Replacing Capacitors - Best Practice? - Page 1
Forum section: electronics / beginners

author: Robbie010
author_rank: Contributor
timestamp: March 07, 2023, 10:59:47 pm
content: Hello all,I’m currently trying to revive an old turntable (Pioneer PL-61) and decided to replace the near on 50 year old electrolytic capacitors as part of the refurbishment process as the speed stability was way off.Having got hold of a schematic - but no no layout drawing - I had a good look over the PCB to try and work out which cap is which and noticed straight away that the existing capacitors do not match those stated on the schematic, in some cases they are wildly different. I’m pretty sure that the existing caps are original factory installed but I’m now questioning whether to proceed with the recap on a like for like basis or follow the schematic.What would be best practice in this scenario?Thanks in advance.

author: thm_w
author_rank: Super Contributor
timestamp: March 08, 2023, 01:35:03 am
content: It could be a schematic for a different model, or a different hardware revision.What value does the schematic show and what value was on the board?Would be safer to go with what was on the board if it was already working.

author: RoGeorge
author_rank: Super Contributor
timestamp: March 08, 2023, 02:25:48 am
content: I'll replace them with what's on the PCB, who knows how many versions of schematics might be out there.

author: james_s
author_rank: Super Contributor
timestamp: March 08, 2023, 02:47:01 am
content: This is pretty common, production changes occur and a manual may not get updated to cover newer versions. I would replace them with the same values that are used on the PCB.

author: nigelwright7557
author_rank: Frequent Contributor
timestamp: March 08, 2023, 04:03:35 am
content: The caps should have values written on them.Just change all the electrolytics and you should be good to go.Just take care with polarity.

author: DimitriP
author_rank: Super Contributor
timestamp: March 08, 2023, 04:21:09 am
content: QuoteIf you want to replace the caps so you can call it "refurbished" that's fine.If you want to fix the speed instability make sure you superclean the speed adjustment pots.

author: Robbie010
author_rank: Contributor
timestamp: March 08, 2023, 08:40:00 am
content: The turntable was of limited production between 1972 - 1975, I’m not aware of any varying versions of it i.e. no mark II or mark III, it was simply supplied with or without a cartridge / stylus.Having had a good look over the pcb, the only thing that differs from the schematic is the electrolytic capacitors. There are 10 in total, 5 or which differ from the schematic. 4 of the ones that do match (C209 - C212) are directly coupled to the main transistors.Cap. Sche. InstalledC201. .47uf/50v 2.2uf/50vC202. 1uf/10v 3.3uf/25vC206. 1uf/16v 1uf/50vC207. 47uf/16v 4.7uf/25vC208. 10uf/16v 100uf/16vC209. .47uf/50v .47uf/50vC210. .47uf/50v .47uf/50vC211. .47uf/50v .47uf/50vC212. .47uf/50v .47uf/50vC213. 33uf/25v 47uf/25vEvery single one of the caps measured more than 20% outside of its stated spec, a couple showing signs of leakage were 70 - 80% out of spec.One theory that a friend suggested is that the actual capacitance of the wrong caps may not be critical to correct function and the only ones that matter are the ones that are coupled to the transistors, C209 - C212 which were as per the specification.

author: Vovk_Z
author_rank: Super Contributor
timestamp: March 08, 2023, 08:44:31 am
content: Quote from: Robbie010 on March 07, 2023, 10:59:47 pmTo make it best some need to analyze schematics. Some caps (in the sound lines) mustn't be changed and it better leave those as on the PCB. Some of them (typically in the power lines) can vary greatly.In general, typically, we can increase the capacitance of almost all electrolytes in an audio device (with an improvement or not), but sometimes that may make sound worse but not better (e.g. when we extend the sound range to low frequencies too much).Oh, if it's turntable so it doesn't have many audio circuits inside but rather has some speed control circuits. It everything with a speed is fine then soldered capacitance values are possibly fine.

