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Old 27th December 2011, 07:22 PM   #1
Dr Zeus is offline Dr Zeus  United States
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Default Rockford BD1501

Here I have this amp which someone previously failed to repair some things. I notice a few wires slightly melted from an iron, and screws missing.

A FET, MTP75N05HD was used to replace CR2 rectifier, so I replaced it with a FEP16DTA. Q6 IRF6215 has a different date code than the others but it is undiagnosible if this transistor was replaced. All 5/6 caps in the power supply next to the power terminals appear to have at least partially vented, but are not measuring shorted (They are still installed). None of the transistors along the sides (Except for the above incorrect FET) were measuring shorted.

Is it possible that the shorted FET in CR2 caused high voltage A/C to fry something in the audio section?

This amp drains my 12A power supply down to 8.6v; but the drive signal on the fets look -ok-. There is -36vDC on the positive speaker terminal, and also on the center of CR2 and CR1. There is no significant DC voltage on CR3 or CR4 (~ +.8v).

Is this amp a gonner?
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Old 27th December 2011, 07:41 PM   #2
Dr Zeus is offline Dr Zeus  United States
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In looking at this amp a little further, I notice that some things missing on the torroid closest to the power terminals. Needless to say; I do not think this amplifier is worth repairing due to this torroid having missing windings. In the photo, you may notice ~4 windings which were removed from the PCB, and then cliped back inside the torroid. I'm kinda disabpointed because I really wanted to fix this amp

Click the image to open in full size.

I guess I'll wait and hope for a donor someday.

Oh well, thanks for looking Heres breakfast.
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Old 27th December 2011, 08:40 PM   #3
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So the amp does power up but draws excess current?

Maybe you should disconnect the preamp section from the output section and then try and power up the amp.

Do you get a square wave form on all of the gate legs of the output fets?

Do you read 30 ohms testing between gate legs of every pair of output fets?

Post the voltage on the pins of the LM6171 (U17)

I recentely repaired a BD15001 that was the same thing on the torroid. One torroid had wires going to all solder pads on the board and the other was missing like 8 wires.

I will check my other bd15001's to see if they are the same, I have never really checked to see in all the ones I have repaired. The one I just repaired works great, no issues.
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Old 27th December 2011, 08:50 PM   #4
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Your in luck!!! I just checked 5 other bd15001's 2 which have never been repaired and they are all missing the 8 wires on the torroid closest to the power terminals. I think the one you have is perfectly normal with the missing wires.

I have seen a few BD15001's with the clipped wires and then epoxy over top. I dont think I would worry about those clipped wires.
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Old 27th December 2011, 08:58 PM   #5
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Parallel outputs must match so you will likely need to replace the 4 outputs that contain the mis matched fet. I would probably do all 8, 4 new IRF3415's and 4 new IRF6215.
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Old 27th December 2011, 09:10 PM   #6
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CR1, CR2, CR3, CR4 are your rectifiers that produce or control rail voltage. You should have good amount of DC on all of them. What is the voltage across the long red and black twisted wires?

The rectifiers could be faulty and may need replaced. I would be almost positive the one paired with the MTP75N05HD is defective.
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Old 27th December 2011, 10:24 PM   #7
Dr Zeus is offline Dr Zeus  United States
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Thanks Sean. I'll get back to ya on if the RectiFET wrecked the other rect. lol
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Old 27th December 2011, 10:48 PM   #8
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RECTIFET I like that. Thats funny.
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Old 27th December 2011, 11:27 PM   #9
Dr Zeus is offline Dr Zeus  United States
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Either that or FETiFire. Either way it probably made some fireworks.
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Old 28th December 2011, 03:35 AM   #10
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They probably had only one transformer for this amp when this run was assembled. One needs the windings for the low voltage supplies. The other doesn't so they cut the extra wires.

Desolder the red/black twisted pair from the POWER SUPPLY side of the amp. Power up the amp and measure the DC voltage directly across the pads where the red and black wires were soldered to the board.

Is the amp still drawing excess current?

What's the voltage across those pads (both sets)?
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