Brilliant video. I do have a couple of ideas for that capacitor. 1) lay and glue the blue wire on the board first, then solder the cap on top of it 2) place a small bit of kapton tape on the board to shield that joint.
@@LearnElectronicsRepair one more idea, solder cap upright (so other end is "in the air") and solder wire on top of it. also, is rewinding that transformator not possible? or too expensive?
13:37 - Always measure dual pot with 2 multimeters in the same moment. I had problem with dual pot with inconsistent values, but when I switch from one side to another side, value was the same, if I was using 2 multimeters, I could see the difference while testing. This lead me to believe pot was OK, and I started chasing signals with oscilloscope. Eventually I got backwards to potentiometer. 14:33 - I used brass paperclip, to make leg for potentiometer. 21:36 - You dont really need to put SMD capacitor there, solder SMD capacitor directly to POT contact, then use wire from smd capacitor to the place where SMD capacitor was. Then cure with solder mask.
Hmmm, replacing that shorted transformer is going to be tricky. Very difficult these days to find multi-secondary toroid mains transformers off the shelf. Even "standard" ones are pretty pricy. If you try the route of replacing the original one with two separate ones that'll probably double the cost even supposing there is room to squeeze a second one in. I'd be tempted to first see if you can diagnose the noise by running the amp from a bench supply, then if that can be fixed easily and cheaply consider the transformer replacement. I have no idea about cost but it might work out better to contact someone like "Custom Transformers Ltd" at Easton Grey in UK to see what they would charge for a suitable replacement. I guess it depends just how much the customer wants to spend getting his amp back working. Good luck whichever path you/the customer decide to take. Oh and Happy New Year. I thoroughly enjoy watching your repair videos, always something to learn, even if sometimes it's what not to do, like hooking a meter set to amps across the mains! - been there done that!!!
On the plus side, these amps are from active speaker cabs so there is plenty of room in there to bolt another transformer. The customer has a bank of these speakers so getting this one working is more about completing the set rather than just fixing a speaker. This I expect is why it is worth fixing for him. I don't know how many of these he has (i've repaired three so far) but I do know he has similar speaker banks of four subs plus eight full range cabs so it could be something like that.
I have taken to add heat shrink on wires like that. That way it stops the insulation plastic from melting. Then tin the end of the wire before I try and connect to the SMD component.
31:30 it's normal to have the buzz on the speaker connected to Low out only. There is a crossover before the power amps Rick. Probably faulty pot. Have a lucky new year to everyone here
@LearnElectronicsRepair right Rick. The point is that if there is a low frequency buzz it will pass only to the Low power amp due to the crossover (before the 2 power amps)
There's a much better solution for gluing down wires: CA (super) glue makes an excellent bond to both the pcb and the wires/insulation, and it's dirt cheap ($1/50ml bottle) from the chinese sites. Also, you can make it set instantly with either an activator spray, or if you're cheap like me, a tiny dusting of baking soda. I put some fine wire mesh over the top of a tiny 20ml hotel shampoo bottle so I can just dust on a tiny amount. Use it all the time, and even though I filled it years ago I'm not even halfway through it. Super strong, instantly setting bonds, and can be removed with acetone if you need to.
The surface mounted capacitor does not have to be laid flat as originally positioned in that small area. Set the capacitor on its long edge to fit in that narrow space so it could lay flat on the board. Had your wire splice and support glue to finish off.
Happy new year Richard. On some transformers, there is a thermal fuse that's typically on primary and found under the insulation wrap at the end of the winding. That can be replaced or bypassed (!) albeit not very easy to do. This transformer seems to have the core filled with epoxy (?) but worth checking if you can have access to check if there's a fuse.
I'd add the capacitor at the potentiometer end and run a wire to the old capacitor position. That should give a more robust solution and remove the chance of shorts.
You had to make it harder for yourself when you could have solder the cap on the potentiometer leg and run a wire from it to the other cap, then secure the connection with solder mask.
Suggestion - get some of the thinnest glue sticks you can find then when you want glue to secure stuff, melt the end of the stick using your hot air gun - sets in a minute and is reversible.
