Professor smith needs help

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#201
Professor, from what you say, I deduce that your soldering iron tip is not whetted properly. In other words, the tip will have some burnt, brown spots/patches on to which solder never sticks. The tip is hot, but its not melting the solder properly and simple not helping with making a good joint; however, it is heating up the board and the copper tracks seem to be coming off the board. This is a bad sign, and if per chance there is a fracture in the track, that state will be worse than the former.

My suggestion is that if you find some of the tracks already lifting off the board, use some super-glue and stick them on.

Do scrape off enamel from wire before soldering.

Are you using a good quality flux, even if you have a flux-cored solder? If not, you need to be using flux, self-cleaning or otherwise.

Professor Smith, please look for help from a qualified technician/engineer or a seasoned diyer. Your questions show that you haven't got to grips with some basics. Take your time and learn, but for this project seek help immediately.
 
#202
Samuel Jayaraj said:
Professor, from what you say, I deduce that your soldering iron tip is not whetted properly. In other words, the tip will have some burnt, brown spots/patches on to which solder never sticks. The tip is hot, but its not melting the solder properly and simple not helping with making a good joint; however, it is heating up the board and the copper tracks seem to be coming off the board. This is a bad sign, and if per chance there is a fracture in the track, that state will be worse than the former.

My suggestion is that if you find some of the tracks already lifting off the board, use some super-glue and stick them on.

Do scrape off enamel from wire before soldering.

Are you using a good quality flux, even if you have a flux-cored solder? If not, you need to be using flux, self-cleaning or otherwise.

Professor Smith, please look for help from a qualified technician/engineer or a seasoned diyer. Your questions show that you haven't got to grips with some basics. Take your time and learn, but for this project seek help immediately.
Click to expand...

If I may make a quick suggestion for the 'professor' - go to
youtube and search "how to solder" "solder magnet wire" etc etc.

It's all there in beautiful detail and will save the poor people here
a -lot- of time.

One tip I will add however is get yourself a couple of packs of
Bluetac. Really really good for holding wires, components, anything
in place while soldering.

cheers

Terry
 
#204
Maybe mechanical connections such as terminal strips and spades could have been easier than soldering but practice is always good.

Lineup & Stuey

Thanks for the encouragement as it all helps. As the song goes "That you don't know what you've got till it's gone". I've got cervical spondylitis so the damage is permanent and the game is to stop further degeneration by anteriocervical decompression and fusion but as it's no longer accelerating it's a wait and see.

Hugh

I'll send you an email and no I'm not lucky enough to be travelling to a warmer climate.
 
#205
I was against this rebuild from the beginning
I did fear something like this
And besides, we dont yet know whether this amp really has a problem or not
If there is a problem we still dont know why or what
Pretty tossy to dismantle something that may have been working ok
As of now I fear this amp will end up not working at all

One is to build something from prebuilt kits
Quite different to mess with amps that have been powered up

I wonder if Smith has discharged supply before dismantling
But please, at least discharge before assembling
Not doing so could do severe damage to curcuits
If there is bleeding resistors this may not matter

It should be well known that soldering on new boards is very different from soldering on something been soldered before
It needs cleaning and very special care
Attention, or this will be down the drain

In my youth, when burning an amp, i replaced ALL components, as I had no clew what else to do

Once I burned a channel of a new built amp, because I was turning the bias pot, when I thought I was turning the DC pot :irked:

btw, loose wires should NOT be just soldered

If I have to solder two loose ends together, I apply plenty of "cold" solder on both ends
Then try to hold them together with one hand and solder iron in other
Problem is that its almost impossible to hold it steady, and just the slightest move will ruin the joint

I know only one place I do it like that, and thats soldering speaker wire directly to driver terminals
I will always avoid touching anything but the solder and solder iron
And theres lots of ways to do so
Use crimping, or maybe just a piece of small solid core wire wrapped around ends needing soldering

Oh, if you have ruined some traces on amp boards or supply, try to figure out how to make the connection in another place
Or if needed, repair with wire or something
 
#206
My suggestion is that if you find some of the tracks already lifting off the board...
Click to expand...

Actually it appears that some of the tracks under the amp were already like that in some places. Not a major problem anyway.

2 questions:

I did NOT discharge the caps before rewiring. I forgot. But its done now. Is there any damage?

Secondly, when I wired the transformer secondaries to the power supply module, I could not see which wires were which so it could be that the two channels left and right are wired differently. I assume because its AC it doesnt matter that they arent matched? IS this correct?

