Sunday, May 8, 2011

Technics Receiver Overload

My first piece of "serious" audio property was Technics SA-EX 300 that I bought in 1997.
After starting receiving overload messages when cranking volume up, I opened it up and saw pristine electronic elements performing without glitch.


Although not opened or cleaned for 11 years:
  • there was very little dust inside
  • capacitors cool after hours of work, original shape, no distortions
  • cooling fan noiselessly gets on and off, depending on internal case temperature
  • huge cooler in the middle of the case was not overheating, just felt warm
  • all soldering intact, connectors firm























It was only after I readjusted clumsy wire connectors at the back of the case, that fixed the problem.

Pulling every individual speaker connection in & out, making sure that it felt connected, I restored firm connection, and receiver started blasting without overload interruptions.






















I feel that receiver's back panel is the only weak spot of this piece of art.

Never paying to much attention on speaker cables, I used most common ones, twisting their connector end with hand, without soldering them. Inevitably, they lose their grip in time
, and cause overload when system draws maximum output power.
In my case, that is 5x100w.
The two front speakers, two surround and one passive sub-woofer, each bearing power of 100W.


 

Update 2 months later:
After performing fantastic for awhile, it went back to the original state.
If volume is left on maximum, when unit is powered, starts to choke right away.
Than, after 4-5 minutes, an error goes away, but the receiver must not be used at 100%.
At this point, I think that the problem is in wires I use to connect speakers with the receiver.
They are of lowest quality. However, the price difference is substantial, so I will give another update when I manage to buy the grounded, shielded speakers' wires.

Update:
It's not the wires. The receiver goes to error without wires connected, so it's logical that the speaker's wires have nothing to do with the problem.

Update Aug2011
I have notices that after disconnecting all the speaker wires from the back of the receiver, and then a couple of hours later connecting them back, the sound system works on loudest without a glitch, and not reporting error for a couple of weeks.
The bass sound , even without the amplifier, is especially impressive.
Then it is back all over again. I am still dwelling on buying expensive shielded audio cables.


Update Sept2011
Still doing unplug-connect back trick.


Update Nov2012
Disconnected the unit and hoping to find some cash to have it repaired by a professional.

Update April2013
Gave it to an experienced electronics repairman, he claimed that output amplifier passed the test, and suspect that a CPU is to blame. Which in this case translates to "dump the thing". I am not giving up yet.


47 comments:

  1. Greetings,

    Are you still trying to troubleshoot this receiver. I have the same overload issue with my techics (not at home so I don't know the model number).

    I brought it to a technician buddy of mine who of course did not experience the over load issue and was therefore unable to troubleshoot.

    In any case, thanks for the blog. I'm going to experiment with my own speaker wiring to see if I might have similar, if only partial, luck. I'll try anything before I replace it.

    Let me know if you'd like me to keep you posted.

    Vince

    ReplyDelete
    Replies
    1. Of course, keep posting, keep me informed.
      As for me, I have grown tired of partial and temporary solutions, and disconnected the thing. When I get some spare money, I will take it for repair to a professional. For some reason, I am convinced that the overload is caused by a single component inside, like capacitor or transistor. My receiver has been used extensively and to the max over the years, and that kind of abuse had to cost me something. However, I will not scrape this exceptional piece of equipment, I am too attached to it.

      Delete
  2. Hello.
    I happened to stumble on this page while searching for a similar solution.
    I've heard also that the fan connections sometimes stretch and need maintenance?

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    1. I don't think so. The thing is well made. I might have a solution soon. A buddy of mine seems to be convinced it's the output amplifier fault. I will keep you posted on what components exactly.

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    2. Thanks for all the ideas. I have never tried to fix any electronics but I'm going to open the thing and try everything you have posted. Thanks again and please keep updating. I have the EUR646489 model.

      Delete
    3. Incidentally my EX300 goes to overload when it's not even quarter of the way round the volume? And happens when there is no music playing too? This is confusing to me. I don't want to replace it either. I was considering stripping it down and reassembling it and maybe put some fresh heatsink compound on the output ICs. I should add that I've not seen the fan work at all? The heatsink does get quite warm but wouldn't say hot. I managed to download a free copy of the complete service manual and it shows that the overload message is produced by the IC901 located on the front panel. I suspect that may be the culprit but have no replacement to test this theory. I have to say I was surprised at the connection this circuit has to the main board, definate place where oxidisation could occur. I'd really appreciate it if you do manage to source the problem so I can resume normal operation. I've never really pushed this Amp to its full potential so I'm confused why it should happen.
      I hope to hear from you soon as it's rather annoying as I don't have another amp to put in it's place while troubleshooting.

