Printed circuit instrument panel repair?

[SRath]

I have a Chevy truck with a printed circuit instrument panel that has a break in one of the printed circuits. It is such a thin piece of copper (like foil) inset into a very thin sheet of plastic that I'm reasonably sure I cannot solder it.



There must be a way to repair the small 1/4" gap where one of the conductors is broken -- some type of cold solder or something -- but I'm way out of my area here.



Any suggestions?



As a last resort, I think I can bypass the broken conductor and use a length of 14 or 16 gauge wire between the wire plugging into the panel and the gauge connection at the end of the broken conductor. It is the volt gauge that it goes to. But I'm hoping there is a relatively simple way to just fix the printed circuit?

 

[SRath]

Would this stuff, or similar work? If so, is it the type of thing I might find at Radio Shack?



New Wahl Silver Bearing Solder Paste 7. 1 Grams Syringe - eBay (item 270682043120 end time Jan-17-11 17:14:20 PST)

 

[seafish]

You could likely take it to a local electronics repair shop and have them solder for you... i'd think that a simple repair like that should not cost too much.

 

[fest3er]

There is no such thing as a cold solder joint unless it's a mistake. The solder and what it's adhering to must be hot enough for the solder to flow and whet the surfaces, then cool slow-ishly while not moving.

14-16 ga. wire is, I think, complete overkill, unless that trace on the PCB is carrying a lot of current (which I doubt).

If the trace it 1/6" to 1/8", you ought to be able to clean it. Carefully and gently scrape it beyond the break, where the trace is still adhered to the board. Then use a pencil eraser to further clean it. Then apply a little bit of paste flux (to help the solder whet and flow and prevent oxidation while soldering). If it's really too brittle, fall back to your plan B. The trace is already broken; you can't hurt it too much more.

If the trace is too narrow (thin) to safely clean and flux for solder or you can't prep it for soldering, then yes, you can run a 20-22 gauge wire between the two endpoints you mentioned. Find a short length of standard household telephone cable and use one wire of it. Use enough wire so you can run it along the trace and glue it down with a few dabs of RTV silicone or hot glue; you don't want it flopping around and cause stress breaks later on. Strip the ends and use a pen knife to scrape the wire ends clean and bright. Then apply a small dab of paste flux. Clean the two end points; remove the solder if you can so the wire will fit in with the existing joint.

Use a soldering pencil; a 140W gun is far more than you need and may well damage the unit with excessive heat. Apply only as much heat as is needed to melt the solder and heat the mating surfaces, and have it flow onto the surfaces. If you haven't soldered in a while, practice on some scrap.

The solder paste may work, but it's probably better to use rather thin solder and apply the smallest amount needed to whet and mate the surfaces. It's kind-of like welding; too much and too little solder are no good. The right amount will yield a good joint that is both mechanically and electrically sound.

Take before and after pictures and post 'em.

 

[SRath]

I'll try that, Neal. Thanks for the detailed step-by-step! Unfortunately seafish, I don't know of any good electronics repair shops around here anymore in this age of "disposable TVs" and such... I do know a couple people who work at Rockwell-Collins Avionics building high-tech electronics. I should also say that I found restoration printed circuits for about $75, but I'm too cheap to spend that much for one broken conductor or "trace" as Neal called it.



I did find the cause of the failure right away, and i suspect this volt gauge quit working a very long time ago. The little foil traces that go to the gauge terminals had overlapped a tiny bit causing a direct short circuit that overheated the two traces and caused them to delaminate a bit from the plastic sheet until one of them melted through and broke, thus ending the short circuit. It was a simple matter of trimming the tiny excess foil traces at the gauge connectors to eliminate the actual cause of the problem. Now I just need to repair the damage.



I really like this 30 year old truck, and have been on a roll with it since finding it rotting in the sun on a southern California ranch and rescuing it back to a new and useful life in Iowa. Everything that has deteriorated over the decades of non-use (it has less than 90k miles on it in 30 years) has been 'fixable'. It required only a basic tuneup and replacement of rotted rubber hoses, tires, etc. to not only drive the 2000+ miles back to here, but it did so flat-towing another identical 3/4 ton 4x4 pickup across a desert and up and over 7000 ft mountains in winter weather. Tough old truck! It starts with one pump of the gas pedal and a mere bump of the starter on these sub-zero Iowa mornings. I spent $100 for a rebuilt steering box, tightened two loose draglink end studs, repacked and adjusted the front wheel bearings, and she steers tighter and smoother than my diesel dodge even after spending over $2000 on all new and upgraded steering components for it!



I have gotten everything from the dual fuel tank selector to the analog mechanical cruise control working and I'm running out of things to fix while waiting for summer and a chance to repaint her. Only the R12 a/c remains to be recharged fully and i need to spend $150 for all-new weatherstripping, too.



