I could use some help with a 1280 problem

Discussion in 'Pioneer Audio' started by Jefferylu98, Apr 4, 2017.

  1. WE6C

    WE6C Active Member

    Messages:
    458
    Location:
    Colfax, Northern California
    Mark, I remember one time on an SX-1250 Q11 on the power amp board was "noisy" which caused protection problems but would test good with a DMM on diode test. Could he have something like this?

    Bob
     
  2. Jefferylu98

    Jefferylu98 AK Subscriber Subscriber

    Messages:
    119
    Location:
    Port Huron, Michigan
    Ok here we go, all caps on the protection board were replaced at the same time (prior to previous post).speaker relay Clicks explained=(Power amps plugged in) I power on, 8 seconds later 1 click to close relay, 2 seconds later 1 click and relay opens back up, and repeats after 8 seconds. (Power amps unplugged) I power on,8 seconds later 1 click and the relay stays closed till I turn power off. PA3004 voltages are, ( I checked with amps unplugged and plugged in) plugged in is as follows: PIN 1-13.1v. PIN 3- .6v. PIN -4 varies with relay open/closing. PIN 5- 0. PIN 6 is -7.4v. PIN 7 - .66 acv. PIN 8 also varies with relay open/closing, starts out at .5v when power on and climbs to 5.5 v then (8seconds later)relay closes and reopens (2seconds later)and starts over. Amps unplugged PIN 4 is 0v and PIN 8 is 7.1 v when relay closes. The rest of the pins stayed the same. I don't how to set my dmm to CURRENT and I didnt see anything in my manual on my fluke 117??
     
  3. markthefixer

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

    Messages:
    20,394
    Location:
    Bensenville,Illinois
    When I had him pull Q1, it eliminated their (Q1 AND both amp board's Q14's) effects (or their operation!!) and kept the fault on that board.

    note that the 1250 protection circuit is implemented as individual transistors, while the 1280 is an integrated circuit, but I admit both use that power amp board protection transistor.
     
  4. markthefixer

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

    Messages:
    20,394
    Location:
    Bensenville,Illinois
    Fluke 117 Current is the A position (Amps) just next to the last position which is the Volt Alert label.
    BUT you don't need to do that now.
    I emphasize this, don't do that now, it is unnecessary risk, the timings exonerated the relay coil drive circuit..

    Please monitor pins 14 and 16 of the protect board with the amps plugged in.

    Tell you what, just plug in the left amp ONLY and see what happens, then unplug the left amp and plug in the right amp ONLY and see what happens.
    I see something... and it isn't likely the protect board.
    (and I'm kicking myself for not calling it out earlier, assumptions again)
    hint to the gallery: stable dc offset?
     
    Last edited: May 19, 2017
  5. Jefferylu98

    Jefferylu98 AK Subscriber Subscriber

    Messages:
    119
    Location:
    Port Huron, Michigan
    I tried the single amp unplug thing and it still does the 8 second open and 2 second closes. I assume q1 is supposed to be back in circuit before test?
     
  6. markthefixer

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

    Messages:
    20,394
    Location:
    Bensenville,Illinois
    leave q1 out. we will address the issues that it could have later. we are simplifying things with it out.

    what I want is a single amp plugged in, it doing it's cycling, and you measuring the awr-157 power supply (+/- 68v) voltages on pins 8 and 2
    and ALSO the (+/- 32v) pins (11 or 12 or 13 , 20 or 21 or 22)
    and awm-123 protect board voltage readings on pins 14 and 16 .
    then swap to the other amp and do the same readings.
    Use the metal of the chassis as your black DMM lead ground reference.

    if it's easier to reach the amp board pins to measure, here's the layout:
    pin 1 (-32v dc reg) ???
    pin 2 (+32v dc reg) ???
    pin 3 audio input, ignore
    pin 4 signal (but not output) ground
    pin 5 (-68v dc reg) ???
    pin 6 (+68v dc reg) ???
    -----------
    pin 7 amplifier output (0.000v) ???
    pin 8 over current protect "output"
    pin 9 zobel output filter ground, hard chassis ground.
     
    Last edited: May 19, 2017
  7. Jefferylu98

    Jefferylu98 AK Subscriber Subscriber

    Messages:
    119
    Location:
    Port Huron, Michigan
    I assume you meant PIN 25 not PIN 2? Lol
     
  8. Jefferylu98

    Jefferylu98 AK Subscriber Subscriber

    Messages:
    119
    Location:
    Port Huron, Michigan
  9. markthefixer

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

    Messages:
    20,394
    Location:
    Bensenville,Illinois
    What work (if at all?) has been done on the amplifiers? I'm probably going to have to reread the thread with a gimlet eye.

    The output(s) should NOT be doing that. When adjusting each power amp channel for 0.000v DC that voltage reading should be STABLE,
    the volume should be set to zero or even the pre-out / amp in jumpers pulled. That's what that 4.7 k ohm resistor bupkus is all about, no
    input to the power amp when setting dc offset at the amplifier's output or setting idle current at the emitter resistors for the power output
    transistors.
    With original trimpots the readings will jump 10 to 30 millivolts as you try to get to 0.000v with them overshooting the target greatly, doing the same adjustment with
    a multi-turn trimpot would be like 0.005v 0.005v 0.005v 0.004v 0.004v 0.004v 0.003v 0.003v 0.003v 0.002v 0.002v 0.001v 0.001v 0.000v -0.001v 0.000v 0.000v
    as you sat there and turned the pot smoothly.
     
  10. Jefferylu98

    Jefferylu98 AK Subscriber Subscriber

    Messages:
    119
    Location:
    Port Huron, Michigan
    I took a look at each amp board, looks all original and unmalested. Pulled jumpers/ volume was down no input and set to aux, of course I get some oddball gremlin stereo, lol.
     
