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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On 15/03/16 10:02, Cursitor Doom wrote:
Hi guys,

I have an EMU from a Land Rover which just suddenly failed one day
without warning as I was driving down the road. I was wondering if
there's any possibility of fixing it, given that schematics are AFAIK
unavailable due to commercial confidentiality. Of course there are some
basic checks that can be done without a diagram, but take a look at this
thing and tell me what I could try doing with it. I've carefully
inspected it close up but can find *nothing* at all visibly wrong with it:

http://tinyurl.com/hvk5eac

BTW, the whole board has been thickly sprayed with clear varnish which
accounts for all the bright dots which appear on some of the parts -
they're not indicative of any failure.

Any suggestions?


"My car is broken. Can you tell me how I can fix it?"

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On 15/03/16 10:39, Cursitor Doom wrote:
On Tue, 15 Mar 2016 00:24:02 +0100, Sjouke Burry wrote:

A:try to get a replacement from a car wreckers shop.
B:Or get a magnifier glass and start searching for damage/discoloration.
And check big caps and big transistors.
If no success, try solution A.
Or let repair shop handle it.


It's up and running again with an exchange unit, but it ran smoother,
quieter and started up quicker with the old unit that failed, so I'd like
to get the old one working again if at all possible.


It can take some time for an ECU to "learn" your engine.
You'll probably find it runs just as well as the old one after
a tank or two of gas.
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Hi guys,

I have an EMU from a Land Rover which just suddenly failed one day
without warning as I was driving down the road. I was wondering if
there's any possibility of fixing it, given that schematics are AFAIK
unavailable due to commercial confidentiality. Of course there are some
basic checks that can be done without a diagram, but take a look at this
thing and tell me what I could try doing with it. I've carefully
inspected it close up but can find *nothing* at all visibly wrong with it:

http://tinyurl.com/hvk5eac

BTW, the whole board has been thickly sprayed with clear varnish which
accounts for all the bright dots which appear on some of the parts -
they're not indicative of any failure.

Any suggestions?
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On 15.03.16 0:02, Cursitor Doom wrote:
Hi guys,

I have an EMU from a Land Rover which just suddenly failed one day
without warning as I was driving down the road. I was wondering if
there's any possibility of fixing it, given that schematics are AFAIK
unavailable due to commercial confidentiality. Of course there are some
basic checks that can be done without a diagram, but take a look at this
thing and tell me what I could try doing with it. I've carefully
inspected it close up but can find *nothing* at all visibly wrong with it:

http://tinyurl.com/hvk5eac

BTW, the whole board has been thickly sprayed with clear varnish which
accounts for all the bright dots which appear on some of the parts -
they're not indicative of any failure.

Any suggestions?

A:try to get a replacement from a car wreckers shop.
B:Or get a magnifier glass and start searching for
damage/discoloration.
And check big caps and big transistors.
If no success, try solution A.
Or let repair shop handle it.
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On Tue, 15 Mar 2016 00:24:02 +0100, Sjouke Burry wrote:

A:try to get a replacement from a car wreckers shop.
B:Or get a magnifier glass and start searching for damage/discoloration.
And check big caps and big transistors.
If no success, try solution A.
Or let repair shop handle it.


It's up and running again with an exchange unit, but it ran smoother,
quieter and started up quicker with the old unit that failed, so I'd like
to get the old one working again if at all possible.



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In article . com,
says...

On 15/03/16 10:02, Cursitor Doom wrote:
Hi guys,

I have an EMU from a Land Rover which just suddenly failed one day
without warning as I was driving down the road. I was wondering if
there's any possibility of fixing it, given that schematics are AFAIK
unavailable due to commercial confidentiality. Of course there are some
basic checks that can be done without a diagram, but take a look at this
thing and tell me what I could try doing with it. I've carefully
inspected it close up but can find *nothing* at all visibly wrong with it:

http://tinyurl.com/hvk5eac

BTW, the whole board has been thickly sprayed with clear varnish which
accounts for all the bright dots which appear on some of the parts -
they're not indicative of any failure.

Any suggestions?


"My car is broken. Can you tell me how I can fix it?"


I have fixed a couple of ECM's and in both cases the Xstal failed
due to mechanical vibration. Power it up using basic shop electrical
prints to the unit and find that the Xstal not operating.

