E361X / E3615A owners, does your unit hum ? Also, case not perfectly aligned.... - Page 1
Forum section: electronics / testgear

author: JeLo
author_rank: Contributor
timestamp: December 23, 2019, 02:29:28 am
content: Got an E3615A for about 100€ from Finland in new like condition. Done a few tests with a cheapo multimeter and everything seems to be ok voltage and current wise, didn't test the advanced function connectors on the back though (Don't even have 2 units to test....).Two things I hate:1- It hums like crazy even without any load! I guess that's subjective, but can you please confirm if your unit hums too ?2- The overvoltage protection screw is not well aligned with the front case. Maybe I'm nitpicking but it looks awful like that. Guess I'm kind of nitpicking as it's operational...Thanks, I'm more of a lurker but I love this forum...CheersJose

author: NoisyBoy
author_rank: Frequent Contributor
timestamp: December 23, 2019, 05:43:34 am
content: No, I bought mine new seven years ago. It is absolutely silent, and the OVP adjustment screw aligns perfectly with the hole on the front plate.If you buy it used, it would definitely be a good idea to open it up and blow out the dust and check the caps if it is an older unit.

author: JeLo
author_rank: Contributor
timestamp: December 23, 2019, 01:26:25 pm
content: Thanks. Actually mine is an Agilent one which even smells new, I don't know where it came from, probably some liquidation, but it still has the original Agilent seal too!I think there's some resonance on the case raising the buzzing because if I put pressure on it it gets lower. It's still buzzing when I do that though...

author: HighVoltage
author_rank: Super Contributor
timestamp: December 23, 2019, 01:35:49 pm
content: They are usually totally silent.Open it up and check if the transformer mounting was damaged during transport.Most likely something got shifted inside.Do not use the PSU until you have fixed the problem, otherwise the problem might get bigger

author: bingo600
author_rank: Super Contributor
timestamp: December 23, 2019, 03:44:43 pm
content: One of my 6632B's were humming a lot (mains (trafo) hum).I opened it and put some rubber-foam on top of the trafo , enough that the lid would squezze on it.No more humming./Bingo

author: JeLo
author_rank: Contributor
timestamp: December 26, 2019, 03:22:29 pm
content: I opened it up and this thing has practically no dust inside. I'm not sure about the transformer mount though, it seems the transformer is tightened to the PCB with big screws, doesn't make sense so there must be something underneath. Removing the entire PCB was too much of a hassle so I decided to leave it.One thing I noticed is that the PCB itself is not screwed but it's hold in place with a sort of round metal notch and a matching PCB hole shape.Do you know if this type of transformer humming can cause electrical interference ?I did find out why the OVP screw wasn't aligned with the front plate hole, the pot was soldered slightly tilted forward!! Either that or it suffered some impact, but I suspect the first because to bend it in place I had to use a lot of strenght (I should've left it alone but hey...). It worked.Another thing, is it normal for the pot shaft to have some slack ?

author: HighVoltage
author_rank: Super Contributor
timestamp: December 27, 2019, 10:21:01 am
content: Is it still humming with the case removed?What happens when you slightly press on different spots of the transformer, will the humming change?What about different load conditions, is the humming changing?What is the spot on the top of the transformer that looks like the case has rubbed against it?

author: JeLo
author_rank: Contributor
timestamp: December 27, 2019, 02:40:35 pm
content: Hi."Is it still humming with the case removed?"Yes. It actually hums less. So I think it's some type of case rosonance that's amplifying it.By the way, I finally found a youtube video showing the bottom of the PCB, but it was a E3620A. Assuming the 3615A is the same mount (which probably it is) it confirmed as I suspected that the transformer is screwed on the PCB, not to the bottom inner metal case. This probably explains why the humming changed a bit when I pressed one of the transformer screws hard with my hand. On 2 of the screws this effect was more pronounced than on the others, probably due to the way the PCB's weight is distributed."What happens when you slightly press on different spots of the transformer, will the humming change?"Nothing, it's exactly the same. When I press hard on some screws it changes only a very tiny bit, but I think it's already screwed tightly with what seems to be glue on the screws too."What about different load conditions, is the humming changing?"I just tried setting the voltage and current to max and then shorted the outputs (turned it off first of course...), the humming stays the same!"What is the spot on the top of the transformer that looks like the case has rubbed against it?"No idea, it's think it was glue residue.Think I'm gonna have to live with it, it's nothing extreme, I was just expecting it to be dead silent based on the reviews I've read about it.

author: JeLo
author_rank: Contributor
timestamp: December 27, 2019, 08:47:53 pm
content: Update, I some help understanding a possible malfunction.Shouldn't it maintain the voltage even with shorted outputs ? i.e. If I set the voltage at 8V and the current at 2A, then it should be able to maintain the 8V because as soon as current raises above 2A the CC mode steps in, not allowing current over 2A. Or it's normal that voltage drops drastically ?This is the 1st power supply I've had so give me a break here, but I think this doesn't make sense.

author: newbrain
author_rank: Super Contributor
timestamp: December 27, 2019, 10:03:13 pm
content: No, it should not.And given Ohm's law, it physically cannot!In CC (or, as some would call it, current limited) mode the PSU will at most push your set value (2 A in this case) through the load.Shorting the output, you can expect the total lead resistance from the + to the - terminal to be in the order of some tenths of one ohm, let's assume 0.2.By Ohm's law (V = R I) we then have 2 * 0.2 = 0.4 V, much less than the set voltage.To measure 8 V across a 0.2load, 8 / 0.2 = 40 A are needed.To have 8 V across a load with 2 A passing through it, itmusthave a resistance of 8/2 = 4.Any load above that value will let the PSU provide the set voltage, any load below will keep the set current by decreasing the voltage.

author: JeLo
author_rank: Contributor
timestamp: December 27, 2019, 10:55:24 pm
content: Just to be clear, I shorted the outputs for a brief instant directly with my multimeter, just to be able to take a measurement. I thought multimeters didn't let all the current pass through but it seems they do... my bad.