Lab Power Supply restore - tips and advices please! - Page 1
Forum section: electronics / beginners

author: Ghitza
author_rank: Contributor
timestamp: May 30, 2021, 04:02:29 pm
content: Good day my dear members,I have a power supply that has been stored for over 30 years in a cellar. At first glance I noticed that the potentiometers are defective and the third channel outputs a maximum of 23-24 volts instead of -32V.The psu is a Systron Donner TL8-3. What I did first was to open and clean it very well. Than I canceled the "fine potentiometers" and I used only for "coarse variation" multi turn potentiometers from Vishay. There are no more variation variations of the output voltage when I turn the dial CW and CCW on all chanels but still I have the same issue on the 3rd channel.I proceeded to check further the capacitors.Normally the ESR value should be as low as possible for a capacitor as far as I know. I used the LCR meter DE-5000 and the frequency of 100Hz because being a linear source I think I do not have frequencies higher than 100Hz. However, at frequencies higher than 120Hz if I choose in LCR Meter, it does NOT even detect any value from the caps by what I noticed.Are those caps all OK? especially as you can see in the picture number 5 the 25V/4700uF it seems to have a little bit issues. I also checked them on the curve tracer from 1508-2 oscilloscope as you can see.What I did further? I charged this 3 power caps with current and I discharged them and they seems to retain a lot of curent.Should I anyway all of them replace with new caps? Also should I replace all the other unpolarised caps for safety or what dou you recommend me to do?Also those power resistor are OK or the get degraded with time?Thank you very much.

author: Refrigerator
author_rank: Super Contributor
timestamp: May 30, 2021, 05:39:15 pm
content: A quick google search leads to a user manual with maintenance info and a full schematic.http://bee.mif.pg.gda.pl/ciasteczkowypotwor/Systron%20Donner/Systron-Donner_TL8-3_Series_Stabilized_Triple_Power_Supply_InstructionManual.pdf

author: Ghitza
author_rank: Contributor
timestamp: May 30, 2021, 06:04:38 pm
content: Quote from: Refrigerator on May 30, 2021, 05:39:15 pmThanks for your reply but my demand is related to those caps if they are good or not and if I should keep those or to replace with new ones.I already have the user and service manual for it.Since I'm a biginer in this filed because it is more like a hobby for me, I don't know a lot of tips and tricks. I also searched the datasheet for those caps to compare the details with what I have measured to see if they are good or not but I didn't found.Are those good to be reused or not? At the moment they are removed and I will buy new ones if someone can confirm that they are damaged.After is clear for me with the caps, than I'll continue further.Thank you very much.

author: Refrigerator
author_rank: Super Contributor
timestamp: May 30, 2021, 07:36:18 pm
content: If you can't find the exact capacitor datasheet, often you can just compare your results to capacitors with similar specifications.For example, a 4700µF 25V cap from united chemi-con has a 0.016 Ohm ESR.This axial 4700µF 25V capacitor here is similar to what you have:https://eu.mouser.com/datasheet/2/88/TTA_series-552998.pdfAnd has 0.085 Ohm ESR - same as yours.Also notice that most capacitor datasheets are just tables to fit specs for the entire series.Most caps have 20% tolerance and your 4700µF cap is only 12% over so i think it's still good to use all things considered.High capacitance can also be an indicator of high leakage current.You can use websites like octopart to search for components by their parameters and find their datasheets.

author: cyp_eev
author_rank: Contributor
timestamp: May 30, 2021, 07:43:33 pm
content: I would replace those 50+ years old caps. They are very failure prone!

author: Ghitza
author_rank: Contributor
timestamp: May 30, 2021, 07:51:39 pm
content: Thanks for the reply guys. I'll replace all the polarized caps. One more thing: what about those unpolarised caps? Should I also those replace or it is OK with them?Best Regards!

author: cyp_eev
author_rank: Contributor
timestamp: May 30, 2021, 08:05:48 pm
content: If there are some paper caps they should also be replaced.The ceramic and mica caps should be ok.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: May 30, 2021, 08:23:23 pm
content: Unless you're really just want to fix it, I'd get something like this. You'll probably save in the long run. Hook it up to an old laptop to get the most out of it. (Or tablet perhaps if you can do some programming.)https://www.amazon.com/dp/B06XCQN82X/ref=cm_sw_r_cp_apa_glt_fabc_K4YK8V4FFQW43BBE3R1Y

author: Refrigerator
author_rank: Super Contributor
timestamp: May 30, 2021, 08:42:27 pm
content: Quote from: Ghitza on May 30, 2021, 07:51:39 pmThe only unpolarized caps that should be always replaced are waxpaper caps but i don't think you'll have any of those here.Those are mostly in old vacuum tube gear.Look out for RIFA capacitors in mains filtering circuits, you find them often in HP gear and they will burn up (and make a huge stink).Electrolyte in electrolytic caps can leak out, dry out or go bad, be it from age or bad chemistry.You can check out capacitor plague if you're interested about the latter.In old gear electrolytic caps are often changed all at once without testing, this is called recapping.Polyethylene capacitors are completely inert, there's nothing that can go bad in them, other than damage from high voltage breakdown.Same for ceramic, polypropylene, mica etc. These caps are all fine.Tantalum caps let you know when they go bad.