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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Attaching flex cable to PCB
I've been given a Mercedes-Benz instrument cluster where a flex cable
has come adrift due to mishandling. The PCB is microcontroller based and interfaces with an odometer via a flex cable. The other gauges connect via long pins. AFAICS, the flex cable is attached with some kind of glue - there are no clamps, no screws, no rubber strain relief. The traces have a very fine pitch, and the cable is almost too short to work on. The PCB is single sided, so I could probably drill two holes and add a clamp with a rubber sandwich, but I need to ensure that the copper traces make reliable contact. Any suggestions? BTW, the mechanic that gave me this job was doing a freebie for a friend. AFAICT, he was trying to cover the empty lamp socket of an annoying glow plug indicator with black tape. - Franc Zabkar -- Please remove one 's' from my address when replying by email. |
#2
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"Franc Zabkar" wrote in message ... | I've been given a Mercedes-Benz instrument cluster where a flex cable | has come adrift due to mishandling. The PCB is microcontroller based .... | BTW, the mechanic that gave me this job was doing a freebie for a | friend. AFAICT, he was trying to cover the empty lamp socket of an | annoying glow plug indicator with black tape. What did the indicator light say? "Don't disassemble this"? N |
#3
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On Mon, 15 Nov 2004 03:58:46 GMT, "NSM" put finger to
keyboard and composed: "Franc Zabkar" wrote in message .. . | I've been given a Mercedes-Benz instrument cluster where a flex cable | has come adrift due to mishandling. The PCB is microcontroller based ... | BTW, the mechanic that gave me this job was doing a freebie for a | friend. AFAICT, he was trying to cover the empty lamp socket of an | annoying glow plug indicator with black tape. What did the indicator light say? "Don't disassemble this"? What it should have said was "CAUTION: PCB obscures very poor design". I do quite a few jobs for this mechanic and find that he and his staff are very competent. Unfortunately I don't have the unit with me, otherwise I would post a photo so you could see it for yourself. As I said in my OP, there is no strain relief for the flex cable, and no connector. The printed traces of the cable and the PCB rely purely on a tiny, almost imperceptible dab of glue to keep them in contact. I've never seen anything so abominably bad. Even children's toys are better built. BTW, this abortion is manufactured by Magneti Marelli. - Franc Zabkar -- Please remove one 's' from my address when replying by email. |
#4
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"Franc Zabkar" wrote in message ... | What it should have said was "CAUTION: PCB obscures very poor design". | | I do quite a few jobs for this mechanic and find that he and his staff | are very competent. Unfortunately I don't have the unit with me, | otherwise I would post a photo so you could see it for yourself. As I | said in my OP, there is no strain relief for the flex cable, and no | connector. The printed traces of the cable and the PCB rely purely on | a tiny, almost imperceptible dab of glue to keep them in contact. I've | never seen anything so abominably bad. Even children's toys are better | built. | | BTW, this abortion is manufactured by Magneti Marelli. Is that Italian for Lucas Electric? http://pw1.netcom.com/~krk/lotus/humor/lucasjokes.html http://members.tripod.com/~tcotrel/lucas.html (think about it) NM |
#5
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On Tue, 16 Nov 2004 07:02:18 +1100, Franc Zabkar
wrote: On Mon, 15 Nov 2004 03:58:46 GMT, "NSM" put finger to keyboard and composed: "Franc Zabkar" wrote in message . .. | I've been given a Mercedes-Benz instrument cluster where a flex cable | has come adrift due to mishandling. The PCB is microcontroller based ... | BTW, the mechanic that gave me this job was doing a freebie for a | friend. AFAICT, he was trying to cover the empty lamp socket of an | annoying glow plug indicator with black tape. What did the indicator light say? "Don't disassemble this"? What it should have said was "CAUTION: PCB obscures very poor design". I do quite a few jobs for this mechanic and find that he and his staff are very competent. Unfortunately I don't have the unit with me, otherwise I would post a photo so you could see it for yourself. As I said in my OP, there is no strain relief for the flex cable, and no connector. The printed traces of the cable and the PCB rely purely on a tiny, almost imperceptible dab of glue to keep them in contact. I've never seen anything so abominably bad. Even children's toys are better built. BTW, this abortion is manufactured by Magneti Marelli. - Franc Zabkar I don't like your chances Franc. The only thing I an think of is electrically conductive epoxy. |
#6
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"Ross Herbert" wrote in message ... | I don't like your chances Franc. The only thing I an think of is | electrically conductive epoxy. If it's a zebra connection wouldn't that be worse? You'd short everything to everything. He could just try to align it as best he can and hold it there to test. Glue it if it works. N |