Another one I did was intermitting in some function and popping up
codes randomly. I replaced a couple of caps, fixed..

The coating is tricky to get off without damage.

Jamie

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On Mon, 14 Mar 2016 19:58:50 -0500, M Philbrook wrote:

That will fix itself.

The same is true if you disconnected the battery for a while with the
other one.


I wish. It's been replaced for over 9 months now and it's still the same
as the day it was fitted.
But this is really about trying to rescue the old one. They don't come
cheap!
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On Tuesday, March 15, 2016 at 7:08:34 AM UTC-4, Cursitor Doom wrote:

I wish. It's been replaced for over 9 months now and it's still the same
as the day it was fitted.
But this is really about trying to rescue the old one. They don't come
cheap!


Try this:

Re-install the new unit. Power up the electrical system, but DO NOT start the engine.

Here is the tricky part and be exceedingly careful: While powered up, disconnect the battery, NEGATIVE FIRST. Make sure when that clamp comes off the battery it does so cleanly and quickly. SHORT the positive clamp to the negative clamp immediately and hold for a minimum of 30 seconds. This is the functional equivalent of rebooting the ECU. Shut off the electrical system. Reinstall the battery. Attempt to start. Does this help?

Note: If you have any coded devices such as so-called 'infotainment' systems and such, you will have to re-code them. If you have a chip-based navigation system, remove the chip for this process. But, 3 times in 10, it works. Not bad odds if the alternative is landfill.

If you have a Bosch unit, this is far more likely to work than if you have a British-made unit.... getting back to that old joke: why do the British drink warm beer?

Peter Wieck
Melrose Park, PA
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On Tue, 15 Mar 2016 09:58:03 -0500, legg wrote:

On Tue, 15 Mar 2016 11:05:24 -0000 (UTC), Cursitor Doom
wrote:

But this is really about trying to rescue the old one. They don't come
cheap!


The issue is with the new part, not the old one.


Wrong! The question *solely* concerns the *old* unit that failed.
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On Tue, 15 Mar 2016 11:05:24 -0000 (UTC), Cursitor Doom
wrote:

On Mon, 14 Mar 2016 19:58:50 -0500, M Philbrook wrote:

That will fix itself.

The same is true if you disconnected the battery for a while with the
other one.


I wish. It's been replaced for over 9 months now and it's still the same
as the day it was fitted.
But this is really about trying to rescue the old one. They don't come
cheap!


The issue is with the new part, not the old one.

Have you mentioned this to the technicians who made the change?

RL
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On Tuesday, March 15, 2016 at 10:06:53 AM UTC-4, Cursitor Doom wrote:
On Tue, 15 Mar 2016 06:21:27 -0700, wrote:

On Tuesday, March 15, 2016 at 7:08:34 AM UTC-4, Cursitor Doom wrote:

I wish. It's been replaced for over 9 months now and it's still the
same as the day it was fitted.
But this is really about trying to rescue the old one. They don't come
cheap!


Try this:

Re-install the new unit. Power up the electrical system, but DO NOT
start the engine.

Here is the tricky part and be exceedingly careful: While powered up,
disconnect the battery, NEGATIVE FIRST. Make sure when that clamp comes
off the battery it does so cleanly and quickly. SHORT the positive clamp
to the negative clamp immediately and hold for a minimum of 30 seconds.
This is the functional equivalent of rebooting the ECU. Shut off the
electrical system. Reinstall the battery. Attempt to start. Does this
help?



We're getting completely off topic in being distracted by the new EMU,
but I'll just answer this point. Every time I leave that vehicle for a
few days, I'll isolate the battery, anyway. So it has been repeatedly
"rebooted" dozens of times since the old one was replaced.

BUT my question is NOT about the new one; it's about how easily the old
ONE can be fixed without schematics (M. Philbrook, many thanks I'll try
your suggestion re xtal).


Whooops! Meant "OLD" unit. Isolating the battery does not constitute a reboot. Shorting the battery leads while the unit capacitors are charged DOES do a reboot. Mere isolation does not. Hence the need to disconnect the battery and short the leads (on the car, not the battery) while the system is energized but the engine not running.

