LPL Digital Timer cracked PCB

Todd Barlow · May 5, 2019

Would dropping some solder across the crack in the PCB between the solder points sticking out be a possible solution?

I am assuming that the reason the timer does not power up is due to the crack in the PCB.

Thanks as always for your input
Todd

bernard_L · May 5, 2019

Todd Barlow said:
dropping some solder across the crack

I woud not trust Solder alone to reliably repair such a crack.

Scrape away the green varnish (the solder mask) on top the broken tracks (two of them as far as I can see) for approx 10mm either side of the crack.
Bridge the break with a piece of bare copper wire, soldered on either side on the bare copper track

Or, easier.

From each crack, locate in either direction to the first solder bump.
Prepare piece of wire of adequate length, strip the insulator approx 3mm each end, solder it on each of these two bumps.

If it were me, I'd try to use one wire from a telephone cable (those that run in the walls). In the US I don't know, but here they are single-strand fairly thin, easier to make a clean solder connection than with multi-strand wire.
And, if you never made a solder before: first melt a little solder on the iron's bit, then use indirect melting, i.e. iron heats wire, solder melts in contact with wire; finally, melt the bump on the PCB while pressing wire in place. Try to get some real solder (lead-tin); lead-free solder is a PITA. That alone will not make you ill from lead poisoning.

Todd Barlow · May 5, 2019

Thanks for the excellent feedback, I will give it a try and let you know!

tedr1 · May 5, 2019

I agree with the advice given above, don't mess with trying to "mend" the break, instead add a piece of wire to join the opposite sides at existing solder points. Tinned wire (shiny silver color) is a lot easier to solder than bare copper (pink) wire. Stranded wire is more flexible than unstranded, you want a piece of fine gauge (18 - 22awg) PVC insulated stranded tinned copper wire.

bdial · May 5, 2019

wire such as this stuff 30 AWG wire should work

AgX · May 5, 2019

Yes, just bridge the respective soder points by wire.

However, missing so far is advice on the crack itself!
You do not want the crack to go further. Thus glue (e.g. hotmelt) a stabilizing plate of an insulating material to the pcb. In addition you could drill small holes at the very end of the cracks. These would hamper the crack going further on line.

shutterfinger · May 6, 2019

I have bridged cracked circuit board with just solder by cleaning the trace at the crack to 1/4 inch either side on small narrow contact strips. The width of the contact strip determines whether to solder only or use wire. The width of the cracked strips shown suggest moderate current and therefore should be bridged with #18 or #20 solid core wire.

cowanw · May 6, 2019

I tried this on a Gralab 500. Worked for a minute then burned up! very exciting. Good luck.

trendland · May 6, 2019

Todd Barlow said:
Would dropping some solder across the crack in the PCB between the solder points sticking out be a possible solution?

I am assuming that the reason the timer does not power up is due to the crack in the PCB.

Thanks as always for your inputView attachment 222945
Todd

Todd - it seams to be you are the luckiest man of the day! Looking at your electronic "Platine"
it is no great deal to repair it - yes?

Compared with mircoelectronic of New generation = all
that parts you show (most of them) are highly integrated with high factor minimalized size!
The imposibility to repair there is the structure, and temperature with :

lucky you!

AgX · May 6, 2019

cowanw said:
I tried this on a Gralab 500. Worked for a minute then burned up! very exciting. Good luck.

Why would a solder bridge over a cracked track burn up within a minute ???
Only explanation would be that even the solder cracked upon remounting the board.

cowanw · May 6, 2019

Or maybe I was a really messy solderer.

trendland · May 6, 2019

AgX said:
Why would a solder bridge over a cracked track burn up within a minute ???
Only explanation would be that even the solder cracked upon remounting the board.

Corrision, interia shock, mecanical break! What ever if that replacement bdial recomended :

(Me too) began to smoke!!!!!!!!
Then Op may have a problem - later the cable can burn!!

with regards - up to that = easy going!

Todd Barlow · May 12, 2019

Success!
Thanks for all you help.
I went with the solid wire from telephone lines that are run within the walls (23 gauge 0.6mm diameter) when I traced the circuit it looks like the cracked portion was on the control side and not the power side the feeds the receptacles for the safelight and enlarger.
I have been testing it and no funny sounds, smells, smoke or flickering LED's.
Thanks again

bernard_L · May 13, 2019

Good! But I would ask myself why the crack happened in the first place, not just out of curiosity, but to prevent a repeat. I would second the advice given by AgX:

However, missing so far is advice on the crack itself!
You do not want the crack to go further. Thus glue (e.g. hotmelt) a stabilizing plate of an insulating material to the pcb. In addition you could drill small holes at the very end of the cracks. These would hamper the crack going further on line.

Todd Barlow · May 13, 2019

The timer came with some other equipment I picked up at a garage sale - it did not look abused but it must have been subjected to some rough treatment.
Now that I have it running I was going to mount the PCB on some rubber or foam washers to try and minimize direct shock transfer.
I like the idea of drilling the holes to stop the crack from continuing but there is limited open space on the other side (the relay covers a good portion of the crack), hot gluing a plate may be an option.
All the best
Todd

AgX · May 13, 2019

I think so far I have not yet come across a cracked pcb. But with that crack at a corner I can imagine the device having fallen on the same corner and that board being warped.
If a pcb has a heavy tranformer in its center and the device falls flat on, that transformer might induce a central crack.

Your board is based on plain paper layers. The better, more modern boards are based on woven textile and should be a bit stronger.

Fin · May 15, 2019

Todd Barlow said:
Success!
Thanks for all you help.

Just saw this thread and was about to reply, but too late! Looks fine though.

For the record if anyone else needs to do a repair like this, an easy (but not quite as neat looking) way to do this is to:

Get a single piece of 0.75mm or 1mm CSA wire (lawnmower cable or something similar is a good size)
Strip a load of the PVC sheath/outer off, like 30cm / 12" or so
Tin the whole thing with 60/40 lead solder (lead free is rubbish, gives off nasty fumes and needs a higher temp)
Find a crack in the trace and gently scratch away 5mm 1/4" each side of the solder resist
Tin the area you have just removed the resist from with loads of solder and while it's still hot and flowing...
Place the end of the tinned wire across the crack and let it cool.

You can now cut the excess wire off the join with some side cutters, and repeat!

I've done loads of PCB repairs in the past that have lasted well using this method, including at least 3 portable CRT TVs that had been previously dropped!

voceumana · May 15, 2019

I recommend mixing some epoxy and use it over the crack to provide support between the two sides of the crack to prevent further expansion of the crack.

LPL Digital Timer cracked PCB

Privacy & Transparency

Privacy & Transparency