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Old 12th January 2011, 07:38 PM   #11
chipper is offline chipper  United States
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Do you know where can i get the smd resistors? I'm going to get IRF3205s and i remember in a post you said to use 47 ohm.
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Old 12th January 2011, 07:38 PM   #12
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You'll have to find all of the defective power transistors (on the heatsink). Post which ones failed (exact circuit board designations) and I'll tell you what else you need to check.
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Old 12th January 2011, 07:42 PM   #13
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Quote:
Originally Posted by Perry Babin View Post
You'll have to find all of the defective power transistors (on the heatsink). Post which ones failed (exact circuit board designations) and I'll tell you what else you need to check.
3x IRF540
3x IRF9540 (the other side not shorted)

4x MTP75N05HD (one is blown up the other 3 read 0 ohms on all legs)
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Old 12th January 2011, 07:47 PM   #14
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I'd bet that not all of those failed. Go back and check them individually.
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Old 12th January 2011, 08:05 PM   #15
chipper is offline chipper  United States
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Quote:
Originally Posted by Perry Babin View Post
I'd bet that not all of those failed. Go back and check them individually.
Which? Power supply transistors? If yes, they really did and were reading 0 ohms, from gate, drain, source and kept blowing the 10 amp fuse. What else can i do??? So if i replace the gate resistors and ps fets with irf3205s will it start again?
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Old 12th January 2011, 08:27 PM   #16
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Check all of them. Check from gate to drain. Cut the ones that read 0 ohms free from the board (all 3 legs) and re-check to see if any others read 0 ohms. When re-checking, also check for shorts from drain to source.
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Old 12th January 2011, 08:52 PM   #17
chipper is offline chipper  United States
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Quote:
Originally Posted by Perry Babin View Post
Check all of them. Check from gate to drain. Cut the ones that read 0 ohms free from the board (all 3 legs) and re-check to see if any others read 0 ohms. When re-checking, also check for shorts from drain to source.
Q7 reads from drain to gate .7 ohms and from drain to source i get 241 ohms
Q11 reads drain to gate .2 ohms & drain to source it reads 526 ohms
Q6 completely shredded itself
Q10 reads from drain to gate .7 ohms & drain to source it reads .3 ohms.

And yes i pulled the fets out of the board. Does this mean its going to survive?
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Old 12th January 2011, 08:57 PM   #18
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Those have all failed.

If you're going to use the 3205s, and need the 47 ohm resistors, you can get them at mouser or digikey. They're 0805 (size).

Do you have any power supply FETs that you can install to allow you to continue troubleshooting?
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Old 12th January 2011, 09:01 PM   #19
chipper is offline chipper  United States
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Quote:
Originally Posted by Perry Babin View Post
Those have all failed.

If you're going to use the 3205s, and need the 47 ohm resistors, you can get them at mouser or digikey. They're 0805 (size).

Do you have any power supply FETs that you can install to allow you to continue troubleshooting?
I have a couple savaged MTP75N's in my tool box in a plastic bag. Could i use two fets to see if it will start on?
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Old 12th January 2011, 09:27 PM   #20
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Yes but you need to remove all defective outputs (check gate to drain).

Check the gate resistors after removing the FETs to confirm that they're within tolerance.

Install them and measure the gate voltage. Make sure that both sides have ~5v DC on the gates. If the voltage is not the same from one side to the other, there may be a problem with the drive circuit.

When measuring the voltage on the gates, do so with ONLY remote and ground connected. Do NOT connect the B+.
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