CAN bus interface and thunderstorm - Page 1
Forum section: electronics / repair

author: e100
author_rank: Frequent Contributor
timestamp: April 22, 2018, 09:07:41 am
content: Had a thunderstorm last night and now my CAN2USB adaptor doesn't seem able to detect or drive the CAN bus. Other devices on the same CAN bus continue to work fine.I can talk to the onboard micro and do an internal loopback test and that works fine, however if nothing is connected, the H and L lines both remain at 0v when idle or attempting to send data.I'm guessing that that something in the isolated driver section has died.The components are tiny so does anyone have any advice before I start trying to measure voltages and potentially cause more damage when the probe inevitably slips.Circuit diagramhttps://www.8devices.com/media/products/usb2can/downloads/usb2can_schematics.pdfLink to user manualhttps://www.8devices.com/media/products/usb2can/downloads/usb2can_user_guide.pdfPhotos

author: coromonadalix
author_rank: Super Contributor
timestamp: April 22, 2018, 03:43:29 pm
content: the mcp2551 may have been damaged if the D2 (2 diode nup2105) is toasted, and / or the r1 100ohms is toasted too ??

author: e100
author_rank: Frequent Contributor
timestamp: April 22, 2018, 05:26:53 pm
content: Hmm no voltage at all on the isolated side.Definitely 5v going into the dc-dc converter but nothing coming out on the other side.Nothing is getting hot.The MCP2551 H and L aren't shorted to ground. Resistance between H and L is 47 kI measure 20 ohms across the isolated supply rails with everything still in place.DC-DC converter datasheethttps://www.recom-power.com/pdf/Econoline/R1SE.pdf

author: coromonadalix
author_rank: Super Contributor
timestamp: April 23, 2018, 10:40:32 am
content: for the dc dc 5v you must be on the ground A not the other since at the output youre now isolated, you have to switch ground points

author: Rerouter
author_rank: Super Contributor
timestamp: April 23, 2018, 10:46:57 am
content: Your transceiver is fried,http://ww1.microchip.com/downloads/en/DeviceDoc/21667E.pdfI dont know why, but these transcievers are easy to damage, (had about 2% failure in automotive)Both can high and can low should measure ~ 2.5V with nothing connected to them, if it doesnt, either it has no power, or its fried.

author: pmichel
author_rank: Contributor
timestamp: April 23, 2018, 12:13:13 pm
content: Quote from: Rerouter on April 23, 2018, 10:46:57 amAgree. CAN transceivers were a common failure when I was working on agriculture vehicles. Should measure 2.5ish volts on each, and most circuits would read around 500k resistance to ground on outputs.

author: e100
author_rank: Frequent Contributor
timestamp: April 23, 2018, 02:42:38 pm
content: Quote from: coromonadalix on April 23, 2018, 10:40:32 amYep, measuring across the dc-dc converter outputs. There's no sign that it's even attempting to startup, just 0 volts flat line.I don't have a hot air gun so this is going to be tricky.

author: e100
author_rank: Frequent Contributor
timestamp: April 23, 2018, 02:44:35 pm
content: Quote from: Rerouter on April 23, 2018, 10:46:57 amWould a fried transceiver typically short circuit the power rail?

author: Niklas
author_rank: Frequent Contributor
timestamp: April 23, 2018, 05:39:22 pm
content: Around 47k between CANH and CANL is normal when the transceiver is not powered. CANH or CANL to GND is >100k.Start by checking that the isolated power supply is ok. Even in the case of low impedance at the output, it should still make some attempts to charge the 5V rail capacitance before disabling the output from overcurrent.

author: pmichel
author_rank: Contributor
timestamp: April 23, 2018, 06:42:00 pm
content: Quote from: e100 on April 23, 2018, 02:44:35 pmNot always, but more often than not it will short the 5V.

author: e100
author_rank: Frequent Contributor
timestamp: April 24, 2018, 01:34:20 am
content: I chopped the MCP2551 transceiver off the board but the DC-DC converter still doesn't start up.I think the next step will be to buy a hot air gun so I can pull the other components without lifting tracks.Any recommendations for what brands or features to look for when looking for a hot air gun?

author: Rerouter
author_rank: Super Contributor
timestamp: April 24, 2018, 08:28:39 am
content: The 858D things will get you by for most things, with all hot air stuff, be patient, and use flux,Main technique is to nudge the component before trying to remove, when its up to temp most components should be able to be pushed about with surface tension restoring them, that is when its safe to lift.Main features are a power switch if its an "auto off" one, so far never had any trouble, but dont trust it 100%,A few nozzle size choices, Its more about keeping the heat only where you need it,And variable airflow, for tiny stuff too much air blows stuff off the board.