Pioneer SA-7500 repair (a new one)

Discussion in 'Technical Repair' started by PioneerVenusia, Nov 11, 2017.

  1. PioneerVenusia

    Thread Starter New Member

    Nov 11, 2017
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    Hello everyone. I am new to this forum.
    I know there is already a post about this amp but i decided to open a new thread cause I have a slightly different problem and also i have less knowledge than other OP.

    The problem is when i turn on rhe amps the rely kicks in but sometimes it kicks out or even not kick at all.
    A weird thing is that when i rise the volume something kicks and than i start to hear music coming from the amps itself.

    I have no idea on where to put my hands but i have a friend with all the tools to solve the problem if it’s possible.

    Can some of you tell me what and how to check?!
    Thank you!
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    Last edited by a moderator: Nov 12, 2017
  2. JoeJester

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    What test equipment do you have ?
     
  3. PioneerVenusia

    Thread Starter New Member

    Nov 11, 2017
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    Some electric testers and an oscilloscope!

    I have watched a video on youtube about a restoration of this amps and he mostly usef those instruments.

    If i need something more i can find it unless is something too specific.

    By the way i found that the problem could be related to some transistor (img in the attach) should i procede to substitute them?
     
  4. JoeJester

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    Do you have a link to the audiokarma page that referenced you to change those two resistors?

    Does your DMM have a transistor hfe function?

    The clicking sounds like the protection circuit.

    Do you have the SA-7500 or the SA-7500II?
     
    Last edited: Nov 12, 2017
  5. PioneerVenusia

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    Nov 11, 2017
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    Yes of course. Im not completely shure if posting link to other website is allowed in this forum so let’s say that if you search on google the right keywords you ll find that page.

    I don’t know what DMM and hfe function means, sorry :(

    I have the sa-7500 as i wrote and as far as i know these two amps inside are totally different.

    Thank you for your interest by the way.

    P.s i thoug about changing those two resistor because the music that i hear come from one of them i suppose (is it possible?)
    plus the other 4 transistors are the well known faulty ones.

    Edit:Later on this day i will try to upload a short video of my issue.
     
  6. PioneerVenusia

    Thread Starter New Member

    Nov 11, 2017
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    Thank you dodgydave even if you linked me the 7500ii manual (i have the 7500i: model and manual)

    Anyway i already read some of your posts, it seems like you have a lot of experience. What do tou think about my problem?
     
  7. PioneerVenusia

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    Nov 11, 2017
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    i didn’t catch this phrase. No i didnt open a thread in another forum. I just took some information on other threads infound on the internet!
     
  8. Dodgydave

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    EDITED WITH CORRECT MANUAL.

    Page 36 of the service manual, transistors Q7 to Q11 sense the Half supply of the speaker outputs, should this go higher or lower the relay won't operate by Q11.
     
    Last edited: Nov 12, 2017
  9. JoeJester

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    Where did you get the advice to change those transistors?

    Did you make the necessary voltage checks that lead you to that conclusion?

    On this image, you visited a website for research ... reading your phone does not provide the necessary context of what you read ....

    [​IMG]

    What voltage measurements have you taken? Do you have a list of the points measured and the voltages read?

    One can always replace items without testing, especially when they are using their own money.

    Your manual can be found at https://elektrotanya.com/pioneer_sa-7500.pdf/download.html
     
    Last edited: Nov 12, 2017
  10. Dodgydave

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    Update on the service manual...

    Page 36 of the service manual, transistors Q7 to Q11 sense the Half supply of the speaker outputs, should this go higher or lower the relay won't operate by Q11.
     
  11. PioneerVenusia

    Thread Starter New Member

    Nov 11, 2017
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    You are right but im not home most of the time and i have to browse the web using my mobile. It’s also the same reason because i didn’t test the voltage cause i had not time.
    I tried to get much information as i could before doing anything. Those transistor are well known to be faulty, the cost of them is ridicuolus so even if the problem is something else, in the future i will have to substitute tem.

    For now i didnt do anything on the amps because i didnt recieve any suggestion by you on my problem and i had no time.

    Changing those transistors was just an idea but im still waiting for help from you :)
     
  12. JoeJester

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    Sometimes you need to remember the website so others can read what you did to provide context. All I saw was parts, no context.

    On page 18 of the service manual (page 16 of 58 according to the pdf reader), illustrates the idle current test. Do not do the adjustments, just do the measurements.

    If they do NOT meet the standard, check the transistors associated with the channel. These are the two transistors that were recommended to you to replace by that other user. Ensure you pull the jumpers and place the two resistors as described.

    If they are close to the standard, do the voltage tests around the transistors that DodgyDave recommended. Ensure you write down the test point, the voltage you expected (printed on the schematic) and the voltage you read on your voltmeter.
     
    Last edited: Nov 13, 2017 at 10:33 AM
  13. PioneerVenusia

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    Nov 11, 2017
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    You are right! I'm sorry!

    Finally today i hope to do the misurements.
    I will report here as soon i have something :)
     
  14. Lyonspride

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    Jan 6, 2014
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    My advice would be to change every single electrolytic capacitor you can see.
    The weird crazy problems i've encountered which can be directly attributed to failing electrolytics, you simply would not believe.
     
    Last edited: Nov 14, 2017 at 10:33 AM
  15. JoeJester

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    If you want to check all the electrolytics, get yourself an ESR meter. Replace those that show degradation. You could wholesale replace all the components with new if you wanted.

    Troubleshooting is about solving the puzzle of the bad component(s) based on the clues you are given.

