Video Teardown & Repair of a Stanford Research PS350 5000V DC Supply - Page 1
Forum section: electronics / testgear

author: Hugoneus
author_rank: Frequent Contributor
timestamp: July 12, 2015, 04:03:33 am
content: In this episode Shahriar repairs a Stanford Research Systems Model PS350 5000V-25W High Voltage Power Supply. The unit continuously displays 2.5kV without the output being enabled and produces no output voltage. Verification of power supply voltages reveals the issue is linked to a disconnected 15V voltage regulator IC. After the repair, the output voltage is verified with both positive and negative outputs. The principle operation of the instrument as well as the Cockroft-Walton high voltage generator is reviewed.Watch the video here: [40 Minutes]youtu.be/09otx2PfphwMore videos at The Signal Path:http://www.TheSignalPath.com

author: Lightages
author_rank: Unknown
timestamp: July 12, 2015, 07:34:40 am
content: Thanks again for the videos! They are always informative, to the point and well worth watching. Can I make one piece of constructive criticism? I know, I am not waiting for you answer!Almost all of your videos have a weird color cast that can be attributed to using auto color balance on your camera. This usually results in this strange color cast when florescent lights are being used. It would not be perfect but you could do a color balance while filling the screen with a white piece of paper first, or buy a white balance card made specifically made for this purpose. They aren't that expensive.The other thing is the use of auto exposure. One video it was tracking all over the place with reflections from the aluminum in the shot and then you blocking the light with your hand. Again, there are grey level cards that can be purchased for very little money to help set the exposure, and then lock it. You can also just do a exposure level setting with the back of your hand in the shot and then lock it. You might need t play a bit get what you like.So again, thanks for all the work you have put into your productions and sharing with everyone else.

author: peter.mitchell
author_rank: Super Contributor
timestamp: July 12, 2015, 07:38:24 am
content: To provide strain relief on the packages attached to the chassis you could mount the devices with the legs facing up, and then wire them point to point with some stranded wire down to the pcb.Usually the component legs are longer and are formed to provide strain relief in these kind of mounting situations.

author: TiN
author_rank: Super Contributor
timestamp: July 12, 2015, 07:49:12 am
content: I bet Dave is envy your easy repairsThis is getting a tradition.

author: BFX
author_rank: Frequent Contributor
timestamp: July 12, 2015, 02:33:47 pm
content: Lucky man ... again

author: Radio Tech
author_rank: Frequent Contributor
timestamp: July 12, 2015, 03:03:18 pm
content: Another great video and repair.I really like the way you explain things. I know you said this was your last repair and I hope you don't mean it was the final repair.Thanks for sharing.

author: Len
author_rank: Frequent Contributor
timestamp: July 12, 2015, 04:15:36 pm
content: I don’t mind that the problem was easy to find and fix because it was an interesting failure mode. Looking at the back of the unit, I noticed the bottom of the case was bent. It looks like that instrument has been knocked around quite a bit.Quote from: Lightages on July 12, 2015, 07:34:40 amOn the plus side, Shahriar has learned that Youtube success can be assured by putting a cat in every video.

author: Hugoneus
author_rank: Frequent Contributor
timestamp: July 12, 2015, 04:52:35 pm
content: Thank you all for your comments.I am hoping to get some better equipment for filming. I'll see what I can do in the meanwhile to improve color balance and exposure. Thanks for the feedback. So better exposure and more cats, got it.I have ordered an SHV connector and cable, I am eager for their arrival. It would be interesting to investigate some dielectric breakdown properties of capacitors.

author: HighVoltage
author_rank: Super Contributor
timestamp: July 12, 2015, 05:02:16 pm
content: You have a great way of finding faults and I learn something from each of your videos.Somehow I always need much longer to find the fault in a test equipment and fix it.Great high voltage power supply.I am looking forward to see some of your experiments with it.A big tank you for all your great videos.