To be fair I'm working on a Cyrus 1 amplifier by Mission for a customer that keeps over driving it and blowing the output transistors. You just have to look at the PCB traces wrong and they lift off the PCB.
I probably would have soldered it to the control and run the wire to the junction but hey, it's whatever works. I was a repair tech for 55 years and any method will work as long as there are no shorts.
Hi. I used to be a main dealer for dB Technologies equipment, I possibly sold hundreds of their powered speakers. Mains transformers were unfortunately a common failure, probably due to the fact that they are over-run on the UK mains. They were once obtainable from dB, but then became totally unobtainable. When they were obtainable, they were very expensive, leading to an almost non cost-effective repair. The speakers have poor second-hand resale value, I sold a pair a couple of years back on Ebay and struggled to get £100. We looked into getting some toroids wound in the UK so that we could carry on supporting the brand but it was just not cost effective. That volume pot was also a very common failure, I changed loads over the years.
Are both sides of the transformer shot? Else you might reuse the good half and add a similar one with middle ground (the 28v seems to be just half of the 58 (roughly…).
Hi Rick. Happy New Year. I see a bad looking resistor on the buzzing amplifier. Time 30:12, just on top of right fuse. And it is related to the bass amplifier circuit power transistors so the issue might be there.
Monolithic ceramic caps other than C0G types are very "low-fi" in audio paths. They suffer from dielectric absorption and many have horrendous voltage coefficient of capacitance, so they introduce substantial distortion. They can be quite microphonic. They are small. They are cheap. They are awful! Proper wire wrap wire has fluoropolymer insulation (e.g. Kynar) that is quite resistant to melting at soldering temperature.
If I was to order some suitable single core cable for such track repairs, what size or spec etc should I look for, as I'm not familiar with wire sizes and gauges ?
Seeing those ripped pads and broken through-holes, I wonder: Have you ever tried those copper rivets that are supposed to repair exactly that kind of PCB damage?
It just never ceases to amaze me--the number of hacks out there who have old radio shack soldering irons, a complete lack of ability, a copious amount Of misplaced confidence and apparently boatloads of amphetamines... I repair car audio equipment almost exclusively. You cannot imagine the amount of stuff I find like this. Most of the time these hacks break out the radio shack iron or worse yet the Weller 350w gun and head straight for the largest components they see, try to desolder/resolder said components and most of the time delaminate the pads and traces from the board. I know everyone has to start somewhere, but sweet lord Jesus, at least start with a book or better yet some classes. Buy a few kits designed to teach how to solder. Buy a decent temp controlled iron. Even the generic knockoffs and clones are worlds better than your dad's old iron he bought in '62. As for the transformer. Just rewind it. It's not even remotely hard to do, especially in one that large, I thought it would be awful, and shied away from doing one for many years. I finally had to do one for a repair and the hardest thing is keeping track of turns # and directions. Just take a video of unwinding the original. The transformers I have to work with are much smaller, like 3-4 inch core and most of mine are wound with 12g enamel wire. Probably the worst case for physical difficulty. You should be able to do a large 60/50hz toroidal core like that lickety split.
I too have a very shaky hands so I really can appreciate how are you able to solder those miniature capacitors. Well done!
Brilliant video. I do have a couple of ideas for that capacitor.
1) lay and glue the blue wire on the board first, then solder the cap on top of it
2) place a small bit of kapton tape on the board to shield that joint.
Yeah that would work
@@LearnElectronicsRepair one more idea, solder cap upright (so other end is "in the air") and solder wire on top of it. also, is rewinding that transformator not possible? or too expensive?
13:37 - Always measure dual pot with 2 multimeters in the same moment. I had problem with dual pot with inconsistent values, but when I switch from one side to another side, value was the same, if I was using 2 multimeters, I could see the difference while testing. This lead me to believe pot was OK, and I started chasing signals with oscilloscope. Eventually I got backwards to potentiometer.
14:33 - I used brass paperclip, to make leg for potentiometer.
