Hi all,
i have got this punch 400x with a some blown ends. I replaced al the output fets and gate driver fets (and a couple of gate resistors), resulting in all outputs working except one (right rear). The signal out of this channel is only the top side of the signal (positive part).
I have measured some signals in this part and it looks like (i think) the signal is there, but its to low (not weak but shifted a few volts down). When i turn de bias completely CW the signal to Q313 increases a bit but doesn't go above ground voltage (same signal in left rear does). Also Q321 gets really hot.
I use the schematic of the punch 400.4 (i think same board) and an 100Hz test signal.
I hope someone can help me out.
PS. On the total picture the output fets (left down) are missing, those have been replaced already. The (current) problem is in the left right part (right rear).
i have got this punch 400x with a some blown ends. I replaced al the output fets and gate driver fets (and a couple of gate resistors), resulting in all outputs working except one (right rear). The signal out of this channel is only the top side of the signal (positive part).
I have measured some signals in this part and it looks like (i think) the signal is there, but its to low (not weak but shifted a few volts down). When i turn de bias completely CW the signal to Q313 increases a bit but doesn't go above ground voltage (same signal in left rear does). Also Q321 gets really hot.
I use the schematic of the punch 400.4 (i think same board) and an 100Hz test signal.
I hope someone can help me out.
PS. On the total picture the output fets (left down) are missing, those have been replaced already. The (current) problem is in the left right part (right rear).
Attachments
thank u.
R362 fine.
R361 bad, so i replaced it (by 2x 10ohm lol. Don't worry, temporary fix until i get the correct resistors inside).
R347, R356, R357, R355, R358, R353, R354, C320, D305, Q318, Q317 All fine.
R359 = 61K in circuit. I think is fine.
D304 & Q316 Dead
Can i replace Q316(mmbt3906) by mmbta56lt1g?
R362 fine.
R361 bad, so i replaced it (by 2x 10ohm lol. Don't worry, temporary fix until i get the correct resistors inside).
R347, R356, R357, R355, R358, R353, R354, C320, D305, Q318, Q317 All fine.
R359 = 61K in circuit. I think is fine.
D304 & Q316 Dead
Can i replace Q316(mmbt3906) by mmbta56lt1g?
Attachments
Just to explain to you this section is Rockford Fosgate Patent.
this is the Over load sensing circuit so when the current that pass over the 0.1R resistor is High this shut down the output mosfets. but when the 0.1R resistor is "lost" value the parallel 12R & 20R take all the output current then they are burned.
About Q316 YES you can do that but replace also Q307 with mmbta06 (the upper side)
my advice? replace R361 & R362 with new resistors. and make double check with R363 the 0.1R make sure that this resistor is not now high resistance value.
this is the Over load sensing circuit so when the current that pass over the 0.1R resistor is High this shut down the output mosfets. but when the 0.1R resistor is "lost" value the parallel 12R & 20R take all the output current then they are burned.
About Q316 YES you can do that but replace also Q307 with mmbta06 (the upper side)
my advice? replace R361 & R362 with new resistors. and make double check with R363 the 0.1R make sure that this resistor is not now high resistance value.
For quick troubleshooting, to determine if the problem is in the protection circuit or in the drive circuit, you can remove/lift the diodes (D302 - high side and D304 - low side). If the waveform and output into a load are OK with those out of the circuit, you know the problem is in protection circuit. If the output is distorted, you can get that channel working properly, then troubleshoot the protection circuit if it's damaged.
Motronix. Thanks for the explanation, would have been my next question lol.
So i replaced Q316, Q307, R362, remeasured R363 (0,1 measured). And i have signal and sound (positive and negative side) but with some noise.
I have added 2 pictures. On both the top signal is signal on RCA (100hz). The other signal is measured on the gate of Q315 (negative output fet). The lower one is without load, the higher one is with 8ohm load on the output. The signal to the other fet (Q319) has the same noise. Changing the bias doesn't change the noise.
Also the current usage of the amp (1.8A idle) goes within a minute to 3A+.
Thanks for the tip Perry. Sounds logic (when u know what that part of the circuit does).
