how to repair this circuit board?

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I have a broken circuit board and accompanying topside components here:

https://imgur.com/a/Pbt1HSU

The red circled areas show the cracked sections.  In a pinch, I have  
glued the broken parts back together with JB Quick Weld.  After several  
hours, it seems stable enough to handle.

Now, the question is, what's the best way to rejoin the broken traces?  
Initial thought was to just jumper over the solid sections and join the  
jumpers between soldered components.  Not so sure what to do about the  
large screened sections (probably serving as a ground screen for the  
flyback topside?).  I welcome any tips or thoughts. If I start trying to  
scrape the conformal coating, it may come apart again.

Unfortunately, the board cannot be replaced.

Thanks in advance.

Abe

Re: how to repair this circuit board?
In sci.electronics.repair, on Sun, 2 Feb 2020 02:47:18 -0500, Abe D

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Sounds good.  

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I'm no pro, but why not the same thing.  Does it matter if the edges of
the screen are touching if the screen itself is all connected to itself.
Then you can see if the thing it comes from works or not.  

40 years ago I had a roommmate whose father threw a clock-tv at him.  I
neve saw another one.  So cute.  9" TV, I would have liked to have had
one. Board was broken in about 20 places but it worked after I jumpered
each of them.  

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Re: how to repair this circuit board?
On Sunday, February 2, 2020 at 2:47:22 AM UTC-5, Abe D wrote:
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It's too late now but repairing board with a topical coating of epoxy is no
t the way to stabilize it.  The epoxy acts like a top hinge and the bottom  
of the board will flex away from the crack.  To make it more stable, you ha
ve to add some epoxy on the other side and hope it adheres.

The proper way to repair a fractured board is to remove any component(s) th
at crosses the break, and fit the board pieces back together where the seam
 doesn't even show.  You may actually have to break the board a bit more to
 get it to fit perfectly.

At this point, apply FRESH cyanoacrylate so it wicks inside the fracture an
d bonds the board completely together from the inside, not just one side.

If done properly, the cracks will be barely visible.  Scrape the green mask
 off the trace just at the break and half the distance the trace is wide.  
A drop of solder across each land will finish it.

In your case, because the pieces don't fit that well, scrape back the mask  
and hand wire from point to point and across the fracture with some fine co
pper stranded wire (one or more strands depending on width of the trace), a
nd coat the entire trace with solder using the copper strand as a sort of "
rebar".

Deflux the board and apply either a conformal coating or get some green nai
l polish to protect the lands.

Re: how to repair this circuit board?
On 2/2/20 8:32 AM, John-Del wrote:
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Not totally clear to me here.  Am I going to try applying more epoxy on  
the board side of the crack, cyanoacrylate, or both?

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What about the large, outer section of the board appearing more like a  
screen rather than solid trace?  I doubt I could find stranded wire wide  
enough and pretty fragile there to try scraping.  Also, what's the best  
tool for the scraping?

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Nail polish would be a go, but what to use for defluxing?

Thanks.



Re: how to repair this circuit board?
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Depends on the flux used.  

Most of the time use IPA .  That is alcohol that is 90% or better with  
no addatives that is often in common rubbing alcohol.

The common rubbing alcohol that is 70 % would be ok except most of it  
contains other chemicals that leave a residue on the boards.


Re: how to repair this circuit board?
On 2/2/20 12:06 PM, Ralph Mowery wrote:
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Have both 70 and 90, so thumbs up, thanks!

Re: how to repair this circuit board?
On 2/2/20 2:35 PM, Tempestinatesttube wrote:
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.


 with
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Maybe not so thumbs up when I read more clearly.  Standard ISO is all I  
have.  What about Everclear?


Re: how to repair this circuit board?
On Sunday, February 2, 2020 at 11:44:57 AM UTC-5, Abe D wrote:
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:
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l
e
to
s not the way to stabilize it.  The epoxy acts like a top hinge and the bot
tom of the board will flex away from the crack.  To make it more stable, yo
u have to add some epoxy on the other side and hope it adheres.
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) that crosses the break, and fit the board pieces back together where the  
seam doesn't even show.  You may actually have to break the board a bit mor
e to get it to fit perfectly.
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e and bonds the board completely together from the inside, not just one sid
e.
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I had two avenues of advice: the first how to properly repair a cracked or  
totally broken PC so it's virtually invisible, and advice directed to you h
aving already attempted a repair with epoxy.