21:36 - You dont really need to put SMD capacitor there, solder SMD capacitor directly to POT contact, then use wire from smd capacitor to the place where SMD capacitor was. Then cure with solder mask.
Brilliant video, looking forward to seeing how this fix finally goes when another tx fitted
😁👍
Hmmm, replacing that shorted transformer is going to be tricky. Very difficult these days to find multi-secondary toroid mains transformers off the shelf. Even "standard" ones are pretty pricy. If you try the route of replacing the original one with two separate ones that'll probably double the cost even supposing there is room to squeeze a second one in.
I'd be tempted to first see if you can diagnose the noise by running the amp from a bench supply, then if that can be fixed easily and cheaply consider the transformer replacement.
I have no idea about cost but it might work out better to contact someone like "Custom Transformers Ltd" at Easton Grey in UK to see what they would charge for a suitable replacement. I guess it depends just how much the customer wants to spend getting his amp back working. Good luck whichever path you/the customer decide to take.
Oh and Happy New Year. I thoroughly enjoy watching your repair videos, always something to learn, even if sometimes it's what not to do, like hooking a meter set to amps across the mains! - been there done that!!!
On the plus side, these amps are from active speaker cabs so there is plenty of room in there to bolt another transformer. The customer has a bank of these speakers so getting this one working is more about completing the set rather than just fixing a speaker. This I expect is why it is worth fixing for him. I don't know how many of these he has (i've repaired three so far) but I do know he has similar speaker banks of four subs plus eight full range cabs so it could be something like that.
I have taken to add heat shrink on wires like that. That way it stops the insulation plastic from melting. Then tin the end of the wire before I try and connect to the SMD component.
31:30 it's normal to have the buzz on the speaker connected to Low out only. There is a crossover before the power amps Rick. Probably faulty pot. Have a lucky new year to everyone here
The other one (once I swapped the transformers) did not buzz
@LearnElectronicsRepair right Rick. The point is that if there is a low frequency buzz it will pass only to the Low power amp due to the crossover (before the 2 power amps)
@@nasosst3092 Fair comment
There's a much better solution for gluing down wires: CA (super) glue makes an excellent bond to both the pcb and the wires/insulation, and it's dirt cheap ($1/50ml bottle) from the chinese sites. Also, you can make it set instantly with either an activator spray, or if you're cheap like me, a tiny dusting of baking soda. I put some fine wire mesh over the top of a tiny 20ml hotel shampoo bottle so I can just dust on a tiny amount. Use it all the time, and even though I filled it years ago I'm not even halfway through it. Super strong, instantly setting bonds, and can be removed with acetone if you need to.
Thankyou! 👍👍👍
The surface mounted capacitor does not have to be laid flat as originally positioned in that small area. Set the capacitor on its long edge to fit in that narrow space so it could lay flat on the board. Had your wire splice and support glue to finish off.
Yep, there are plenty of good ways to tackle this particular problem
Happy new year Richard. On some transformers, there is a thermal fuse that's typically on primary and found under the insulation wrap at the end of the winding. That can be replaced or bypassed (!) albeit not very easy to do. This transformer seems to have the core filled with epoxy (?) but worth checking if you can have access to check if there's a fuse.
This one has shorted turns, it is not open circuit
I'd add the capacitor at the potentiometer end and run a wire to the old capacitor position. That should give a more robust solution and remove the chance of shorts.
Yes as I suggested there are plenty of different ways to do this
Hi Richard Happy New Year.. I would have put the cap on it's thin side. Great video
Yeah that would do the job nicely
You could put the capacitor in on its side
You had to make it harder for yourself when you could have solder the cap on the potentiometer leg and run a wire from it to the other cap, then secure the connection with solder mask.
Suggestion - get some of the thinnest glue sticks you can find then when you want glue to secure stuff, melt the end of the stick using your hot air gun - sets in a minute and is reversible.
To be fair I'm working on a Cyrus 1 amplifier by Mission for a customer that keeps over driving it and blowing the output transistors. You just have to look at the PCB traces wrong and they lift off the PCB.
