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PCB needs repairs

KrisBlueNZ

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The problem is between measurement points D and E. They should be connected together by a wide track on the top layer, so you should be seeing 17.7V on point E, but there's nothing.

My guess is that the top right relay hole has lost its through-plating and the relay pin isn't making contact with the top-side copper. Another possibility is that there's the same problem with the bottom hole of the big resistor. Or maybe the track doesn't connect to the big resistor - I can't be sure, because the resistor itself is obscuring that part of the board, but I doubt the track would be connecting anywhere else.

So you need to inspect and repair the top right relay hole.

QuantumCheese, yes, hot components are always a concern, but I think that problem will disappear when the track is fixed.
 

partyanimallighting

Oct 22, 2012
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Hi QC, I hear a click when the pcb is powered down and I can feel the vibration of the relay also when my finger is on it when I power down. I already swapped out this relay with the one from the other working pcb so I know it's working. The relay isn't really hot, just warm, but I can't touch the resistors for long. They're really hot. If you look carefully at the pix you can see the solder thread I ran out from the bottom right hand pin on the relay to the little black "thingy" (what's that?). Don't know the jargon...yes, I'm a novice. Duh...how do I measure the current range? Do I connect the leads to the amperage side of the meter and connect between the 12V input?
 

KrisBlueNZ

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An easier way to fix the board would be to just run an insulated wire from point D to point E on the underside. That way you don't have to remove the relay. It's not as tidy but would at least confirm that that's where the problem is.
 

partyanimallighting

Oct 22, 2012
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Hi Kris, I did as you said, and soldered a wire across D and E, installed all the IC's, re-installed the pcb into the unit, started up and......the unit booted up fine and all functions are fully operational. So, judging from this, am I to assume the problem is somewhere between the relay and the grey resistor? Probably that the resistor is not seated or soldered properly? I seems to be one solitary trace from D to E without devices in between.
 

QuantumCheese

Apr 27, 2012
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Sounds like we got there in the end :)
I must have missed the bit about swapping relays while trying to catch up -nice to know I wasn't far out, i was sure it was in that region, i just got latched (pun not intended) on the relay itself & tracing the tracks was difficult with the board populated

Oh and the 'little black thing' is probably a small-signal transistor - if i was building this circuit it would be something like a bc184 but that's just because i have buckets of them, there are many others to choose from.
 
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partyanimallighting

Oct 22, 2012
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So what you're telling is that the problem's that solitary trace from the relay to the grey resistor? Is it that it's probably open at the solder point below the resistor or is it another problem that I don't understand? Is it that the through-hole at this point has a short and needs to be repaired similar to the one bottom right?
 

CocaCola

Apr 7, 2012
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Yes, the trace between D and E is faulty...

In the end the simple repair is as Kris stated use a jumper wire between those two points, besides it not looking pretty there it's not going to cause any issues... Use a few dabs of epoxy to hold the wire down if you want it to be secure, or simply cover it with some tape... If you want to get all fancy you need to diagnose where that trace is no making contact with the components... As Kris has stated it's probably a break in the through hole plating, meaning the solder is not properly flowing between the bottom of the board and the top... If it doesn't flow properly it won't make the connection it's supposed to... You can if you want attempt to fix the trace but only if 'looks' are important... One way to fix the through hole is to take the clipped leg of a resistor or some thin gauge wire... Take a razor and remove the green resist off the area of the board around the hole (you might need to slightly enlarge the hole at this point) anyway, feed the resistor leg through the hole and bend it over to the now exposed trace copper and solder in place... Insert the real component and solder it into the hole, the short section of wire you inserted into the hole should now replace the plate through area that is faulty... This is is a lot of tinkering vs just using a jumper wire...
 
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QuantumCheese

Apr 27, 2012
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I think so. it looks that way. I would go with CC's suggestions for a fix.

with a footnote of - "double sided (or more layers) are 'quite delicate' especially when re-working joints. you need to be really careful when de-soldering to make sure the joint is melted all the way through to the other side or you might pull the through-hole out with the component!"

Good luck on your next one, it's all just one big learning curve m8 :)

QC.
 

KrisBlueNZ

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It seems the problem was a break between the relay pin (point D) and the big resistor (point E). It's hard to be sure exactly WHERE the problem is. My guess is that it's the relay pin, and you probably pulled the through-hole collar out of the board when you removed the relay.

If the board already had this fault before you started working on it, then it could be that the through-hole collar failed, due to a fault in the PCB manufacture. I doubt it though, because through-hole plating is MOST reliable on large holes like those for the relay pins.

As CocaCola said, you can either just leave the jumper wire there, or do a tidier fix. I would do the tidy fix. Here's my suggestion for how to repair a failed through-hole collar, from post #29 in this thread, with "capacitor" changed to "relay". It's pretty similar to CocaCola's suggestion.
Scratch an area of the solder-resist coating off the track on the top side near the hole, tin the exposed area on the track, and solder a thin wire onto the exposed track and poke it down through the hole. Then you refit the relay, and solder the thin wire and the relay lead to the track on the underside. You can use a single strand from a stranded wire, and/or you can drill the hole out slightly so both the wire and the relay lead will fit through it. The rework should be covered completely by the relay itself. You can clean up the PCB with isopropyl alcohol (or any solvent really) and a cotton swab. Push hard and it will remove all the crusty stuff.

Clean the top side of the board before you refit the relay, and clean the other side afterwards.

BTW the black component with the silver stripe that's near the relay is a diode, not a diac.

Have the components stopped getting hot now?
 

partyanimallighting

Oct 22, 2012
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Hi Kris, QC, CC and anyone else who put in their two cents worth. I went the resistor wire way and ran this through the relay hole, soldered up and cleaned up the pcb thoroughly, front and back, tested and it's working fine. This particular unit never functioned from brand new out of box so it was probably tested in the factory, passed quality control and then failed upon startup. Because of my very very basic knowledge of electronics, I would have never repaired this pcb without the assistance of all of you guys and for this I am very grateful. I also gained a little knowledge along the way but I know I have a very long way to go before I am anywhere near the "Jedi" level of you guys. The good news is, I have a lot of stuff to repair so I'll obviously gain more experience along the way, with your help. Thanks ever so much once again and look out for a new post over the course of this weekend.
 

(*steve*)

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Sounds like a fantastic result.
 
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