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

[CoopDaKill]

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

[Jazz P Bass]

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.

[52 Bill]

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.

[CoopDaKill]

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.

[CoopDaKill]

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

[Alex R]

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.

[g1]

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?

[52 Bill]

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.

[g1]

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.

[CoopDaKill]

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

[52 Bill]

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.

[g1]

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.

[CoopDaKill]

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!!

[g1]

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"

[olddawg]

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.