I probably would have soldered it to the control and run the wire to the junction but hey, it's whatever works. I was a repair tech for 55 years and
any method will work as long as there are no shorts.
did you try to set the switch on the buzzing one from mic to line?
Hi. I used to be a main dealer for dB Technologies equipment, I possibly sold hundreds of their powered speakers. Mains transformers were unfortunately a common failure, probably due to the fact that they are over-run on the UK mains. They were once obtainable from dB, but then became totally unobtainable. When they were obtainable, they were very expensive, leading to an almost non cost-effective repair. The speakers have poor second-hand resale value, I sold a pair a couple of years back on Ebay and struggled to get £100. We looked into getting some toroids wound in the UK so that we could carry on supporting the brand but it was just not cost effective. That volume pot was also a very common failure, I changed loads over the years.
Are both sides of the transformer shot? Else you might reuse the good half and add a similar one with middle ground (the 28v seems to be just half of the 58 (roughly…).
Sounds like 50Hz hum? Is there a ripple on the audio input into the bass side PA?
Hi Rick. Happy New Year. I see a bad looking resistor on the buzzing amplifier. Time 30:12, just on top of right fuse. And it is related to the bass amplifier circuit power transistors so the issue might be there.
It looks bad initially but at 30.19 I can make out a yellow stripe. So might be ok.
Thanks for the suggestion 🙂
Heya, and does ring trafos are expancive. hope to see a video about the zooming pcb and what the problem is I gues it's gone be a capicitor.
If you use hot glue, it can be easily removed later on with IPA.
How can you remove that resin later?
It wasn't resin it was impact adhesive
Sounds like a 50Hz hum. Ground problem?
Monolithic ceramic caps other than C0G types are very "low-fi" in audio paths. They suffer from dielectric absorption and many have horrendous voltage coefficient of capacitance, so they introduce substantial distortion. They can be quite microphonic. They are small. They are cheap. They are awful!
Proper wire wrap wire has fluoropolymer insulation (e.g. Kynar) that is quite resistant to melting at soldering temperature.
If I was to order some suitable single core cable for such track repairs, what size or spec etc should I look for, as I'm not familiar with wire sizes and gauges ?
Look for wire wrap wire, it is thin and single core
Seeing those ripped pads and broken through-holes, I wonder: Have you ever tried those copper rivets that are supposed to repair exactly that kind of PCB damage?
I haven't needed to myself but I have seen them used by TH-camrs such as Mend It Mark 🙂
3:43 poor lady in the background making just soft mouse clicks
perhaps theres a blown-protection in the trans-former ...
no it has shorted turns as he showed, if it has blown protection, it would not power the lightbulb at all
Shango066 (TH-cam creator) knows a guy in Europe who rewinds and/or builds transformers
What glue did you use?
it looks like moment transparent glue
Impact adhesive, like UHU glue in the UK or something similar
they are called windings not turns
OK, if it matters 😉
It just never ceases to amaze me--the number of hacks out there who have old radio shack soldering irons, a complete lack of ability, a copious amount Of misplaced confidence and apparently boatloads of amphetamines...
I repair car audio equipment almost exclusively. You cannot imagine the amount of stuff I find like this. Most of the time these hacks break out the radio shack iron or worse yet the Weller 350w gun and head straight for the largest components they see, try to desolder/resolder said components and most of the time delaminate the pads and traces from the board.
I know everyone has to start somewhere, but sweet lord Jesus, at least start with a book or better yet some classes. Buy a few kits designed to teach how to solder. Buy a decent temp controlled iron. Even the generic knockoffs and clones are worlds better than your dad's old iron he bought in '62.
As for the transformer. Just rewind it. It's not even remotely hard to do, especially in one that large, I thought it would be awful, and shied away from doing one for many years. I finally had to do one for a repair and the hardest thing is keeping track of turns # and directions. Just take a video of unwinding the original. The transformers I have to work with are much smaller, like 3-4 inch core and most of mine are wound with 12g enamel wire. Probably the worst case for physical difficulty. You should be able to do a large 60/50hz toroidal core like that lickety split.
kapton tape to avoid the trace too short together 😉
Yeah that would do the job nicely