Root cause insight into the common BMW blower motor resistor failures

Page 5 of 9  
On Mon, 25 Mar 2013 15:51:34 +0000 (UTC), Bimmer Owner

Bet I can do it in less than half an hour - without the MaxiTester and in about 5 or 10 minutes with it.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 25 Mar 2013 12:26:52 -0400, clare wrote:

I'd be very happy to see pictures of the test leads in situ because I personally tried (and succeeded) in getting the 40 amp blower motor fuse F76 out and back in, but I wouldn't want to do it more than once in my life.
From memory, here's what I did: . I moved the passenger front seat as far back as I could . I lowered the passenger front seat back as far back as it goes . I removed the ignition key and disconnected the battery negative lead . I removed the panel from the bottom of the glovebox . I removed the Phillips screw and panel off to the passenger left kneecap . I lay upside down on the flattened passenger seat, head in the footwell . I located the general module III (GMIII) . With my arms bent wildly arms over my head, I disconnected harness connectors . The first enigmatic connector was the white connector X332 . The next diabolical connector was the small black X253 . And the last puzzling connector was the large black X254 . By now, I could slightly see the yellow 40 & red 50 amp fuses F76 & F77 . With a flathead 1/8" screwdriver, I lifted the yellow fuse F76 up & out . That took about an hour or three. . Putting the fuse back was even harder than removing it
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Hi, I am frustratingly having similar issues with a FSU on a 2002 E39 and on the topic of why does the FSU not fry up any quicker when the blower motor is suspect, mine did just that. It lasted all of 2 months!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I'm an atty investigating this problem & car fires. Plz call my cell: 1-800-279-6996 or email me your cell: snipped-for-privacy@aol.com if you suspect your BMW fire was due to blower fan resistor (Final Stage Unit) failure. Thx. Jos. Santoli, Esq.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 7/10/2015 11:27 AM, snipped-for-privacy@aol.com wrote:

Pretty sleazy when lawyers resort to trolling here for new fish.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 21 Mar 2013 15:22:42 +0000 (UTC), Bimmer Owner

If one replaces one of these perhaps it would be advisable to put a fuse in the blower motor lines (it sounds like those can be gotten to easily unlike the motor itself). If it's being blown by intermittent high current draws the fuse could protect the $100 FSU. Another option would be, at least for those who can live without the highest blower setting and who think excess current draw is the culprit, would be to put a power resistor in the blower motor line to limit the current a bit. On the cheap pedestrian cars I drive the whole speed control is just a trio of power resistors placed in the air flow to help cool them. If they burn out (which is rare) they can sometimes be fixed with a pop rivet.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 21 Mar 2013 15:03:45 -0700, Ashton Crusher wrote:

That's an interesting idea. The FSU supposedly consumes the most power when the blower motor is set to the LOW settings (simply because it has to dissipate the power as heat), so, we could prevent excess current by fusing... say with a 10A fuse, the blower motor (which is said to consume 5 to 6 A).
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Are you sure it is not already a pulse width regulator? Those transistors look like they are TO-220 packages, not TO-3. PWM has been around longer than SMT parts.
Maybe it is transients from the motor that are causing the failures.
Another place you could measure the current is by putting an ammeter in place of the blower motor fuse.
tm
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
tm wrote:

I've seen 20W power resistors in TO-220 packages.

--

Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

It does indeed look like a TO-220 from the pin spacing (since there are no actual transistors in the photos, just spots from which they were removed).
But if it had been a PWM device, there would have been some filtering in there, inductors and capacitors to keep the noise from getting into the power lines. Designing clean and quiet PWM controllers is not quite as trivial as some folks have made it out to be.

This is possible, if it is the transistors that are failing. I don't see any big protection diodes in there either.
If it's a RoHS soldering issue, though, I would not be surprised. --scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Scott Dorsey wrote:

A few car manufacturers use resistor wire in the harness leading to the motor connection at the blower box.
This lowers the Q significantly giving you a voltage drop of course, but it also reduces electrical noise and helps suppress the wheeling voltages.
Blower motors in this case are normally designed to operate lets say 8 volts for example, for full RPM.
I learned this years ago when going through the pain of removing the blower in an air box of a Chrysler product, only to find there was nothing wrong with the motor. Symptoms led on to the fact there was since the output of the speed control circuit was alive and happy but no obvious connection to the motor. If I had unplugged it from the air box before pulling that all apart, I would of noticed it.
The problem was the resistor wire in the harness which had open at the crimp point, also in the harness.
Jamie
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Scott Dorsey wrote:

All those photos only show one side. I full reverse engineering should be done to draw a full schematic but I've never had my hands on that module. It would probably take a couple of them, because ot the potting.