Because you have already epoxied the board together, it's really too late t
o use the cyano adhesive, particularly if you put epoxy into the crack. We  
never want to use cyano as a filler.  The beauty of cyanoacrylate is that i
t doesn't require a gap in order to put the epoxy in.  With cyano, you can  
fit the board together perfecly and the cyano will wet *into* the PC (eithe
r glass or phenolic) and bond it with no gap whatsoever.  Properly done, th
ere is virtually no gap across the broken foil and the foil ends butt toget
her almost perfectly.

If you can remove the epoxy you already put down, and there is no epoxy in  
the break line, then you can refit the pieces so the crack is perfectly joi
ned and virtually invisible.  At this point, you can use cyanoacrylate to p
ermanently bond the board internally, as opposed to using external adhesive
.

If done properly, no jumpers are even required as the mask can be scrapped  
off right at the crack and a dot of solder put across the gap. Because the  
board is bonded internally, there is is virtually no flex and the solder ba
ll will make a perfectly clean and virtually indestructible connection acro
ss the break.

If you can't remove the epoxy, you're better off adding a layer to the bott
om to reduce the "hinge" effect you will get with epoxy on one side or the  
other allowing flexing.

As for the large areas of damaged foil, you can add strips of solder wick b
raid to add some physical strength as well as complete the circuit.

Re: how to repair this circuit board?
On 2/2/20 1:16 PM, John-Del wrote:
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Too well bonded now, even though not perfectly aligned.  And I did use  
some cyano on the board side just a little while ago to fill in.  Not  
the best idea for sure and it's only about 49 F in the room where the  
board is, so I better wait a full day before doing anything else.

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The board rejoining is too imperfect for solder dots.  Looks like I will  
be using jumpers and solder braid, removing flux afterwards, and  
covering with nail polish.


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I'm going to glue a couple of round wooden sticks along each length of  
the board on the underside.  There will be one horizontal stick along  
each edge.  This won't interfere when I reinstall the board.  Hopefully  
it will help augment any strengthening needed.



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Solder braid, good idea.  Don't have any though, will have to order  
some.  What's the best way to remove the conformal coating?



Re: how to repair this circuit board?
On Sunday, February 2, 2020 at 1:58:34 PM UTC-5, Tempestinatesttube wrote:

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I just use a jeweler's screwdriver that's not knackered up.  If it has a cr
isp edge, you can easily scrape off the conformal coating (if the board has
 it) as well as the green solder mask.  Expose the copper and use a bit of  
flux to improve the wetting and bonding of the solder to the copper.


Re: how to repair this circuit board?
On 2/2/20 4:06 PM, John-Del wrote:
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Very good, thanks again.  Will tackle this tomorrow once I have the  
braid in hand.

Re: how to repair this circuit board?
On 2/2/2020 11:44 AM, Abe D wrote:
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JB weld is conductive.

Re: how to repair this circuit board?
On 2/2/20 7:51 PM, Tom Biasi wrote:
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I found that out the hard way.
I replaced a thermal fuse on a crystal heating oven.
Turned the power on and Blam!
It took a bit to clean that mess up.

--  
"I am a river to my people."
Jeff-1.0
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Re: how to repair this circuit board?
On Sunday, February 2, 2020 at 8:32:25 AM UTC-5, John-Del wrote:
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o  
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not the way to stabilize it.  The epoxy acts like a top hinge and the botto
m of the board will flex away from the crack.  To make it more stable, you  
have to add some epoxy on the other side and hope it adheres.
Quoted text here. Click to load it
that crosses the break, and fit the board pieces back together where the se
am doesn't even show.  You may actually have to break the board a bit more  
to get it to fit perfectly.
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and bonds the board completely together from the inside, not just one side.
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sk off the trace just at the break and half the distance the trace is wide.
  A drop of solder across each land will finish it.
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k and hand wire from point to point and across the fracture with some fine  
copper stranded wire (one or more strands depending on width of the trace),
 and coat the entire trace with solder using the copper strand as a sort of
 "rebar".
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ail polish to protect the lands.


