R-500 initial checkout

Discussion in 'Yamaha' started by Hak Foo, Jul 7, 2018.

  1. Hak Foo

    Hak Foo Active Member

    Messages:
    279
    I picked up a R-500 at the local thrift shop today. $35-- expensive for thrift shop stuff when several heavy modern receivers were $15, and it had the input selection knob replaced with a clearly non-matching substitute, but otherwise not hideously dirty; all lights seem to work and it really hits the classic aesthetic in a way my beloved JVC gear doesn't :).

    When I powered it up in the shop, I saw the signal gauge flicker at times, but no relay click. It didn't dawn on me at the time, and then I spent a while reading "the protection circuit caps like to give out" and thinking that was in front of me.

    I blew it out with canned air, and the first few times it went on there was intermittent popping and clicking, little sound, and no consistent relay. But now it seems to have the relay pop in more consistently on power up-- as if it's back to normal-- are there parts of the system that misbehave that way? (Reminds me of a Commodore 128DCR I bought-- it wouldn't power up the first few times, then suddenly started working)

    The big concern I see right now is that the "Stereo/S-lock" function works pretty erratically. I can't get stereo on many strong stations, and only a handful of stations escape muting in S-lock/stereo mode. The signal strength meter is zero on plenty of very listenable signals, and full on dead or static spots.. Using some broken rabbit ears as antenna.

    The SM shows DC offset adjustments, so I'll do that along with the obligatory Deoxit sprays, but is there an adjustable bias? Given it's a STK module unit, I'd prefer to keep it cool for longevity's sake-- new parts are a pain.

    The caps don't look bad from an immediate inspection, but the glue holding the heatsink in the "12v supply" zone of the PCB does look horrible and dirty and gungy.

    Also, the loudness control seems to just quiet the sound, not change its character much. Could be my headphones (those beige Koss ones Massdrop was selling a few months ago) though. Are my expectations wrong based on units with conventional loudness buttons?
     

     

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  2. avionic

    avionic " Black Knights " Subscriber

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    Location:
    Fort Dodge, Iowa
    Try a better external antenna.
     
  3. avionic

    avionic " Black Knights " Subscriber

    Messages:
    41,240
    Location:
    Fort Dodge, Iowa
    You have the manual. If its not in the manual then your SOL. Usually STK's have a fixed bias.
     
  4. avionic

    avionic " Black Knights " Subscriber

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    41,240
    Location:
    Fort Dodge, Iowa
    DSBG google it. Glue becomes corrosive by now.
     
  5. Hak Foo

    Hak Foo Active Member

    Messages:
    279
    I pulled down the offsets to like .1mV today (they were already pretty low) and scraped off as much of that glue as I could. Had a few weird relay clicks during thw "wait 5 minutes before adjusting" warmup.... maybe it does need protection capacitors after all.

    Then I got into a dilemma. I wanted to strip the unit down for a cleaning, so I had to take off the front panel.

    The three screws that hold the front on are evidently made out of a space-age alloy of Chinesium and candyfloss, drilled in with Odin's Phillips-head (lesser known accessory to Thor's Hammer) and were gouging wildly as I tried to remove them. So now I've got one out and two ground-up messes that won't really take a bit Trying to glue in a screwdriver bit and work them out. Don't want to just Dremel in a new opening for a flathead to get them out, because that's kicking up a lot of metal dust in a situation where I can't really remove everything electrical near it.
     
  6. avionic

    avionic " Black Knights " Subscriber

    Messages:
    41,240
    Location:
    Fort Dodge, Iowa
    I've had good luck with reverse flute (left hand) drill bits
    https://www.mcmaster.com/#standard-drill-bits/=1dmr2z0

    Inch Size Left-Hand Drill Bits
    [​IMG]

    Also known as reverse-flute bits, the flutes spiral in the opposite direction of other bits. They are for use in reverse tool operation—most commonly to remove broken screws. Jobbers'length are the most common bits and have the rigidity and length required for most applications.

    A split point keeps the bit centered without a pilot hole.

    Bits with 135° point angle produce smaller chips than 118°point to prevent clogging.

    Keep a shop vac nozzle close to the work to catch the swarffing.
     
    Last edited: Jul 8, 2018

     

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  7. OMGCat!

    OMGCat! AK Subscriber Subscriber

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    Location:
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    For Japanese gear you're much better off using a JIS screwdriver over any other kind.
    I have a set of Vessell that I love which fits these screws perfectly.
     
  8. Hak Foo

    Hak Foo Active Member

    Messages:
    279
    Well, time to come back with more details.

    It was having a lot of issues with the relay suddenly clicking mid-operation or not coming up quickly at power on.

    I replaced all electrolytic capacitors on the power-amplifier board (C3xx series) with the following exceptions:

    * The big 8200uF ones (C340 and 341) -- that denomination seems to be unstocked these days
    * The lone 33uF 6.3v cap (C346) - I ordered 22uF by mistake and I don't want to spend 9 cents for the part plus $5.95 for postage unless it seems like a worthwhile culprit. The pulled caps seem to be within a 20% band, so I'm hesitant to make another order unless it seems a strong culprit.
    * C325 and 326 were listed in the SM at 100uF, but the caps in my unit were 47uF. I went with 100s here since that's what I ordered.

    It seems like it's not dying mid-use under brief testing anymore, and still sounds good and tunes strong,, but when cold, it sometimes takes a long time to relay click, or it will do a soft click and no sound, followed by a later, full switch on, or a frantic series of clicks.

    Working on the "when cold" aspect, I reflowed most of the solder joints on the power board. Perhaps marginal improvement.

    It seems like a very sensitive part of the unit is the three transistors roughly in a line in the protection circuit. TR306, 308, 309. Tapping those with a probe-- once it's already deprotected-- will often cause a pop to be injected into the sound. Sometimes it pushes into a noisy mode or even causes the relay to click out momentarily. TR306 seems most likely to cause the relay click when tapped, but that could be because it's physically closest to the relay. 308 and 309 make different sounding clicks. When it's in "not yet warmed up mode", tapping the transistors doesn't seem to get any closer to launch.

    Since they're closely wired, is it likely one is iffy and propagates trouble through the circuit, or should I just consider replacing all three? I've heard to use KSC2383 for the 2SC2320s, and KSC1015 for the 2SA999s. The other transistor in the area (TR305) doesn't seem to cause issues when tapped.

    Also, the STK3042II seems to get fairly warm for a non-heatsinked part. Typical?
     
    Last edited: Jul 22, 2018 at 1:45 PM

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