author: c4757p
author_rank: Super Contributor
timestamp: July 12, 2015, 05:48:05 pm
content: Wow, that regulator/transistor mounting is really dodgy. I would definitely consider drilling a couple new holes a cm or so higher and connecting them to the board with short, flexible wires. They must have had alotof failures from that.

author: edpalmer42
author_rank: Super Contributor
timestamp: July 12, 2015, 06:22:56 pm
content: Quote from: c4757p on July 12, 2015, 05:48:05 pmActually, Shahriar should consider moving all three of those regulators. If the one that broke is moved, the next one in line becomes vulnerable. However, as Len mentioned, it looked like the case was bent or maybe just a foot was missing. If the unit was dropped (are there any mangled corners or edges?) that could have caused the transformer to shift violently and snap the regulator leads. If that was the case, maybe changes aren't necessary.

author: TheAmmoniacal
author_rank: Unknown
timestamp: July 12, 2015, 06:47:46 pm
content: Some capacitor experimentation could be very interesting!Run a series of comparisons between rated voltage and failure voltages (different brands?).See how the capacitor characteristics change over time the more they spark over (ESR, capacitance, dissipation factor, phase angle).See if they consistently spark over at the same spot or if it continues to burn holes in the dielectric.Explain why electrolytic capacitors are polarized and why they don't like having reverse polarity applied to them. Would also be fun to see if you could reverse the polarity of a capacitor (have it powered reverse-current limited for a long time).And if you got some precise micrometers (or calipers), examine the dielectric breakdown voltage of some substances and compare with table values. (PTFE, air, PE, HDPE, 'vacuum', etc.)(Just some ideas)

author: Mark Hennessy
author_rank: Frequent Contributor
timestamp: July 12, 2015, 07:04:24 pm
content: Rather than using short wires, I would consider forming a strain-relief loop in the leads of the replacement ICs (and consider replacing them all for the same reason. It might just about be possible to do that with the existing mountings, but new holes about 5mm higher than the current ones might be better.Do the threads belong to screws, or did they press threaded inserts into the aluminium side? If the latter, moving upwards becomes difficult.

author: TheSteve
author_rank: Unknown
timestamp: July 12, 2015, 07:16:46 pm
content: Shahriar - you have to start showing us the hard to fix stuff too! Hah, just kidding around, I really enjoy your videos. I think you've inspired many of us to hunt for the "good" broken stuff on ebay.Now when we can expect your cat to start helping with the repairs, maybe getting screwdrivers for you.

author: German_EE
author_rank: Super Contributor
timestamp: July 12, 2015, 07:54:32 pm
content: <sigh> my girlfriend wants to know what the cat is called, I think her priorities are elsewhere

author: PA0PBZ
author_rank: Super Contributor
timestamp: July 12, 2015, 08:01:46 pm
content: I wonder what the bandwidth is when using it as a voltage multiplier. I'm thinking way below audio frequencies seeing it regulate and thinking of all the caps in there.

author: Hugoneus
author_rank: Frequent Contributor
timestamp: July 12, 2015, 08:09:47 pm
content: Quote from: German_EE on July 12, 2015, 07:54:32 pmHaha... The cat's name is Pooch!

author: owiecc
author_rank: Frequent Contributor
timestamp: July 12, 2015, 08:15:02 pm
content: I have the same unit. We tested some film caps to see how they die. We put 5kV on a 1kV cap for a few minutes. There were some sparks inside but the cap survived. No apparent loss in capacitance.

author: Hugoneus
author_rank: Frequent Contributor
timestamp: July 12, 2015, 08:21:56 pm
content: Quote from: owiecc on July 12, 2015, 08:15:02 pmInteresting, I just tried a 250V foil capacitor with 1kV on it. Failed after about 30 seconds or so and became a short. Punch-through failure.

author: HighVoltage
author_rank: Super Contributor
timestamp: July 12, 2015, 08:43:09 pm
content: Some polypropylene capacitors have a self healing process.http://www.wima.com/EN/selfhealing.htmWith your new instrument, you should be able to analyze this behavior.Would be interesting to see how fast they recover.May be you can make this visible with a scope connected.