The instrument panel was removed due to intermittent functioning of the high beam indicator and the non-functioning volt gauge. The analog quartz clock was utterly frozen, too, and the speedo cable needed to be removed from it's housing for lube since the needle tended to bounce. No invisible electrons or finicky computer brains to deal with in diagnosing problems on this truck.



A little white grease sprayed on the cable and in the housing fixed the speedo needle fluctuations. I even removed the clock and, figuring I had nothing to lose, sprayed the crap out of the guts with WD-40 and managed to get it to where the adjustment knob actually moved the clock hands. After working the hands a bit, I then just plugged it back in and it has kept perfect time ever since! Wow!



The 30 year old instrument bulbs are all replaced now and the contacts cleaned. I only need to get the volt gauge working to declare victory over ALL the "electronics" this rust-free non-computerized blessing has.



I love these old Chevys! Nobody builds 'em that tough and reliable anymore...

 

[PBJ2500CTD]

The Wahl product may work in your situation. It is a solder "product" containing special flux and has a low initial melting point. Heat is required - but much lower than a standard soldering iron. Once it has been initially heated/cured the subsequent re-melting point goes up a couple of hundred degrees. You get a good electrical and mechanical bond. Ideal for the repair of a small, low current circuit board. I have successfully used similar products to repair a defective trace on a variety of circuit boards in the past. I'm not sure if Radio Shack would carry such a product since their business model has changed over the years.
If you are looking for a quick and effective repair using existing equipment and supplies laying around the house, follow Neal's guideline. Most automotive instrument panel circuit boards are fairly sturdy and can handle a bit more "judicial" abuse than they appear capable of. Still it is best to err on the light and easy side. The important thing is to take your time in preparation, and be quick and deliberate in execution. Carefully clean the surface coating from the trace; don't scrape too hard, the trace is very thin and delicate. You should use a wire or other conductor to bridge the break. Lightly coat the unions to be soldered with a non-corrosive electronics flux. Depending on the delicacy of the circuit I prefer to pre-tin all mating surfaces/unions. Clean prepare and clean all surfaces. Lightly coat each surface with electronics flux. Insure the soldering tip is clean, lightly coat with flux, followed immediately with a small bit of solder, then to the surface of a union, just enough action to have the solder flow and adhere to the union surface/conductor. Repeat for the three other surfaces. CLEAN is important! With a steady hand and needle nose pliers holding the bridge wire/conductor, position one side of the union together then gently and quickly apply the soldering iron tip to the union. As soon as the solder flows remove the tip from the union - HOLD UNION STEADY until the union cools/solidifies. The whole process is very quick. Too much heat will destroy your work, circuit board, and remaining patience. Insure flux on next union joint - needle nose pliers on bridge conductor (acts as heat sink so you don't undo first union) - briefly apply soldering iron tip to new union as in previous union... hold union steady while it cools... done. Time to have a Nectar of the Gods... then test/re-install panel... have another delicious nectar.
It is always a good idea to practice on some scrap pieces to get a feel for your particular equipment.

Note: Well moistened tiny strips of paper towel may be used as a heat sink to protect the surrounding circuit or case from unnecessary heat stresses/damage during soldering. In this case it shouldn't be necessary unless the break is really close to other delicate stuff. Just keep the work area clean and dry.

 

[PBJ2500CTD]

...
I did find the cause of the failure right away, and i suspect this volt gauge quit working a very long time ago. The little foil traces that go to the gauge terminals had overlapped a tiny bit causing a direct short circuit that overheated the two traces and caused them to delaminate a bit from the plastic sheet until one of them melted through and broke, thus ending the short circuit. It was a simple matter of trimming the tiny excess foil traces at the gauge connectors to eliminate the actual cause of the problem. Now I just need to repair the damage.
...

Aw heck. Easier fix possible??? If the voltmeter has the terminal lugs attaching it to the shell and circuit board it should be a piece of cake. Clean the trace at a spot just outside of the melted part of the trace and solder a small wire with a crimped lug to fit the voltmeter's stud.
Sure beats the heck out of the '70's Dodges with the ammeter circuit meltdown.

 

[SRath]

The job certainly looks doable, and you and Neal sure make it sound straightforward, Bruce. I was eyeing the lugs that crimp down on the printed circuit at the gauge (it was here where the excess exposed conductor foils sticking out from under the lugs touched each other) and the plug-in wiring harness and knew I could simply bend one lug contact up, insert a wire, clamp it back down (soldering would be better), then scotchlok or splice the other end of the wire directly to the corresponding harness wire just before it enters the panel connector. Not sexy, but no one would ever see the bridge wire.