     
    Last edited: Nov 14, 2017 at 12:01 PM
  16. Lyonspride

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    Jan 6, 2014
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    When you do it for a living, you don't have time to mess about, do a bit of probing, replace everything that commonly fails, then start a more detailed diagnostics based on having fresh components in key places. I replace components that "age" because I don't want a customer coming back to me in 2 months time with a fault I could have prevented for the price of a few good quality capacitors.

    I may even do this if there was an obvious fault elsewhere and if for example I find a component has blown up, everything directly affected by that component gets replaced.

    Besides, regarding ESR meters, usually they don't give an accurate reading in circuit, which means removal and doing half the job of replacing them anyway, and electrolytics shouldn't really be reused........ Although some of my personal projects do contain very expensive large value electrolytics (like 22000uF 16v low ESR) that came out of faulty equipment :p
     
    Last edited: Nov 15, 2017 at 3:47 AM
  17. JoeJester

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    That technique is why some shops got a bad reputation years ago. Those shops didn't know their shop hourly rate nor the time requisites for various complexity levels with repairs. The faster in and out meant more money, and some dogs were put aside. A friend of mine used a program called real time in his auto shop. It gave the average time to replace various items. So, the shop had a diagnostic fee to find the trouble, then the average time to replace the problem. The auto mechanics could show you where they came up with a price, and lessen their chance of having a bad reputation. The master mechanic, completes the job faster than the average mechanic, so their "income" is higher without resorting unethical practices. The less than average mechanic, takes longer and the shop loses less money because of their "inexperience."

    Years ago, there was a similar book for electronics called "Sperry Pricing." When you ask your insurance agent how much it costs, they break out a book, albeit a virtual one, and tell you.

    If by "age" do you mean "time since built" or "exceeding half the maximum ESR"? I would rather tell a customer I replaced something for what I measured vice saying "age". But that's just me.

    My response is similar to the preceding response.

    I will agree with that statement if two or more capacitors were in parallel, and you should know that by looking at your schematic. Then again, I don't know the specifications of your ESR meter.

    You might want to clarify that statement. Some could see that as "removing from the circuit to test, then replace it because you removed it from the circuit even though it tested within the normal specifications of a new component."

    It's your shop, do what you want. I hope some consumer advocacy group never visits your shop with a "failed" equipment to have you repair it. Your Standard Operating Procedure might make the evening news.
     
  18. Lyonspride

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    Jan 6, 2014
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    It's not my shop and I don't agree with many of the practices, but our customers are not technical sorts, they want a fixed price repair as cheap as possible and "no fix no fee". That's how the industry is going, these people don't want to ask themselves if they've been ripped off, they want to pay one fee for the same type of product.

    If i'm repairing an airport security metal detector, the customer wants that thing fixed, they never want to have the hassle of it failing again further down the line and I don't want it coming back to haunt me, so what I do is a repair and refurb to factory new, fix the fault, replace parts that "age", like electrolytic capacitors, MOVs, cooling fans, relays and anything else I think could fail within our warranty period (and beyond even though we've encouraged to only fix things for long enough to just about get past warranty). I don't want to ever see that unit again, i'll even modify the thing to mitigate common failure modes that were designed into it.
    At the end of the day it's a fixed fee and all they care about is throughput, so the customers pay the same whether I change all that stuff or not, they pay the same for a "no fault found", so I just choose to be better, to give them more for their money.

    This isn't a back street hifi, TV, etc repair shop though......... There is a fixed price for each product and if a job takes too long, it goes in the skip. In truth the fee's are extortionate and perfectly repairable stuff worth thousands of £ goes in the bin, because there are targets to meet, but the customer thinks they're getting a great service because we're not able to do precisely what they fear, charging for extra work...... When a repair shop charges based on each job, that's when customers start to question your honesty.

    I do what I have to do to maintain my own professional integrity, I make sure I do a decent job and I make sure I hit stupid targets, if that means using experience to shortcut my fault finding then so be it.

    The customers that visit us, they never send engineers, they always send idiots in suits, the bimbo personal assistant or receptionist, they don't notice the 30+ year old equipment, the ESD precautions that are purely for show, the staff wearing lab coats that prevent them moving whilst sitting, yeah it's pretty crappy, but the sad truth is that's what customers want, they don't trust technical people they trust salesmen. There's no room for traditional repair shops and THAT is why they're disappearing, believe me when I say I wish this was not the case, but the few have spoiled it for the many.

    You have to bare in mind that most people don't have the slightest clue, if one shop fixes their laptop by swapping the system fan and then the next repair shop has to replace the motherboard 2 months later, they're going to see £50 bill versus £250 bill and immediately assume they got ripped off, and before you know it you're swimming in a cesspit of bad reviews all over the internet.
     
    Last edited: Nov 15, 2017 at 6:46 PM
  19. JoeJester

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    The consumer advocates would have mystery shoppers ... common folk ... bringing in the equipment for repair. If it were a broadcast station doing the "investigation", their engineer would inject the fault.

    The blanket fee is high enough to support the massive replacements and you probably don't produce an itemized listing of what was failed, it was just Fixed. In a way that is good for the consumer as there is ONE price.

    One thing in common with yesteryear and today is the consumer remains clueless.

    What is the "decision point" to NOT fix something? Time?
     
  20. Lyonspride

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    Jan 6, 2014
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    Time, cost and reliability, you have to make an informed decision really. If I get a bad intermittent fault and I can't be sure it's fixed, then I won't put my name to it. The customer doesn't mind a rejected repair as much as they mind getting something back that is still faulty. Ultimately from their perspective, when they install that kit for their customer, they don't want it to fail.

    I think this is something that has change over the years, people underestimate the skills required, they like to think it's simple to fix things and if the repair goes wrong they get angry. This is partly because devices like smart phones trick people into thinking they're experts, when I did IT repairs I quite regularly got the comment "i'm sure if I had kids they could fix it" (or similar).
     
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