltage terminals?

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: October 03, 2019, 02:18:20 pm
content: Thanks for your reply.As above... Whatever display digit is highlighted and flashing, drifts slowly down, and the output voltage measured drifts down with it.Maybe that isn't clear enough? Digit and measured output slowly drift down. The drift is so slow it takes maybe 24 hours to see. Have not measured the drift percentage because it is so slow.

author: spiff72
author_rank: Regular Contributor
timestamp: February 02, 2021, 03:03:20 pm
content: I know this is an old post, but I have a problem with drift on channel 1 of my E3646A, but it seems different than what you described. I really want to figure out how to repair and troubleshoot this issue!Mine will slowly drift down, until it hits a certain threshold, and then jump back up to the set voltage (or close to it). See video above (and sorry about the noisy kids in the background). Only happens on channel 1, so i don't use that one anymore. Bought it off ebay for $160-ish (a steal!), and after finding this issue, the seller offered are partial or full refund (so i asked for $100 refund if I could keep it).

author: WattsThat
author_rank: Frequent Contributor
timestamp: February 02, 2021, 03:22:37 pm
content: A likely culprit would be a leaky sample and hold capacitor in the DAC output circuit.

author: spiff72
author_rank: Regular Contributor
timestamp: February 02, 2021, 03:35:07 pm
content: Thanks - I think I downloaded schematics for this a while back - just need to find where I put them.Will have to make it a rainy day project - I think I tried to do some troubleshooting shortly after I bought it but the issue is sort of intermittent. After it has been running for a long time, it seems to do it less, so it was hard to probe things while it was malfunctioning. (I am an ME who dabbles in electronics - so not an expert by any means).

author: spiff72
author_rank: Regular Contributor
timestamp: February 02, 2021, 03:49:19 pm
content: Would these be the caps to be looking at?

author: WattsThat
author_rank: Frequent Contributor
timestamp: February 02, 2021, 05:09:01 pm
content: Yes, that was the circuit area I was thinking of. Of course there is a lot more downstream of that voltage source but that is the point of origin for all of the programmable output voltages and currents in the unit.