I think I’ve posted these instructions elsewhere in this thread…but to get the 4-channel groups of input channels out of the frame you:
1. Remove the screws that run along the front of the meter bridge from left to right…the ones below the meters and right above the input strips and master section. With these removed you can tip the meter bridge back exposing the top of the sub-chassis for the input channels and the master section, as well as the wiring that connects the input channels to the backplane.
2. Now remove trim strip that runs in between the wrist rest and the input channel and master section modules…the one that has the channel numbers on it. You’ll see there are some screws that fasten that trim strip to the frame. With that removed you’ll see the bottom of the sub-chassis for the input channels and master section are now exposed.
3. For the input channel module you want to remove from the frame, remove the four screws that fasten the module sub-chassis to the console frame, two at the top and two at the bottom of the sub-chassis. You’ll see them. These are the two pairs of screws that were exposed when you tipped the meter bridge back and removed the trim strip. The module is now unmounted, but before you can remove it from the chassis you have to…
4. Unplug everything. This includes all the plugs for the module you are removing that connect it to the backplane and IIRC there are also two larger plugs that connect the module to the adjacent module. It’s been too long since I’ve done this on an M-500 console so I can’t remember the detail, and my spare M-500 input and master section modules (I have enough to make an M-512…I don’t know why I have these anymore…) are semi-buried in the attic somewhere, and it’s faster to type this than go on an archeological-like dig to get to the spares. What I really wanted to do was exhume those spares and do another video sort of demonstrating this process, but without the console frame. Anyway, I *think* if you unplug everything at the backplane, you can then tip the module up at the rear and access the connections that join the module to any adjacent modules. Once those connections are unplugged you can remove the module completely from the frame. It’s possible I’m missing a step. But hopefully that’s enough info to carry you through. The plugs, a mini Molex type connector, have a little retaining tab…just look at them…you’ll see what I mean. Often you can gently rock the plug away from the side of the connection with the retaining tab and then unplug the plug with a gentle rocking motion while pulling. Again, be gentle. It’s not like eggshell fragile, but you don’t want to be a gorilla about it either. The concern here is the solder joints of the jack to which the plug is connected on those backplane jack PCBs. So just take some reasonable care not to be a muscle head about it. If you need to you may be able to, in most cases, slip the tip of a small flat-blade screwdriver or better yet a small plastic spudger in between the plug housing and the retaining tab, effectively separating the two and making it easier to unplug the plug…or you may even be able to lift the tab away from the plug housing with the finger or thumbnail of one hand while grasping and gently rocking/pulling a plug with the other hand. I usually use a mix of all of these techniques when disassembling a bunch of these connections. IIRC they are all color coded and have varying pin counts, so it’s relatively easy to put the connections back together correctly, just make note the connections are in rows that correspond to the channel and it’s jacks, and there is nothing wrong with taking lots of pictures and labeling connections with blue masking tape and a sharpie or whatever.
5. Now you have to disassemble the module to get the one channel PCB out that needs serviced. The first step to this is getting the beige dress label free of the sub-chassis. Remove all the knobs, remove the two screws that fasten each of the four faders to the module (8 screws total)…the faders will fall free of the module chassis, hanging by their wires. You can unplug them from their respective channel PCBs…you should be able to get to those 3-pin connectors. No need to label…the faders are all identical and can be reconnected to any channel PCB in any order. Be aware each fader has two screws and likely a small toothed washer on the underside, between the fader body and the sub-chassis. As you remove the faders these may fall free or they may be stuck to the rubber dust shield. But they’ll be there somewhere and you want to be aware of this so you don’t loose them, because they need to be there when you put the faders back in.
6. Now that the faders our removed and the knobs are all removed, there are two more small screws that fasten the dress panel to the sub-chassis, you’ll see them along the center line of the panel, one down toward the faders and the other up toward the input TRIM pots. Remove those two screws and you should be able to lift the dress panel free of the sub-chassis.
7. Look at the underside of the module. You’ll see each PCB is connected to its adjacent PCB by at least a couple (can’t recall exactly how many) larger connectors and cabling, just like what you had to disconnect from the adjacent modules when removing the module from the frame. Identify the specific PCB you want to remove from the module and disconnect any connectors from it and/or the adjacent PCB so there are no connections terminated that will prevent the PCB from being removed from the module assembly.
8. Turn the module back over so you are looking at the control surface again. With the dress panel removed, you will now see all the pot shafts and pot nuts. Remove all the pot nuts for the PCB you want to service. I think there may also be a screw or two to remove, like up by the source select, phase and pad switches, and maybe a couple other places? You’ll see them. Once those screws are removed and the pot nuts are removed, the PCB should be free of the module.
Do the steps in reverse to reassemble.
This should apply to the M-520, M-512 and M-50.
This is all from memory so forgive me if I missed a step or two.
Yes, it’s a little bit of a PITA, but it’s not too terrible. But recounting these steps makes me appreciate my Studer console…each channel is an individual module, connected to a motherboard via high quality PCB-mounted “eurocard” connectors with gold-plated pins. Loosen the two captive screws that fasten the module to the console frame, slip the two module pullers under each screw, gently rock and pull upward, the module pops out, disconnect the ground wire plug and the module is out for service; both sides of the PCB are fully exposed. I can get a module out in about 15 seconds. Reinstalling takes even less time.
But hopefully you don’t have to do this very often, and I appreciate the tilt-back meter bridge concept on the M-500 series consoles…makes it super easy to get to the jack PCBs and backplane connections. I think with all the tools handy one, with practice, can get an individual PCB out of an input channel module of an M-500 series console in about 15 minutes.