Cruise Control Amp techie question
 

I'm in the process of reworking the Cruise Control amp in my '85 300SD. There are 4 main power transistors with copper heatsinks on them. Does anyone know what the transistor part numbers are supposed to be?

I've cross-referenced everthing else but the part numbers are so obscured I can't tell what they are, primarily thanks to the corrosion inhibitive coating that removed the numbers.

Thanks for any and all help in answering this question for me.

Tim

Looks like Motorola symbol.
#1 (from the front,pin side) BD 437 243
#2 BD 438 240
#3 BD 438 240
#4 BD 437 243

Cruise amp # 002 545 16 32.

Hope this helps. I have been on the "hunt" for the component most likely to be the source of our collective aggravation on these PCB's and have been successful (by luck) on one and am still testing (with no luck) on another. Keep us posted on your efforts. Good luck.

Where's the part #?
 

JBA, is the part # for the amp itself (the #002 etc) on the aluminum case or on the printed circuit board? The 10mm nut that held the bracket on was an 11mm bolt. 10 wouldn't fit, and... it is on sooo tight that it rounded off even with a tight fitting box-end wrench on it. Man! So, if I have to get it off of the case, I might have a problem. I just bent the tabs back on the case and removed the PCB out if it.

Thanks for the help. I really appreciate it.

Looks like I'll get to tackle vacuum pump rebuild, seeings how it failed this am on the way in to work.... in the snow!:eek:

A little addition here:

JBAJ007, It looks like my components match. I can see a 437 vaguely on one of them. I crossed them over to ECG and NTE part numbers. Here they are:

BD438 = NTE 185 = ECG 185 = TO-126 case, T-PNP, SI, AF, PO
BD437 = NTE 184 = ECG 184 = TO-126 case, T-NPN, SI, AF, PO
Looks like everything is a match. I'm going to start checking compenents today and see if I can russle these up locally. I figure that beings these are toasted, that probably my actuator may very well be toasted too. Thoughts???

transistors and other silicon devices are prone to destruction from voltage spikes that can be produced by inductive loads like the solenoid coil in the cruise actuator.im going to troubleshoot my amp soon and thats where ill start looking

There are many incarnations of the cruise amp. over the years as MB has improved/modified it. The part # (on the alum. case) that I gave was for the one I had in my hand at the time, just so you would know which one I was referencing. I've taken out many of these by contorting and loosening the 10mm. bolt. It is NOT 11mm. in any I have ever seen (which is many). You were probably on the welded nut; the bolt hex head is on the other side (in a recess that you won't believe, push some rubber stuff slightly to the side and feel into the recess with your pinkie). You will be undoing it blind, but it IS 10mm. (deep socket helps). If you can put a box end wrench on it (or even see it) you weren't on the bolt, but on a nut welded to the bracket. That's why it wouldn't turn.

Dohh!
 

JBA, I had a Bart Simpson moment while I read your post. The information I downloaded on removal said to use a 1/4 drive 10mm socket on a short extension but when I saw that nut in plain view, and it was an 11mm well...Dohh! Makes sense now.

If you can, verify for me the order in which these IC's are installed. Holding the Amp with the 14 pin connector facing your chest and the component side up, they are located along the left side of the board. The first one closest to you is, we'll call it #1, a BD438. Behind #1 and rotated 180 degs , is #2 a BD437. Then there is an almost 2" space to get to the next pair. Number 3 is a BD437 and lastly, backing up to and rotated 180 degs is #4 a BD438. Is that right?

The manuals don't happen to have a schematic for this critter, do they? I know that the BD437 and BD438 can be purchased in matched pairs. Sometimes do to tolerence levels they have to be done that way. I wonder if these should be replaced in matching sets. I'll probably do it that way.

Micheal, thanks for the input. I haven't started testing the actuator but I suspect something is up with it. Can possibly a very stiff throttle cause the actuator to pull enough current to fry these things? My throttle linkage hadn't been lubed in years. It was very hard when I bought the car. I have since taken care of most of that. I'll post what I find out about it though.


Tim

Using your positioning: pin side to chest, P. transistors to left:
#1. BD437
#2.BD438
#3.BD438
#4. BD437

Set up as two sets of two, similar to what you describe, but in a straight line with no rotations (variations occurred within the several new and improved part #'s)

Tim,

"Can possibly a very stiff throttle cause the actuator to pull enough current to fry these things?"

YES!!!

You can actually measure current draw to the actuator. Normal current draw will be between 120-180mA @ 13.8VDC.

Test the actuator spinning in both directions when measuring.
Operation should be smooth, not loud, not rattle, nor have current spikes while running.