Got a Fosgate 225.2 from a guy who said it works but gets hot (hot is pretty subjective on these). Checked it over and didn't find any problems other than maybe needing to reflow the RCA block. No excessive DC on the outputs, but powered up it drew about 1.2A...a bit high. Marked the bias pots and turned them all the way down, powered back up and it drew 0.98A - still a little high I would say. Adjusted the bias pots for 0.05A rise on each, so now it's at 1.08A idle.
At this point I connected speakers and RCA and the amp has clean output, and the amp draw drops to 0.95A at idle. That seems strange. If I unplug either RCA the draw goes back up to 1.08A, and I get low level static hiss on the right speaker with either RCA disconnected, which I assume means I have a broken RCA shield on the right channel. But why the change in idle amp draw?
At this point I connected speakers and RCA and the amp has clean output, and the amp draw drops to 0.95A at idle. That seems strange. If I unplug either RCA the draw goes back up to 1.08A, and I get low level static hiss on the right speaker with either RCA disconnected, which I assume means I have a broken RCA shield on the right channel. But why the change in idle amp draw?
What's your budget?
I can't stand the donkey-kong displays of most LCD based scopes. Siglent (for some of their scopes) have decent displays. I'd still prefer to have virtually any CRT based scope in good working order. That's a personal preference.
If 12v was driven into the shields, that could burn that resistor.
I can't stand the donkey-kong displays of most LCD based scopes. Siglent (for some of their scopes) have decent displays. I'd still prefer to have virtually any CRT based scope in good working order. That's a personal preference.
If 12v was driven into the shields, that could burn that resistor.
Budget is TBD...just moved, looking to buy a house, etc. I saw a Tek 2465 for what seemed like a good price, but then I read they had some unobtainable parts, and their age turned me off.
Pulled R33 and it continued to read over 3k ohms. I didn't have any 1ohm resistors so I put in a 10ohm for the time being. Replaced the scratchy gains and reflowed the RCAs and some other parts. Now have 0.92A idle after bias adjustment without RCAs connected. Drops to 0.89A when they are connected. This is just an RCA to 1/8" miniplug, so the grounds are shared.
Pulled R33 and it continued to read over 3k ohms. I didn't have any 1ohm resistors so I put in a 10ohm for the time being. Replaced the scratchy gains and reflowed the RCAs and some other parts. Now have 0.92A idle after bias adjustment without RCAs connected. Drops to 0.89A when they are connected. This is just an RCA to 1/8" miniplug, so the grounds are shared.
If the noise is an issue that you want to find, you'll have to trace it through the circuit to find where it's entering the circuit.
If there is no noise with RCAs plugged in, it may not be a problem that needs to be resolved.
The decision will be yours and/or the owner's on which way to go.
If there is no noise with RCAs plugged in, it may not be a problem that needs to be resolved.
The decision will be yours and/or the owner's on which way to go.
