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Discussion Starter · #1 · (Edited)
Hi Everyone!
Sadly about a year ago my instrument cluster started to act up. I believe I may have located the issue but I am not 100%. I did do a continuity test on the connectors to the neighboring solider joints but to my surprise upon parting the cluster I discovered a loose transistor falling off the board. Anyone know what kind of transistor this is? I can order a few and resolder it myself as I'm pretty handy with electronics. Furthermore anyone have a schematic, I'm actually wondering if the issue I'm fixing is even related to the problem Im having where the whole cluster would shut off while driving. I can put pressure on the back of the cable and it would kick back on but as soon as I release pressure from the 3-wire harness and hit a bump the cluster would again shut off.


My second thought is to replace it with an aftermarket one, Anyone have any recommendations for a upgraded replacement?

This is the only one I could find: Lotus Elise Lotus digital-dash 'aim' - LOTAC05587 | Lotus Parts Online, Birmingham MI

I appreciate any feedback!

Oh and one more question, My assumption is its the PIN in the upper right if you were to orotate this picture in the correct position. The way it is uploaded it looks like the most bottom right pin, runs to a capacitor then into the bottom of the TDK block, but want to confirm if that's the common joint that others have found to be the problem child.

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If you G search and end with lotustalk you'll find several threads that might help you. Here's one

 

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2020 Evora GT in Formula Red, coordinated black+red interior, windowed engine hatch
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That is a SOT23-3 surface mount package. Many, many different components come in that package: NPN/PNP bipolar transistors, N- and P-channel MOS transistors, voltage regulators, diode arrays, the list is almost literally endless.

Sadly too, there is no standard nor central list for the markings on such packages. Back in the days when throughhole packages reigned supreme, the complete part number would be on the package along with a date code and sometimes even a factory (location) marker. Small SMD packages don't allow for that much detail, and the abbreviations are frustratingly company specific. You can still see full markings on the larger SMD packages on that board, though.

Side note: I get a kick out of resistor markings. Resistors used to be considered too small for human readable text so they used bands of color. There are two of them on your board, the large-ish brown devices with the color bands. Yet today, SMD resistors get far smaller but they mark them with text digits!!!

Back on topic: If I had access to the PCB we could trace out some of the circuitry and see if that helped narrow down the possibilities. Lacking that, my best guess from the "A4" marking is it's a BAV70 which is (was) a very popular pair of fast small signal diodes in a common cathode configuration. Here's a BAV70 spec sheet. A curve tracer is the better instrument for divining what your part actually is, but if you have a multimeter you can check for BAV70 behavior. If it tests as a "good" BAV70 I'd solder it back onto the board. Heck, I'd probably start there anyway... it's more likely that the part is still in good shape than that we're going to guess what the part happens to be from an "A4" on the package.

While you're at it, reflow every connection that looks even slightly strange. Solder joints should appear bright and shiny. If you have any which are dark, corroded, cracked, etc. those should be reflowed with a touch of fresh solder. Use 63/37 leaded solder; ROHS didn't go into effect until 2006 so there's a decent chance this board (which has a "0536" date code, meaning the 36th week of 2005) used leaded solder. Don't even get me started on the nightmares that lead-free solder have caused worldwide... there's a reason space-based equipment uses real, lead-based solder!
 

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BTW Atlanta Speedometer does cluster repair and might be able to provide you with components or advise. Like IDEengineer and link in Post#2 advised reflow all solder joints.
 

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Discussion Starter · #6 ·
Thanks all for the great feedback. Your right, the transistor is probably still good and just had fault soldering so Ill make an attempt to re-solder the part and give it a go! Ill post the results.
I'm wondering, What are the chances the solder job came from the factory like that. I've never opened one of these units before, are you say you guys are certain this has been opened by a 3rd party and reflowed once already by the looks of it?
 

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2020 Evora GT in Formula Red, coordinated black+red interior, windowed engine hatch
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It didn't come from the factory like that, it probably just aged into that condition. Cars are high vibration environments which isn't friendly to lots of things, including surface mount electronics. Sure, it's possible they had a bad batch of soldering but most of the joints look nice and shiny so I'd attribute it to age and environment.

Yep, just resolder the part into place. Don't build stress into the joints or it might pop off again. First, remove as much of the solder on the three PCB pads as possible. Then put a fresh dot of solder on just one pad. Hold the part right next to its footprint on the board, reheat that dot of solder, slide the part into place so it's lined up, and hold it there while you remove the soldering iron and let the solder cool.

Next, press gently on the body of the part and reheat the solder again. This insures the part is fully seated against the PCB. Hold it there while you remove the iron and let the solder cool. This pad is now done, and when you solder the other two you won't build stress into that first lead by pressing the part into the board - you already know it's flush against the board's surface. Just solder the last two pads and you're done.

It's always a good idea to clean up the remaining flux. If you don't have actual flux remover, isopropyl alcohol is a reasonable substitute. Blobs of flux attract dust and other contaminants which are not your friend. Cleanliness is a good thing for electronics.

Finally, be sure to reflow - and perhaps add a touch of solder to - at least the pins of the connectors on the board. This goes double for anything that leaves the board, like a wiring harness. Those are both mechanically stressed AND prone to fracture, which is often the cause of intermittent operation. There will never be a better time to do it than right now, when it's already disassembled.

Report back!
 

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Discussion Starter · #8 ·
It didn't come from the factory like that, it probably just aged into that condition. Cars are high vibration environments which isn't friendly to lots of things, including surface mount electronics. Sure, it's possible they had a bad batch of soldering but most of the joints look nice and shiny so I'd attribute it to age and environment.

Yep, just resolder the part into place. Don't build stress into the joints or it might pop off again. First, remove as much of the solder on the three PCB pads as possible. Then put a fresh dot of solder on just one pad. Hold the part right next to its footprint on the board, reheat that dot of solder, slide the part into place so it's lined up, and hold it there while you remove the soldering iron and let the solder cool.

Next, press gently on the body of the part and reheat the solder again. This insures the part is fully seated against the PCB. Hold it there while you remove the iron and let the solder cool. This pad is now done, and when you solder the other two you won't build stress into that first lead by pressing the part into the board - you already know it's flush against the board's surface. Just solder the last two pads and you're done.

It's always a good idea to clean up the remaining flux. If you don't have actual flux remover, isopropyl alcohol is a reasonable substitute. Blobs of flux attract dust and other contaminants which are not your friend. Cleanliness is a good thing for electronics.

Finally, be sure to reflow - and perhaps add a touch of solder to - at least the pins of the connectors on the board. This goes double for anything that leaves the board, like a wiring harness. Those are both mechanically stressed AND prone to fracture, which is often the cause of intermittent operation. There will never be a better time to do it than right now, when it's already disassembled.

Report back!
I got that, Ill crank on it this next week or so and am also looking for an upgrade encase the repair fails.
 
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