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Stage Line 500W amp repair project

Discussion in 'General Electronics Discussion' started by bikemech, Oct 23, 2014.

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  1. bikemech

    bikemech

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    Oct 23, 2014
    just noticed also fuses F5 and F6 have blown 0.1A 250V
     
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    I'm not really sure how far back to go into the circuit with checking semiconductors. Let's start with the driver components, which are the four transistors that are clipped to the sides of the heatsinks, and several other smaller components in that area. Here is a complete list:

    LEFTRIGHTTYPEActionDigi-Key reference
    D4, D6D24, D261N4148Replacehttp://www.digikey.com/product-detail/en/1N4148/1N4148FS-ND/458603
    D5, D7D25, D27BZX79-C3V3Replacehttp://www.digikey.com/product-detail/en/BZX79-C3V3,113/568-8059-1-ND/2762749
    D9, D10D21, D321N4004Replacehttp://www.digikey.com/product-detail/en/1N4004/1N4004FSCT-ND/1626118
    Q1, Q10Q23, Q25MPSA42Replacehttp://www.digikey.com/product-detail/en/MPSA42ZL1G/MPSA42ZL1GOSCT-ND/2623431
    Q11, Q22Q37, Q40MPSA92Replacehttp://www.digikey.com/product-detail/en/MPSA92G/MPSA92GOS-ND/1482523
    Q12Q262SD1763A (clipped to heatsink)Remove and test
    Q13Q342SB1186A (clipped to heatsink)Remove and test.
    The parts I've listed as just "Replace" are so cheap that it's not even worth testing them. The only ones that are worth testing are the four driver transistors, because the original type number is no longer available. Here's how to test them.
    epoint 270979 transistor tests.png

    You'll need to remove them from the board first. Set your multimeter to the range shown (for the Ω range, use the 2000 kΩ range), and connect the probes to the leads as indicated by the coloured dots. You can make contact with one probe, but not both, because the resistance of your body will affect the reading. Don't hold the mounting tabs of the transistor either; these are connected to the middle pin. Check that the multimeter reads as shown in the "Should show" column. If all of the indications are right, the transistor is probably OK.

    That covers the driver transistors. There are a lot more small transistors, and some more diodes, that I think are less likely to be damaged.

    Let me know the result of testing those driver transistors before you order the others, in case I need to look for suitable replacements for them.
     
  3. bikemech

    bikemech

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    Oct 23, 2014
    Hi kris,
    Ok tested all the driver transistors and all but one are good,
    Q26 reads 0000,
    As for the others you said not to bother testing so I havent!,
    And they the small glass type red diodes ? Marked on the board as D4--D6 and so on ?
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    OK. I think it's best to replace the driver transistors as well. The original types are obsolete but Sanken make some pretty close equivalents. Here are the specifications for the original parts, from data sheets from SavantIC. This is mainly for my future reference.

    2SD1763, 2SB1186
    TO-220 full pack
    120V; 2A (2SB1186: 1.5A) (3A peak); 20W
    hFE 100~320 @ 100 mA, 5V
    hFE classifications: E = 100~200; F = 160~320
    ft typ 80 MHz (2SB1186: 50 MHz)
    output capacitance typ 20 pF (2SB1186: 30 pF)

    Here are my suggested replacements. You will need two of each.
    Sanken 2SC4883 http://www.digikey.com/product-detail/en/2SC4883/2SC4883-ND/3929414 USD 1.54
    Sanken 2SA1859 http://www.digikey.com/product-detail/en/2SA1859/2SA1859-ND/3929366 USD 1.58

    Yes, D4~7 etc are small glass diodes. They're listed in my table in post #42.

    So now you should be in a position to create a bill of materials to order from Digi-Key.

    Now you've removed the semiconductors from the output stage, you should check the resistors in that area of the board. Here's a resistor colour code chart that I found at http://www.diyaudioandvideo.com/Electronics/Color/

    ResistorColorCode.gif

    For each resistor, work out what value it should be, set your multimeter to the resistance range that's closest to, but higher than, that value, and measure the resistor. For example, if the resistor is green-blue-red, its value is 5600Ω or 5.6 kΩ so you set your meter to the 20kΩ range.

    Those resistors probably have gold tolerance bands, so their measured value should be within ±5% of the marked value. Most of the resistors should measure correctly in circuit now that the semiconductors are gone, but some may measure lower than the printed value because of other resistors in the circuit. No resistor should measure higher than its marked value. Make a list of resistors that measure significantly lower for me to check against the schematic.

    Just measure the resistors in the area where you have removed the diodes and transistors.

    Once we're confident that you don't need to replace any resistors, you can send your order off to Digi-Key and replace the semiconductors, then you can clean the board, install the replacement semiconductors, and take some photos of the underside, then we can start powering it up!
     
  5. bikemech

    bikemech

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    Oct 23, 2014
    Thanks kris, will do that over the next couple of days and get back to you with my results.
     
  6. bikemech

    bikemech

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    Oct 23, 2014
    getting ready to order some parts now,
    does this look correct kris ? minus any resistors i may need?[​IMG]
     
  7. bikemech

    bikemech

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    Oct 23, 2014
    ok i have ordered these!! just got to wait for them to arrive to do any more,
    any resistors i may need i can get from MAPLIN electronics store near me , altho its much more expencive
    [​IMG]

    thanks for all your help and guidance kris youve been a star so far,

    i have a good idea of what i am doing now, been youtubing and googleing like mad trying to learn how to test all the componants, just looking forward to powering it up and see what happens,
    am i going to have to replace all the componants before i start putting powere in , or is it fit some and power it then fit some more and see how it goes?
     