Have you looked at the National Semiconductor (Now part of T.I) 'Simple Switcher' series of controllers? Generally only one inductor and a couple small electrolytics. A lot simpler than older designs, and little noise because of the small footprint.

--

Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 25 Mar 2013 09:42:51 -0400, Michael A. Terrell wrote:

These photos show both sides. http://www.bimmerfest.com/forums/showthread.php?t09399
Nothing was removed, so I can't figure out WHAT you guys are saying is the transistor removed.
Can you circle one of these pictures to show WHERE you think something was removed?
http://www.bimmerfest.com/forums/attachment.php?attachmentid67580&d 63957253 http://www.bimmerfest.com/forums/attachment.php?attachmentid63800&stc=1&d 61831815 http://www.bimmerfest.com/forums/attachment.php?attachmentid63808&stc=1&d 61837887
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Bimmer Owner wrote:

http://www.bimmerfest.com/forums/attachment.php?attachmentid67580&d 63957253

http://www.bimmerfest.com/forums/attachment.php?attachmentid63800&stc=1&d 61831815
Do you see the two groups of three empty holes on the right side? They look like cracked solder joints on TO-220 packages which could be semiconductors or power resistors.

http://www.bimmerfest.com/forums/attachment.php?attachmentid63808&stc=1&d 61837887
You can see the leads in those holes, in this photo. They look cracked. That is a common failure due to stress caused by uneven heating of potted components.
--

Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sun, 24 Mar 2013 09:24:13 -0400, Scott Dorsey wrote:

I doubt anything was removed since all the authors of those pictures are expressly NOT trying to remove anything.
Those round metal "dots" in the pictures are the five pin connectors of the harness connector.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Are there any other pictures of the module showing if or where the transistors are attached to the heat sink?
Has anyone ever fully dissected the unit so you can see what is under the PC board? Maybe an X-ray from several angles done at the dentist?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 25 Mar 2013 12:04:20 -0400, tm wrote:

All I have are the following: These photos show both sides. http://www.bimmerfest.com/forums/showthread.php?t09399
Nothing was removed, so I can't figure out WHAT you guys are saying is the transistor removed.
Can you circle one of these pictures to show WHERE you think something was removed?
http://www.bimmerfest.com/forums/attachment.php?attachmentid67580&d 63957253 http://www.bimmerfest.com/forums/attachment.php?attachmentid63800&stc=1&d 61831815 http://www.bimmerfest.com/forums/attachment.php?attachmentid63808&stc=1&d 61837887
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Okay, notice on the lefthand photo, there are two sets of three solder joints on the lefthand side of the board, which show signs of recent rework. There are TO-220 transistors attached to them, which are behind the board and you cannot see.
On the righthand photo the board is reversed... you can see two sets of three holes on the righthand side of the board which is where those TO-220 transistors were attached. You can see that they overheated the board and lifted pads in the process too.
But you cannot in either of these photos see the transistors or what the part number on the face of them is. Knowing what kind of transistors are used will go far toward explaining some possible failure modes. --scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Yes, what Scott said. Where are the two transistors that were soldered in the pair of three holes on the right of the right photo.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 25 Mar 2013 18:12:53 -0400, tm wrote:

I always thought those were just "posts" tying the circuit board to something inside the FSU - but I do agree that all the FSU autopsies show those posts being unsoldered to remove the board. Here's the quote that came with this picture, for example:

[QUOTE=sudnut]Ok, here are a couple of pics of my FSR from a 2002 E46 which is identical to FSR's in many other models and series of BMW. The first is what you see when you scrape off the epoxy-like filling covering the PCB. Using a hairdryer or better still a heatshrink gun carefully without overheating. If you smell burning its too hot. You should get a faint hot plastic odour that's all. I used one of those cheap sets of precision flat screwdrivers, they can be sharp so again be careful. You can see I gouged and scratched the circuit board a little in places, just make sure you don't slice through any tracks or lever off any components. The second picture is a zoom of the 2 groups of 3 pins which I believe are the cause of my FSR going crazy. If you look closely, all six pins have cracks in the solder around the pins, most noticeable are pins 1, 4 and 5 from left to right. My repair was simply to remelt and resolder these pins with a little more solder using a hot and fine tipped soldering iron, until I felt that the lead had flowed through the board and hopefully to the other side where the components/resistors are. If this repair doesn't last, I may remove the board fully and have a better look on the other side.[/QUOTE]
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.