Well there's nothing like having a fuse blow instantly upon turn on to dampen your spirits. I have been working on this Opera M99 power amp for a week now tuning the feedback loop among other things and was getting ready to make the final adjustments today and when I turned it on the main fuse blew instantly. I have spent the afternoon working my way thru the problem and to me, it has to be the transformer, or the way I wired it 10 years ago when I replaced the original which had burned to the core (I got it this way) along with one of the output xfmrs. I managed to get the original xfmrs from Opera and went to my favorite Chinese restaurant to help me translate the wire colors on the label. It ran fine up until now, I pulled the cover off it, it's a nice heavy torroid and there is no indication of burn or failure, no shorts between windings and no shorted windings, as far as I can tell. So with all tubes out and HV and bias wires pulled from the rectifier board my 200W light bulb tester still comes on full brightness, I measure about 10VAC on the input to the xfmr and get about .5VAC on the heaters, 12V on the bias and about 20VAC on the HV windings.
So I am now thinking I may have wired the primary incorrectly back in the day and something finally let go, I don't know I'm just taking a stab at it. Anyway, I have attached the label from the xfmr with a web based translation, as well as the original in case anyone here can translate it better. The measured R between primary windings seems normal, about 2.3-2.5 depending on voltage tap. There is one yellow wire, 2 reds, 2 blacks and one green on the primary side. One of the blacks is, or seems to be, directly connected to the yellow. Not sure if that is a short or is by design.
In your opinion, how should the primary windings be connected for 115VAC?
Thanks!
PS I am not sure "fuse" is the correct translation for the yellow wire, I got several interpretations each time I reloaded the image.
So I am now thinking I may have wired the primary incorrectly back in the day and something finally let go, I don't know I'm just taking a stab at it. Anyway, I have attached the label from the xfmr with a web based translation, as well as the original in case anyone here can translate it better. The measured R between primary windings seems normal, about 2.3-2.5 depending on voltage tap. There is one yellow wire, 2 reds, 2 blacks and one green on the primary side. One of the blacks is, or seems to be, directly connected to the yellow. Not sure if that is a short or is by design.
In your opinion, how should the primary windings be connected for 115VAC?
Thanks!
PS I am not sure "fuse" is the correct translation for the yellow wire, I got several interpretations each time I reloaded the image.
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Yes, those translations exactly correct!
In Chinese it means fuse. But I not sure where to connect it. Maybe it's screen?
I believe connect both black wires together to neutral, and both red wires together to live for 115VAC.
Hi Chris,
Thank you for confirming, much appreciated. As you described it is how I had it connected 🙁 except I had the yellow wire as neutral, but it measures like it is internally connected to one of the black wires, but not both, and the red wires connected to hot. Maybe I'll try just the blk-red pairs leaving the yellow disconnected.
Thank you for your help.
cheers
Thank you for confirming, much appreciated. As you described it is how I had it connected 🙁 except I had the yellow wire as neutral, but it measures like it is internally connected to one of the black wires, but not both, and the red wires connected to hot. Maybe I'll try just the blk-red pairs leaving the yellow disconnected.
Thank you for your help.
cheers
I see two possibilities for the yellow. It could be a shield between the primary and secondary or it could be a thermal breaker. If the latter it would make sense that it's connected to one of the black wires, but I would then expect there to be two of them - one for each primary winding.
If the yellow is indeed a shield and the shield is shorted to one of the primaries I'd toss the transformer.
It wouldn't cost too much to have Toroidy in Poland wind you a transformer to match the specs: www.toroidy.pl
Tom
If the yellow is indeed a shield and the shield is shorted to one of the primaries I'd toss the transformer.
It wouldn't cost too much to have Toroidy in Poland wind you a transformer to match the specs: www.toroidy.pl
Tom
Connecting the yellow wire to mains neutral puts the fuse in series with the trafo primaries. Makes sense that the internal fuse is between (one of) BLK and YEL wires.
Incidentally the trafo's labelling is M100 whereas your amp is M99. Any differences between those two amp models?
PS - I think the trafo's labelling has an error in that the 70V winding (4th line down) should be included in the secondaries 'block', not the primaries.
Incidentally the trafo's labelling is M100 whereas your amp is M99. Any differences between those two amp models?
PS - I think the trafo's labelling has an error in that the 70V winding (4th line down) should be included in the secondaries 'block', not the primaries.
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Sorry I missed this line, it should be a thermal fuse! I think for 115VAC better connect two black wire together via a wire nut, and the yellow wire go to neutral.
