So You Want To Repair Audio gear, Eh? Here's the tools you need...

Discussion in 'DIY' started by EchoWars, Nov 16, 2010.

  1. SaturationPt

    SaturationPt AK Subscriber Subscriber

    Messages:
    1,196
    Location:
    N.E. Indiana
    The grounding varies by equipment. Things to remember are:

    > Some (mostly high-end consumer and pro equipment) pieces are chassis grounded to earth ground, some of these have a ground-lift switch and some not. If the equipment is powered from a two-prong cord, there should be no connection between either the ground, hot, or neutral and the equipment's chassis. The power should go to the transformer where it is isolated even if one of the transformer outs is grounded.

    > Even if you have isolated your ground either via the normal non-grounded equipment or an isolation transformer, there are still voltages in your equipment that can harm or kill you. This is more in tube gear (600v or so) and in higher-power SS gear (80vdc-up) so IMO this sketch above is nothing more than false security that can lead to carelessness and a shock.

    You need to take the same precautions in servicing powered gear whether it's on an isolation transformer or not, good safety practice is required either way.

    As far as protection for the equipment, if you plug your scope and the equipment being tested into the same isolation transformer it seems that you haven't prevented the potential for damage from accidental grounding of the scope to the wrong part of your equipment.

    I have an isolation transformer, but it's too large and noisy to be convenient so I do not use it, never really saw a need, just remain careful.
     
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  2. H2ohm

    H2ohm Member

    Messages:
    78
    Location:
    Canada
    Jeff,

    So, when you are using your scope, you have to make sure you do not cross the leads or I mean put the positive onto say somewhere that needs to have the negative probe on right? Otherwise, you short your scope and damage both unit and scope is that correct?

    Buying the isolation transformer is a bit of a waste as the currents are still nasty inside! Should get a badge with that logo! LOL

    I want to test these relays to see if they are bad in my Pioneer A676. What I have done was test all the resistors and all are fine except 2 that are in parallel to some bare-wire looking coils which according to the schematic are on the negative side of the relays.

    What I did was I deoxit my spkr selector switch but I had the power on working it back and forth, but the volume was very low. I thought this was okay as I kept hearing the relays click, but then they stopped. Another person on here said that there should be no major damage as the volume was low (I did not have any speakers hooked up yet).

    The switch is now junk, it is so loose that you barely notice it click in place for Off/A/B/A+B so I ordered those.

    I appreciate you input on this subject as it seems confusing on which gear to buy to have a budget bench for learning stuff. I have a Hitachi 100mhz scope like new and fully calibrated by the guy I bought off 10 years ago. I have a great multimeter that tests caps, that hFE, diodes...I later will buy the ESR by Peak (Purple case one). I need a signal generator I believe and a variac? I know about the 'dim bulb' thing I will build that soon and there is a neat probe using a cap and nail and a mono cord where you just touch components in say a GX-700 Boss and it gives off a beep, but you need a Radio Shack Amp/speaker which I cannot find and do not know another alternative I could use...all this to come but for now, I am repairing a good sounding amp and do not wish to further create more issues.

    I am hoping it is those two resistors that are shorted are the only damage done (100 ohm / 1W: R901 and R902) they run parallel to inductors/coils??

    upload_2018-4-12_8-34-49.png

    Thanks for the input!
     
  3. SaturationPt

    SaturationPt AK Subscriber Subscriber

    Messages:
    1,196
    Location:
    N.E. Indiana
    Most vintage gear has the signal ground tied to the chassis, some through a cap and some directly. When I'm chasing signals through a circuit I connect the scope ground to the chassis or to signal ground, and nothing that I touch with the probe is going to damage my gear as it is isolated and the probe is designed for the voltage (I believe mine are 600v), the greater risk is that you cross two traces or pins with the probe and short something.

    The easy way is to replace your scope with a nice handheld, which doesn't even plug in, ...

    Your Pioneer troubleshooting should be in its own thread, you will get more answers in the Pioneer forum.
     
  4. H2ohm

    H2ohm Member

    Messages:
    78
    Location:
    Canada
    Thanks for that info. Yes I forgot this is all there I did not know that I could not follow up here so I will try to remember the rules on AK. Well off I go to try to find more stuff and gear!
     
  5. Bill Ferris

    Bill Ferris Super Member

    Messages:
    1,648
    Location:
    NE. FL.
    I`ll throw in a few things..
    I find the Leader LAG-126S audio sig. gen to be an excellent inexpensive low distortion sine wave+ square wave signal source, and when coupled with the Leader LDM-171 THD +N distortion analyzer can be bought used inexpensively(when found on eBay) measure down to below .01 THD with auto null below 1%..

    I bought my first set brand new in 1992 for my second bench, because I couldn`t financially justify duplicating my Tek 500 series very low distortion(.0009 % sig. gen./ THD+N/IMD Dist. test set that I was using on my main bench since it was purchased new in 1987.

    I find those two Leader instruments an excellent value, both in quality, flexibility, and performance, so much so, that I tracked down both Leader units on eBay and purchased for day to day use on my main bench, thus saving the Tek. units for IMD & very low THD+N certification when necessary.
    I also think the world of the Fluke 45 bench/portable dual display DVM as another very versatile and highly accurate daily bench meter for audio work, in which I also bought my first brand new in 1992 for bench # 2 ,and about 5 years ago used on eBay, when my 1990 Sencore DVM began acting up, so I found a very clean 45 on eBay for very low money and purchased it.

