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Thread: Balder lightning guitar amp schematic please!

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    Balder lightning guitar amp schematic please!

    I am desperately searching for any documentation for a BALDER LIGHTNING GUITAR AMP.
    I believe Balder was located in Sweden, then bought out by Nady Systems in Oakland, CA.
    I have checked with Nady but they say they got rid of all Balder/Nady docs years ago.
    If anyone can point me in a likely direction it would be appreciated greatly.
    One of the problems I'm having with this amp is high frequency parasitic oscillation.
    I'm told this was an ongoing problem with these, but a great SS amp otherwise

    On the circuit board it reads "S.O.S. LIGHTNING LMk 82-2

    Thank you

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    "Thermionic Apocalypse" -JT nickb's Avatar
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    I see you asked once before Balder lightning schematic needed - it's not looking good.

    I think you safely say you are on your own with this. Can you post some gut shots so we can see what you are dealing with? How do the controls affect the problem?

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    Last edited by nickb; 09-24-2017 at 08:10 AM.
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    Thanks Nick, I wasn't sure if I posted previously or not.

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    In this pic the 4ea TO3 output transistors have been removed.
    When they were in I could not prevent it from going into oscillation.

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    This pic is of the circuit just before the output. I was able to determine one of the trim pots is for DC offset. Still don't know what the other is for

    Recently I found upwards of 166 VAC nearest the missing output transistors. But this only occurs when a plug is inserted into the channel 1 input.
    It doesn't have any signal on it, just inserting it causes the high AC voltage to appear, disappears when removed. It does not occur inserted into the
    channel 2 input jack. Not sure but it may be related to the tube overdrive circuit in this amp.
    The AC is strange but the oscillation is the one I need to tackle.

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    Old Timer J M Fahey's Avatar
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    Just thinking aloud and in no particular order:
    1) expensive Darlington output transistors.
    2) you can do nothing until you remount them, amp is running and showing nasty oscillation.
    3) just a hunch but I would not be surprised if it had some family resemblance to old Hughes ¬ Kattner amps.
    They also once loved these Darlingtons, this designer might have "borrowed" that design (something way more common than most think), so that *might* help-
    4)
    How do the controls effect the problem?
    5)
    I found upwards of 166 VAC nearest the missing output transistors. But this only occurs when a plug is inserted into the channel 1 input.
    "near" (physical proximity) means nothing, connections mean everything.
    "166VAC" might very well be *60V DC* improperly understood by a cheap multimeter, measuring DC but set to the AC scale.

    So in a nutshell:
    6) rebuild the amp as original and we´ll suggests some tests.

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    "Thermionic Apocalypse" -JT nickb's Avatar
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    As Juan said + make sure no speaker is connected to avoid stressing the output transistors. Also, loose that badly wired jack plug before it shorts out and destroys the output transistors.

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    Supporting Member Jazz P Bass's Avatar
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    What in the world are they using that UPC2002 for?

    It's a 5W power amp.

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    "Thermionic Apocalypse" -JT nickb's Avatar
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    Quote Originally Posted by Jazz P Bass View Post
    What in the world are they using that UPC2002 for?

    It's a 5W power amp.
    Reverb driver (with attitude)?

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    Old Timer J M Fahey's Avatar
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    Most certainly.
    Roland and Yamaha typically used a "car radio" type chip amp to drive low impedance (8 ohms ) reverb tanks.

    They *might* also use it for an independent headphone out although that would be more unlikely.

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    The UPC2002 probably does drive the reverb. I removed the "tank" to get a better look at the traces, and the "tank" mounts just above the 2002 chip on a set of four springs. Not that it matters but the reverb springs have no cover, never did.
    I removed the Darlington's to see if the oscillation occurred prior to and without them in. Results were nonconclusive. It was at that time I noticed the high AC. I understand near means nothing, but the output drivers which connect directly to the Darlington's are there so.....and without the schematic was trying to get a general understanding of the signal flow paths.

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    Ok.
    The main point was that VERY probably you do NOT have 166VAC there, but your meter is lying to you.

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    Juan Manuel Fahey

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    Senior Member nosaj's Avatar
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    Quote Originally Posted by J M Fahey View Post
    Ok.
    The main point was that VERY probably you do NOT have 166VAC there, but your meter is lying to you.
    Ground reference could be very important in this case, no?

    nosaj

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    Before I put the Darlington's back in can anyone suggest a way to test them with certainty?
    I have a simple transistor tester but it gives me different results depending on which lead I put where.
    The manual that came with it suggests it shouldn't matter which lead goes where
    However it does say it might not test high gain Darlington's accurately
    It is a radio shack cat No. 22-330 electronic components tester

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    Quote Originally Posted by bigdrums925 View Post
    it does say it might not test high gain Darlington's accurately
    Test them using the diode function in your multimeter, they will test like any other NPN or PNP transistor with just two minor quirks because of their internal construction:
    1) forward bias Vbe will be around 1.3V instead of around 0.65V for the very good reason that you are measuring *two* BE junctions in series
    2) in many power Darlingtons , certainly in TIP142/147 , not sure on these, you will find an internal EC diode, connected "backwards" so it does not pass current under normal operation, so if you find it , don´t worry.
    It´s a "parasitic" diode which appears as a byproduct when the transistor is made, but since it does not cause any problem, they leave it there.