Peter Wieck
Melrose Park, PA
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On 15 Mar 2016, Cursitor Doom wrote
(in article ):

Wrong! The question *solely* concerns the *old* unit that failed.


Welcome to USENET. There is no €śon-topic€ť!

Under conformal coating it is difficult to examine anything.

Check any large transistors.

Id also look for broken solder joints on the large devices (caps,
transformer, choke, I/O connectors). Also look closely at the cap €śnorth€ť
of the big choke. Has it leaked and damaged a trace?

Also check ESR of all the electro caps.

And as was mentioned earlier, be sure the xtal is working.
A success story:

https://www.youtube.com/watch?v=uLIHxqqrY_M

Good luck!

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If all else looks good, a winding in that transformer might be open. Remove
and €śring€ť it.




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On Tue, 15 Mar 2016 14:04:46 -0000 (UTC), Cursitor Doom
wrote:

On Tue, 15 Mar 2016 09:58:03 -0500, legg wrote:

On Tue, 15 Mar 2016 11:05:24 -0000 (UTC), Cursitor Doom
wrote:

But this is really about trying to rescue the old one. They don't come
cheap!


The issue is with the new part, not the old one.


Wrong! The question *solely* concerns the *old* unit that failed.


The issue is your dissatisfaction with the repaired automobile.

You're not in a position to resurrect the old ECU.

RL
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On Tue, 15 Mar 2016 14:25:41 -0500, legg wrote:

On Tue, 15 Mar 2016 14:04:46 -0000 (UTC), Cursitor Doom
wrote:

On Tue, 15 Mar 2016 09:58:03 -0500, legg wrote:

On Tue, 15 Mar 2016 11:05:24 -0000 (UTC), Cursitor Doom
wrote:

But this is really about trying to rescue the old one. They don't come
cheap!

The issue is with the new part, not the old one.


Wrong! The question *solely* concerns the *old* unit that failed.


The issue is your dissatisfaction with the repaired automobile.

You're not in a position to resurrect the old ECU.


The new ECU in all probability just requires a software tweak. My
question was about the OLD one (at the risk of repeating myself).

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Cursitor Doom wrote:

Hi guys,

I have an EMU from a Land Rover which just suddenly failed one day
without warning as I was driving down the road. I was wondering if
there's any possibility of fixing it, given that schematics are AFAIK
unavailable due to commercial confidentiality. Of course there are some
basic checks that can be done without a diagram, but take a look at this
thing and tell me what I could try doing with it. I've carefully
inspected it close up but can find *nothing* at all visibly wrong with it:

http://tinyurl.com/hvk5eac

BTW, the whole board has been thickly sprayed with clear varnish which
accounts for all the bright dots which appear on some of the parts -
they're not indicative of any failure.

Any suggestions?

Well, are there any symptoms that can be figured out? Do dash indicators do
something like what they used to do? If it appeas totally dead, there's a
possibility that a voltage regulator or other power switching circuit has
failed. Looks like it has a switching power supply, that will make things a
little harder. Yeah, the conformal coating is really necessary in
automotive gear, but makes rework tough.

Also, check all connectors and other large parts soldered to the board,
breaks in the solder joints are supposed to be a very common cause of
failure.

Jon
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http://tinyurl.com/hvk5eac

Any chance of posting a super-high resolution image?

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On Tue, 15 Mar 2016 17:21:08 -0700, DaveC wrote:

http://tinyurl.com/hvk5eac


Any chance of posting a super-high resolution image?


If I can figure out how to get the back off and photograph both sides,
I'll do it. The blurring issue I am having is with the autofocus which is
being hijacked by the two big electrolytics. I'll have to read the
camera's FM and find out how to switch it to manual. These damn things
are so complicated nowadays.


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On Tue, 15 Mar 2016 20:01:54 -0000 (UTC), Cursitor Doom
wrote:

On Tue, 15 Mar 2016 14:25:41 -0500, legg wrote:

On Tue, 15 Mar 2016 14:04:46 -0000 (UTC), Cursitor Doom
wrote:

On Tue, 15 Mar 2016 09:58:03 -0500, legg wrote:

On Tue, 15 Mar 2016 11:05:24 -0000 (UTC), Cursitor Doom
wrote:

But this is really about trying to rescue the old one. They don't come
cheap!

