1. Time for some upgrades in server hardware and software to enhance security and take AK to the next level. Please contribute what you can to sales@audiokarma.org at PayPal.com - Thanks from the AK Team
    Dismiss Notice

why a recap makes no difference

Discussion in 'Solid State' started by yotems, Feb 7, 2018.

  1. leesonic

    leesonic Hold on, here comes the bass. Subscriber

    Messages:
    4,647
    Location:
    Southern NJ
    Modern caps are physically smaller than older ones, that's just progress.

    Mouser states quite clearly on their baggies where the capacitors they sell come from. Nichicons that I use tend to be made in Japan or Malaysia.

    Lee.
     
    yotems likes this.

     

    Please register to disable this ad.

  2. leesonic

    leesonic Hold on, here comes the bass. Subscriber

    Messages:
    4,647
    Location:
    Southern NJ
    This part is very true. Just replacing the caps is time consuming enough. Add to this the time taken to physically get access to the boards in order to change them. And there's all the other work involved when doing a restoration. I've had "restored" units sent to me for repair where the other party never removed the output transistors to replace the old dried out heatsink grease. Or made no attempt to check the bias, since the original captive resistors were still fitted instead of the trimmers that I fit.

    Lee.
     
  3. quaddriver

    quaddriver 120 What's per channel Subscriber

    passes the white scarf test with flying colors.

    I know, I owned 3 of them and racked up a half million miles on them. One was even white. the invisible odorless colorless Nox emissions however....(which was a total BS standard for a D, but I dont make the rules)
     
    yotems likes this.
  4. drumbum

    drumbum Super Member

    Messages:
    1,207
    Bias is one thing, but I don't think renewing heatsink paste is needed.
     
    steveUK likes this.
  5. Hyperion

    Hyperion Roobarb & Custard Subscriber

    Messages:
    47,290
    Location:
    Hertfordshire, UK
    Yes it is, I would consider myself negligent if I did not do this for every restore I do.
     
  6. steveUK

    steveUK AK Subscriber Subscriber

    Messages:
    488
    Location:
    Midlands, UK.
    Is that backed up data, not personal opinion? A link to proper, lab or manufacturer based test results or recomendations would be good. Otherwise, like lots of stuff on here it's just 'an opinion'. That's not to say that peoples' opinions are not worthy of consideration, but true data is much better.
     

     

    Please register to disable this ad.

  7. Hyperion

    Hyperion Roobarb & Custard Subscriber

    Messages:
    47,290
    Location:
    Hertfordshire, UK
    Just an opinion I suppose, but in order to inspect the original stuff has been applied correctly, I have to take the semiconductor device off, then it is obvious that the best thing to do is replace the old compound. It can have been unevenly applied, or simply have been made a total mess by someone, who may have replaced semiconductor devices before - and not changed it then. So I always re-do it - neatly and correctly, rather than guessing it is OK.... make sense?

    Do I need to go into detail about how important the proper contact of semiconductor (and other) devices with their associated heatsinks is? i.e. too much compound, not enough, or voids due to poor application.
     
    Last edited: Feb 10, 2018
    Multimode, RTally and yotems like this.
  8. leesonic

    leesonic Hold on, here comes the bass. Subscriber

    Messages:
    4,647
    Location:
    Southern NJ
    I've seen too many amps where the grease has just dried out. And what happens in that case? Someone buys an amp from a charity shop or eBay, turns the volume up, the transistors can't conduct the heat away to the heatsink and BANG!

    Stuff like this, replacing trimmers, death diodes and black leg transistors, adding heatsinks to hot running TO220 transistors, upping the wattage value on dropper resistors, replacing fusible resistors... all this goes towards doing the job properly, and separates those that care about their work from the also-rans. It's also why I offer a years warranty on my work.

    Lee.
     
  9. sssboa

    sssboa Well-Known Member

    Messages:
    623
    I don't know what's about that rising esr with time. Or maybe we do not measure it correctly.

    I have recapped now over 10 units from the early 1970s and I am still to find a capacitor bigger than 10uF with ESR higher than say Nichicon PM equivalent. I found 1uF and 3.3uF Elnas which were in 4ohm territory, 10uF in around 2.5ohm. All bigger caps than 10uF measured better esr than new Nichicon PM which are considered low esr by today standards, there are ultra-low esr caps like Panasonic FM/FR, Nippon KZL or Nichicon HW/PX which beat the old caps on esr just slightly.