  11. markthefixer

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

    Messages:
    20,394
    Location:
    Bensenville,Illinois
    with the pre-out / amp-in jumpers pulled, I want you to set the Fluke 117 meter to DC volts (the V with the lines both solid and dashed over it)
    connect the red probe to pin 14 of that amp card, and the black probe to a metal chassis ground,
    look at the voltage reading and WATCH the voltage reading to see if it changes AT ALL!!

    If the reading does change I need for you to describe the new readings,
    and how long they take to get somewhere else, if the readings decrease, and if there appears to be a pattern.

    when you did the DC offset adjusts before, How did they adjust? where did the numbers end up at?

    I'm feeling there's a fundamental disconnect and huge blind spot going on between us,
    especially on the subject of the dc output adjust of the power amplifier's outputs.

    I expected something like :
    with the original trim pots, the DC offset adjust was tricky, and jumped hundreds of millivolts when I tried to turn the pot, and getting the pot into a position of a dc voltage reading of less then 30 millivolts and greater than -30 millivolts depended more upon luck of where it landed when I let off turning torque rather than skill in hitting a specific location when turning the pot.
     
    Last edited: May 20, 2017 at 7:19 PM
  12. Jefferylu98

    Jefferylu98 AK Subscriber Subscriber

    Messages:
    119
    Location:
    Port Huron, Michigan
    Left amp/PIN 14 is -2.74dcv. Right amp/PIN 14 is -3.60dcv. Both amps voltage held rock steady after one minute of voltage rise from 0. The speaker relay clicking in and out does not seem to affect the readings on the dmm.
     
  13. Jefferylu98

    Jefferylu98 AK Subscriber Subscriber

    Messages:
    119
    Location:
    Port Huron, Michigan
    Fired up my working 1280. And I am getting very different reading on the protection board, r6 is 76.4 in 54.6 out and r5 is 54.6 in and 40.9 out. The 1280 we are working on is 76.3 all four spots??
     
  14. Jefferylu98

    Jefferylu98 AK Subscriber Subscriber

    Messages:
    119
    Location:
    Port Huron, Michigan
    I have some 820 ohm but they are 2 watts/ will they work for test purposes only??
     
  15. markthefixer

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

    Messages:
    20,394
    Location:
    Bensenville,Illinois
    That is not an issue at this time.


    Are those VOLTS on pin 14????????? Haven't you tried to dial those amps down to 0.000v on pin 14??? The only excuse would be that the trimpots would not budge the voltage and that would be even more noteworthy.

    Quite frankly the achievement of 0.000v at pin 14 outputs of the power amps SUPERSEDES and precedes the setting of idle current.
    NOT getting under 0.025v is reason to stop and fix things before moving on to idle current.

    here is the test procedure, copied in laboriously from the service manual in case you haven't downloaded it. These last posts indicate some sort of knowledge gap that must be corrected.

    \
    Rereading my posts, I didn't explicitly say pin 14 of the amp cards MUST be 0.000v (+/- 20mV = +/- 0.020V)
    I just assumed that if you were posting about and testing idle current, you KNEW about DC (offset) Balance.
     
    Last edited: May 21, 2017 at 1:36 AM
  16. Jefferylu98

    Jefferylu98 AK Subscriber Subscriber

    Messages:
    119
    Location:
    Port Huron, Michigan
    Ok mark, I played with the trim pots again (vr1) (pin14) to try to get them to 0volts, after turning them a few times each I did get them to 0 out in volts. They are so sensitive, they jump all over with the slightest movement. But after messing with them and got both to 0volts, the speaker relay is now staying closed and not clicking anymore. I do have page 30 of the service manual that tells how to set the D.C. Balance and idle current, and have used it sucessfully in the past.
     
  17. LesE

    LesE 110284 Subscriber

    Messages:
    525
    Location:
    Ontario, Canada
    If you haven't already done so, you may want to consider replacing trim pots VR1 & VR2 on the amplifier assemblies. The following are replacements recommended by Markthefixer in the SX-1280 recap thread:

    sx-1280 awh-074L vr1 150k 25 turns offset adjust 652-3296P-1-204LF
    sx-1280 awh-074L vr2 100 ohms 1 turn idle current 652-3386H-1-101LF

    sx-1280 awh-074R vr1 150k 25 turns offset adjust 652-3296P-1-204LF
    sx-1280 awh-074R vr2 100 ohms 1 turn idle current 652-3386H-1-101LF

    With the 25 turn trimmers, you should find much easier to optimize the offset adjustment.

    Les
     
  18. markthefixer

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

    Messages:
    20,394
    Location:
    Bensenville,Illinois
    If I came off as harsh in my last posts, I apologize. I re-read my last posts and wondered.

    I'm GLAD it's finally staying closed.

    now for cleanup.... put q1 back in and see if things behave themselves.
    q1 is part of the over current sensing part of the protect system.
     
  19. Jefferylu98

    Jefferylu98 AK Subscriber Subscriber

    Messages:
    119
    Location:
    Port Huron, Michigan
    MTF, no offense taken. It must be difficult at times to navigate thru these things with people such as myself with very limited knowledge of these units. I think Les made a correct statement to replace these pots, I will order tonight. Q1 is back installed and things seem to be stable at the moment. Has been powered on for an hour or so.
     
  20. markthefixer

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

    Messages:
    20,394
    Location:
    Bensenville,Illinois
    Good news.

    I'm out of practice on the "tech empathy" and "second guessing the blind spots" skills.
    My jaw just about fell off when I read the pin 14 voltages and realized you didn't understand the significance of the massive DC offsets present.
    Not when we sweat hundreds to tens of millivolts there.
    And that you had gone past that point, to set the idle currents.
     

Share This Page