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Thread: Traynor YBA-3 Power Xformer making arching noise, Is it about to fry?

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    Traynor YBA-3 Power Xformer making arching noise, Is it about to fry?

    Hey guys,
    I bought this Traynor YBA-3 at the flea mrkt. Upon powering it on and playing it for about 10 minutes, One of the big can caps (80uf) started making some popping sounds, So I replaced all electrolytic caps with same value. I've changed all PH204 diodes with 1n4007 & 1n4004 diodes. Bought new power tubes (EL34). Here's the big issue, I turn on power, amp is in standby, power transformer is humming, as soon as I flip the standby switch to operate, the power tranny starts popping and cracking, certainly sounds like electrical arcing inside of it. I turn it off because one of the 80uf caps starts to smoke. Is the power tranny about to die? Any suggetions? Thanks to all. traynor_customspecial_yba3c.pdf
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    Supporting Member Jazz P Bass's Avatar
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    It would help to know which '80uf' cap is giving off smoke.
    If the power transformer was stressed to the point of crackling, it very well may be bad now.
    I do not see how the PT could make a cap smoke.
    It appears that the initial problem may not have been found.
    (or a new one was introduced)
    Seeing that you did all of that replacing of parts, it may be wise to go back & check your work.
    I would remove all of the tubes before powering it up again.

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    Quote Originally Posted by Jazz P Bass View Post
    Seeing that you did all of that replacing of parts, it may be wise to go back & check your work.
    I would remove all of the tubes before powering it up again.
    The second photo shows that the cap that is directly to the right of the fiberboard is wired in backwards. The positive B+ line from the diode string is wired to the negative end of the cap.

    Double check all of your wiring.

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    Quote Originally Posted by Jazz P Bass View Post
    It would help to know which '80uf' cap is giving off smoke.
    If the power transformer was stressed to the point of crackling, it very well may be bad now.
    I do not see how the PT could make a cap smoke.
    It appears that the initial problem may not have been found.
    (or a new one was introduced)
    Seeing that you did all of that replacing of parts, it may be wise to go back & check your work.
    I would remove all of the tubes before powering it up again.
    C27 was the smoking cap. I'll check my wiring too. I wired everything like it was originally. But I know someone else has been in it before me.

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    I've circled the cap in the picture, that was smoking. I'm going to check all wiring/connections later today and report back. If anyone notice other wiring errors, please let me know. Thank You ALL.

    Coop
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    Looks to me as if the old can cap that your circled cap is partly replacing, is still in position on the other side of the chassis, and that its tag is being used for the new circled cap. Lazy and/or stupid techs sometimes do that as it saves them putting in a tagstrip. It leaves the old bad cap in circuit which is obviously not good. If the old can cap is still in there it needs removing. Possibly the smoke was coming from the can cap beneath rather than the new cap.

    Plus as 52Bill says that cap to the right of the fibreboard may be wired the wrong way around, I can't quite see for sure.

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    Your smoking cap appears to be C26 rather than C27. Or rather it is where the totem pole arrangement of C26 AND C27 are supposed to be. So it can't handle the voltage.
    This thing is pretty messed up as far as the power supply filter caps go. Get it straightened out before powering it up again, hopefully it's not to late for the PT.
    The cap 52Bill mentioned I can't even figure what it is supposed to be. The yellow wire it connects to (becomes a twisted pair with the black), where is it going? Is that a choke? Is this for sure the right version of the schematic?

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    Quote Originally Posted by g-one View Post
    Your smoking cap appears to be C26 rather than C27. Or rather it is where the totem pole arrangement of C26 AND C27 are supposed to be. So it can't handle the voltage.
    This thing is pretty messed up as far as the power supply filter caps go. Get it straightened out before powering it up again, hopefully it's not to late for the PT.
    The cap 52Bill mentioned I can't even figure what it is supposed to be. The yellow wire it connects to (becomes a twisted pair with the black), where is it going? Is that a choke? Is this for sure the right version of the schematic?
    Okay, I've looked closely at the photo and the smoking cap is C27A, which is the bottom cap of the totem stack. The B+ line from the rectifiers is wired to the wrong side of C26 which is the middle of the stack. I can only assume that the yellow wire is the center tap of the OT primary.

    And I'll agree with both Alex and g that the work here is far from pretty. I hope that you are only temporarily soldering in parts to test the circuit, and will go back later and straighten things up.

    Edit: On a third look, the yellow and black do look like they are leads to a filter choke. They are wired between two nodes of the power supply.

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    Last edited by 52 Bill; 12-17-2012 at 06:06 PM.

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    Quote Originally Posted by 52 Bill View Post
    Okay, I've looked closely at the photo and the smoking cap is C27A, which is the bottom cap of the totem stack. The B+ line from the rectifiers is wired to the wrong side of C26 which is the middle of the stack.
    That makes more sense, thanks. So the cap to the right of the fibreboard (C26) is not really backwards, but the lead from the diodes is connected to the wrong side of it. This put the full rectified DC from the diodes across C27, causing it to overheat and smoke.