"In your case, because the pieces don't fit that well, scrape back the mask
 and hand wire from point to point and across the fracture with some fine c
opper stranded wire (one or more strands depending on width of the trace),  
and coat the entire trace with solder using the copper strand as a sort of  
"rebar". "

This is exactly what I would recommend. For small traces, 22awg or 24awg co
pper wire would work fine.  For larger traces that carry more power, add tw
o or three strands of wire instead of 1 strand.  Not sure of the board moun
ting arrangement, or  how much stress the board may be subject to,  but, I'
d suggest you consider applying a board stiffener along each side of the bo
ard.  the stiffener could be  wood/plastic and could be screwed (#4 machine
 screw?) or epoxied in place.  If you mount with screws, make sure the hole
s do not short copper traces. Nylon screws should work well.
This is a general recommendation. An exact spec would be based on seeing th
e board and mounting arrangement.  

Re: how to repair this circuit board?
On 2020/02/03 9:17 a.m., three_jeeps wrote:
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I agree with the above repairs - we have done similar with other HV  
Xformers PCBs successfully that have lasted for many years.

This PC Board was broken either by stress from the weight of the flyback  
or bad handling if the board was not mounted. Perhaps rough handling  
during a move or the monitor was dropped a foot or so to a floor...

To reduce the risk of future fractures make sure the weight of the HV  
transformer/flyback is properly supported otherwise it will break again.

Take care that HV route between the switching transistor and Xformer are  
kept clear of any potentially (yeah, I know) conductive material when  
you are supporting it - as it sees back EMF of up to 1500VDC. Other HV  
traces also need to be kept isolated from the supports. Note that any  
added supports can accumulate dust over the coming years and that this  
dust can provide a conductive path...

John :-#)#

--  
(Please post followups or tech inquiries to the USENET newsgroup)
                      John's Jukes Ltd.
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Re: how to repair this circuit board? **WORKING**
I picked up some desoldering braid and used that across the broken  
traces.  I was careful to first scrape away any coatings with a flat  
blade screw driver.  After maybe 20 min of work, all of the gaps were  
bridged and time to test.  Once plugged in and switched on, whola!  All  
working again.

Thanks for the group's help.  Lots of helpful suggestions.  I really  
didn't know if it would work even after doing all this as it had arrived  
that way through the mail, and the person I got it from sent it parcel  
post with no insurance and in a single flimsy box.  About the worst way  
anyone could send fragile electronics.  However, it is working again and  
I am happy.  I do want to add supports across the ends of the board  
horizontally for more strength, but otherwise I think it's all good now.

By the way, some of you might want to check JB Weld's website.  Only  
certain of their epoxies are conductive and others are not.  The one I  
used (JB Quick Weld) was not.  Just FYI.

Thanks again!

Re: how to repair this circuit board?
wrote:

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I think some JB weld formulations have very fine metal powder in them
for strength. Maybe you should see if the stuff you used is conductive
before you apply power to the board again.
Eric

Re: how to repair this circuit board?
On 2/2/20 12:32 PM, snipped-for-privacy@whidbey.com wrote:
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No conductivity, so thumbs up there.  Thanks for pointing that out.  
Would have hated to go through all this only to realize I was  
shortchanged by the epoxy.



Re: how to repair this circuit board?
On Sun, 2 Feb 2020 14:27:47 -0500, Tempestinatesttube

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Yeah, that would suck.

Re: how to repair this circuit board?
I could do that in a half hour. I should show you the regulator board in my
 bench receiver, it is twice as busted up as that. Send it over and I'll do
 it for, umm, forty bucks.  

First, get a scraper. I got a special tool to remove the soldermask. (the g
reen shit)Then bridge most of the bigger foils with solder - only. Then tak
e cyanoacryilate (super glue) and glue it together from the top. Then go to
 each connection you bridged, of course to made it to the right position, I
 have had to use a hammer to pound them back together at times, and that is
 why you do not want the extra thick glue, you want low viscosity. And at e
ach connection reflow the solder blob and embed used solder wick in it. It  
will lend some strength and therefore longevity.  

After that get to the smaller connections, any which way. The short distanc
e makes it easy. Some you can do with the cutoffs from the leads of compone
nts you have installed in other stuff. (that is REALLY what the tray on you
r soldering station is for :-)  

Shit, the one you got is so easy, if you can get to Cleveland bring it over
 with a case of Bud and I will just do it right in front of you.

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