    Example: TIP142 showing the internal parts, see the two BE junctions in series and the parasitic diode (pointing "the other way" so it does not pass current under normal operation) ; yours shouldn´t be very different.

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    Lifetime Member Enzo's Avatar
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    And to be thorough, the two internal resistors are parallel the two BE junctions and can confuse readings.

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    I checked the Darlington's seemed ok but didn't find a double junction in every case, however the were all the same as its pair.
    Put them in and brought up the variac with the scope on the output, no load. no input plug either 0-1/2 way very little current draw, then at 50%
    the variac amp meter slams on full (1.5 amp meter) and about 20mV of oscillation appears on the scope. Same as before.
    Turned it off. Any suggestions?
    Btw the ground pin is missing from the power plug.

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    "Thermionic Apocalypse" -JT nickb's Avatar
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    I don't think oscillation is your problem, at least not primarily. I'd say idle current is too high. This brings me to something I had wondered about from looking at the pictures. In order to balance the output transistors it is usual to put small value resistors in the emitters. The problem is I don't see any. There is a row of four resistors that seem to be the same value on the top left but I can't make out the value and they seem a bit wimpy for the purpose. You should be able to determine if they are going to the four emitters with a continuity check. The whole point of this is that you would normally measure the idle current by looking a the voltage drop across those resistors.

    I see there is trimmer pot between what look like two driver transistors on black heatsinks. I suspect this is idle current adjustment. You can note the position and set then it to one end then the other with the power off and see what effect it has on the point at which the idle current shoots up. It might simply be a case of a bad trimmer. Failing that I don't think there are any great choices. My preference would be to lift the PCB and trace out the power amp section and draw a schematic of it.

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    Old Timer J M Fahey's Avatar
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    Were you using a speaker or t was unloded?
    Try both ways.
    20mV at the speaker out is *nothing*, it does not justify the 1.5A mains current jump which amounts to over 150W mains consumption.
    Where would/could that current be going?
    Place a scope probe *across* an emitter resistor (ground clip to one end, hot clip to the other, you might have to disable mains grounding on the scope) to check transistor current consumption.

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    Quote Originally Posted by J M Fahey View Post
    Were you using a speaker or t was unloded?......
    That's a good question. If you are bringing the amp up slowly on a variac with a speaker attached, you could have problems. Often, power supplies do not come up in a linear fashion when you bring them up slowly. This causes DC on the output until the amp rails balance and, of course, lots of current. So, rule of thumb, don't use a load when bringing an amp up slowly on a variac.

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    I understood he did it with no load, see post #15. :

    scope on the output, no load.

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    Quote Originally Posted by nickb View Post
    I understood he did it with no load, see post #15. :
    Oops! Apologies, I missed that part. Carry on.

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    Here's a look at the other side of the board. These are probably the resistors you spoke of. Except there are twice as many resistors as there should be (1.3 ohm)
    Click image for larger version. 

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    Yes I thought it was idle current problem too at first. And assumed that trim pot would be for idle current.
    At the point when the current shoots up the drop across one of the resistors is 1 volt.
    again this is at half power on the variac, and more interesting is I get a 16 v p-p ac sine wave at the speaker output.

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    Supporting Member The Dude's Avatar
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    On a side note, whatever that part is that's had it's solder pads lifted off (near the emitter resistors) does not look like it's very well attached. I'd unsolder it, clean the traces a bit and solder it in there better. Looks like it's barely (if at all) tacked in there.

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    Quote Originally Posted by The Dude View Post
    On a side note, whatever that part is that's had it's solder pads lifted off (near the emitter resistors) does not look like it's very well attached. I'd unsolder it, clean the traces a bit and solder it in there better. Looks like it's barely (if at all) tacked in there.
    I understand at this point you all are trying to figure out whats wrong. I haven't seen it mentioned yet. The power transformer what kind of voltages is it giving out disconnected from the PCB? With the transformer disconnected from the circuit and a load put on the PT will it still give a high amp draw? just trying to start from the beginning of the circuit.

    nosaj

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    I understand. Does it help that the rail voltages are +- 46v and +- 12.6volts without disconnecting the trans?
    If not I can do that.

