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Hi BB,
Hope the photos are satisfactory. These were taken with my Android phone.
"Did you check EZK C903 ? a rectangular green block "ERO" cap?
It's adjacent to a crystal and likely part of an oscillator circuit"
--> No. I didn't suspect anything wrong with the MKT (metallized polyester) cap. Yes its a part of oscillating circuit because that Siemens microprocessor is basically an 8-bit 12MHz computer. The 12MHz speed is determined by the Xtal oscillator. I've read Siemens's datasheet sometime ago that you could increase the speed by upgrading the Xtal but that won't increase the car's horsepower. Increasing the speed would make the microprocessor runs hotter than usual that might require extra cooling (attaching heatsink or add fan maybe).
"The coating over the board can be carefully scraped off around the PTH's
so that solder flows to the PCB track when you reflow."
--> Exactly. One more helpful thing is to use soldering iron with pointed tip.
"Look at PTH.JPG upper right just between D332 / D504 and T322
for a solder joint that looks like it needs attention"
--> Already done afterwards.
"I wonder if the Siemens 30191 voltage regulator mounted on the big heat sink might benefit from new thermal compound? It looks like it's riveted on to the heatsink."
--> Yes its riveted. I think its ok to let it be. I did think of additional cooling like a small fan with ventilation hole (cutting hole to the plastic EZK box) but that would introduce outside dust to the components. The board is almost dust-free as it is. I did wonder why the EZK box is not a Faraday cage like the all-metal LH box. Anyway the car still works.
"The LH2.3 ECUs are very easily damaged by voltage spikes and surges."
--> Could be but for our LH2.4 ECU there are MLCC (multilayer ceramic capacitor) soldered to every connector pins on the board. If you look closely at bottom of the pins at board-side there's a row of small brown square things (ie MLCC). I think these are to absorb voltage spikes.
"Is there some adjustment in Volvo AMMs?"
--> Only for LH2.2 I think. Its supposed to be adjusted with a CO meter attached at the exhaust tip. Aimed for less than 0.5% CO level if I'm not mistaken. However no adjustments for LH2.4 AMM.
Best regards,
Amarin
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