    Edit: Near as I can tell, choke is replacing R42, feed for R31 (now 10W) is now post choke, and R30 has been changed to the big brown 500 ohm.

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    Last edited by g1; 12-17-2012 at 06:50 PM.
    "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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    Quote Originally Posted by g-one View Post
    That makes more sense, thanks. So the cap to the right of the fibreboard (C26) is not really backwards, but the lead from the diodes is connected to the wrong side of it. This put the full rectified DC from the diodes across C27, causing it to overheat and smoke.

    Edit: Near as I can tell, choke is replacing R42, feed for R31 (now 10W) is now post choke, and R30 has been changed to the big brown 500 ohm.
    Thanks guys for pointing out my wiring mistake. I looked at some before pics, and the diode lead wire, was hooked to the wrong side of C26. The plastic insulated yellow & black twisted wires are the choke. Yes, my messy work is temporary only. I want to ask a silly question. When I replaced the original 80uf caps, I used 80uf @ 450 volts, but on the schematic, It has two 40uf - 450v sections (multi-sect can caps) tied together, which would handle 900 volts. Correct? Should I have used two new 40uf - 450vdc caps stacked together? i noticed +540v on C26, on schematic. So, my current 80uf-450v caps, can't handle that +540v? Forgive my ignorance. I'm still trying to learn this stuff. I really appreciated all of help, knowledge, and advise. I have NOT fired up the amp since correcting the diode lead error. What should I do next?

    Coop

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    Quote Originally Posted by CoopDaKill View Post
    When I replaced the original 80uf caps, I used 80uf @ 450 volts, but on the schematic, It has two 40uf - 450v sections (multi-sect can caps) tied together, which would handle 900 volts. Correct? Should I have used two new 40uf - 450vdc caps stacked together? i noticed +540v on C26, on schematic. So, my current 80uf-450v caps, can't handle that +540v?
    No, when two caps are wired in parallel, the capacitance adds up but the voltage stays the same. So two 40uF @ 450 volts in parallel become equivalent of 80uF @ 450 volts.

    When two caps are wired in series the capacitance halves and the voltage doubles. So two 80uF @ 450 volt caps in series becomes the equivalent of a 40uF @ 900 volt cap.

    Of course this assumes caps of equal values and voltages.

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    This particular (original) cap arrangement is a bit tricky to learn series or parallel capacitors with. The two 40uf sections tied together (C27A & C27B) are in parallel, so the voltage remains the same but the capacitance doubles. (capacitance adds in parallel but divides in series, the opposite of resistance). So the combination of C27A&B forms an equivalent cap (C27E I'll call it) which is 80uf, 450V as the voltage stays the same for parallel caps.
    The series arrangement is C26 and C27E. In series, the capacitance divides but the voltage rating adds. So the combination of C26&C27E becomes equivalent of a 40uf 900V cap. The 540V shown is across the series arrangement.
    The same will be true for the C30 and C28A&B arrangement.
    So you have used the correct caps for the arrangement.

    Edit: Sorry Bill, posting at the same time.

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    "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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    Well, good news & bad news. I fired it up, fliped the standby off, and all seemed normal. Plugged in a guitar, and played for about 5 minutes, and then the fuse blew. I fear the power tranny finally bit the dust. There were no real strange anomilies before the fuse blew. No arcing sounds. The amp sounded great. Only thing I recall doing last was, using the treble boost swith on then off. That switch sounded dirty with some static. Then fuse blew. Coincidence probally. ???? Guess I'll unhook all power tranny leads tomorrow and see what ohm readings I get on the windings. I never changed that cap that was smoking previously either. It is a little bulged. Tested within spec on my meter. I know I should've changed it, but I had no more same value caps. That cap wouldn't make it blow a fuse, if it shorted, would it? Disregard that last question. Just checked that cap, it reads OK. None of the caps were warm / hot this time. No smoke.

    Also, Thanks guys for re-educating me on wiring schemes. After I read it, I had a deja vu moment. Duh.........

    g-one: I recognize the Rollins Band "Liar" lyric. My wife and I love that album. We have "Weight" on clear vinyl. Rock On!!

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    Last edited by CoopDaKill; 12-18-2012 at 01:14 AM.

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    If the cap was smoking it needs to be changed, especially if it is bulged. It could read ok but be shorting at higher voltages. However then I would expect it to be warm!
    A blown fuse could also be caused by a bad power tube or bias circuit problem.

