@Dahoxic
Regarding the general noise floor of the console, I've decided I should recap my power supply to see what my baseline for other channel repairs might be. I've never recapped any old electronics, but I have soldered together a new wiring harness for a Les Paul, switch, pots, pickups, etc. My question being what's the safe way to do this? How did you safely discharge the caps in the power supply? Honestly, how did you do it lol?.
Note: by offering you advice, tips, guidance, etc. regarding electronics repair I assume absolutely no responsibility or liability for anything that happens to you or your equipment. I’m not a professional, I’m a hobbyist. Work on your gear at your own risk and treat it like it could kill you, because electricity can kill you.
Okay. Like Dave said you can just leave the device to sit and the caps will discharge over a little time. Generally if I’m going to be working on something I’ll just unplug it for a couple hours. If I have any question about whether or not there is energy stored in any caps I’ll just measure with a voltmeter. After power is disconnected you can measure a cap and just watch the voltage drop. If I have to discharge a cap I bleed it using a resistor. But the easiest thing is just to unplug it and let it sit for an hour or two. And as to the rest of the procedure there is nothing different about removing through-hole caps and soldering in new parts than any other board level soldering job. There’s nothing special about caps per se. Find a scrap PCB from an electronics surplus store or something and practice. I use a good quality manual vacuum type solder sucker. And you want a good iron with a clean tip that’s the correct size, generally about 2/3 the size of the solder pads you’ll be welding. But practice on something. You’ll have to remove the power supply PCB from the PS-520, or IIRC the inputs unplug, the outputs are hard-wired. So unplug the inputs, remove the mounting screws and if there are plastic pins squeeze those with needle nose pliers and pop the board off. It’ll stay attached to the output wires, but at least you’ll be able to have the board out of the chassis if not tethered by the wires, and be able to flip it to either side. Have some kind of cloth or padding you can put on the top of the chassis to lay the board on to avoid damaging the board or the chassis. I like rubber shelf liner. The meshy stuff. It’s soft, grippy, and non-conductive. Also, I strongly suggest you take proper electrostatic discharge measures. This means you ground yourself and your work and anything the work is going to touch to a common low-impedance connection to earth. It’s just good practice. It becomes more critical the more micro the electronics get, but static discharge can potentially damage any integrated circuit, and there are IC regulators in the supply.
Hopefully the above gets you started. Acquire the parts. Prep the work. Remove the caps. Weld the new ones in. Double and triple check your work throughout the process, especially the orientation of any polar caps. I generally remove an area of caps or a common cluster or something like that and put the new ones in rather than remove all and increase the risk of putting a cap in a wrong spot. And did I mention to double and triple check your work as you go? Do it. I’ve replaced thousands of caps. I am careful. Putting one of those bigger main filter caps in backwards will sound like a Glock 45 going off when it blows. And it will make a hella mess. You want to point assemblies with new caps away from you when you power them up after replacing parts, or if the chassis is steel then reinstall the covers to contain the explosion. Ask me how I know all that. And I double and triple check…even with that mistakes can happen. Never underestimate your capacity to be an ignoramus.
If you believe there's sufficient information posted about this already, I'd really appreciate a direct link.
I’ve said all this stuff many times but it’s buried in threads; time consuming to repeat it, but time consuming to do the same hunting and searching you can do to look for it. So, ultimately it’s easier to just repeat myself.
Otherwise if you have time to type out a general guide to recapping the power supply, I'd appreciate that even more.
Done…at least to some degree.
…how do you get the bank of four channels removed from the console chassis…couldn't pull the channel out of the chassis.
Here again I’ve posted this a bunch. I’m sure it’s in my M-520 Story thread more than once. I’ve not owned an M-500 console in a decade now so this is from dusty memory:
- Look at the leading edge of the meter bridge chassis…right above the modules…IIRC there are 6 screws left to right across the console. Remove them and tip the meter bridge assembly back. It tips back on hinges like opening the hood of a Corvette.
