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Old 17th March 2014, 08:14 PM   #1
chipper is offline chipper  United States
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Default Old rockford fosgate punch 150

Hey guys im back at this project. It's my old school rockford fosgate punch 150. The problem is the left channel is not working. I remember a while back I replaced NE5532P ic's to see if that would work. The amplifier still powers on and plays through one channel. What do I check? It's missing a driver transistor (D40D8) hard to find those. Has anyone fixed these?


Btw what year is this one from?
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Old 17th March 2014, 08:15 PM   #2
chipper is offline chipper  United States
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This is the left channel that needs work
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Old 17th March 2014, 08:17 PM   #3
chipper is offline chipper  United States
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The inside
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Old 17th March 2014, 10:22 PM   #4
rickcl is offline rickcl  United States
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Why is that fuse holder empty? For testing?
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Old 17th March 2014, 10:39 PM   #5
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You should check, the FET output that faulty channel, to see if they are short, or open, also resistors, capacitors, and check voltages at different points.

I see a fuse missing on that side of the amp, and there is a resistor 1/4 watt, which has a suspicious color ...

I've seen on ebay, a seller who has these transistors (D40D8) and seems reliable.
It is this:

http://www.ebay.es/itm/HARRIS-TO-202...item5655cf0ff3
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Old 17th March 2014, 10:53 PM   #6
chipper is offline chipper  United States
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Quote:
Originally Posted by josesony68 View Post
You should check, the FET output that faulty channel, to see if they are short, or open, also resistors, capacitors, and check voltages at different points.

I see a fuse missing on that side of the amp, and there is a resistor 1/4 watt, which has a suspicious color ...

I've seen on ebay, a seller who has these transistors (D40D8) and seems reliable.
It is this:

HARRIS TO-202 CASE D40D08 D40D8 TRANSISTOR 2ea FREE USA SHIPPINGnew | eBay

I removed the fuse because that channel had DC on it. I'm guessing maybe just replace all the components in that channel? The outputs are BJT 2N6487 & 2N6490. I can use 2N6491 & 2N6488?
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Old 17th March 2014, 11:04 PM   #7
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If you got DC on the speaker output of the channel, because there is a blown fet, check them.
I prefer to do the replacement, always identical to the original parts of the amplifier.

If you replace those with equivalent FETS, it may not work properly, you have to adjust the bias, or, burn a few minutes ..
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Old 17th March 2014, 11:15 PM   #8
chipper is offline chipper  United States
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Quote:
Originally Posted by josesony68 View Post
If you got DC on the speaker output of the channel, because there is a blown fet, check them.
I prefer to do the replacement, always identical to the original parts of the amplifier.

If you replace those with equivalent FETS, it may not work properly, you have to adjust the bias, or, burn a few minutes ..
They're bipolar transistors? I'm guessing early Fosgate used bipolar outputs in these early amps? Seems a lot different from all the other amps I've worked on..
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Old 17th March 2014, 11:35 PM   #9
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Sorry, if I referred to as FET output transistors, (is the usual,) I think they are just power transistors, "plain" I'm not sure if they are bipolar or not ....

I noticed some time ago a 75HD, but I remember, yes, were mosfet output transistors, specifically IRF 540 or 640'S ....

Anyway, I will repeat, that would try to replace them with the originals, the same channel that is in the works.
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Old 18th March 2014, 01:34 AM   #10
WSJ is offline WSJ  United States
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Using the DMM diode test function, check the devices (diodes, NPNs and PNPs) for open in the reverse direction and 600 +/-100 mV in the forward direction. You may need to lift one end of the base emitter resistor or lift the base of each device to get a valid measurement. If they all look good, remove the op amp (on my schematic it’s marked U3) and post a list of all the voltages. Install a socket for U3 incase needs replacing.

I worked for a company who made discrete op amps in 1969 and repaired over 70 amplifiers in one day by troubleshooting with only a DMM. The next day the company shipped over $10,000 worth of op amps. I made $28 a day minus taxes about $17, then the laid me off.

Let me know if you need the schematic.

Last edited by WSJ; 18th March 2014 at 02:00 AM.
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