author: IanB
author_rank: Super Contributor
timestamp: July 13, 2015, 12:17:02 am
content: Quote from: Hugoneus on July 12, 2015, 04:52:35 pmI have to say I've noticed nothing that bothers me about the video quality. White balance, exposure, focusing, all seem perfectly acceptable. Even if they are not perfect there is nothing that intrudes or distracts from my enjoyment of the videos.

author: c4757p
author_rank: Super Contributor
timestamp: July 13, 2015, 12:33:26 am
content: Quote from: IanB on July 13, 2015, 12:17:02 amYes, this. Perhaps I could nitpick the video if I wanted to, but I would gain nothing from it being "better".

author: Lightages
author_rank: Unknown
timestamp: July 13, 2015, 12:37:17 am
content: Actually when he was poking around inside one of the instruments, the shiny aluminum was reflecting the light directly into the camera and causing the rest of the image to be very dark. As he moved his hand across the shiny aluminum the exposure would shift rapidly to good and then rapidly to underexposed again when he moved his hand away. The color balance is the typical green cast from florescent lighting too. I did not bring this up to be critical of his great work, but rather to suggest a way to make better quality for almost no effort.

author: IanB
author_rank: Super Contributor
timestamp: July 13, 2015, 01:06:04 am
content: It's odd, but on my screen the video seems to have a yellow cast. To check this I just sampled a few RGB values from some of the whitest things I could find in the video (like paper or white plastic) and they all were equally saturated in red and green (= yellow) and lacking in blue. None of my samples were lacking in red. Ho hum. Maybe color is in the eye of the beholder?

author: BravoV
author_rank: Super Contributor
timestamp: July 13, 2015, 03:47:03 am
content: Quote from: IanB on July 13, 2015, 01:06:04 amhttps://en.wikipedia.org/wiki/Tetrachromacy#Human_tetrachromats

author: Hugoneus
author_rank: Frequent Contributor
timestamp: July 13, 2015, 02:31:15 pm
content: The camera is set to indoor lighting, but the exposure is on auto.

author: Lightages
author_rank: Unknown
timestamp: July 13, 2015, 04:25:38 pm
content: Florescent lights are the nemesis of video. "Indoor lighting" assumes incandescent lighting of a color temperature around 3900°K and black body radiation spectrum. Florescent light are usually around 4400-4700°K and have peaks at some colors. This makes the image look yellow/green instead of normal. It should be possible for you to set the color temperature to florescent, or use a piece of white paper and do a manual white balance. This still won't be correct because white paper is actually a bit bluish but it will be much better than the mismatch with the color temperature settings you are using now.The auto-exposure issue is a bit fiddly to correct but not expensive. Set your seen up, make sure there are no specular reflections from the lighting and then lock the exposure. If you find the image to bright or dark, then if your camera has manual compensation control, but that up or down to get it closer to correct. If not, Stick your face on the scene and lock exposure on that. Again, it won't be perfect but better.The better way is to buy one of these. It won't break the bankhttp://www.bhphotovideo.com/c/product/101853-REG/Delta_22030_Gray_Card_8x10_1.htmland one of thesehttp://www.bhphotovideo.com/c/product/300868-REG/Porta_Brace_WBC_White_Balance_Card.html

author: Muxr
author_rank: Super Contributor
timestamp: July 13, 2015, 07:18:36 pm
content: So the first thing that caught my eye with this unit was how it wasn't sitting flush on the table. You'll notice the front left leg is lifted off the table. My guess is that it was dropped, and it's the most likely reason why the 15V regulator had its pins severed due to the transformer weight on that side.

author: MarkL
author_rank: Unknown
timestamp: July 23, 2015, 02:07:28 am
content: I was surprised you trusted the survival of your nice Fluke to a single 1G resistor at the input of the voltage divider.Perhaps that 1G resistor is rated for 5kV, but it doesn't look like it to me. I'd be worried about arc-over or internal breakdown.