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Well shoot, that didn't do it, I also tried just one set of blk-red windings, no difference, full bright light bulb on the dim bulb tester.
Any other thoughts?
Cheers
Any other thoughts?
Cheers
I suppose it's possible the primary windings were wired correctly and there is an internal short somewhere but I should be able to measure on the output leads with my ohm meter, yet there is nothing abnormal.
Strange, and it just happened all of a sudden for no obvious reason.
Mmmm??
BTW, what is the purpose of the grn-red-blk winding, how would it be used?
Strange, and it just happened all of a sudden for no obvious reason.
Mmmm??
BTW, what is the purpose of the grn-red-blk winding, how would it be used?
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Green is 125V, red is 115V and black is 0V. For 115V mains the green wire should leave open.
The green wire for 240V only (0-115 + 0-125).
Check the transformer mounting bolt and washers? It look rusty on the bottom.
Well it's terminal, I pulled it out this morning and unwound the outer wrapper, no obvious signs of damage and it still draws full 200W thru my dim bulb tester.
I guess it's toast unless anyone has any ideas on how to further test/repair it.
Thanks for everyone's help getting me this far.
Cheers
I guess it's toast unless anyone has any ideas on how to further test/repair it.
Thanks for everyone's help getting me this far.
Cheers
I don't think your dim bulb test can be conclusive. It could just mean the bulb consumes the power more easily than the transformer. What was the rating of the fuse that blew, and was it fast or slow?
I have a general purpose power supply where someone fitted a toroid for the heater output, and that was blowing fuses too, but the toroid is OK, it is just too much to handle at power on. I intend to fit an inrush current limiter.
I have a general purpose power supply where someone fitted a toroid for the heater output, and that was blowing fuses too, but the toroid is OK, it is just too much to handle at power on. I intend to fit an inrush current limiter.
Thanks.
It blew a 6A slow blow. In the last week I have turned it on/off several dozen times, sometimes only 30 seconds apart as I made changes to the feedback loop. Not sure why it popped this time. The dim bulb has worked for 20 years for me, have never seen it do this unless there is a real problem, and I have used it on this amp previously when I first fired it up after sitting for a few years, worked fine. I'm using a 200 and 300W bulb depending on amplifier.
thank you
It blew a 6A slow blow. In the last week I have turned it on/off several dozen times, sometimes only 30 seconds apart as I made changes to the feedback loop. Not sure why it popped this time. The dim bulb has worked for 20 years for me, have never seen it do this unless there is a real problem, and I have used it on this amp previously when I first fired it up after sitting for a few years, worked fine. I'm using a 200 and 300W bulb depending on amplifier.
thank you
When you measured the AC voltages with the bulb in series, you had "10VAC on the input to the xfmr and get about .5VAC on the heaters, 12V on the bias and about 20VAC on the HV windings." Given that the line voltage is around 120VAC, there is a factor of about 12. That would mean that the voltages would be about 6VAC for heater, 144VAC for bias, and 240VAC for HV for 120VAC input to the primaries.
There are discrepancies with the bias and HV winding voltages compared to specs. Did you check for shorts from each winding to other windings?
There are discrepancies with the bias and HV winding voltages compared to specs. Did you check for shorts from each winding to other windings?
After so many tests and such I can't recall if the tubes were in or out, or some in and some out when I made those voltage measurements, and they weren't exact, I was just going from memory, but I recall none were zero which is what I was looking for, a short.
Yes checked all windings to and from each other in all the combos I could, and each one's ohmic values seem to be appropriate for the various voltages they are rated for.
I just put it back on the bench and made exact measurements. All using a 200W bulb, current measured 1A @115VAC in.
When I changed to a 300W bulb current rose to 1.35A.
red-blk 11.1 VAC 2.4R
wht-wht 1.2V 1.1R
yel-blk-yel .62V .1R
grn-grn .62V .1R
blu-blu .62V .1R
blk-blk 6.95V 5.9R
brn-brn 23.4V 15R
Thanks again!
PS grn-wht 70v/.2 wires were not wound on this xfmr
Yes checked all windings to and from each other in all the combos I could, and each one's ohmic values seem to be appropriate for the various voltages they are rated for.
I just put it back on the bench and made exact measurements. All using a 200W bulb, current measured 1A @115VAC in.
When I changed to a 300W bulb current rose to 1.35A.
red-blk 11.1 VAC 2.4R
wht-wht 1.2V 1.1R
yel-blk-yel .62V .1R
grn-grn .62V .1R
blu-blu .62V .1R
blk-blk 6.95V 5.9R
brn-brn 23.4V 15R
Thanks again!