    I found so few suspicious caps in those old units that I remember each of them, it's crazy.
    1. high ESR Elnas of 1uF/25v, 3.3uF/35v and 10uF/16v in tone and power amps of Marantz 2270
    2. one Nippon 47uF/80V with high voltage leak of 50% in Yamaha CR-800 power supply
    3. Nippon filter caps 6800uF-18000uF with 60-70% of capacitance in Yamaha CR-800/CR-1000/CA-1000/CA-1010 but still had excellent ESR like 0.02ohm.
     
  10. restorer-john

    restorer-john Addicted Member

    Messages:
    6,256
    Location:
    Australia
    The heat transfer compound functions perfectly well whether it is dried out or not. It is the heat conductive fillers in the compound that perform the transfer of heat, not the silicone grease. It is merely the carrier.

    The problems you describe occur if there has been considerable differential expansion/contraction between the device and the heatsink with resultant loosening of the mounting hardware, all of which creates a less intimate contact between the mating surfaces.

    As Hyperion said, you can't inspect it without dismantling and it can't be re-used so it must be replaced.

    Some brands (Marantz) used virtually no heat transfer compound on some early gear, or the compound was very poorly applied so it is always prudent to inspect, clean and replace heat transfer compound. That said, there are instances where possible damage or package stress to unobtanium output devices can result from dismantling (multiple paralleled, wire-wrapped, TO3s on double sided boards, etc) and inspection is sufficient.
     
    Last edited: Feb 10, 2018
    Hyperion, steveUK and yotems like this.
  11. Eastham

    Eastham More Class-A than ever!

    Messages:
    2,165
    Location:
    North West UK
    This whole argument is like religion or politics, you can argure 'till you're both blue in the face but nobody is going to change their opinion. Personally I like re-capping, it's the tedious kinda thing I enjoy and it makes me feel like I'm making a difference, even if I'm not. On the topic of thermal grease, I've had several old computers that show a significant differance in tempratures when replacing the old, crusty, dry thermal compound.
     
    slimecity likes this.

     

    Please register to disable this ad.

  12. Sriskie

    Sriskie AK Subscriber Subscriber

    Messages:
    745
    Location:
    Kingston, On
    I always replace the thermal compound but have often wondered about the clear Vaseline type grease. It never seems to be dried out...
     
    Oldsansui441 likes this.
  13. gslikker

    gslikker Super Member

    Messages:
    2,114
    Location:
    Close to Alkmaar, Netherlands
    Sometimes "new" thermal grease looks too old and thick already, myself I added some DC4 electrical compound when having the impression compound was too "thick".
    Of course, it was guesswork.
    Now member Eastham concludes progress as his computer chips measure temperature. For amps, a temp probe on a multimeter can help to measure differences, myself I have a Fluke 62 for that which performs "reasonably well" if the parts to be checked are not too small.
     
    Last edited: Feb 11, 2018
  14. Hyperion

    Hyperion Roobarb & Custard Subscriber

    Messages:
    47,290
    Location:
    Hertfordshire, UK
    That's 'Silicone Grease' I don't think its heat transfer properties are as good as the 'white stuff' - but it probably lasts longer.
     
  15. steveUK

    steveUK AK Subscriber Subscriber

    Messages:
    488
    Location:
    Midlands, UK.
    Like many aspects of restoration, a lot of these things are down to the individual; and how far they want to go, or to get the set working and/or looking good, how far they need to go. Often it's a case of how 'happy' someone feels about the final job. But what no-one needs - whichever camp they sit in - is someone 'from the other side' telling them what is right and what is wrong. Unless of course there is real, objective proof to the contrary. Someone just saying that the difference "is like night and day, loads better" means nothing, as you get all sorts of people on forums and some of them 'talk the talk', but in truth don't have the knowledge, ability or experience to substantiate what is only a view, an opinion. And then there are people with vested interests in a procedure. So it's a melting pot of opinions, no more, unless it's irrefutably substantiated.
     