Heres the pic:

www.sendspace.com/file/jre1mx


cheers

its sounding no different, and harsh after an hour of powering it up.
 
#207
Professor smith said:


I did NOT discharge the caps before rewiring. I forgot. But its done now. Is there any damage?

transformer secondaries
I could not see which wires were which
so it could be that the two channels left and right are wired differently.

I assume because its AC it doesnt matter that they arent matched? IS this correct?
Click to expand...

Maybe not

Transformer secondaries
Sure it matters
Only one way to do it
Wires are coloured fore a reason

Man, could this be the whole issue from start 😕
 
#212
Professor smith said:
I have unsoldered the wires to rewire the whole thing however I am having difficulty making a good soldering joint between the enamelled wire leads which come out of the transformer and copper leads. It's also difficult to hold the two wires together, and twisting them together risks a cold joint.

Also the power supply board on the underside is swelling up. This is also slightly apparent on the main amp board. Too much heat applied.

Maybe I need a new soldering iron?

If I twist the secondary wires of each of the toroidal centre taps, and twist the other two, do I twist thes pairs again together?

Whats the best way to twist ?
Click to expand...


Hello

Use sand paper to take out the enamel on the transformer wires.

And even new wires can have oxidations, so it is better to sand the copper before doing the soldering of any connexions wires.

I t is easyer to do soldering wen you put rosin flux on all the wire, the capacitor posts and the on the pcb soldering pads, before doing the soldering.

Go to a place who sell electronics parts and buy some rosin flux.

Bye

Gaetan
 
#213
Hugh,

Have I done the wiring right?

Also any comments on the transformer secondaries. Should they be matched polarities from one channel to the other?

Also I am going to have to get a new dac. Could you tell me which dacs or cd players you use? I need to know that it wont cause any humming this time.

I have never had this problem with my previous amp no matter what I connected to it.
 
#215
Professor, this is very disapointing

You got very fine offer of help, step by step
Theres professional people here offering help

But you go ahead and do the rebuild without asking any questions
In a hurry, and not very carefully as it should have been
Now you ask after having assembled about things of which you have had doubts how to do it properly

This whole mess might have been cleared with even simple measurements of supply voltage
Might not have been
But point is you never made any of these simple measurements when asked fore
Instead you just responded trafos were good and everything fine

This way you could just as well rip the whole thing apart again, and start all over
Unfortunately theres big risk of even more damage, and no good solder all over the place

Even it doesnt sound that way, but I hope the best fore you, but Im sorry to say, this could be just one step further backwards

Man, if only you had asked first, shown pictures of damaged areas etc
This is just awful
 
#216
By aksa - Please email me the latest wiring update, also if possible the foil side of the board. I want to see these lifted tracks you refer to.
Click to expand...

I wondered about that, most compliant FR-4 these days is nearly immune to lifted tracks. As a test , even a torch burned away the epoxy before the patterns peeled. With an iron nearly unlimited time.
I use the MG chemical 1 OZ 1/16" FR-4.
OS
 
#217
ostripper said:


I wondered about that, most compliant FR-4 these days is nearly immune to lifted tracks. As a test , even a torch burned away the epoxy before the patterns peeled. With an iron nearly unlimited time.
I use the MG chemical 1 OZ 1/16" FR-4.
OS
Click to expand...

when I say lifted tracks I actually mean swelling. I dont know if we are talking abuot the same thing. The pcb looks like it's been lacquered so I dont think it will be an issue even if the tracks have come up slightly. Not much can be done at any rate.
 
#218
when I say lifted tracks I actually mean swelling.
Click to expand...

A bubbling of the lacquer of a thicker layer of solder is not what I meant. A true delaminization of fiberglass layers or a separation of
the copper from the epoxy// fiberglass.

I saw this on the FR4 that radioshack sells .. looks good , but after
a few component changes , one can see bubbles INSIDE the layers, also after 20 seconds , small traces physically separate from the board. 🙁
OS
 
#219
ostripper said:


A bubbling of the lacquer of a thicker layer of solder is not what I meant. A true delaminization of fiberglass layers or a separation of
the copper from the epoxy// fiberglass.

I saw this on the FR4 that radioshack sells .. looks good , but after
a few component changes , one can see bubbles INSIDE the layers, also after 20 seconds , small traces physically separate from the board. 🙁
OS
Click to expand...


in which case, yes we are talking about the same thing. I see bubbles.

But the bottom line is this is not good news and there is nothing I can do about it.
 
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