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Old 5th December 2007, 01:04 AM   #1
jol50 is offline jol50  United States
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Default burnt resistors on speaker output?

I have this cheap amp, a bazooka 2x75. It has blown power transistors. Was looking around and see two resistors right on the speaker outputs (at terminals) that are burnt black enough so no stripes are left but not completely torched. One end goes to the driven terminals, they show 6.3 and 5.8 ohms. I checked some other amps and they are 5 and 6 ohms....what should I do with these? Yeah I think I am fixing it just for fun.
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Old 5th December 2007, 01:37 AM   #2
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Output Zobel maybe ? ZED used 4.7 ohms..2 watt. What's the cap value its attached to ???
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Old 5th December 2007, 01:41 AM   #3
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I'm assuming that you're talking about the Zobel (resistor/capacitor) network across the speaker output. If so, the resistor is in series with a capacitor. In the bazooka amp photos I have, the resistors are all 4.7 ohms.
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Old 5th December 2007, 01:47 AM   #4
jol50 is offline jol50  United States
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I will try to take a pic...they go into the board and trace under it. They are right next to post for speaker terminal.
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Old 5th December 2007, 02:04 AM   #5
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What model is the amp?
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Old 5th December 2007, 02:13 AM   #6
jol50 is offline jol50  United States
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It is a RSA75.2HC if you want to copy the pics. The green capacitors say 104J 100v right next to them.
Click the image to open in full size.
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Old 5th December 2007, 02:47 AM   #7
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Let me guess... Power supply blown for no apparent reason?


The resistors are indeed 4.7 ohms. I'd suggest going to the next higher wattage (at least 1 watt). Check the capacitors to make sure they are not shorted.

These amps have problems with several feed-through connections. In the next two images, you can see the most critical points. You need to desolder the components, scrape the leads both above and below the board (to remove oxidation), tin the leads and resolder on both sides of the board. If any of these connections fails, either the amp will not power up or the power supply will go up in smoke.

Click the image to open in full size.

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Old 5th December 2007, 04:02 AM   #8
jol50 is offline jol50  United States
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I bet you are right on the money. Most of the IRFZ46 are blown, but have no idea what happened. I did wonder what the blobs of solder here and there were, some are even big globs on jumpers it is all over the place. They must spend some time doing that. So they jumper both sides and they short....that will take me a while. I ordered 1w resistors for it, thanks again everyone. You must not be tired of me yet, lol, but I'm out of amps and no parts so it's time for a break and maybe I'll read about Zobel networks.
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