Date: Fri, 17 Mar 2000 10:54:29 -0500
Reply-To: "Karl F. Bloss" <bloss@ENTER.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: "Karl F. Bloss" <bloss@ENTER.NET>
Subject: ECU repair
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Since we're on the subject, here's a message I've kept regarding ECU repair.
All credits to Harry Yates, of course.
-Karl
------- Forwarded Message Follows -------
Date sent: Fri, 6 Feb 1998 22:02:01 -0700
From: "Harry Yates" <hyates@bert.cr.bcit.bc.ca>
To: vanagon@zuni.likeminds.com
Subject: '90 ECU - report (long)
Send reply to: hyates@bert.cr.bcit.bc.ca
Copies to: Helmut_Zeidler@notesmail.nokia.com
Priority: normal
Hi Folks. Well, after much reading, thinking, procrastinating, and
analyzing, I decided to take the plunge today and have a look at the ECU
in our '90 Syncro. Our van has 145000 km (90000 miles) on it now with 99%
of that mileage driven at highway speeds... it's not used in town, and is
generally unused unless being camped in :) The shortest trip it does is
2.5 hours of continuous driving at 100 km/hr. In other words, that ECU
has a lot of continuous hours on it.
Last fall, I had a disturbing one hour where the van started
violently bucking, was extremely thirsty on fuel, and would not run
in the 2000 to 3000 rpm range at all. RPM's would jump from 2000 to over
3000, but would not operate normally throughout the rev range. After
about an hour of this nonsense, it was normal. Like, HUH??
I enlisted the help of my friend who has a background in electronics, and
computers with many years experience. So, during lunch today, we checked
it out. Now, keep in mind that this is a very expensive part of your van.
All precautions against static discharge must be taken... and don't drop
it ;)
We removed the 4 screws at the heat sink, and the 3 screws at the
connector end of the ECU, and slid the circuit boards out of the
plastic box. We gently removed the plastic cover which was just
placed over some plastic posts to expose the circuit boards.
There are 2 circuit boards on this ECU. A smaller one supported by
posts, and connected by a ribbon cable. We didn't remove the
"daughter board" from the main board.
Well, my friend was quite amazed. Bosch made the ECU in three
pieces. There are two circuit boards, and one heatsink. The two
circuit boards were "waved" on a production line. This meaning that all
connections were consistent, solder was even, and cleanly done. This was
probably done by a machine. Both circuit boards were probably attached
together as the next step. The heatsink had some driver transistors
attached to it. These babies get hot. There are pressure tabs of metal
that push these transistors firmly in place against the heatsink to
maximize thermal efficiency. Also, each transistor was isolated in a kind
of "nylon plastic" so that vibration doesn't disturb them. Nicely done :)
Now, here's the weak part of this. The heatsink was riveted to the
ends of the circuit board, which is OK. But, the legs of the
transistors that are fixed to the heatsink, were more than likely
inserted by hand into the appropriate holes in the circuit board, and then
hand soldered into place. The outcome was a little inconsistency in those
solder joints. The solder is supposed to "wick" through the circuit board
hole as you solder from one side only. The solder was uneven, and was
oxidized... not good. There are 3 of these transistors with 3 legs
each... so, nine joints that look suspect here.
The big find actually weren't the transistor solder joints, though.
There are 3 ceramic resistors in a small group at the top/right side of
the main circuit board. One resistor was getting really hot, and started
to burn the circuit board. The solder joints for this resistor were also
suspect as it was also oxidized, and could be flakey. Now, Bosch knew
that these components would get hot... that's why they are ceramic. They
also put a heat-absorbant cloth under these resistors against the circuit
board to help with the heat. Well, that didn't work too well. Most of
the heat would come out of the wire ends of the resistor, and that weakens
the solder joint. The edge of the circuit board is now black on my ECU...
the board itself is green. As the ECU is mounted vertically, and heat
rises, it scorched nearly 1 cm above the resistor.
So, how to best fix this? It's not that bad. If you are familiar
with electronics, and how to handle these devices, and have the
correct soldering tools (fine tip, variable heat soldering iron, and
solder sucker), a steady hand, and some patience you can do this work.
Plan of attack:
1. Wash circuit board with a cleaner of some sort (I use
gasoline, but there are other chemicals that are made
specifically for this purpose) and a toothbrush. This will clean up any
oxidants, old flux, etc from the solder joints.
2. Use an old dry paintbrush to wipe the cleaner, and clean the
circuit boards. Brush the board until it is clean and dry. Let all the
cleaner totally evaporate before soldering unless you like things hot ;)
3. Heat and suck up all solder from the transistor legs and
resolder. Do one at a time or you'll hose yourself if they all move out
of alignment.
4. The HOT resistor. I'm replacing mine. If it takes that much
heat, it's even cheaper insurance to replace the part after all these
years. The resistor doesn't have coloured bands on it, but the value of
the resistor is printed on it. Now, we aren't going to lay the resistor
onto the circuit board. We are going to leave a bit of an airspace under
the resistor to save the circuit board, and let the air in the computer
housing absorb all the heat.
On the daughter board, there is a nice metal shielded case. This
metal case is probably for radio interference (RFI). I haven't taken it
off yet to have a look. The EPROM is probably located in there. Someone
on the list asked me to dump the code of the EPROM. My friend has an
EPROM programmer as well. So, does anybody know if the EPROM is socketed?
If it's soldered on the circuit board, we'll not bother. If it is
socketed, we could have a look at it, and dump the code. Depending on the
type of EPROM, these could fade in time. Some types last about 10 years
or so only.
Anyway, I haven't done the repair to my ECU yet. I will do that next
weekend when my friend and I both have some time. Given what we saw
today, it is worthwhile to check these ECU's out. My friend was quite
adamant that if this ECU wasn't a problem already, it would be very soon.
Hope this helps
Harry.
---------------------------------------------------------
Harry Yates, Langley, BC, Canada
'90 Syncro Westfalia www: http://syncro.bcit.bc.ca/hyates
'87 Golf Diesel email: hyates@bert.cr.bcit.bc.ca
'91 Miata (Millie)
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