Hi, I have a PS3, GP9 diesel that has recently started to open the rear coupler randomly in use. This afternoon the rear coupler continuously ‘buzzes’ and won’t close at all. I would appreciate any help with this please.
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I'm guessing it gets hot as well. First thing to check is the wiring.
I didn’t check too see if it was hot, I didn’t leave it on the track. If I checked the wiring, what would I be looking for?
You would remove the shell and inspect the wiring for physical defects. This could be broken insulation, loose connections and so on. This sets a baseline before going the "electronic route"
Thank you for clarifying where to look, I did wonder if meant to look at the copper winding on the coupler ( which looks ok). I will remove the shell later and have a look.
If this shorted to chassis, I am sure you also damaged the coupler FET and it is shorted proving continuous voltage/current. The board needs to be tested and repaired most likely. IF you put a new coupler in and wire is all good and it immediately buzzes with power applied, turn it off until board fixed.
Couplers also can occasionally short internally, so that may be the issue, but need to ensure board not damaged. G
GGG posted:If this shorted to chassis, I am sure you also damaged the coupler FET and it is shorted proving continuous voltage/current. The board needs to be tested and repaired most likely. IF you put a new coupler in and wire is all good and it immediately buzzes with power applied, turn it off until board fixed.
Couplers also can occasionally short internally, so that may be the issue, but need to ensure board not damaged. G
George,
Have you replaced a coupler FET on a PS3 board yet? They are pretty tiny.
Dave
I can't even find Q76 on the board or the drawing. 
gunrunnerjohn posted:I can't even find Q76 on the board or the drawing.
John,
They are Q221 and Q228 roughly middle if the board left to right. Right below the middle cap.
I would have to wear two pair of glasses to get those LOL.
Dave
Took the shell off earlier, everything looks fine inside. Looks like I will have to get to a (the only) UK service agent. Thank you all for taking the time to reply to this.
David Minarik posted:gunrunnerjohn posted:I can't even find Q76 on the board or the drawing.
They are Q221 and Q228 roughly middle if the board left to right. Right below the middle cap.
Stupid me, I was looking at the steam tender board. However, the list of replaceable parts says Q76, but the steam tender board doesn't have that part.
Those parts on the diesel board are the SOT-23 form factor. Small, but not impossible to replace. For stuff that small, I tend to use the small nozzle on my rework station and just release the part and flick it off. Then I can heat the new part holding it on the pads, usually that works.
Or you could cut the wires and rubber band the coupler shut.
Rubber bands on electrocouplers don't so much. 
Where would you put the rubber band?
Attachments
Yes I have. I have occasionally jumped the led resistor stack also with a thru hole resistor if you lose a headlight and the buffer chip is good.
Biggest problem is too much heat when fails that damages traces. G
What do you use to replace those George? Do you do it with an iron or a hot air tool? The last couple of PS/2 audio amps I did I used my hot air tool, it went a lot smoother and quicker.
You have fancier stuff then me. I just use an iron. The coupler chips are not hard to come off. As far as the lighting buffer, I soldered a normal resistor across the pads. Have to be careful because of close spacing. I think the new chip is larger, but would need a hot air set up to remove in my opinion. G
I was initially reluctant to use the hot air tool, but the more I use it, the better I like it. It does make some of this a lot easier.