    Checked it out on all functions with precision resistors, voltage, current, freq. sources(yes, it even has a very accurate freq. counter function !), and compared it to my original 45, and all was with in factory spec.

    As to test equipment grounding, in my case, working on/testing all types of audio gear, from grounded, to non grounded gear, high/low gain, I have found it`s best to float all grounded test equipment plugged in to a grounded filtered/spike/surge protected metal power strip, and put ground lift "cheater`s" on each test equip`s pwr. plug, and use a 12ga. very flexible rope wire with a heavy duty alligator clip connected to my grounded variac for a common ground reference, with the same type ground wire for each piece of test equip`s ground post, which sometimes need to be also clipped to the gear under test, especially high gain audio gear, to avoid troublesome increased noise when doing S/N+ THD/IMD measurements with various combinations of ground connections for best results.

    And a couple of years ago, I decided to upgrade both benches with a Trippe lite 15 amp 120 volt line regulators, & a 120 volt line isolator transformers for the test equip only, for improved line noise rejection, and performance during summertime , or when I`m on my whole house generator mains low voltages, plus one switch shuts off the benches test equip/solder /de-solder station.

    Oh, and I find locking(like vise gripe style) long nose pliers very handy for me, where hemostats are not strong enough.
    And I quit buying in the early nineties, quality Xcelite replacement screw drivers as I wore them out repairing 17 hours a day, and just now I use a magnetic 1/4" socket replaceable bit driver & buy all the bits I need, including any security types, except for clutch type, in which I bought a full set of Stanley clutch drivers, when I was brought a Ampeg guitar/bass amplifier for repair many, many years ago.
    And I`ve found the line of Peak testers very handy for quick evaluation, with my 1991 purchased/ Sencore LC-102 for more complete cap./inductor/SCR/Triac checking/testing at their rated voltages.

    And my B&K 520 transistor checker for more detailed/critical and complete evaluation/matching @ higher voltages than my Peak tester/s, but of course this test equipment level is not necessary for the hobbyist , but sure increased my repair confidence/turn around time, when churning out the repairs, and have paid for themselves many times over.. :thumbsup:

    Anyway, enough noise from me !! :blah:

    Take care folks.

    Kind regards, OKB
     
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  6. bobva

    bobva AK Subscriber Subscriber

    Messages:
    436
    Location:
    granite falls washington
    Ok Im sorry but I got to ask after all no such thing as a dumb question.

    What is a signal generator for? I've watched a few vids on u-tube and none has explained what is for except for showing the how the functions a oscilloscope controls work.

    Sorry for my ignorance how does it fall into repair of audio or anything for that matter.

    edit=====================edit==================edit===================edit===

    Never mind I finally found a video that kind answers the above



    Now it make a bit of sense
     
    Last edited: Apr 15, 2018
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  7. Paul Mills

    Paul Mills New Member

    Messages:
    1
    Location:
    Melbourne
    Wow! that is a large list but necessary if you intend to make profit out of your work.
    I'd be happy with the signal generator and the oscilloscope, i'm doing just basic D.I.Y. guitar pedals and amps, and have repaired some small amplifiers that had simple flaws. I'd like to see the output signal of my pedals and learn how to measure gain and noise floor, this is really interesting for me!
     
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  8. oldman55

    oldman55 Well-Known Member

    Messages:
    777
    I know I'm late to the game here and apologize for the hijack but as new equipment is constantly changing…. would this type of signal/function generator have the accuracy and functions required for a distortion analyzer? Not taking reliability or quality into consideration, just specs.

    https://www.ebay.com/itm/FY3200S-24...e=STRK:MEBIDX:IT&_trksid=p2055119.m1438.l2649

    Also looking for a minimalist digital stand alone oscilloscope with a small footprint for basic audio troubleshooting on occasion to use with this type unit.


    Help is always appreciated...and needed - oldman
     
  9. Bill Ferris

    Bill Ferris Super Member

    Messages:
    1,648
    Location:
    NE. FL.
    You see Skitz, I know this is dated reply by me to you, but this is what I was referring about your unexpected off the cuff response to a/the on going thread that has me laughing, as I stumbled across it !!

    Mr.thread T-bone..(unexpected humorous interjection into the on going thread!)..
    Hey, maybe I can easily be entertained by your unexpected, at least by me, humorous post/replies.
    Again, I do enjoy..
    Take care.
    You may ignore me, if you wish Sir.
     
  10. sKiZo

    sKiZo Hates received: 8642 Subscriber

    My work here is done then.

    (And please don't call me Sir ... save that for the old folk and people who sign your paychecks) ;-}
     
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  11. Bill Ferris

    Bill Ferris Super Member

    Messages:
    1,648
    Location:
    NE. FL.
    As you see fit
    Sorry about the Sir. then.
    It`s just a residual of respectfulness from my Southern upbringing, even to men younger than me, and I`m 63.

    Take care sKiZo.

    Kind regards, OKB
     

     

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