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Pioneer SX-2500 KSC3503D vs. KSC3503E

Discussion in 'Pioneer Audio' started by KeithD, Oct 12, 2018.

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  1. KeithD

    KeithD AK Subscriber Subscriber

    Messages:
    649
    Location:
    La Crosse, WI
    I'm doing some repair on an SX-2500 I picked up. It had been running ok with a couple of issues. One was with the auto-tuning, but fixed that. The other is a constant background hum.

    Following the thread here: http://www.audiokarma.org/forums/index.php?threads/sx2500-main-amp-unit-w23-004.412024/

    My first fix was to recap the power supply, main amp, and protect boards, in that order. The hum got a little better, but did not go away.

    Next thing I did was re-flow all of the solder joints on the main amp board. Figured there could be a bad connection/bad ground somewhere. The hum is much less, but now I have a new issue - static/static bursts on both channels, though more so on the right channel. I thought maybe re-flowing the solder on one or more transistor connections may have been enough to push an old transistor over the edge. Decided to replace Q1 and 2 (2SC458) with KSC1845F, since 2SC458 is on the bad transistor list anyway. This did not cure the static issue.

    Now, I'm wondering what should be next? Q3 and 4 are 2SC627. Replacement from the above mentioned thread is KSC3503ES. However, I have KSC3503DSTU on hand. Looking at the spec sheets, these seem almost identical; however, KSC3503DSTU lists a maximum DC collector current as 0.6V, whereas KSC3503ES does not list this value. Can I use the KSC3503DSTU I have on hand, or do I need KSC3503ES in the repair thread I referenced? OR, is something else suspect?
     
    Last edited: Oct 12, 2018

     

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  2. markthefixer

    markthefixer On Hiatus, dealing with Dad's estate full time Subscriber

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    exclusively answering the D versus E question: yes, it's OK to use.
    Verifying that that particular circuit position calls for or needs a ksc3503 I have NOT looked, nor can I go any deeper for now.
     
  3. KeithD

    KeithD AK Subscriber Subscriber

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    649
    Location:
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    Thanks Mark, will give those two a try unless something else would be better?

    Here is the full list from the other thread of replacements the OP used on the Main amp board:

    Main Amp Unit W23-004:
    C1 1µF/50V -> 1µF/63V ECQV
    C2 1µF/50V -> 1µF/63V ECQV
    C7 4.7µF/50V -> 4.7µF/100V UKL + 1µF/63V ECQV paralleled
    C8 4.7µF/50V -> 4.7µF/100V UKL + 1µF/63V ECQV paralleled
    C9 47µF/35V -> 47µF/63V UKL
    C10 47µF/35V -> 47µF/63V UKL
    C11 100µF/50V -> 100µF/63V UKL
    C12 100µF/50V -> 100µF/63V UKL
    C11 100µF/3V -> 100µF/63V UKL
    C12 100µF/3V -> 100µF/63V UKL

    VR3 220ohm -> 500ohm 25-turn (bias current)
    VR4 220ohm -> 500ohm 25-turn (bias current)

    Q1 2SC458 -> KSC1845F
    Q2 2SC458 -> KSC1845F
    Q3 2SC627 -> KSC3503ES
    Q4 2SC627 -> KSC3503ES
    Q5 2SC984 -> KSC2383Y
    Q6 2SC984 -> KSC2383Y
    Q7 2SC484 -> KSC2073TU + heatsink
    Q8 2SC484 -> KSC2073TU + heatsink
    Q9 2SA484 -> KSA940TU + heatsink
    Q10 2SA484 -> KSA940TU + heatsink
    Q11 2C1079 -> MJ21194 (on heatsink)
    Q12 2C1079 -> MJ21194 (on heatsink)
    Q13 2C1079 -> MJ21194 (on heatsink)
    Q14 2C1079 -> MJ21194 (on heatsink)

    I actually did not replace C7 and 8, since I don't know why he added the 1 µF caps in parallel with the 4.7 µF caps in those locations. Are those needed? What is the purpose?
     
  4. rcs16

    rcs16 Super Member

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    Location:
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    Panasonic ECQ-V stacked film caps are discontinued, you can use other film types that fit, use long leaded types or ones with 5mm lead centers
    You do not need the films to be in parallel with UKL types, wima.kemet.avx all make good quality caps
     
  5. KeithD

    KeithD AK Subscriber Subscriber

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    Location:
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    OK, so it would be all right to just use 4.7 µF UKL caps for C7 and 8 and NOT put the 1 µF caps in parallel? Still wonder what the purpose of that is?
     
  6. markthefixer

    markthefixer On Hiatus, dealing with Dad's estate full time Subscriber

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    C7 and C8 are inter stage coupling caps that carry the audio from one stage of the power amp to the next stage, while isolating different DC voltages on the two stages from each other.

    Film caps ( 1µF/63V ECQV) have a different internal construction that results in shorter LINEAR distances from the component connections to the capacitor plates.
    That results in less parasitic inductance that interferes with the higher frequency information that carries a lot of what we are sensitive to to detect "presence", crispness, position and a whole host of what we call "great audio".

    The INTENT is that the lower frequencies that are in the bass region pass through the 4.7uf "toilet paper roll" with it's inherent inductance un attenuated, while the film caps make the amp "sparkle".

    Takes some GOOD ears (and trained brain) to recognize the difference.
     
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  7. spicer

    spicer Super Member

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    Having owned and repaired a few of those... bought one brand new from Olsen Electronics in Whittier California years ago... assuming hum in both channels, I think that unit has grounds on some of the boards through a pad on the underside of the board which is secured to the chassis with a mounting screw.. those develop ground issues because the solder on the pad squishes out causing a bad connection. Also, check for wire wrap connections on any grounds... solder them if in doubt.. solder them anyway. Attractive units.
     