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    Old Timer J M Fahey's Avatar
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    Yes I thought it was idle current problem too at first. And assumed that trim pot would be for idle current.
    And it can still be an idle current problem: who says the trimmer or the circuit associated to it is working properly?
    In fact I see the area where the Bias trimmer and bias sensing transistor should live, with signs of broken tracks and poor repairs.
    That alone is an alarm siren going full blast.

    At the point when the current shoots up the drop across one of the resistors is 1 volt.
    again this is at half power on the variac,
    Another red flag: 1V means >1.5A per transistor, or over 3A , at idle and with only half voltage applied or less.

    and more interesting is I get a 16 v p-p ac sine wave at the speaker output.
    What frequency sinewave?
    Are you injecting a tone while you do this test? You shouldn´t.
    And no load connected.

    To be able to suggest tests, we need that output stage schematic, specifically so you can follow instructions and we all speak the same, so grab pencil and paper and draw it.

    Not all of the amp (hopefully) but at least the power rails, ground, main filter caps, speaker out, Zobel network, grounding, power transistors and mainly the bias circuit.

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    Curiously just before the amp meter swings full on, a 600Hz signal @ 14Vp-p appears at the output with no input signal.
    The sine wave output remains after the meter swings full on and I see no oscillation. However the speaker plug was only half way in.
    So it seems possible that the 600Hz is on the ground plane perhaps. When the speaker plug is in I see the oscillation and no 600 Hz.
    Now can't recreate the 600Hz at all or the oscillation but the meter still swings hard 1/2 way on. I ramped up the variac all the way momentarily and measured 3.4 volts drop across the emitter resistor.

    The schematic for the output will probably take a little time because I've never drawn one before and following the traces on this amp is a nightmare. But I will try in the next day or so. I don't know what a Zobel network is, can you explain?

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    "Thermionic Apocalypse" -JT nickb's Avatar
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    The 1.3 ohm resistors may be in four parallel pairs giving 0.65 ohms. That makes your idle current huge so there is no question there is a problem there. It might help to look at other solid state power amp schematics to get a feel of what's there as there are often great similarities between designs.

    A Zobel network is a capacitor and resistor connected across the speaker. It's there to improved the amplifier's stability especially at higher frequencies. Zobel networks


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    It's clear that the amp failed in the past and the question is whether it was fixed correctly, or not. You can easily see that several components were replaced. The bias can be altered with the upper trimmer (2k2). It works together with the little transistor on the top of the board. So I would check the trimmer and the transistor. Also, what are the voltages on collector and emitter of the transistor. It seems to me that there is no other way to fix the amp then drawing its schematic and verifying whether it is correct. This shouldn't be to difficult since I think that this is typical solid state amp.

    Mark

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    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by bigdrums925 View Post
    The schematic for the output will probably take a little time because I've never drawn one before and following the traces on this amp is a nightmare. But I will try in the next day or so. I don't know what a Zobel network is, can you explain?
    We don´t need the full schematic, just the power transistors, what´s directly connected to them, and mainly
    the bias circuit , which basically is a transistor, a trimmer and 4 or 5 resistors.
    To be able to suggest what to measure and how to adjust it, we need at least that, specially so we all talk the same.
    Draw what you can and if we find something missing, we´ll ask you to add it ... but we have to start with *something*

    This is the area we are interested in:
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    Attempt:

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    Did you acquire the amp in this condition?

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    What worries me is the resistors that are in series with the BIAS trimmer are both 33k and they both were replaced. 33k seems to much for me. But it look like the OP lost interest of fixing the amp

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    Old Timer J M Fahey's Avatar
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    Hey, maybe we have good news in a week or two

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    Obviously I have too much time on my hands, but I do love a puzzle. The 220 ohm feedback resistor
    probably should be 2.2k -looks like it has been replaced with the wrong value, might even solve the
    oscillation problem. It's the 1W resistor on the left

    Doug



    http://music-electronics-forum.com/a...1&d=1506712143



    (I've edited this post to make a few corrections)
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    Last edited by dmeek; 09-29-2017 at 08:10 PM.

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    "Thermionic Apocalypse" -JT nickb's Avatar
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    Way to go Doug! I think there are some errors a so I'll try a redraw in due course...


    Agree with other suggestions plus I'd check the small TO92 transistor next to the heatsink. I suspect it's dead.


    ... this is my interpretation, with suggested value corrections based on Doug's hard work
    Balder Lightning Power amp- not verifed V1 .pdf

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    Last edited by nickb; 09-29-2017 at 10:32 PM.
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    Nice . I wonder whether some resistors that we think are 33k, are actually 2k2 (the stripes are red instead of orange). But if someone replaced the resistors in series with the bias trimmer with 33k, such high values make it impossible for the bias transistor to work correctly. The OP could measure some of the 33k resistors.

    Mark

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