Another big Pioneer receiver on the bench and this one is a beast. Pioneer SX-1050 120wpc monster. The receiver was ran up to over 120w and produced clean sine and square waves. Rick would like some preventative maintenance done which I completely agree with to keep this amp playing for many more years.

So far the protection circuit was serviced and has new capacitors and a couple new transistors. The small 0.22uf caps were replaced with Panasonic film and the elec caps with Nichicon PW series. Two transistor subs were installed. Here’s some pics of the work.

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Next, on to the power supply. This guy has got two power supply boards, a surge suppression board, and two huge 22000uf 80v filter caps. For those doing their own restoration the caps are ~64mm in diameter and 115mm tall. I will be replacing them with two screw terminal chemi-cons which were not cheap. I will also bypass them with 2.2uf 250v Panasonic film caps. First up though is the main power supply board on top of the chassis. Capacitors have been replaced. In the next session the regulators and a few choice transistors will be replaced. Here the before and after on the recap and then regulators and other transistors. Those electrolytics were begging to be replaced.

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Ok now onto the flat amp and control amp. To gain access to these boards you need to remove the faceplate and I screw them from the chassis. Many tantalum caps on these boards replaced with low leakage Nichicon KL electrolytics.

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Next the EQ section which resides under a cover under the chassis was recapped. Note the tantalums were also replaced with Nichicon KL for low noise.

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On to the power amp section which you can remove the entire heat sink and outputs easily with the harnesses. The pins on the harness was cleaned with deoxit and the board recapped. More tantalums to replace on this board as well.

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There is an electrolytic on the surge suppression board which should also be changed. Much easier to do with the filter caps pulled.

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New filter caps installed and all ready to go home after another bench test. These were a costly part but fit nicely in the original brackets.

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8 Responses

  1. Hi. I have a Pioneer SX-1050 with no output whatso ever. The preamp out works fine. Help. Does the protection board relay supposed to activate at startup? Thanks.

    1. Hi Wayne, yes the relay is for speaker protection and should pull the contacts in a few seconds after you power up the receiver. There are amplifier alignment instructions in the service manual which you can check if you have a voltmeter.

  2. Hi ,I have sx-1050 that smoked ( Main Amp Board) I need to find replacement transistors. seems like most have been discontinued. Any Ideas ?

    1. Hi Vince, the transistors in your 1050 were produced in Japan in the 70s. Unfortunately those plants are long gone so we are left to find modern substitutes for the vintage transistors. Luckily there are many transistors now that are better made and exceed the specs of the vintage counterpart. Here is a short list of common transistor subs :

      http://hudsonvalleyhifi.com/technical-data/transistor-substitutions

      If there is a transistor that is not on the list shoot me an email and I will get you an appropriate sub and add it. Also, remember of transistors are damaged capacitors and resistors around the transistor may also have been damaged. Good luck and let me know how your project turns out.

      1. Thanks so much Mike , I’ll check the local parts stores ASAP.
        Do you have a recommended source for these transistors ?
        Thanks Again Buddy ! You are a great help to us !

        1. I use several parts houses. Mouser, digi-key, Newark, are all good. Don’t buy on eBay too many counterfeits.

  3. Where do you recommend getting the 22000uf 100v main capacitors with screw on connectors that fit into the existing brackets on an SX-1050. I have one of these receivers and the left channel of the power amp has an intermittant crackling noise in the back ground. Do you think changing the 2 main caps would fix that?

    I did the full dexoit treatment, the noise is there even when the pre amp to amp metal connectors are removed so I know it’s a problem in the output amp.

    Thanks for your help.

    1. Hi Jeff. First off, no, changing the filter capacitors will not fix the problem with your 1050. The purpose of the two capacitors is to take the rectified (AC to DC) voltage and smoothen out the ripple created to make clean DC power. An issue with those caps would present as a hum in both channels.

      Since it is left channel only and you have isolated the problem to the power amp I would lean to a leaky transistor or failed capacitor in the left power amp. When the crackling occurs measure mvDC across the left speaker terminals and see if you are having DC leakage issues. I can get more into the repair if you would like to email me mike@hudsonvalleyhifi.com

      Cheers!

      Mike

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