Is this a good candidate for newbie repair? - Page 1
Forum section: electronics / beginners

author: Matthematik
author_rank: Contributor
timestamp: November 18, 2016, 11:17:24 am
content: I just bought an Agilent E3630a from eBay and the display stays at zero voltage no matter the output. All of the functions seem to work appropriately. I'm considering working out a partial refund with the seller and then trying my hand at repairing it. Is something like this usually pretty simple, or is there not enough information to answer that question?

author: mzacharias
author_rank: Frequent Contributor
timestamp: November 18, 2016, 03:45:37 pm
content: Just based on what you have said, if service literature is available an experienced tech should have no problem. As a "newbie" my best advice would to take your time, consider the block diagram first, and BE CAREFUL, not just for obvious safety issues but to avoid further damage to the equipment, from probe slips, etc.Since you have indicated there is output but no display, I would look for whatever changing signal or data going into the display encoding section, not forgetting to look at power supply issues pertaining to that. Data signals "clamped" at a low level would be a clue also. I think it's worth a try!Good luck!

author: Matthematik
author_rank: Contributor
timestamp: November 18, 2016, 06:56:56 pm
content: Thanks for the great response. Regarding safety, I have found it difficult to find any sort of safety procedure for working on power supplies. Dave mentioned discharging using LoZ on a DMM but I'm not sure what I'm discharging. Is it the transformer? A certain capacitor?

author: PA0PBZ
author_rank: Super Contributor
timestamp: November 18, 2016, 07:06:13 pm
content: Quote from: Matthematik on November 18, 2016, 11:17:24 amAre you saying that there is an output voltage, just that the display stays at zero? Is it only the volts part that stays at zero, or does the amp part shows no current when you connect something up to the supply?In this case "be careful" means don't touch anything high voltage like the primary of the transformer when the supply is powered on and you want to measure inside.

author: PA4TIM
author_rank: Super Contributor
timestamp: November 18, 2016, 07:37:10 pm
content: Quote from: Matthematik on November 18, 2016, 06:56:56 pmIf that is your level of knowledge my advise is to first try something easy and study more before you try this repair.Dave is talking about capacitors. If they do not have a bleeder they can stay charged for some time. But most times you need to measure when it is powered on and in a SMPS the bulk caps can have a lot of energy. I was repairing a Tek scope. There was no service manual so I'm extra careful but not enough. From a USA brand scope I had not expected this dangerous construction without flashing lights and at least 200 warning stickersSo I touched the big heatsinks while measuring. That was no fun. It turned out they had 350VDC on them.

author: DaJMasta
author_rank: Super Contributor
timestamp: November 18, 2016, 07:43:58 pm
content: Quote from: Matthematik on November 18, 2016, 06:56:56 pmIf you're working unplugged:Generally, it's the high voltage main capacitor - usually the largest, highest rated one on the board. Depending on the power supply, there can be more than one, but the risk is the ones that store a lot of energy. Waiting several minutes and being certain that everything's unplugged go a long way as well. Systems won't hold their charge indefinitely (though there are some exceptions that discharge very slowly) and a lot of particularly slow or dangerous ones generally have a bleeder resistor or LED built in to show you, so when in doubt, give it a few minutes and things will get safer, at least.If you're plugged in:Don't try to discharge anything, as it should be charged when operating. This is where careful proving comes into play, since a slip can short something sensitive or connect to something that's not safe to be probing with your current settings. If your DMM comes with those little plastic caps that cover most of the pins, they can help with minimizing the risk of touching them accidentally or shorting them to something else.When I have the opportunity, I like using spring hooks when probing this kind of stuff - you power down, hook up the clips, then you can power up while they're connected and monitor things. Not suitable for every check and not nearly as quick, but you can make the risk really only be your equipment this way, since you don't actually have to be touching anything.Make sure your workspace is clear, the device is properly supported (not sliding around or at a strange angle), and minimize what you touch.

author: raspberrypi
author_rank: Frequent Contributor
timestamp: November 18, 2016, 11:03:42 pm
content: Quote from: Matthematik on November 18, 2016, 06:56:56 pmYou might be getting in over your head for a first repair, and not want to risk your money if you can still get your ebay money back.. After something is unplugged really the only thing that can zap you are the big electrolytic caps. If your are not sure what can zap you when its plugged in I would recommend you watch alot* more of the videos. The worst shocks are the ones you don't know about. The only time I have had a transformer that had voltage on it was this crazy potted cylinder step up 3 to 7000 volts transformer from china. I unplugged it and then touched the leads with pliers to be safe and saw a spark. I'm still not sure how it did that if its just a transformer, but glad I was safe.

author: Matthematik
author_rank: Contributor
timestamp: November 19, 2016, 03:34:39 am
content: Quote from: PA0PBZ on November 18, 2016, 07:06:13 pmIt seems to have full functionality with the exception of the display reading zero at all times. Yeah, I'm too much of a wuss/lacking in knowledge to poke around in this this while it's plugged in. I guess I won't get very far until I tackle that obstacle. I waited like 24 hours after unplugging to even open the thing up!Quote from: PA4TIM on November 18, 2016, 07:37:10 pmI figured as much but I'm just not clear on which ones. For now I will just discharge them all and will put more effort into researching this. Good story, I'll do my best to learn from that mistakeQuote from: DaJMasta on November 18, 2016, 07:43:58 pmI like this, will definitely take advantage of this strategy, thanks.So it looks like the seller just wants to give me a full refund so I'll be sending it back. I told them if they can't fix it and want to sell it as is that I would consider it. In the meantime I think I'll take the advise of a couple of you and work on something cheaper once I gain a little more know how. Thanks for all the input everyone.

author: PA4TIM
author_rank: Super Contributor
timestamp: November 19, 2016, 09:32:45 am
content: I made a page on my website with tips about how to repair test gear. (Myhobby and my job is repairing measurement- and calibration gear) :http://www.pa4tim.nl/?p=4776Before sending it back make it open for a good optical inspection. Maybe it is just as simple as a connector that is flapping in the breeze caused by the transport .