#7
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On Tue, 16 Nov 2004 02:03:45 GMT, "NSM" wrote:
"Ross Herbert" wrote in message .. . | I don't like your chances Franc. The only thing I an think of is | electrically conductive epoxy. If it's a zebra connection wouldn't that be worse? You'd short everything to everything. He could just try to align it as best he can and hold it there to test. Glue it if it works. N Franc made no mention of a zebra connection otherwise I wouldn't have suggested epoxy. He did say that the original seemed to be attached with some sort of adhesive so that's the reason for my suggestion. |
#8
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On Tue, 16 Nov 2004 02:03:45 GMT, "NSM" put finger to
keyboard and composed: "Ross Herbert" wrote in message .. . | I don't like your chances Franc. The only thing I an think of is | electrically conductive epoxy. If it's a zebra connection wouldn't that be worse? You'd short everything to everything. It's not a zebra elastomer connection. The copper traces of the flex cable bear directly against the copper traces of the PCB. The two are retained with some kind of glue. It's a very peculiar and IMO very poor connection method. In fact, I've seen more adhesive on a postage stamp. He could just try to align it as best he can and hold it there to test. Glue it if it works. On closer inspection some of the printed copper traces on the flex lead have delaminated. It appears this job is a lost cause. :-( Anyway, here are some pics. The original 5MP photos have been compressed to 90%, so the quality is poor. http://members.optusnet.com.au/~fzabkar/label.jpg http://members.optusnet.com.au/~fzabkar/instruments.jpg http://members.optusnet.com.au/~fzabkar/flex_lead2.jpg http://members.optusnet.com.au/~fzabkar/flex_lead.jpg http://members.optusnet.com.au/~fzabkar/pcb_trace.jpg - Franc Zabkar -- Please remove one 's' from my address when replying by email. |
#9
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On Mon, 15 Nov 2004 14:53:39 +1100, Franc Zabkar
wrote: I've been given a Mercedes-Benz instrument cluster where a flex cable has come adrift due to mishandling. The PCB is microcontroller based and interfaces with an odometer via a flex cable. The other gauges connect via long pins. AFAICS, the flex cable is attached with some kind of glue - there are no clamps, no screws, no rubber strain relief. The traces have a very fine pitch, and the cable is almost too short to work on. The PCB is single sided, so I could probably drill two holes Are you very sure ? 'Very fine pitch' and 'single sided PCB' sound like a contradiction to me. (Or as a euphemism for 'multi layer :-) -- Kind regards, Gerard Bok |
#11
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There are no thru-holes. All components are smt. The mechanic says an
instrument specialist told him that these flex cables are known to separate in normal use, probably due to heat and vibration. He claims these units are irreparable. Here is a photo of the PCB: http://members.optusnet.com.au/~fzabkar/pcb_trace.jpg The connection point is above and between the two lamps. The traces go directly to a microcontroller. Note that there are numerous test points which look like thru-holes, but I believe these could be for bed-of-nails testing (???). Yes, those "bumps" are for the bed of nail test points. Looks like the ribbon and the pads on the circuit board are good, Why not do a low-temp soldering? Next time use a good older program like photo shop pro 5.x (ebay hopefully) to crop it (this chops off the unneeded pixels) then shrink it down to 50% to cut down bytes, 30% is minimum for smallest size without losing too much details. Cheers, Wizard - Franc Zabkar -- Please remove one 's' from my address when replying by email. |
#12
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On Thu, 18 Nov 2004 02:23:43 GMT, (Jason D.) put
finger to keyboard and composed: There are no thru-holes. All components are smt. The mechanic says an instrument specialist told him that these flex cables are known to separate in normal use, probably due to heat and vibration. He claims these units are irreparable. Here is a photo of the PCB: http://members.optusnet.com.au/~fzabkar/pcb_trace.jpg The connection point is above and between the two lamps. The traces go directly to a microcontroller. Note that there are numerous test points which look like thru-holes, but I believe these could be for bed-of-nails testing (???). Yes, those "bumps" are for the bed of nail test points. Looks like the ribbon and the pads on the circuit board are good, Why not do a low-temp soldering? My patience and eyesight aren't good enough for this. In any case an email from a kind gent has cleared up the mystery for me. The connection method is 3M Scotch 9703 conductive tape: http://products3.3m.com/catalog/us/e...er/output_html "Tape 9703 is an isotropic, electrically conductive, pressure sensitive adhesive (PSA) transfer tape. It is a permanently tacky system consisting of a PSA matrix with aligned conductive particles. These particles allow electrical conduction through the adhesive thickness ("Z-axis"), but not in the plane of the tape." Next time use a good older program like photo shop pro 5.x (ebay hopefully) to crop it (this chops off the unneeded pixels) then shrink it down to 50% to cut down bytes, 30% is minimum for smallest size without losing too much details. Sorry for the abysmal quality. I should have made better use of Paint Shop Pro, and I should have taken more care with the photography. Here are the same photos with better processing: http://members.optusnet.com.au/~fzabkar/pcb_trace.jpg (33KB) http://members.optusnet.com.au/~fzabkar/flex_lead.jpg (19KB) http://members.optusnet.com.au/~fzabkar/flex_lead2.jpg (17KB) http://members.optusnet.com.au/~fzabkar/label.jpg (13KB) http://members.optusnet.com.au/~fzabkar/instruments.jpg (13KB) Cheers, Wizard I wonder if Scotch 9703 conductive tape may be a viable solution for repairing broken flex leads? - Franc Zabkar -- Please remove one 's' from my address when replying by email. |
