Rockford Fosgate P800.2 [Repair] - Page 3 - diyAudio
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Old 16th April 2009, 02:52 PM   #21
woutzor is offline woutzor  Netherlands
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Default Update

Parts ordered! Hopefully I'll get them this weekend
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Old 19th April 2009, 08:13 PM   #22
woutzor is offline woutzor  Netherlands
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Well, Yesterday I received the following parts from Conrad.nl:
  • IRF3205 (International Rectifier)
  • IRF9640 (International Rectifier)
  • IRF640 (STMicroelectronics)
Hopefully I'll receive the other parts ordered at Farnell later this week.


Today I've got the new parts soldered in place (Yes, got the backsides of the FET's pre-soldered ) but not yet soldered to the MEHSA thermal management system.
I wanted to see if the beast would power up.. So I hooked it up to my trusty Delta Elekronika Power Supply E 030-3 (30V 3A both adjustable) without the remote connected. The amp doesn't draw any current so that's a good thing. But when I connect the Remote to B+ it shorts out (Amp draws the full 3A).

Here's a picture of the amp's board in current state:
Click the image to open in full size.
Green arrow: Parts newly installed
Red arrow: Parts removed

What could be the problem? Is it because there are parts missing?
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Old 19th April 2009, 09:00 PM   #23
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It's probably because Q2 is out of the circuit.
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Old 19th April 2009, 09:25 PM   #24
woutzor is offline woutzor  Netherlands
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Thanks for the reply Perry. Just out of curiosity, how could this component got blown in the first place?
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Old 20th April 2009, 12:54 AM   #25
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When the power supply FETs fail, they generally short 12v to the gate. Q2 and Q3 in this power supply try to pull the 12v on the gate back down but they often can't handle the current passing from the gates and often fail, especially if the gate resistors don't open.
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Old 21st April 2009, 10:41 PM   #26
woutzor is offline woutzor  Netherlands
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Talking Parts from Farnell arrived

Quote:
Originally posted by Perry Babin
When the power supply FETs fail, they generally short 12v to the gate. Q2 and Q3 in this power supply try to pull the 12v on the gate back down but they often can't handle the current passing from the gates and often fail, especially if the gate resistors don't open.
Alright, thanks for explaining .


Well, the parts from Farnell finally arrived.
The first thing I did was soldering new MMBTA56's and 06's. I also replaced all other SMD resistors and some other parts (see picture below).

After that I tried powering it up. When connected to B+ and GND the amp doesn't draw anything, so far so good.
But when I connect the remote to B+ it draws the full 3 Amps (just like before). On the bright side, the power LED shows sign of life

Here's a picture of the amplifier in current state: Click the image to open in full size.
Green arrow: Parts newly installed
Red arrow: Parts not installed

I measure 3.89V on the right and 1.50V on the left speaker output. When the power supply draws the full 3 Amps, the supplied voltage goes from 13V to 9V.

What could be the problem? Does it need more components installed to see if the power supply of the amp is functional? I want to make sure that it is and its safe to install the other parts.
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Old 21st April 2009, 10:53 PM   #27
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Connect only remote and ground. Measure the DC voltage on the gate leg of all 8 of the power supply transistors.
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Old 22nd April 2009, 07:07 AM   #28
woutzor is offline woutzor  Netherlands
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They all measure 5.07V. I've used GND as ground.
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Old 22nd April 2009, 08:00 AM   #29
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I don't see where the current could be going with the source resistors out of the circuit.

Does one group of 4 FETs get hot and the others remain cool?

How long have you allowed it to draw 3 amps? It may take more than a few seconds to charge the rail caps.
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Old 22nd April 2009, 09:27 AM   #30
woutzor is offline woutzor  Netherlands
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Hmm, I didn't notice that any of the FETs got hot.
I only applied power to the amp like 5 seconds.
I'll see to it when I get home. I'm at school atm.
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