But this isn't the first time I have encountered printed circuit instrument panel issues, and learning to actually fix a broken trace would be useful. And the gap I need to close is less than 1/4" and a crude repair shouldn't be necessary. My son's '73 Camaro has a similar issue, though a fellow member of the NastyZ Camaro website sold and shipped me a replacement printed circuit so cheap ($10) it wasn't worth considering fixing the old one at that time.



Since Chevy built these trucks, including Blazers and Suburbans, and panels for over 18 years in all kinds of configurations, and with constant minor tweaks and changes, finding the exact Silverado 4x4 with clock gauge package in an old parts truck might take more fuel running around than what a reproduction printed circuit costs. Even with a repop, getting the correct one the 1st time out the dozens to choose from based on a catalog description with no factory part number cross-reference seems iffy to me. There are many, many variations even within the same model year: 4x4 or 2x4?; tach or no tach?; idiot lights or gauges?; how many indicator lights and for which options? clock or no clock?; gauge positioning?; etc, etc. Chevy offered lots of choices.



I'm also entertaining notions of using some old and fairly rare gauge panels, in various states of repair, that I have for these trucks to put together a custom "factory-tach" panel for this truck. That would require some 'customization' and hybridization of both printed circuit and direct wiring.



So there are potential benefits from getting proficient at this.



Electronics guys are kinda like those other 'dabblers in the black arts': automatic transmission gurus. They always claim "it's easy if you know how".



I'm a good welder, but a welding expert and an electronics soldering expert have as much in common as a butcher and a surgeon, or an artillery gunner and a sniper. :-laf

 

[fest3er]

... I'm a good welder, but a welding expert and an electronics soldering expert have as much in common as a butcher and a surgeon, or an artillery gunner and a sniper. :-laf

Not necessarily. Both welding and soldering require the *right* amount of heat applied for the *right* amount of time. Both the weld and the solder joint must be mechanically sound.



Perhaps comparing a rabbi with a Catholic priest would be closer; they're very different, but they still have definite commonalities.

 

[SRath]

I ended up going with Plan B: a jumper wire from the incoming wiring plug directly to the volt gauge lug, bypassing the broken printed circuit trace altogether.



I did try to solder a small copper wire bridge across the broken gap, but the plastic laminate and the unbelievably thin foil trace just made it impossible for me with my $6 soldering iron and i was in serious danger of damaging the printed circuit even more.



The "right amount of heat" (enough to melt the solder) applied in the "right place" (at the break) far exceeded what the thin foil, and certainly the plastic laminate, could handle.



The good news is that Plan B worked very well and that the direct short from long ago did not hurt the gauge. It works perfectly now.



I think an electrically conductive epoxy is the only way to fix such a printed circuit. Heck, JBWeld probably would have done it. That tiny, thin copper trace certainly doesn't carry much juice. I'll experiment and play around with that sometime, I think.

 

[PBJ2500CTD]

Good job Scott! That's some good ol' fashioned fixin's ya done there.

 

[sarj]

I didn't see this thread or I would have responded earlier. There's a trace rebuilder that's designed for repair, but it uses a lot of real estate when it's applied, you brush it on to create the smallest trace possible, and it's real hard to control the flow. I'm not sure of the current capacity. It's like a nail polish with silver in it. I repaired a microwave with it a few years back, and it held up well. It came from a commercial electronics store quite a few steps above a Radio Shack. Radio Shack is good for resistors if you're in a pinch, and that's about it. This stuff was for very low current application though. I used it as a bonding agent too.



Board repairs are always best with jumper repairs running pad to pad, where components are soldered in. Stay away from chips though. Solder flows towards the heat, so the best technique is to work from both sides of the board. That usually means heat from the bottom, but it gets real ugly if components are mounted on both sides of the board. Another technique it to lightly scrape a trace so you're on the foil, and lay some tinned strands on there and hit it quick with heat. You need some fairly robust traces to do this, and if you don't cause more damage, this is a preferred approach. Once a board is repaired, so long as the aren't any high current shorts in the circuit, repairs can last a very long time. Usually you need to find the initial problem that took the board out in the first place.



It's worth it to get a couple of good butane soldering irons. A good one isn't cheap. I have three sizes with the smallest being a very sharp pencil point. Controlling heat, and the amount of time heat is applied is the key to a successful repair. You want it just hot enough with the minimal amount of time applied. Like welding, it takes a little practice to get good at it, but it can save plenty of money.

 

[SRath]

That sounds like what I think it would take and what that "silver bearing paste" seems to describe. Really just a highly conductive epoxy if my guess is right. Expensive, too! But so little is needed that the cost is mitigated by the tiny amount that comes in the syringe.

 

[BullyDogJason]

good job getting it fixed