The issue is with the new part, not the old one.

Wrong! The question *solely* concerns the *old* unit that failed.


The issue is your dissatisfaction with the repaired automobile.

You're not in a position to resurrect the old ECU.


The new ECU in all probability just requires a software tweak. My
question was about the OLD one (at the risk of repeating myself).


There's not much you can tell from a photograph of limited resolution.
Looking at what you've offered, you might re-examine locally:

http://www.magma.ca/~legg/TVS/EMU_captive_detritus.jpg
http://www.magma.ca/~legg/TVS/EMU_green_reflection.jpg
http://www.magma.ca/~legg/TVS/EMU_red_reflection.jpg
http://www.magma.ca/~legg/TVS/EMU_so...ontaminant.jpg
http://www.magma.ca/~legg/TVS/EMU_so...taminant_2.jpg

I expect these are mostly reflections in the protective epoxy, or
flow/tension marks formed in its application, but could be signs of
contamination or damage.

Even checking point to point contact is a trial with this stuff.

Vibration produces intermittent faults on assemblies (where the parts
don't actually shear off completely) The most suspect parts are those
with mechanical attributes - the crystal as previously suggested, the
connectors and bulky components. Reflowing the SJ of the latter might
be informative - any uncharacteristic loosness in the soldered
material of the melted joint is a giveaway.

As previous - an intermittent fault is unlikely to result in repeated
DOA symptoms, but it can be recorded for posterity in the firmware,
with DOA symptoms, or break small-signal paths with the same effect.

Did you try a reset on the 'dead' unit, before replacing it?

The fact that its replacement didn't involve the surrender of the
defect unit (for a discount in pricing) is a signal from the mfr
regarding their view on the viability of repair. They are in the most
sensible position to do so, after-warranty.

RL
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On Tue, 15 Mar 2016 19:59:53 -0500, legg wrote:

On Tue, 15 Mar 2016 20:01:54 -0000 (UTC), Cursitor Doom
wrote:

On Tue, 15 Mar 2016 14:25:41 -0500, legg wrote:

On Tue, 15 Mar 2016 14:04:46 -0000 (UTC), Cursitor Doom
wrote:

On Tue, 15 Mar 2016 09:58:03 -0500, legg wrote:

On Tue, 15 Mar 2016 11:05:24 -0000 (UTC), Cursitor Doom
wrote:

But this is really about trying to rescue the old one. They don't
come cheap!

The issue is with the new part, not the old one.

Wrong! The question *solely* concerns the *old* unit that failed.

The issue is your dissatisfaction with the repaired automobile.

You're not in a position to resurrect the old ECU.


The new ECU in all probability just requires a software tweak. My
question was about the OLD one (at the risk of repeating myself).


There's not much you can tell from a photograph of limited resolution.
Looking at what you've offered, you might re-examine locally:

http://www.magma.ca/~legg/TVS/EMU_captive_detritus.jpg
http://www.magma.ca/~legg/TVS/EMU_green_reflection.jpg
http://www.magma.ca/~legg/TVS/EMU_red_reflection.jpg
http://www.magma.ca/~legg/TVS/EMU_so...ontaminant.jpg
http://www.magma.ca/~legg/TVS/EMU_so...taminant_2.jpg

I expect these are mostly reflections in the protective epoxy, or
flow/tension marks formed in its application, but could be signs of
contamination or damage.

Even checking point to point contact is a trial with this stuff.

Vibration produces intermittent faults on assemblies (where the parts
don't actually shear off completely) The most suspect parts are those
with mechanical attributes - the crystal as previously suggested, the
connectors and bulky components. Reflowing the SJ of the latter might be
informative - any uncharacteristic loosness in the soldered material of
the melted joint is a giveaway.

As previous - an intermittent fault is unlikely to result in repeated
DOA symptoms, but it can be recorded for posterity in the firmware, with
DOA symptoms, or break small-signal paths with the same effect.

Did you try a reset on the 'dead' unit, before replacing it?

The fact that its replacement didn't involve the surrender of the defect
unit (for a discount in pricing) is a signal from the mfr regarding
their view on the viability of repair. They are in the most sensible
position to do so, after-warranty.

