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Old 17th September 2011, 09:05 AM   #1
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Default Memphis 16-MCH1300 help

I have this amp that I was wanting to try and repair. I hooked this thing up in my car the little light on the side was green but no sound came out from any of the channels. After taking the bottom off it was clear that the power supply section was messed up. So far I have removed all 8 of the 3205s and all 8 of the gate resistors 4 of the IRF3205s were melted so I took them all out all 8 of the resistors were melted. On the other side of the amp in the power supply section It has 6 FQP50n06 none of them appear to be burnt but all 6 of the gate resistors are burnt. Also the power supply driver board has two transistors that are burnt the board is two burnt to really make out which ones they are. The one closest to them that i can see is Q14 so they are possibly Q15 and Q16. So my question is can someone tell me anything else I should check before I start ordering parts
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File Type: jpg FQP50n06.jpg (152.3 KB, 181 views)
File Type: jpg IRF3205s.jpg (133.2 KB, 176 views)
File Type: jpg driver board.jpg (127.3 KB, 177 views)
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Old 17th September 2011, 03:38 PM   #2
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If the gate resistors are burned for the FQP FETs, the FETs have likely failed (assuming that the resistors are burned and out of tolerance and not just darkened by a previous failure of the supply).

The transistors are 2SA1266s (or KTA1266s) but are difficult to find. The BD140 is a bit larger but should be a good replacement.

Confirm that the two 220 ohm SMD resistors at the top right corner of the driver board are within tolerance.

Have you checked the output transistors?
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Old 17th September 2011, 06:12 PM   #3
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Do I need to check all of the output transistors out of the circuit
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Old 17th September 2011, 10:00 PM   #4
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If you don't find any that read near 0 ohms between the legs of any individual transistor, they don't need to be removed.
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Old 18th September 2011, 12:25 AM   #5
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The first group of outputs are 8 IRF9640 4 on each side of amp. All 4 on one side all read 0 the same as if i touched both probes together (black probe on leg 1 red probe on leg 2 and black probe on leg 1 and red probe on leg 3). The 4 on the other side all read 024 ohms on leg 1 and 2 and leg 1 and 3. There is also 4 FB31N20D in this section do you test those the same as the fets? The next section has 4 IRF540 and 4 IRF9540. All 4 of the 540s with black probe on leg 1 and red probe on leg 2 start at 240 ohms and just keep dropping. With black probe on leg 1 and red probe on leg 3 they all 4 read 053 ohms. All 4 of the IRF9540 read the exact same way as the 540s. There is 4 C2690A one inbetween each 540 and 9540 what are these ?
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Old 18th September 2011, 01:15 AM   #6
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Using the word 'group' to refer to components on the opposite sides of the amp will be confusing. Use the circuit board designations printed in white on the board adjacent to each transistor.

It's VERY rare that all of the parallel outputs will read 0 ohms from leg 1 to either of the other legs. Are you counting from left to right?

053 ohms? Is there a missing decimal point or does your meter use a leading zero for readings that have only two digits?
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Old 22nd September 2011, 07:17 AM   #7
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I am thinking my meter is confusing me It's a SPERRY DM-4400a . When it is set to ohms the display shows 10.00m then a ohm symbol the 1 is flashing. Also when both probes are touched together it reads 00.5 ohms. Before I go and test everyone of the outputs in circuit do you need to know what kind of fet that it is that im testing or can i just post what the circuit board designation is and the readings i get on each one?
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Old 22nd September 2011, 07:36 AM   #8
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Here is a better picture of the driver board. I was just curious about what part of the output does the IRF9540 and the IRF540 power is it the class d mono part or the class a/b 4 channel part also what are the C2690a in between the 9540s and the 540s are they output transistors to? I also noticed that the 3 200v capacitors are a little swollen
Attached Images
File Type: jpg irf540.jpg (179.5 KB, 146 views)
File Type: jpg caps.jpg (85.4 KB, 60 views)
File Type: jpg driver3.jpg (155.8 KB, 61 views)
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Old 22nd September 2011, 07:49 AM   #9
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You should not read anything near 0 ohms between the legs of any transistor.

The 540s and 9540s are in the class AB section. The #!N20s and the 9640s are for the class D section.

The small transistor is the bias compensation transistor.

The 10uf/200v caps appear to have vented so they will need to be replaced. They are typically unavailable so you'll probably have to use mylar caps.
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Old 23rd September 2011, 12:48 PM   #10
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Is there a online store that I would be able to buy IRF3205, IRF9640, FQP50n06, 10uf/200v caps, bd140, 22ohm resistors there is more to add to all of that I'm sure. I just looked around online for a while looking up all of these various parts and haven't found anywhere that has all of the parts that I need. So my question is do you usually have to order parts from more than one place
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