Roland MC-8 Sequencer Malfunction w/ Sequential Pro-One Synth

hi this is synth chaser from synth chaser comm and I'm here today with the roland micro composer mc8 which is a early sequencer from roland this preceded the MC for the embassy 8 is a very large and very full-featured sequencer and apparently there weren't very many of them made I'm told around 200 of them were made so this is definitely something that we don't see every day so I thought I'd show my viewers a peek inside this particular MC 8 is having some issues we turn it on it either boots into an error mode so the display is flashing or this time it boots up but it won't take the time bass and tempo parameters it flashes an error there and then sometimes when it boots up it just boots up into garbage I'll see if I can reproduce that for you so here I just turned it on and the displays are just filled with random data so this guy is sick and he needs a little bit of help but it's going to be a challenge because there's no schematic available anywhere that that I can find for this thing and the owner of this device is very knowledgeable about the MCA and its history and and even he hasn't been able to come up with a schematic for it so we're gonna wing it and also base our investigations a little bit on the MC for service notes which are published by roland and available on the internet so let's open this up and have a look so here we've gotten inside and unfortunately it doesn't look like the service notes for the MC 4 looks pretty different so we've got a power supply here we've got a CPU board here we've got this board here which bridges the CPU and the switch matrix and displays so obviously this is some kind of driver for the displays and and processor for the switch matrix for the keypad on the front and there's one board he behind the displays which according the manuals called the timer display board and that's pretty much it underneath this is the transformer so let's take a closer look at each of the boards so here's the power supply and I can see there's five voltage regulators here each one of is marked with the part number that's a fixed voltage regulator so this you a 79 15 is a minus 15 volt regulator there's 70 905 78 15 as a positive 15 volt regulator there's a 78 12 and a 7805 so there's a lot of different power rails here because most likely the RAM that this thing uses is a really primitive Ram that uses actually three different voltages besides ground it uses like a three volt sorry a five volt a 12 volt and a minus five volts so that's why there's all these voltage regulators but kind of the way they're laid out we can kind of see these black wires are going to be ground this pair of blue wires is coming from this 79 15 so we can check the voltages for each of these rails so we know to look for five voltage rails and and what color wire they should be on back here we can see some computer grade capacitors those large can capacitors with screw terminals looks like there's there's one here that you can see but then right behind it there's an even bigger one these are the filter capacitors for the power supply and they appear to be original here's a CPU board and it uses really really old-school chips you can see this 8080 processor is like a white ceramic chip with gold leads it's really really vintage stuff and then there's 20 chips here which have little stickers numbering them 0 to 19 so the little stickers are probably covering window on an erasable ROM probably so these are probably the wrong chips and then these ceramic chips here I'll check the part numbers but these are probably gonna be the RAM chips and then there's a few other TTL logic chips some trimmers down here but not much else and then here's this little board which we think to be the switch matrix and or display driver which comes up here this is the back of the LED displays and then these are the bottoms of the buttons the switches and there's a pot there for for adjusting the tempo so the first thing I'm gonna do is I'm gonna verify all of the power rails so we have five fixed voltage regulators and I should verify all five of them are working okay so I'm going to put my lead here on the ground side and then run down the line first one is that minus fifteen volt regulator or at minus fifteen point O three which is good next one was a 70 905 which is a minus 5 volt and that's good the next one is the plus 15 volt and that's that's acceptable it's not on the nose but with these fixed regulators you can't always get them on the nose next one was the 12 volts so eleven point nine five which is fine and last we have the five volts which is five point zero one three so we are getting all of the correct voltages coming out of the power supply so since we confirm the power supply is okay it looks like power distribution is not going to be an issue either because these wires are soldered to the power supply board and then soldered to each of the boards that that use them so power distribution is not going to be an issue you so the next thing that I'm going to do is I'm going to go through and reseat all the connectors sometimes connectors can be an issue and we'll see if that makes any progress so the connectors were actually gold-plated