    P.S. Rollins somehow always makes me think of IceT, I guess because they both went from hardcore to become actors on TV. I had the IceT "bodycount", it was so bad it just made me laugh. "there goes the neighbourhood"

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    Don't disconnect the PT. Replace the the fuse and the cap with the correct ones. Pull the output tubes. Use a lightbulb limiter and take some voltage measurements first. You shouldn't be testing the amp without some type of current limiting. The blown fuse may have been stressed from your earlier antics.

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    If the PT were shorted, it would freak out even in standby. Yours only freaks out when the standby switch is turned on. Your caps are exxploding. That is not likely the fault of the transformer, all the transformer does is make AC voltages. If you replaced the bad caps and the new ones blew up, then either the voltage across them (wwhich you could measure) is WAY above their rating

    ORRRRRRR

    you have a bad rectifier sending AC (reverse voltage ) into the caps. I like that second suspect the best.

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    OK, replaced the 1N4007 diodes, with 1N4002's. Thats all I had. The old ones tested OK on meter. Changed that 80uf-450v cap that was smoking previously. Check other caps. Put in new fuse, Took out power tubes, Plugged amp into lightbulb dimmer and fired it up. Took some voltage readings, seemed OK, So, I put the power tubes back in and plugged into to wall outlet. Took some voltage readings. The biggest voltage issue I noticed is: I'm getting +590v on pin 3 of the output tubes. Schematic says +540v. I know line voltage is a little higher, as compared to yesteryear, but +50v difference is alot. What should I do I'm only running the amp (out of standby) long enough to take voltage readings. Thanks.
    Coop
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    Last edited by CoopDaKill; 12-18-2012 at 10:23 PM. Reason: spelling

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    If you are taking your readings real quick, the power tubes may not be warming up. The voltage may come down some as they start to conduct properly. Also the bias setting (idle current) will affect the pin 3 voltage, the colder the amp is biased, the higher the plate (pin3) voltage will be.
    Any decent EL34's should be able to handle that kind of voltage, it's the 450V caps you need to worry about. Check that none of them have more than 450V across them.
    Because the fuse only blew after playing for 5 minutes, I'm inclined to think you have a bad power tube that is shorting under use. Either that or a leaky coupling cap or bias problem.
    Watch for any sign of an output tube turning red or bright flashes, if so, try to shut down before blowing more fuses.

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    Changed a few more resistors. One of the carbon comps drifted badly. Amp is starting to stablize, I think. But, I'm getting about 584v on R37. Schematic says 540v. All other 80uf-450v caps are close to normal voltages.

    This amp has a bias adjust pot, So, what would be an ideal bias voltage? EL34's. Also,

    This amp is missing the tube cooling fan, that mounts in the side of the head cabinet. Am I correct in saying it's a 117v AC fan? I'd like to find a replacement. Thanks Again
    Coop

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    Old Timer Gtr_tech's Avatar
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    Its a 120vac fan. It doesn't need to stir up a hurricane inside the chassis, just move some air around so you don't get too much heat build up.

    I'd replace those HT rectifiers with 4007s. 4002s are not gonna cut it.

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    44V difference from 540V is about 8%.

    The amp was designed for a wall voltage of 110V. Modern US mains voltage is closer to 120V (which is ~ 9% higher).

    So 584 sounds about right.

    You really can't set the bias in any meaningful way by measuring the bias voltage.

    Best bet is to measure the DC resistance of the O/P Transformer primaries from centre tap to plate (having first powered the amp down, disconnected it at the wall and discharged power electrolytics) . Then with the amp powered up you can measure the voltage across them and work out the plate current of each tube by Ohms Law. You can work out the tube dissipation by measuring the plate voltage of each tube and multiplying it by the current you just calculated. You probably want to see your EL34s dissipating between 14 and 17W at idle.

    If you didn't understand what I just wrote. Don't do it. Take it to someone who knows how to do it.

    If you did: Be careful. There's nearly 600V on both ends of those windings and the centre tap. Touching DC voltages that high can do rather more than spoil your day.

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    Quote Originally Posted by Gtr_tech View Post
    Its a 120vac fan. It doesn't need to stir up a hurricane inside the chassis, just move some air around so you don't get too much heat build up.

    I'd replace those HT rectifiers with 4007s. 4002s are not gonna cut it.
    Thanks guys. I'm grateful for the valuable knowledge that you have given.

    Will you educate me as to why the 1N4002 diodes should be replaced with 1N4007 diodes, in this circuit?

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    Last edited by CoopDaKill; 12-20-2012 at 08:17 PM.

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    1N4002s are rated at 100V. 1N4007s at 1000V. You actually want diodes that are rated at at least twice the B+ voltage as that is the reverse voltage that will appear across them from the transformer. You can put diodes in series to achieve the desired voltage rating. (You can see from the schematic that the original design used series diodes). Call me paranoid, but I'd be inclined to use two 1N4007 per side for an HT Voltage of 580V. Or use something rated at 1.5kV like a BY448

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