author: EPAIII
author_rank: Super Contributor
timestamp: March 08, 2023, 09:00:10 am
content: If there is a speed problem, after replacing the caps and before worrying about cleaning any pots, I would clean and properly lubricate all the mechanical parts. Oil and grease can dry up, leaving something like peanut butter behind.PS: WD-40, while great for many things, like cleaning mechanical parts, is NOT a very good lubricant. You can use it for cleaning, but alcohol would work too. When used as a lubricant, WD-40 can TEMPORARILY dilute and re-flow old, dried up oil or grease so it seems to work. But then it evaporates leaving you back where you started with dried up lubricant. Get some real lubricant like LPS-1 (one of the best) or 3-IN-ONE or a similar type. Don't use motor oil due to the additives.If you do then need to clean the pots, I recommend DeoxIT D5. But I would not spray anything into any pots unless I definitely know they need a cleaning. And be absolutely sure there isn't anything around that the cleaner can pick up and carry into the pot. Introducing contaminants is a lot easier then removing them. Soldering flux can be a real problem and old PCBs often have flux that was not cleaned off (cleaning costs money).Quote from: DimitriP on March 08, 2023, 04:21:09 am

author: Robbie010
author_rank: Contributor
timestamp: March 08, 2023, 09:47:29 am
content: Thanks all.I’ve already done a full service, every pot has been thoroughly cleaned using D5 multiple times, both the motor and main spindle have been stripped, cleaned and re-lubricated. I’ve also installed a new belt and thrust bearing.There are no mechanical faults with the turntable, no play in the bearings, no abnormal wear, it can only be an electrical fault.The deck, although belt driven, has a servo controlled Hall motor, which I assumed would be quite sensitive when it comes to the components of the main speed control PCB, so in the first instance I think I’ll stick to the specs of the schematic and if that doesn’t do the trick I’ll re-cap again with the values I found in the board.

author: JohanH
author_rank: Frequent Contributor
timestamp: March 08, 2023, 11:16:01 am
content: You can use higher value voltage rating for replacement capacitors, because this doesn't matter for the functionality of the capacitor (other than makes it more resistant to damage) and might make it easier to find correct capacitance value in a given capacitor size and leg spacing. In general, modern capacitors have shrunk a bit in size.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 08, 2023, 12:10:53 pm
content: Many of the electrolytic capacitors are not that critical in value and they usually come with quite some tolerance anyway (e.g. +50/-20%). There may be a very few to set the speed of a control loop that can be a bit more relevant.It in doubt the values installed from the factory is the usually the better choice.With a schematics at hand it would be easy to see which capacitors are just supply filtering and thus not critical with the value.

author: Robbie010
author_rank: Contributor
timestamp: March 08, 2023, 01:05:19 pm
content: See attached.

author: Robbie010
author_rank: Contributor
timestamp: March 08, 2023, 01:06:14 pm
content: Sorry, see schematic attached above.

author: james_s
author_rank: Super Contributor
timestamp: March 08, 2023, 06:36:07 pm
content: At a glance, most of those capacitors look like they're coupling (DC blocking), the capacitance is not critical at all for that application so they might have just used whatever they had on hand. Electrolytic capacitors have rather loose tolerances and are typically used for filtering and DC blocking where the exact value is not important.

author: Robbie010
author_rank: Contributor
timestamp: March 08, 2023, 07:38:21 pm
content: Thanks.I put the new capacitors in the board today and while there was a definite improvement it’s still not as stable as it should be. I then realised that there are four or five 50 year old caps in the power supply board, which I had completely ignored.Will replace them too and see how I get on.

author: opabob
author_rank: Contributor
timestamp: March 20, 2023, 05:50:33 pm
content: Quote from: nigelwright7557 on March 08, 2023, 04:03:35 amI like to refurbish older ham radios. Kenwood TS-830, C-80 on the PLL board the polarity mark on the PCB is wrong, and that wrongness is supported by the schematic. It's when you dig deeper into the schematic that you see that it is connected to a (-) supply, and the cap is correct AS INSTALLED.https://forums.qrz.com/index.php?threads/ts-830s-capacitor-polarity.462406/