      Delete
  3. Hi there, throw me a link to that service manual, will you?
    I suppose it would be prudent to see if IC901 could be purchased somewhere and replace the original with it. I think you can safely forget the notion that overheat is the problem. My unit goes to error mode straight away, with no time for any of the board elements to heat up. The cooling fan is noiseless, and works great too. It is controlled very well, and engages only when activated by temperature sensor.

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  4. I can't remember where I got the manual from but I can certainly send you it direct if you can advise where ?

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  5. Just found the link after a bit of a history search lol

    http://elektrotanya.com/technics_sa_ex300_e_eb_eg_sm.pdf/download.html

    Hope this helps you , and obviously me too (",)

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  6. I'm working on a similar amplifier. If you're close-by maybe I can help?

    ReplyDelete
    Replies
    1. Close by with solution or close by geographically?
      I am in Croatia, Europe.
      It seems that the next step for me is to find out if motherboard IC chip can be replaced, and if replacement can be found anywhere, since it is an obsolete part.

      Delete
    2. This blog shows up (to me) as a .ca site so I thought you were in Canada. My mistake!

      Anyway, I'm very sure the IC you mention is not the problem. You will likely need to find an electronic technician (AKA 'The Wizard') who can help you troubleshoot and repair this issue. A professional service would like cost much more than a new amplifier. There are many common issues that show up in this type of equipment and most are heat/age related.

      If you think I can assist from here let me know.

      Delete
    3. Those are my thoughts too. The cost of repair would top the price of a new, improved unit. That is why I am dancing around this issue for years now. If there is no quick fix for it, it is not cost efficient to bather with it. What surprises me is the number of people with the same issue, and the fact that I could not find the single one who had solved it.

      Delete
  7. Yes, these problems are very common and sometimes they are relatively easy to fix. Many who are able to are also charging for their work so are less likely to spend time explaining and posting about it. There are plenty of resources available to learn about electronic repair and if you spend enough time working on it you'll figure it out.

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  8. Well yesterday I decided to strip my amp down and give it a thorough clean again. I took the back plate off completely and removed the tuner block and phono input card. I ensured all dust etc was removed from all. I paid attention to the speaker outputs making sure they were clean. Then I also removed the front fascia complete. Then before I reassembled it again I had a look at the contacts on the pront panel where they meet the main board and they looked a little oxidised so I gave each of the connections a couple of short squirts with some Servisol Switch Cleaner.
    When I put it back together I tested it on a moderate level of volume as it was 11pm by that time. It didn't give me the error at all all night. I've used it today and still no error message yet. I haven't put the volume up very high yet but I may do this evening. I will let you know if it cuts out on me.

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  9. If it happens again then you'll want to check the circuit boards (main & inputs) for any bad looking solder joints. Reflowing might be all that is required.

    ReplyDelete
    Replies
    1. Yeah I've done a check for dry solder but it seems to be fine in that respect. I've had experience in the past of what dry solder can do to electrical equipment, can be all manner of strange and unusual symptoms.

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  10. I had a couple of "healed" symptoms after a long rest period, but it went back to the error mode after a day or two. Curious to hear what will happen to yours.

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    Replies
    1. Mine had different symptoms. Some channels were cutting out and the fan was stuck on. Resolution was replacing some transistors in the fan-circuit and reflowing the main, 6-ch direct and input boards. Interestingly, Panasonic has the fan-circuit connected to the overload sense. Your problem could be connected to the fan-circuit in some way.

      I've had an overload/safety problem on other amps and replacing the cooked capacitors resolved that. Look for areas of heat-damage (changing board colour or solder sheen).

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  11. Well my solution didn't last long. It's returned sporadically again. Pfft!!. Back to the drawing board I suppose. I still haven't seen my fan working yet at all though?

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  12. The fan only comes on at a sustained volume (voltage) level. Did you have a chance to get it loud or turn up the volume without speakers attached?

    If you did and the fan did not come on then your overload-trip could be due to to a fault in the fan circuit.

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    Replies
    1. No I wasn't able to get it loud. It just clicks into the error without warning and sometimes it just comes back on again after a few seconds but then other times it lasts for a few minutes. I can't understand why it's happening. I've never really pushed this amp to its full potential so I'm at a loss.