RL


Many thanks for that lot above (and the other tips & suggestions others
have come up with). I don't think I will have sufficient time at this
stage to see this through to the end if it turns out to be tricky; I
can't face the prospect of this becoming another saga like the Philips
scope turned out to be.
I'll try to get the back off tomorrow...
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I would say the 2 electrolytic caps.

Cursitor Doom a Ă©crit :
Hi guys,

I have an EMU from a Land Rover which just suddenly failed one day
without warning as I was driving down the road. I was wondering if
there's any possibility of fixing it, given that schematics are AFAIK
unavailable due to commercial confidentiality. Of course there are some
basic checks that can be done without a diagram, but take a look at this
thing and tell me what I could try doing with it. I've carefully
inspected it close up but can find *nothing* at all visibly wrong with it:

http://tinyurl.com/hvk5eac

BTW, the whole board has been thickly sprayed with clear varnish which
accounts for all the bright dots which appear on some of the parts -
they're not indicative of any failure.

Any suggestions?


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On Tuesday, March 15, 2016 at 8:59:44 PM UTC-4, Cursitor Doom wrote:
On Tue, 15 Mar 2016 17:21:08 -0700, DaveC wrote:

http://tinyurl.com/hvk5eac


Any chance of posting a super-high resolution image?






If I can figure out how to get the back off and photograph both sides,
I'll do it.



There may be nothing on the back side. I repair (take a shot at) a lot of car electronics from a nearby car dealership (mostly clusters) and have seen some PCMs that are pretty much bonded to the bottom of the pan for heat sinking purposes. Nothing to see on the other side except foil damage if there was a water leak.

Never been in a Rover PCM.


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On Wed, 16 Mar 2016 11:30:49 +0100, Look165 wrote:

I would say the 2 electrolytic caps.



I've heard that's a common failure point with these units, but all the
electros have checked out fine on this particular one.


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Check them instead of usisng random statistics.

Cursitor Doom a Ă©crit :
On Wed, 16 Mar 2016 11:30:49 +0100, Look165 wrote:

I would say the 2 electrolytic caps.



I've heard that's a common failure point with these units, but all the
electros have checked out fine on this particular one.


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On 16 Mar 2016, Cursitor Doom wrote
(in article ):

I would say the 2 electrolytic caps.


I've heard that's a common failure point with these units, but all the
electros have checked out fine on this particular one.


€śchecked out fine...€ť means you tested what? Capacitance? ESR?
In-circuit? Removed?

Details!

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On Wed, 16 Mar 2016 09:42:30 -0700, DaveC wrote:

€śchecked out fine...€ť means you tested what? Capacitance? ESR?
In-circuit? Removed?

Details!


The ESRs were slightly high (in circuit) but not enough to cause sudden
total failure. But they appear to be easily removeable so I'll take them
out and check them independently.
I should repeat I don't have the time right now to go down every avenue
if this turns out to be more than a simple fix; I'm really just trying to
establish whether the thing is salvageable at all. However, I am noting
down all the suggestions made here for future reference for when I do
have time.
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€śchecked out fine...€ť means you tested what? Capacitance? ESR?
In-circuit? Removed?


Visually?

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On Wed, 16 Mar 2016 11:45:04 -0700, DaveC wrote:

€śchecked out fine...€ť means you tested what? Capacitance? ESR?
In-circuit? Removed?


Visually?


No signs of bulging or seepage.

I was just taking a closer look at the board a moment ago under a glass
and spotted something that requires further investigation. Going to have
to get my stereoscope out of storage for this one. Tiny clusters of what
look like *very* fine gauge enamel copper wire clearly bridging across
vias in various points around the board and obviously not *supposed* to
be there. If they turn out to be conductive, I could be in business!
Don't want to get my hopes up on this one, though. Probably just a false
alarm but *definitely* requiring closer examination with something more
powerful than a glass....

Turns out to get the caps out of circuit requires a 6mm ring spanner
which I shall have to procure from a local emporium tomorrow when they re-
open. Fortunately I already have a 13mm one for the other ends.


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Turns out to get the caps out of circuit requires a 6mm ring spanner
which I shall have to procure from a local emporium tomorrow when they re-
open. Fortunately I already have a 13mm one for the other ends.


Try 1/4€ť. Thats 6.35mm. Might work...

