DR #58 - A Bit of Troubleshooting - Parasound HCA2003A High Current Power Amplifier

this is the very impressive parasound HCA 2003a High current power amplifier it has three channels each with 220 watts of output but this one only has one functioning Channel let's see if we can fix that so let's see what each channel is doing here's channel one no output at all and channel two we do get a response but it is defin definitely not what we want and channel three that's our good Channel let's open it up before we get started let's go over the layout of this parasound in the front we have a comically large Transformer on the bottom we have a very large power supply each channel has its own power supply in the back on the top is the input board this handles the signals for all three channels and you'll notice we only have two amplifier boards one on the left and one on the right but this actually does handle the signals for all three channels it's a relatively unique layout at least from what I've seen channel one is handled by this section of this board channel three is handled by this section of this board and channel two is split between both boards this section here and this section here unfortunately I do see some work's been done on Channel 2 this transistor's been replaced this resistor has been been replaced looks like some other work's been done in that area so I'm going to save that channel for later I'm going to start with channel one I'll start with the power supply since the schematic doesn't tell me what the voltages should be I'm going to use our good channel 3 as a reference here's the positive rail 77 volts and the negative rail negative 77 volts now let's check channel one here's the positive rail nothing not a good start and the negative rail only about 1.1 volts that's not going to cut it so looks like we're going in deep to the power supply let's check Channel 1's fuses on the power supply board that's going to be F1 and F2 F1 is open as is F2 these are 10 amp fuses one of the most common causes for a blown fuse in the power supply is a shorted output transistor for channel one that's going to be these eight right here so let's check for shorts on those we'll start on the negative rail first one's good second's good third is good and the fourth is good negative rail is okay let's check the positive rail shorted all the way through second one completely shorted as well third one also shorted all the way through and the fourth one you guessed it completely shorted now I think I can do some work from the top on this board without removing anything but I think it's going to be a lot easier to just remove this entire board I don't think it's going to be too difficult I've removed all four shorted output transistors and clean their pads I also inspected all of the components related to channel one I think I got lucky the transistors didn't seem to take out anything but themselves I am going to replace a few other components though there are four electrolytic capacitors on this board I'm going to replace all four of those they're relatively inexpensive and easy to replace I'll also replace this single turn bias potentiometer with a multi-turn potentiometer and of course I need to replace the two 10 amp fuses here are the parts I'll be replacing as well as a list of the parts I'll be using to replace them with this parts list is in the description of this video as well if you'd like to see the conclusion of channel one see how it turns out as well as how the rest of this parasound turns out channel two and Beyond add on over to my patreon page which is also called Duality repair I'll post any follow-up videos on this there thanks for watching