      Delete
  13. Should the fan get busy without any speakers attached? Since there is no power consumption in that case, there should be no overload of any case, don't you think?
    The slow and sporadic appearance of overload message seems to be a trademark of this unit. My receiver had been working perfectly for about 6 years before error message slowly started to kick in.

    ReplyDelete
    Replies
    1. Yes it should. The fan is not triggered by power or temperature, only a RMS voltage level. You can test this without speakers attached.

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  14. Well I'm afraid it's becoming quite irritating now. And sometimes it shuts into overload when there's no music playing. I've yet to hear the fan operate. I'm seriously thinking of shelving this one for a while and maybe picking up a Yamaha or similar Amp Receiver. I think it'll be a bit more reliable.
    Quite disappointed as when it worked flawlessly the sound quality was amazing .

    ReplyDelete
    Replies
    1. Yep. Hard to let go a good thing.

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    2. I would start by getting ahold of the schematics and tracing out the overload circuit. If you want to try a shot-in-the-dark fix, replace all the small electrolytic caps.

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  15. I already forwarded a copy of the circuit diagrams, I was hoping someone could shed some light on it. What caps do you propose changing Martin? I've replaced a few in other units and it has solved some issues. How many are we talking? 20? 30?

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    Replies
    1. I've looked over the service manual (it's a good one) and although all the info is there it's much easier to trace-out and identify the components when you have the actual board in hand.

      Most of the overload circuit seems to be on p16 and connects to the front panel via 'E'. Find the cluster of transistors Q701-708 and look for poor solder joints and/or electro-caps in that area. Get a voltmeter and check the reference voltages listed in the manual.

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    2. Yeah I agree with you in that it's easier to have the board in your hand to trace the paths. I will have a look at these soon. I may even have a few replacement transistors and electro caps already in stock, I've been hording a load for a while now, it's time they came in handy for something.

      Thanks for your input Martin. Much appreciated.

      Delete
  16. I just opened sa-gx470 and this one the overload message comes when you move the speaker connectors. It seem that the is at least one broken soldering where the speaker terminal connects to the main board. I will resolder speaker terminal connectors on main and hope it will work.

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  17. Resoldering the speaker terminals might do the trick for ya. I own an electronics repair shop and 90% of the time its one of the power modules on its way out. Let me know if I can be of any more help.

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  18. Well I stripped mine down again completely and turned over the main board. After inspecting it closely I discovered quite a few dry solder joints to the power modules and other components. I spent about an hour replacing the solder at these points and also renewed quite a few others on high power resistors and transistors. Anything which looked suspect to be honest. I've reassembled and am currently testing. I checked the electro caps but none of them seemed to be failing, no bulges or fluid leakage. I will advise of my success or failure in due course.

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  19. Excellent work and thanks for the update. Keep us posted!

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  20. Well it's been 7 days since I performed surgery on it and so far (touch wood) I haven't received the overload message. I will report back again. I hope I have solved my issue.

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  21. After a full two weeks of pretty much continuous operation I've still yet to receive any overload message and I have been cranking the volume up recently as the outside of the house is having work done and I wanted to drown out the noise. But yay me, I think I've cracked it, my problem anyhow. :)

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    Replies
    1. Good work! A good reflow can fix many a problem.

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  22. Over four weeks now and still going strong. Not even a hint of a problem. I still don't know if my fan operates yet though :)

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    1. How come? It usually spins seconds after powering the unit on.

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    2. I've never seen it operate in all the time I've owned the amp. It doesn't spin up when I power on and I've never known it to kick in while in use. I suspect the fan may be faulty as it's quite old now. I wouldn't mind sourcing a replacement if it's possible.

      Delete
    3. I've already posted previously on how to test the fan and it's really easy. Play some audio or a test signal, disconnect the speakers, turn up the volume.

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    4. Yeah I did all that but I've yet to see it spin up.

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    5. Then there is a problem with the fan or the driver circuit. Other than curiosity, I wouldn't worry about it as long as you aren't in 'party-mode' and keep the unit cool.

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  23. Feck :(. Well it was good while it lasted, but I've had two more occurences of the dreaded Overload. Starting to think I'll never fix this properly.

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  24. Not happened since though, jeez this is so confusing.

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  25. I took mine apart. Pics to follow.

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