  8. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Pete, sorry I didn't reply soon enough! Now you screen shot doesn't show up so I can't check it!

    That's great that you've been doing your own "research":)

    You're going to check the resistors in the output stage before you install the new semiconductors, right?

    I suggest you install everything except the output transistors and heatsinks (leave the driver transistors just standing freely), don't connect the speakers, make sure you have the resistor fuses installed, and power it up and make some measurements.

    Measure these voltages with the black probe connected to terminal T4 or terminal T9. These are unconnected terminals buried roughly in the middle of the output stage componentry for each channel.

    To make it quicker and safer to measure voltages relative to 0V, I recommend that you connect your multimeter's black probe to one of those terminals using a piece of wire, and insulate it so it can't touch anything if it moves. You could use an alligator clip lead (a short piece of wire with an alligator clip at each end), or you could solder a piece of wire onto the tag and twist the other end around the probe point and hold it with a rubber band or something like that. Wrap some electrician's tape around that connection so it can't touch onto anything. Then set the meter for DC voltage and measure away!

    Start by measuring the positive and negative supply rails for the output stages:

    D9 cathode should be around +43~45V
    D10 anode should be around -43~45V
    D21 cathode should be around +43~45V
    D32 anode should be around -43~45V

    If not, there may be a problem in the power supply, or the resistor fuses may have gone open - check the LEDs on the fuses. If so, that indicates a short or other serious problem.

    If that's OK, check the idle DC voltages on the outputs, at either end of R39 (left channel) and either end of R68 (right channel). These should both be no more than 0.2V positive or negative. Ideally they should be exactly 0V but there is always a small offset.

    Next, check the output bias voltages. Disconnect the black probe from 0V and measure between D5 cathode (red probe) and D7 anode (black probe) for the left channel, and between D25 cathode (red) and D27 anode (black) for the right channel. Both channels should measure around 1.5V. This voltage is the sum total base bias voltage for the two output transistors in each channel; each output transistor should be receiving about 0.75V base-emitter bias voltage.

    Once you get that far, let me know!
     
  9. bikemech

    bikemech

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    Oct 23, 2014
    [​IMG] Arrived today
     
    Frenoy Osburn and KrisBlueNZ like this.
  10. bikemech

    bikemech

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    Oct 23, 2014
    when you say output stage do you mean R30 and R32 on the left chanel and R62 and R71 on the right,
    these are the main two between the driver transistors?
     
  11. bikemech

    bikemech

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    Oct 23, 2014
    tested
    Left chanel right chanel
    R2 673 R25 672
    R31 673 R78 675
    R30 10.0 R26 10.0
    R32 10.0 R71 10.1

    meter set at 2000Ω for R2 R25 and R37 and R78

    set at 200Ω for the others
     
  12. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    I'm not sure what those numbers mean in post #51. I think it's unlikely that any of the resistors are damaged but it's probably worth checking them before you install the semiconductors.

    See post #44 starting from the resistor colour code chart. There's full details in that post.

    You can check all of the resistors in the output stage area - the section where the circuit board gets narrower. If any resistor measures more than ±5% different from its marked value, make a note of the reference (e.g. R23) and the value you measured, and post the list. Do this all before you fit the new semiconductors because they can affect the value you will measure.
     
  13. bikemech

    bikemech

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    Oct 23, 2014
    does that make any scence to you now kris
     
  14. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    You mean that R2 measures 673 ohms? That's within ±5 of 680Ω so that's OK.

    In the right channel, the matching componen is R52, not R25, right? Again 672Ω is fine.

    R31 (left) and R78 (right) are also 680Ω resistors, so measurements of 673Ω and 675Ω are fine.

    R30, R32, R62 (not R26) and R71 are 10Ω resistors, so measurements of 10.0Ω and 10.1Ω are fine too.

    Do all the other resistors measure OK in the output stage?
     
  15. bikemech

    bikemech

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    Oct 23, 2014
    yes

    Correct

    R31 (left) and R78 (right) are also 680Ω resistors, so measurements of 673Ω and 675Ω are fine.

    R30, R32, R62 (not R26) and R71 are 10Ω resistors, so measurements of 10.0Ω and 10.1Ω are fine too.

    sorry if am being dim but i am not sure i understand what you mean when you say output stage??

    do you mean ALL the resistors in each chanel
    [​IMG][/QUOTE]
     
    Last edited: Nov 15, 2014
  16. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Yes that's what I mean. But it's unlikely that any of them have failed, so it's your call whether you do it or not.
     
  17. bikemech

    bikemech

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    Oct 23, 2014
    Ok so if I don't check them all now, could I damage the new components one fitted, or would I just have to check and replace later?
     
  18. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Unlikely to damage the new components because we'll be using the resistor fuses.
     
  19. bikemech

    bikemech

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    Oct 23, 2014
    On the schematic it shows all the resistors, there location and valves, could I make a note of them on paper, and test each one that way until I have tested them all, am having trouble working out the values from the chart, some of them are hard to see and I don't have a magnifying glass at present .
     
  20. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Sure. If you get a mismatch though, check the marking on the resistor - the schematic may be slightly different from the board. In any case, post a list of all discrepancies you find.
     
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