#13
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"Franc Zabkar" wrote in message ... | My patience and eyesight aren't good enough for this. In any case an | email from a kind gent has cleared up the mystery for me. The | connection method is 3M Scotch 9703 conductive tape: Most interesting. I wonder if this is obtainable in service quantities? N |
#14
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On Thu, 18 Nov 2004 16:03:08 +1100, Franc Zabkar
wrote: Here is a photo of the PCB: http://members.optusnet.com.au/~fzabkar/pcb_trace.jpg My patience and eyesight aren't good enough for this. In any case an email from a kind gent has cleared up the mystery for me. The connection method is 3M Scotch 9703 conductive tape: http://products3.3m.com/catalog/us/e...er/output_html "Tape 9703 is an isotropic, electrically conductive, pressure sensitive adhesive (PSA) transfer tape. It is a permanently tacky system consisting of a PSA matrix with aligned conductive particles. These particles allow electrical conduction through the adhesive thickness ("Z-axis"), but not in the plane of the tape." In other words: self adhesive zebra strip :-) -- Kind regards, Gerard Bok |
#15
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Here are the same photos with better processing:
http://members.optusnet.com.au/~fzabkar/pcb_trace.jpg (33KB) http://members.optusnet.com.au/~fzabkar/flex_lead.jpg (19KB) http://members.optusnet.com.au/~fzabkar/flex_lead2.jpg (17KB) http://members.optusnet.com.au/~fzabkar/label.jpg (13KB) http://members.optusnet.com.au/~fzabkar/instruments.jpg (13KB) Cheers, Wizard I wonder if Scotch 9703 conductive tape may be a viable solution for repairing broken flex leads? - Franc Zabkar That special tape will work! Key is clean both real good. Careful on that flex cable, it is made of conductive paint printed on clear plastic sheet. Many chemicals will attack that paint. This is same kind of flex circuit with this printed on conductive paint. Otherwise, there is room on PCB to drill two holes and use two thick (say .050" to .100") strips of aluminum and screws & nuts, one thin rubber strip from your junk stuff to pad the flex so both flex and circuit board is squeezed together. Much better design IHMO!! What type of display panel? LCD? Cheers, Wizard |
#16
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On Thu, 18 Nov 2004 16:03:08 +1100 Franc Zabkar
wrote: In any case an email from a kind gent has cleared up the mystery for me. The connection method is 3M Scotch 9703 conductive tape: http://products3.3m.com/catalog/us/e...er/output_html "Tape 9703 is an isotropic, electrically conductive, pressure sensitive adhesive (PSA) transfer tape. It is a permanently tacky system consisting of a PSA matrix with aligned conductive particles. These particles allow electrical conduction through the adhesive thickness ("Z-axis"), but not in the plane of the tape." I agree with the others that this is a VERY interesting product, but I don't think that it was what was used on the calculator I worked on many years ago. That stuff did not look like tape, and it certainly wasn't tacky any more. There must be something else that is suitable for OE use. Perhaps it is ultraviolet curing. - ----------------------------------------------- Jim Adney Madison, WI 53711 USA ----------------------------------------------- |
#17
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"Jason D." wrote in message ... There are no thru-holes. All components are smt. The mechanic says an instrument specialist told him that these flex cables are known to separate in normal use, probably due to heat and vibration. He claims these units are irreparable. Here is a photo of the PCB: http://members.optusnet.com.au/~fzabkar/pcb_trace.jpg The connection point is above and between the two lamps. The traces go directly to a microcontroller. Note that there are numerous test points which look like thru-holes, but I believe these could be for bed-of-nails testing (???). Yes, those "bumps" are for the bed of nail test points. Looks like the ribbon and the pads on the circuit board are good, Why not do a low-temp soldering? Next time use a good older program like photo shop pro 5.x (ebay hopefully) to crop it (this chops off the unneeded pixels) then shrink it down to 50% to cut down bytes, 30% is minimum for smallest size without losing too much details. You don't even need that, you can get IrfanView for free, it'll resize, convert formats, colors, etc not to mention view just about anything. |
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