TR7V8mike Posted May 30, 2014 Report Share Posted May 30, 2014 Hi folks The car's developed a new electrical problem. When I turn the headlights on the instrument panel does strange things: the tacho stops working, the indicator lights both come on, the instrument lights don't work and several of the gauges go to one end of their range. Any ideas? The printed circuit board does not look like its in very good shape with a couple of breaks. Can someone point me to some guidelines on how to repair it? Thanks Mike Quote Link to post Share on other sites
DaveR Posted May 30, 2014 Report Share Posted May 30, 2014 Hello Mike, The normal process is to scrape off the protective lacquer around the break and then solder a piece of thin tin copper wire (26 SWG) over the break. Other than that if you trace the effected run (on the board) from start to finish and then solder a jumper (insulated) wire across those points. Don't put to much heat from the soldering iron on the board. e. g. Don't leave the iron on the board for long. Cheers, Dave Quote Link to post Share on other sites
AlanT Posted May 30, 2014 Report Share Posted May 30, 2014 This is the ideal wire for fixing a circuit board. http://uk.rs-online.com/web/p/hookup-equipment-wire/2094798/ The insulation does not melt. You can strip the end, make a tiny hook and solder one end in place. Then you can slip the insulation along so there is no gap. Obviously take care if its a heavy current circuit but this wire will carry 1A. Quote Link to post Share on other sites
RogerH Posted May 30, 2014 Report Share Posted May 30, 2014 If the copper track has simply cracked in two you can use 'silver' paint. This is a highly conductive paint with high silver content - RSComps used to do it, worth a look. However the linking using copper wire may be more durable. Roger Quote Link to post Share on other sites
TR7V8mike Posted May 31, 2014 Author Report Share Posted May 31, 2014 Thanks guys, that's very helpful. I read on another forum somewhere that running a new earth from somewhere on the back of the instrument panel to the metal dash support frame would fix the strange things happening among the instruments. Has anyone heard about this? Best regards Mike Quote Link to post Share on other sites
TR7V8mike Posted May 31, 2014 Author Report Share Posted May 31, 2014 If part of a run has separated from the plastic board, what's the best way to stick it back down and seal it? Quote Link to post Share on other sites
AlanT Posted May 31, 2014 Report Share Posted May 31, 2014 You can super-glue it. Works well as there is no weight. Super-glue likes to set quickly on circuit boards. But really its safer to "wire-it out". You can then pull the broken pieces off so they can't "get in the works". I am assuming these are a pain to get in and out and you only want to mess with it once. Don't feel to bad about doing this. When IBM made the first PC's they were about 40 wire links in the circuit board correcting various errors. And there are loads of planes flying with wires on the circuit boards. Quote Link to post Share on other sites
AnthonyF Posted June 1, 2014 Report Share Posted June 1, 2014 Mike, I don't think it will be easy to solder, the heat of a soldering iron near the flexible plastic circuit board will melt it very quickly. The metal paint suggestion could work. You might find it easier to get a circuit board from another instrument pod, although of course there is always that concern that it will be no better than your existing one. They are all the same except the ones from the very late cars (the ones with the ISO symbol gauges & trip/clock adjusters through the plastic face) are different. Or even easier swap the whole pod & transplant your speedo (and tacho if a V8). As with most TR7 electrical problems, its probably to do with the earths. Yours sounds like everything is finding an earth when you put the lights on - the secondary gauges (temp, fuel) work on variable resistance to earth through their circuits so if theses gauges go straight to full then they are finding an earth outside of their normal circuit! Check the 2 multipin plugs that connect to the circuit board. Quote Link to post Share on other sites
TR7V8mike Posted June 7, 2014 Author Report Share Posted June 7, 2014 Hi Anthony, What should I be looking for with the multi-pin plugs? Quote Link to post Share on other sites
AnthonyF Posted June 9, 2014 Report Share Posted June 9, 2014 Hi Mike, sorry, my comments about the multipin plugs were not very clear, I just meant check that they are not damaged, are clean & properly seated in the sockets. Reading your original post again, do these strange things only happen with the lights turned on? If everything works correctly with the lights off then it might be worth trying another headlight switch, and checking/cleaning the contacts at the end of the instrument stalks under the plastic cowl where they connect to the loom. Quote Link to post Share on other sites
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