PS grn-wht 70v/.2 wires were not wound on this xfmr
If you multiply the secondary voltages by 10, the results for the windings are pretty good except for the high voltage winding. That comes out to about 234VAC which is pretty close to the 240VAC from your first measurements. The spec says 330VAC. I think a portion of that winding is shorted.
If all the secondary windings are disconnected, then the primary current draw should be minimal and the bulb in series would not be glowing brightly.
Also, what was your B+ voltage when it was working? With 240VAC, the resulting B+ would be maybe 320VDC.
If all the secondary windings are disconnected, then the primary current draw should be minimal and the bulb in series would not be glowing brightly.
Also, what was your B+ voltage when it was working? With 240VAC, the resulting B+ would be maybe 320VDC.
B+ was 445VDC, 5 volts under the capacitors rating. Gotta love minimalist engineering. 🙄
I think I will wait for the snow to melt and go thru my great big bin of transformers, there will probably be something in there that will work. One of the benefits of at one time living in the big city of Vancouver and hanging out every weekend at the surplus electronics shops. I must have about 5 tons of surplus here, rarely have to order from Digikey etc. 🤣
Thanks for the guidance.
I think I will wait for the snow to melt and go thru my great big bin of transformers, there will probably be something in there that will work. One of the benefits of at one time living in the big city of Vancouver and hanging out every weekend at the surplus electronics shops. I must have about 5 tons of surplus here, rarely have to order from Digikey etc. 🤣
Thanks for the guidance.
Well SXIT! I can't ******* believe it. I went to do some capacitor leakage tests and plugged in my fancy pants Tenma digital supply and it immediately blew the fuse, holy crap, what kind of luck am I having this week. This is just too bizarre! 🤔😵
So I decided to pull it apart and check all the caps and active devices, reflowed all the solder joints, went out to the shop and found some big *** caps to replace the 3300uF@160V in the switcher, swapped caps, fired it up on my bulb tester to avoid any further fuse blowing and the same thing, full brightness and huge growling out of the transformer in the supply. Pulled it all apart again and measured all the taps, all seem fine, no shorts. Then I thought this is too coincidental, maybe there's something up with the line voltage so I measured the HP plug out of the dim bulb tester and it read 3 VAC, tried another meter, same thing 3VAC. WTF. Changed the power cord, same thing. Measured the power bar it was plugged into same 3VAC. Ok something is wrong so I pulled up the extension cord from under the table that the power bar was plugged into and found it was the extension cord I built years ago with a 1N4007 in series with one leg so I can run the antique Christmas lights on the tree at 1/4 power. Holy FXCK! What a dipshit I am. I couldn't believe it. So I replaced the cord with a proper one, reassembled the power supply and it works perfectly. Now all of you stop laughing. 🤣
So to conclude this tragic waste of time, I would like to apologize to everyone who helped me here and sorry to waste your time. I lost 2 days over this and now I get to reassemble all the protective wrapping and tape on the power transformer and reinstall it in the amp, what a complete PITA! And I'll probably have to replace that diode in the cord, although maybe it survived. Too funny.
I need a beer.
Cheers
So I decided to pull it apart and check all the caps and active devices, reflowed all the solder joints, went out to the shop and found some big *** caps to replace the 3300uF@160V in the switcher, swapped caps, fired it up on my bulb tester to avoid any further fuse blowing and the same thing, full brightness and huge growling out of the transformer in the supply. Pulled it all apart again and measured all the taps, all seem fine, no shorts. Then I thought this is too coincidental, maybe there's something up with the line voltage so I measured the HP plug out of the dim bulb tester and it read 3 VAC, tried another meter, same thing 3VAC. WTF. Changed the power cord, same thing. Measured the power bar it was plugged into same 3VAC. Ok something is wrong so I pulled up the extension cord from under the table that the power bar was plugged into and found it was the extension cord I built years ago with a 1N4007 in series with one leg so I can run the antique Christmas lights on the tree at 1/4 power. Holy FXCK! What a dipshit I am. I couldn't believe it. So I replaced the cord with a proper one, reassembled the power supply and it works perfectly. Now all of you stop laughing. 🤣
So to conclude this tragic waste of time, I would like to apologize to everyone who helped me here and sorry to waste your time. I lost 2 days over this and now I get to reassemble all the protective wrapping and tape on the power transformer and reinstall it in the amp, what a complete PITA! And I'll probably have to replace that diode in the cord, although maybe it survived. Too funny.
I need a beer.
Cheers
So if I have it correctly, the TL;DR version is that the reason the fuse was blowing was you were feeding half-wave rectified AC into the trafo?