- With the meter bridge tipped back you’ll see the inside of the backplane, a shit-ton of connectors, the balance amp PCB assembly to the right, and also now exposed are two screws per 4-channel module that fasten the top of each module to the console frame. Remove them from the module you want to pull from the frame.
- Remove the trim strip between the wrist rest and the modules…6 screws? 7 screws?
- With the trim strip removed you’ll see two screws per 4-channel module that fasten the bottom of the module to the console frame. Remove them from the module you want to pull from the frame.
- The module is now unfastened from the frame. Now is the fun part where you carefully disconnect 500,000 mini Molex connectors from the backplane as well as the motherboard and also to disconnect the module from the adjoining module. Once all that is disconnected you can, in theory, lift the entire module free from the console frame, though it will remind you it doesn’t want to leave its cozy nest as 500,000 mini Molex connectors snag on wires and other facets of the interior of the frame while you try to lift it free like some cruel Chinese puzzle, and you’ll start to consider replacing some of the fish hooks in your tackle box with these connectors.
- Reassembly is the reverse of the above. Take pictures of connections prior to disconnecting if that’s helpful, or get some blue masking tape and a Sharpie and label as you disconnect them. You don’t have to know what they all are, just come up with your own numbering or naming scheme. The blue tape is also great for wrapping around a bleeding knuckle because #%!$&@ it’s tight in there and there’s sharp stuff. Also have confidence that, assuming you’re only removing one module at a time, you can refer to the connections of the installed modules when reconnecting and reinstalling a module you removed.
I never cleaned my master section, how does taking this section apart for cleaning differ from the rest of the channel banks.
It comes out the same way as the input channel modules, but, yes, it’s a double-wide module and so there are 4 mounting screws at the top and four at the bottom, and more connectors. Take pictures. The master section is a mashup of horizontal and vertical boards. And you just have to start stumbling through what to unplug/remove/disassemble to access what you want to get to. The monitor mixer PCBs are vertical, but they are buried above a large horizontal PCB. It’s not the easiest thing but it’s not terrible either. IIRC the main boards are held by two screws at one end and the other end they’re mounted on a hinge so you may be able to keep things semi-assembled to get to the monitor mixer boards…remove two screws and tip the big board up and semi out of the way, but it’ll fight you as a result of the connections and wiring…you mostly want to get to the monitor mixer boards right? To clean the pots? But I wouldn’t hassle with that unless you *know* they are dirty. If they have a lot of skritchies it may be time to recap. A lot of times that’s where the skritchies come from is DC present in the signal path because of failed coupling caps.
If you end up trying this and something breaks, I do have, I think, most of the master section PCB assemblies in storage.
[/QUOTE]I've noticed this console has a test oscillator and I've been using it to put out 0vu on my program bus meter…I set the interface preamp gain until it reads -18dbfs. I'm a bit confused if this is the right way to calibrate. I read the 0vu is -18dbfs, but isn't that at +4dbu? And if the output of the program busses is -10dBV how does this effect calibration.[/QUOTE]
What are you trying to calibrate? Your DAW interface? I’ve never done anything like that. Your console meters are going to help you see if you are overloading your summing amps in the groups. Does your DAW have input meters? Run your program material and set the trims on the interface for good signal without clipping. Done. dBu and dBv measure or reference something completely different than dbfs. They are entirely apples and oranges. So there’s not an equivalent conversion, it’s based on the operating level of the converter and its capabilities. You can feed tone to your PGM group outputs and push the level to see where your DAW inputs clip…I don’t know what interface you have but it should have some way of monitoring if you are overloading the analog input amp and then decent DAW software has a way to monitor the post AD conversion input signal for level. Just figure out what level on the VU meters corresponds to clipping on the analog front-end of the interface as well as the AD converted signal if you want, but at the end of the day that won’t equate to clipping levels of program material because program peaks are not steady sinus tones. I always set levels on the interface and DAW software based on the program content I’ll be recording. Does that help at all?
) that shoestring and deoxit usually brings it around. My recordings on both my 2 track and 16 track are quiet and clear. I’d love to better understand what you are hearing so I can keep a notice of it if it pops up and then hope that a fix is in these threads.