    malden likes this.
  16. ic-racer

    ic-racer Well-Known Member

    Messages:
    850
    Location:
    USA
    Without factual data the argument for capacitor replacement is opinion at best.
    Here is a frequency response curve of a 1990s speaker with new capacitors. No benefit to replacement.
    Alesis_response-before_and_after-recap_Page001.jpg
    This capacitor still was working!! However it leaks hot gas from a hole in the polypropylene. Yes benefit to replacement.
    bad capacitor.jpg
    These capacitors look OK but measure 0.6 to 0.5, in spite of markings 0.22. They are from a vintage Les Paul guitar that "Sounds Good."
    ??? Replacement ??? (I put them back in the guitar).

    file-763.jpg

    These capacitors had already been removed for other repairs (glue cleaning). I did not bother to test them, the pragmatic decision was replacement with new items of equal or better specs.

    Screen Shot 2018-02-11 at 11.03.33 AM.png
     
    Last edited: Feb 11, 2018
    steveUK likes this.

     

    Please register to disable this ad.

  17. ConradH

    ConradH Addicted Member

    Messages:
    7,857
    Location:
    Canandaigua, NY
    You can't tell by looking if the thermal connection between transistors and their heat sinks is good or not. IMO, the job isn't done if you don't pull outputs, clean everything, re-grease and torque to spec. That last one is important and people usually over torque the hardware. Understand that thermal grease comes in various degrees of bad. Yes, it's a horrible thermal conductor compared to metals. The only reason it works is because its used in as thin a layer as possible. This is not a case of more is better. Comparing some numbers, all conductivities in W/(m•k):

    1050 Aluminum (used for heat sinks) 229
    Steel 50
    Aavid Thermalcote 0.765
    Dow 340 0.67
    Vaseline 0.18
    Silicone oil 0.157
    Paraffin wax (varies) 0.23

    Clear unfilled greases, be they silicone or petro aren't going to be very good. In their favor, they probably squeeze to a very thin layer. The base oil of silicone grease isn't very good. The filler in thermal grease makes it better, but I'm not sure how effective it would be dry. My guess is it takes some minimal amount of oil to couple the particles, but that amount might be just a trace. Thus, even thermal grease that looks dried out might still be doing most of its job. I don't know, so I replace it. For less mess and maybe a slight improvement in conductivity, I like the Aavid Ultrastick. It's a filled wax that actually melts under hot semiconductors, giving as small a gap as is possible. Unfortunately, it's quite expensive. The well known silicone greases that have been around for decades probably have accurate thermal conductivities. Newer companies making claims that are vastly better should be viewed with suspicion until other sources confirm the numbers. If the grease layer is as thin as it should be, the actual numbers may matter less then you'd think.

    From the above you can calculate temperature rise in degrees C/W for a given thickness. Then you can compare to something like a Silpad. You'll probably find the better (expensive) grades of Silpads are pretty good, but grease will beat the cheap grey ones.
     
  18. Hyperion

    Hyperion Roobarb & Custard Subscriber

    Messages:
    47,290
    Location:
    Hertfordshire, UK
    Not everyone knows where to find, or could be bothered to post here after being queried, 'irrefutable substantiation' of everything they do during a vintage audio restore. ;)

    But as you can see, my suggestion that I think it good practice to always replace heatsink compound, has found agreement from highly experienced members here - that to me is 'irrefutable substantiation' enough. :) (I probably learnt it from them in the first place!).
     
    Last edited: Mar 22, 2018
    roger2 likes this.
  19. gslikker

    gslikker Super Member

    Messages:
    2,114
    Location:
    Close to Alkmaar, Netherlands
    Although I took apart the whole amp for a refurb instead of troubleshooting the cause of some failure (which included the transistor mounted on the bad spot), the following is "proof" the practice of replacing the grease also prevents overlooking the fact a heatsink may not be flat :D:D:D
    See the "hill" of some 0.3 millimeters which was hidden below a transistor at middle of picture, before it was filed and sanded away.
    So before applying the grease, make sure the heatsink is flat ;) (another opinion).

    [​IMG]
     
    roger2, Hyperion and Oldsansui441 like this.
  20. Eastham

    Eastham More Class-A than ever!

    Messages:
    2,165
    Location:
    North West UK
    Plus I don't really see a downside to re-capping. Besides spending a little mula and a bit of your time. Any chances of problems arising from capacitors failing become nullified.

    Holy... How does that even happen?
     

Share This Page