PPI PC225 blowing fuses

Deadly Sones · 22nd March 2011, 02:24 PM

This amp had a smoked IRFZ44N and a bad resistor. I replaced Q1 (it was cracked but not blown), Q2 (melted), R6 (out of tolerance) and R7 which was completely burned up. Verified that all solder connections are good.

When I place a 10amp fuse in line (gain all the way off) everything is fine until I turn on the radio. It blows a fuse right away.

What to check next?

Thanks in advance.

Perry Babin · 22nd March 2011, 03:06 PM

Did you check the output transistors?

Deadly Sones · 05:29 PM

No... They visually looked fine. I will pull them and check them too. I did check all of the gate resistors they are good.

Perry Babin · 22nd March 2011, 05:34 PM

Initially, you probably don't need to pull the outputs. You'll be able to determine if they're shorted while they're in the circuit.

Deadly Sones · 05:49 PM

Whats the best way to test them in the circuit? I've always pulled them out.

Edit: Oops... R106 is only reading .3-4 ohms and should be 47 ohms.

Perry Babin · 22nd March 2011, 05:58 PM

Initially, when an amp is pulling excessive current (only after remote voltage is applied), you check to see if the output transistors are shorted. Whey they short, they generally read very low resistance between the legs. They should not read anything near 0 ohms between the legs of any individual transistor. If none are shorted, you have to do a bit more troubleshooting. For now, see if any are shorted.

Deadly Sones · 06:37 PM

I pulled the transistor 2N6488 in location Q28 as it was connected to the R206 that initially read as .3-4 ohms but when I removed it from the circuit it reads fine.

All the legs on the 6488 read 0.000v no matter what config I use with DVM set to diode.

Thanks for your help Perry. :-)

Deadly Sones · 22nd March 2011, 06:57 PM

Hmmmm, I tried to power it back up with the 6488 in Q28 removed. Clamped the cover back on. The 47ohm resistor in R106 burned up after power turned on for like 5 sec. Did it just burn up because of the transistor being removed or is this a sign of something bigger? The 10amp fuse didn't blow this time. Just burned up the resistor till I removed the fuse.

Perry Babin · 22nd March 2011, 07:05 PM

Can you post (or email me) a high resolution photo? The circuit board designations are meaningless without the photo (or a schematic diagram).

Deadly Sones · 22nd March 2011, 07:22 PM

Sorry. I`ll have to email them... apparently they are too high res to upload here, lol.

Thanks

22nd March 2011, 02:24 PM	#1
Deadly Sones diyAudio Member Join Date: Feb 2011 Location: Windsor, Ontario	PPI PC225 blowing fuses This amp had a smoked IRFZ44N and a bad resistor. I replaced Q1 (it was cracked but not blown), Q2 (melted), R6 (out of tolerance) and R7 which was completely burned up. Verified that all solder connections are good. When I place a 10amp fuse in line (gain all the way off) everything is fine until I turn on the radio. It blows a fuse right away. What to check next? Thanks in advance.

22nd March 2011, 03:06 PM	#2
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Did you check the output transistors? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

22nd March 2011, 05:18 PM	#3
Deadly Sones diyAudio Member Join Date: Feb 2011 Location: Windsor, Ontario	No... They visually looked fine. I will pull them and check them too. I did check all of the gate resistors they are good. Last edited by Deadly Sones; 22nd March 2011 at 05:29 PM.

22nd March 2011, 05:34 PM	#4
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Initially, you probably don't need to pull the outputs. You'll be able to determine if they're shorted while they're in the circuit. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

22nd March 2011, 05:41 PM	#5
Deadly Sones diyAudio Member Join Date: Feb 2011 Location: Windsor, Ontario	Whats the best way to test them in the circuit? I've always pulled them out. Edit: Oops... R106 is only reading .3-4 ohms and should be 47 ohms. Last edited by Deadly Sones; 22nd March 2011 at 05:49 PM.


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22nd March 2011, 05:58 PM	#6
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Initially, when an amp is pulling excessive current (only after remote voltage is applied), you check to see if the output transistors are shorted. Whey they short, they generally read very low resistance between the legs. They should not read anything near 0 ohms between the legs of any individual transistor. If none are shorted, you have to do a bit more troubleshooting. For now, see if any are shorted. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

22nd March 2011, 06:19 PM	#7
Deadly Sones diyAudio Member Join Date: Feb 2011 Location: Windsor, Ontario	I pulled the transistor 2N6488 in location Q28 as it was connected to the R206 that initially read as .3-4 ohms but when I removed it from the circuit it reads fine. All the legs on the 6488 read 0.000v no matter what config I use with DVM set to diode. Thanks for your help Perry. :-) Last edited by Deadly Sones; 22nd March 2011 at 06:37 PM.

22nd March 2011, 06:57 PM	#8
Deadly Sones diyAudio Member Join Date: Feb 2011 Location: Windsor, Ontario	Hmmmm, I tried to power it back up with the 6488 in Q28 removed. Clamped the cover back on. The 47ohm resistor in R106 burned up after power turned on for like 5 sec. Did it just burn up because of the transistor being removed or is this a sign of something bigger? The 10amp fuse didn't blow this time. Just burned up the resistor till I removed the fuse.

22nd March 2011, 07:05 PM	#9
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Can you post (or email me) a high resolution photo? The circuit board designations are meaningless without the photo (or a schematic diagram). __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

22nd March 2011, 07:22 PM	#10
Deadly Sones diyAudio Member Join Date: Feb 2011 Location: Windsor, Ontario	Sorry. I`ll have to email them... apparently they are too high res to upload here, lol. Thanks

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