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On Wed, 16 Mar 2016 13:00:19 -0700, DaveC wrote:

Turns out to get the caps out of circuit requires a 6mm ring spanner
which I shall have to procure from a local emporium tomorrow when they
re-
open. Fortunately I already have a 13mm one for the other ends.


Try 1/4€ť. Thats 6.35mm. Might work...


I simply don't have anything that small (apart from sockets which are no
good in this case) in either metric or imperial, I'm afraid. It won't
kill me to buy one the correct size tomorrow.
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On Tue, 15 Mar 2016 19:59:53 -0500, legg wrote:

On Tue, 15 Mar 2016 20:01:54 -0000 (UTC), Cursitor Doom
wrote:

On Tue, 15 Mar 2016 14:25:41 -0500, legg wrote:

On Tue, 15 Mar 2016 14:04:46 -0000 (UTC), Cursitor Doom
wrote:

On Tue, 15 Mar 2016 09:58:03 -0500, legg wrote:

On Tue, 15 Mar 2016 11:05:24 -0000 (UTC), Cursitor Doom
wrote:

But this is really about trying to rescue the old one. They don't
come cheap!

The issue is with the new part, not the old one.

Wrong! The question *solely* concerns the *old* unit that failed.

The issue is your dissatisfaction with the repaired automobile.

You're not in a position to resurrect the old ECU.


The new ECU in all probability just requires a software tweak. My
question was about the OLD one (at the risk of repeating myself).


There's not much you can tell from a photograph of limited resolution.
Looking at what you've offered, you might re-examine locally:

http://www.magma.ca/~legg/TVS/EMU_captive_detritus.jpg
http://www.magma.ca/~legg/TVS/EMU_green_reflection.jpg
http://www.magma.ca/~legg/TVS/EMU_red_reflection.jpg
http://www.magma.ca/~legg/TVS/EMU_so...ontaminant.jpg
http://www.magma.ca/~legg/TVS/EMU_so...taminant_2.jpg


I don't know how the hell you were able to spot those markings from the
poor detail in the photo. The last two details you posted show the
extremely fine enamel copper wire-looking debris which crops up in other
places on the board and across vias and traces. If this debris conducts,
it could easily be the cause of the problem. I have to hoist my
stereoscope out of storage and take a better look tomorrow. Well spotted
indeed. Remarkable!

As for the other bits you found, I'll investigate them at the same time
when my stereoscope is set up.
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Cursitor Doom wrote:

On Wed, 16 Mar 2016 11:45:04 -0700, DaveC wrote:

€śchecked out fine...€ť means you tested what? Capacitance? ESR?
In-circuit? Removed?


Visually?


No signs of bulging or seepage.

I was just taking a closer look at the board a moment ago under a glass
and spotted something that requires further investigation. Going to have
to get my stereoscope out of storage for this one. Tiny clusters of what
look like *very* fine gauge enamel copper wire clearly bridging across
vias in various points around the board and obviously not *supposed* to
be there.

Woo Hoo! Sounds like tin whiskers! The conformal coat is "SUPPOSED" to
suppress the whisker growth, but there are quite a few reports that the
whiskers just poke through the coating, they ARE real sharp.

Jon
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On Wed, 16 Mar 2016 23:21:41 -0000 (UTC), Cursitor Doom
wrote:

On Tue, 15 Mar 2016 19:59:53 -0500, legg wrote:

On Tue, 15 Mar 2016 20:01:54 -0000 (UTC), Cursitor Doom
wrote:

On Tue, 15 Mar 2016 14:25:41 -0500, legg wrote:

On Tue, 15 Mar 2016 14:04:46 -0000 (UTC), Cursitor Doom
wrote:

On Tue, 15 Mar 2016 09:58:03 -0500, legg wrote:

On Tue, 15 Mar 2016 11:05:24 -0000 (UTC), Cursitor Doom
wrote:

But this is really about trying to rescue the old one. They don't
come cheap!

The issue is with the new part, not the old one.

Wrong! The question *solely* concerns the *old* unit that failed.

The issue is your dissatisfaction with the repaired automobile.

You're not in a position to resurrect the old ECU.

The new ECU in all probability just requires a software tweak. My
question was about the OLD one (at the risk of repeating myself).