  8. KeithD

    KeithD AK Subscriber Subscriber

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    Location:
    La Crosse, WI
    Thanks for the explanation, Mark. That puts the suggestion for two caps at each position in context. His list has two caps in some other positions as well, including the three large caps. I do have 1 µF 50V WIMA film caps, which I assume will work, since the original spec was 50 V.

    Will also do the Q3 and 4 replacements with KSC3503DSTU.

    Spicer, thanks for the direction on grounding. Will take a look at all ground positions.
     
  9. KeithD

    KeithD AK Subscriber Subscriber

    Messages:
    649
    Location:
    La Crosse, WI
    Replaced Q3 and 4, and checked ground connections on main amp.

    Hum is nearly all gone, but static remains. Also, after playing the receiver for about 5 minutes, both channels suddenly loose power, volume drops to near zero. Turned it on the next day, and same cycle repeats. Any suggestion of what to look at next? Working my way down the circuits, Q5 and 6 would be next (2SC984). Suggested replacement is KSC2383Y. However, is this the most likely issue?

    The Protector board (AWM-004) is also in circuit after the main amp. I've recapped that, but it has 5 2SC945s, and two 2SK30s. Are either of those suspect? As I recall, there is no replacement for the 2SK30, correct? I was thinking the Protector board was not the problem because the static began after I re-flowed the solder joints on the main amp board.
     
  10. KeithD

    KeithD AK Subscriber Subscriber

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    Location:
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    Replaced Q5 and 6, no change in static. Q7-10 need heat sinks according to restoration thread mentioned earlier. I’ll have to see if I can scrounge some of them. Have the replacement transistors on hand, but no spare heat sinks. I do have four of the correct replacement output transistors, so might end up just replacing all transistors on the main amp. Sure hoping the static disappears with one of these replacements. At this point the static is primarily on the left channel.
     
  11. KeithD

    KeithD AK Subscriber Subscriber

    Messages:
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    Location:
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    Swapped Q9 and 10 just to see if that moved the static from one channel to the other. Not really, but the static reduced substantially; however, still a bit in the background. So, decided to replace with the recommended KSA940TU. No change in static. So, went ahead and replaced Q7 and 8 with recommended KSC2073TU. Again, no real change, though static is now limited to just the right channel. Does not change with volume or source.

    Is my next step the output transistors? I've never done these before. Any way to check them before removing and replacing?

    The only other board in the signal path is the Protect board. However, looks like the signal only goes through a couple of capacitors in each channel (which I already replaced) and a 2SK30 in each channel, but my understanding is there is no equivalent replacement for those, correct?
     

     

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  12. rcs16

    rcs16 Super Member

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    Wackamolly
    first determine where the hiss/noise is coming from, test the pre-amp and power amp sections separately.
    As for 'both channels suddenly loose power," does this still happen? if so trace the signal thru to figure out where it stops/why?
    with power off, switch rear main power amp input to "main external inputs", ground both L/R inputs, power on, speakers on, do you hear any hiss/noise?
    if yes issue is power amp or power supplies.
    if no then it is coming from the pre-amp, wiring/grounding
    if you suspect 2sk30, swap them between channels to verify, I see one guy on ebay selling them, you can use 2sk117 as well. what printed on the top of them should be either "GR" or "Y"
    did you change out the 2sc458LG on control (W15-050)? recap?
    Do you get hum/hiss in FM? in FM muted condition?
     
  13. KeithD

    KeithD AK Subscriber Subscriber

    Messages:
    649
    Location:
    La Crosse, WI
    Update: turned the receiver on today, and no static at this point. Will continue to test.

    Yes, I forgot to mention, that I did move the pre-out/power-in button, and this did not affect the static/hum. Also, switching Q7 and 8 on the main amp lessened the static, so there was clearly an issue there.

    No more channel dropout after swapping Q7&8 or after replacing Q7-10, so that issue is solved.

    I don't specifically suspect 2SK30, but after the main amp, those are the only silicon left before speakers, so before going to the hassle of replacing the 4 output transistors (Q11-14) I thought I'd ask about 2SK30 on the protect board. I have the Y version of 2SK30.

    Yes, 2SC458 (Q1&2) were the first two I replaced as they are on the bad transistor list. I then worked my way up the circuit to where I am now, so not really "whakamolly", but using the logic of the circuit from observational data to guide me. Sorry I was not clearer about what I had done in order.
     
  14. KeithD

    KeithD AK Subscriber Subscriber

    Messages:
    649
    Location:
    La Crosse, WI
    After further testing, this seems to be a dirty function selector issue and/or pre-out/main-in switch issue. Did another round of Deoxit on both, and the static has cleared up.

    Man, this receiver is really worth the effort if you like the early Pioneer warm sound, AND it has the super cool auto-tuning feature. This may be the best Pioneer I have heard. The SX-2500 is not very common, but I think it is definitely a sleeper, and fairy easy to work on.
     
  15. rcs16

    rcs16 Super Member

    Messages:
    4,067
    Location:
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    yes the old switches are the Achilles heels. i have a qx-9900 same /similar design and issues.
    sometimes hard to follow whats been done in these threads. thx for the update
    the auto tuning was unique.
     
  16. KeithD

    KeithD AK Subscriber Subscriber

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    649
    Location:
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    Yes, of the major brands I think only Kenwood had an auto-tuning receiver (KR-7070) in the era of analog tuning. If you read more about the auto-tuner, Pioneer claims to have the best one. From the description of how it works, it seems believable. The SX-2500 was TOTL in '70 and '71. The x2x series was introduced in 1972, but the SX-2500 and SX-9000 were still cataloged and the 72 wpc of the 2500 was not surpassed until the SX-1010 (the 828 is 60 wpc.)
     

     

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