punch 200s problems

bdgf2004 · 24th November 2010, 01:56 AM

i have a punch 200s and when i got it it had some distortion in the left channel ( i can take pic later). i found one of the output fets (Q119/irf9540) out of tollerance. red probe to drain black to source my meter reads 792 ohms. any other time it's closer to 500 ohms. so i replaced it and checked the drivers but the distortiion is still there. any suggestions?

schem attetched

Perry Babin · 24th November 2010, 04:25 AM

It may be leaky. Compare the resistance between its gate and other two legs to the other IRF9540.

bdgf2004 · 24th November 2010, 03:08 PM

everything tested ok on the fet except what i previously stated

Perry Babin · 24th November 2010, 03:11 PM

You'll have to remove it from the circuit to check it.

bdgf2004 · 24th November 2010, 04:26 PM

the fet was out of the circuit before testing. ive already replaced it and still have the distortion

Perry Babin · 24th November 2010, 07:50 PM

I don't know how you tested the FET. Did the new one read open in one direction (leg 2-3)?

Did the failed FET read open from leg 1 to each of the other legs?

bdgf2004 · 24th November 2010, 08:52 PM

new fet:
black probe on leg #2 red on #3= open
red on #2 black on #3=590

old fet:
yes, with probes either way #1 is completely open from #2 and #3.

i was about to take pics but when i fired it up (60 hz wave) both channels looked very good (no load) for several minutes and then out of the blue the left (repaired channel) lost its bottom half. at this time the right channel remained perfect. i tapped and wiggled around on several components with no result. so i was getting ready to take a pic again so i left the room to get my phone and when i came back it looked okay again. i put a load on it and it distorted on the bottom half badly, so i tried the right channel and i was perfect. now i have done nothing and both of the channels have lost their bottom half ( no load). this is the first time i have had problems out of the right channel.

Perry Babin · 24th November 2010, 10:02 PM

That's 0.590? 590 would seem to indicate resistance which is entirely different.

Do you have negative rail voltage on the IRF540s when the bottom half isn't being produced?

bdgf2004 · 25th November 2010, 01:39 PM

i hate this new internet service we have!!! i have already replied 4 times and none of them have posted!!!

yes i have negitive rail voltage at the fet. -27v on lef #3

Perry Babin · 25th November 2010, 05:12 PM

Remove Dx04 from one or both channels. Does that allow the amp to produce the negative half of the waveform?

24th November 2010, 03:11 PM	#4
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	You'll have to remove it from the circuit to check it. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

24th November 2010, 07:50 PM	#6
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	I don't know how you tested the FET. Did the new one read open in one direction (leg 2-3)? Did the failed FET read open from leg 1 to each of the other legs? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

24th November 2010, 10:02 PM	#8
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	That's 0.590? 590 would seem to indicate resistance which is entirely different. Do you have negative rail voltage on the IRF540s when the bottom half isn't being produced? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

25th November 2010, 05:12 PM	#10
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Remove Dx04 from one or both channels. Does that allow the amp to produce the negative half of the waveform? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

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24th November 2010, 04:25 AM	#2
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	It may be leaky. Compare the resistance between its gate and other two legs to the other IRF9540. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

24th November 2010, 03:08 PM	#3
bdgf2004 diyAudio Member Join Date: Oct 2010	everything tested ok on the fet except what i previously stated

24th November 2010, 04:26 PM	#5
bdgf2004 diyAudio Member Join Date: Oct 2010	the fet was out of the circuit before testing. ive already replaced it and still have the distortion

24th November 2010, 08:52 PM	#7
bdgf2004 diyAudio Member Join Date: Oct 2010	new fet: black probe on leg #2 red on #3= open red on #2 black on #3=590 old fet: yes, with probes either way #1 is completely open from #2 and #3. i was about to take pics but when i fired it up (60 hz wave) both channels looked very good (no load) for several minutes and then out of the blue the left (repaired channel) lost its bottom half. at this time the right channel remained perfect. i tapped and wiggled around on several components with no result. so i was getting ready to take a pic again so i left the room to get my phone and when i came back it looked okay again. i put a load on it and it distorted on the bottom half badly, so i tried the right channel and i was perfect. now i have done nothing and both of the channels have lost their bottom half ( no load). this is the first time i have had problems out of the right channel.

25th November 2010, 01:39 PM	#9
bdgf2004 diyAudio Member Join Date: Oct 2010	i hate this new internet service we have!!! i have already replied 4 times and none of them have posted!!! yes i have negitive rail voltage at the fet. -27v on lef #3

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