There's not much you can tell from a photograph of limited resolution.
Looking at what you've offered, you might re-examine locally:

http://www.magma.ca/~legg/TVS/EMU_captive_detritus.jpg
http://www.magma.ca/~legg/TVS/EMU_green_reflection.jpg
http://www.magma.ca/~legg/TVS/EMU_red_reflection.jpg
http://www.magma.ca/~legg/TVS/EMU_so...ontaminant.jpg
http://www.magma.ca/~legg/TVS/EMU_so...taminant_2.jpg


I don't know how the hell you were able to spot those markings from the
poor detail in the photo. The last two details you posted show the
extremely fine enamel copper wire-looking debris which crops up in other
places on the board and across vias and traces. If this debris conducts,
it could easily be the cause of the problem. I have to hoist my
stereoscope out of storage and take a better look tomorrow. Well spotted
indeed. Remarkable!

As for the other bits you found, I'll investigate them at the same time
when my stereoscope is set up.


Looked to me more like dye concentrating as the curing epoxy puckered.

Did you ever reset this thing, while it was still in the vehicle?

RL


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On Wed, 16 Mar 2016 22:50:06 -0500, legg wrote:

Looked to me more like dye concentrating as the curing epoxy puckered.


So not likely to cause a fault then?

Did you ever reset this thing, while it was still in the vehicle?


No. I think if the fix were that simple the service specialists who
swapped the unit over wouldn't have gone to the trouble of sourcing a
replacement. They charged me next to nothing for the job so I trust them.
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On Wed, 16 Mar 2016 20:51:46 -0500, Jon Elson wrote:

Cursitor Doom wrote:

On Wed, 16 Mar 2016 11:45:04 -0700, DaveC wrote:

€śchecked out fine...€ť means you tested what? Capacitance? ESR?
In-circuit? Removed?

Visually?


No signs of bulging or seepage.

I was just taking a closer look at the board a moment ago under a glass
and spotted something that requires further investigation. Going to
have to get my stereoscope out of storage for this one. Tiny clusters
of what look like *very* fine gauge enamel copper wire clearly bridging
across vias in various points around the board and obviously not
*supposed* to be there.

Woo Hoo! Sounds like tin whiskers! The conformal coat is "SUPPOSED" to
suppress the whisker growth, but there are quite a few reports that the
whiskers just poke through the coating, they ARE real sharp.

Jon


Thank you, Jon. An interesting suggestion! But I was under the impression
that:

1. TW growth happened solely inside chips and so was normally invisible.

2. tin whiskers were invariably silver in colour.

These I have here are like the old kind of enamel copper wire. Nowadays
all enamel copper seems to be clear, but back in the day the enamel was a
sort of deep plum shade - which is what I see here. I'll do some searches
for pictures of TW and see if some match what I see on this board....
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I wonnder how you can determine an ESR visually !

And technically, it's not so easy to measure this parameter.


Cursitor Doom a Ă©crit :
On Wed, 16 Mar 2016 09:42:30 -0700, DaveC wrote:

€śchecked out fine...€ť means you tested what? Capacitance? ESR?
In-circuit? Removed?

Details!


The ESRs were slightly high (in circuit) but not enough to cause sudden
total failure. But they appear to be easily removeable so I'll take them
out and check them independently.
I should repeat I don't have the time right now to go down every avenue
if this turns out to be more than a simple fix; I'm really just trying to
establish whether the thing is salvageable at all. However, I am noting
down all the suggestions made here for future reference for when I do
have time.


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On Thu, 17 Mar 2016 10:08:49 -0000 (UTC), Cursitor Doom
wrote:

On Wed, 16 Mar 2016 22:50:06 -0500, legg wrote:

Looked to me more like dye concentrating as the curing epoxy puckered.


So not likely to cause a fault then?


Must have been pretty strong stuff, to strip colour out of the mask,
but no, not a conductive path.

Did you ever reset this thing, while it was still in the vehicle?


No. I think if the fix were that simple the service specialists who
swapped the unit over wouldn't have gone to the trouble of sourcing a
replacement. They charged me next to nothing for the job so I trust them.


?? Just charged you for the ECU, that they happened to have lying
around? Very obliging...

If you trusted them from past work, that's another thing entirely.

RL
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