Edit: lifting the diodes doesn't change the signal.
So i replaced Q316, Q307, R362, remeasured R363 (0,1 measured). And i have signal and sound (positive and negative side) but with some noise.
I have added 2 pictures. On both the top signal is signal on RCA (100hz). The other signal is measured on the gate of Q315 (negative output fet). The lower one is without load, the higher one is with 8ohm load on the output. The signal to the other fet (Q319) has the same noise. Changing the bias doesn't change the noise.
Also the current usage of the amp (1.8A idle) goes within a minute to 3A+.
Thanks for the tip Perry. Sounds logic (when u know what that part of the circuit does).
Edit: lifting the diodes doesn't change the signal.
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Last edited:
The gates won't look like audio. The amplitude is higher with a load because the amp has to drive the outputs harder to keep the signal as it should be at the output.
What does the output look like? Set the scope to 2ms/div and 5v/div and drive the amp until the amplitude of the output is about 3/4 of the entire display.
What does the output look like? Set the scope to 2ms/div and 5v/div and drive the amp until the amplitude of the output is about 3/4 of the entire display.
Motronix. Thanks for the explanation, would have been my next question lol.
So i replaced Q316, Q307, R362, remeasured R363 (0,1 measured). And i have signal and sound (positive and negative side) but with some noise.
I have added 2 pictures. On both the top signal is signal on RCA (100hz). The other signal is measured on the gate of Q315 (negative output fet). The lower one is without load, the higher one is with 8ohm load on the output. The signal to the other fet (Q319) has the same noise. Changing the bias doesn't change the noise.
Also the current usage of the amp (1.8A idle) goes within a minute to 3A+.
Thanks for the tip Perry. Sounds logic (when u know what that part of the circuit does).
Edit: lifting the diodes doesn't change the signal.
OK let's start first with the Bias calibration. do you know the procedure?
if not here is the instructions:
Proper bias setting should be measured as a 4 to 5 millivolt drop across the .1 ohm resistors in each channel. BUT just for start calibrate it to 2 millivolt !!!
This procedure should be done with the unit mounted to the heat sink to avoid thermal run away and operating at an idle state (unloaded). Turn bias pots up till the proper voltage drop is achieved. On units with more than one MOSFET on either the positive or negative rail, Use the 4 to 5 millivolt drop as a maximum reading. These multiple MOSFET units will have reading that vary from one .1 ohm to another. This procedure is meant as a reference, part tolerances can vary results. Always keep an eye on the idle current of the unit after the bias has been set. Idle current should only increase slightly after the bias is set.
about the noise do you have it when nothing connected to the RCA?
I know the gates wont look like audio, but other channels there gate looks way cleaner.
My scope (me) don't like anything slower than 1ms/div (it wil be a stroboscope) so i used 1ms/div (and 5v/div).
The signal looks good to me, but it doesn't sound completely clean. Especially with music. I will test tomorrow again (other speakers).
Also the current rising thing is gone. It was a bad bias setting on a other channel.
My scope (me) don't like anything slower than 1ms/div (it wil be a stroboscope) so i used 1ms/div (and 5v/div).
The signal looks good to me, but it doesn't sound completely clean. Especially with music. I will test tomorrow again (other speakers).
Also the current rising thing is gone. It was a bad bias setting on a other channel.
Attachments
Sorry this late reaction.
The output(s) are clean, the noise is coming from my pc. I guess the sound card slowly dies.
About setting the bias, i normally only look at the idle current. When is shoots up, i turn the bias a bit back. But i haven't done much with bias setup. What are the effects of a bad bias setup? I know to much CW results to much(or increasing) idle current but what if it is to low (not CW enough / lower idle current)?
The output(s) are clean, the noise is coming from my pc. I guess the sound card slowly dies.
About setting the bias, i normally only look at the idle current. When is shoots up, i turn the bias a bit back. But i haven't done much with bias setup. What are the effects of a bad bias setup? I know to much CW results to much(or increasing) idle current but what if it is to low (not CW enough / lower idle current)?
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