so they and they look to be in really good condition so the next thing I'm going to do is I'm going to go through and I'm going to just probe some of the key IC chips so we have the CPU here the roms and the RAM up here and I'm gonna probe it with the oscilloscope because this particular set of chips uses three different supplies it uses a 12 volt 5 volt and a negative 5 volt if it were a regular CPU that uses 0 and 5 volt a single 5 volt supply I could get away with this device which is a lot easier to use than the oscilloscope this is a logic probe so I would connect this to my power supply ground and this to my power supply 5 volt and then I could go probe around and it would beep and tell me whether things are high or pulsing or whatnot but I'm going to use the oscilloscope because there's different supplies here and I'm going to go through and I'm going to just verify that I see activity on the data bus that I see the clock all the different supplies and when i probe I'm going to touch the pin of the IC not the pin of the socket because I want to make sure that that the connection is actually good a lot of times these old IC sockets can fail so for example we'll start here with the CPU so this is the address bus PNA 10 there's nothing really happening there we've got the ground the data bus so here's a few pins of data bus type stuff and there's there's activity occurring on the date of us so it looks like things are alive and running down I think we're going to get to the negative five volt supply soon yep so there's a negative five volt supply here's an important one the reset line on a CPU this 8080 processor the reset is non-inverting normally it's it's inverted so you need to have a high reset for the CPU to be running but on the 8080 it's low so this actually is correct and I'm just going to keep running down this is our clock my frequency counter on the oscilloscope says two megahertz so everything is looking pretty good I'll continue down this and then I'll take a sampling of the ROM chips and we'll go from there so the CPU and the roms checked out ok and then I moved on to the RAM and I mentioned I was expecting to see 41:16 ram chips here which are obsolete and archaic chips that are used by the mc4 and listed in their schematic but they're also commonly used and were commonly used in in early 80s arcade games and they use three supply voltages 12 volts 5 volts and negative 5 volts which is the same as the 8080 CPU here but what I actually found was an even more obsolete and archaic chip it's called a UPD 410 and I couldn't even find a data sheet for this Ram chip it's that obsolete but I did find a schematic for some computer peripheral that used that chip so from that I can see that there's 12 bits of address and one date a bit coming out of that so now I can probe this and see if there's signs of life on those chips so as I was working my way around I came to this board and again I'm checking kind of the main chips on each board to see if they're you know receiving and stuff on their data lines and and and now putting what they're supposed to be and this chip kind of caught my eye this is an Intel 8250 3 which is a programmable interval timer and so basically you feed it some some timing information on a date of us and it spits out a clock and when I got to probing it there was no clock coming out of it unfortunately can't show you that since I press the chip and now it seems to be working so since we have a problem with a chip and an icy socket the solution is to replace the socket not just push the chip back in and hope the problem goes away because if you do that it's gonna the problem is going to come back so I've kind of folded that board back and there's some rework there but fortunately the chip that we're changing is here so well that we're changing the socket of not geni other chip so with the chip out I don't know if you're going to be able to see it but there's a huge amount of oxidation on the pins of this chip so I'm gonna clean it up with a fiberglass scratch brush and change the socket as well and here's the socket that I've removed and that you can see in the the right - most pins there's all kinds of crud in there that definitely did not help make a good connection for this chip here's the Intel chip with the pins clean then you have to clean both the outside of the legs and the inside of the legs because it's going to make contact on both sides and you're gonna want that to be clean the pins got a little bent when I pulled it from the socket since it was kind of corroded into place but I straighten them out well enough that I can get it back into the new socket so now that I've changed the socket and cleaned up the chip it's reliably turning on every time I turn it on and we're gonna load up a sequence through the audio jack on the back which takes a computer data file it sounds like an old so we're gonna load it in a sequence through that and then once I've loaded it in I can hit start and it's going to run through at the proper tempo before when he loaded from the file it was kind of going at a snail's pace [Music] [Music] [Laughter] [Music] so hopefully you found this to be an interesting peek inside this very rare sequencer the Micro Composer mc8 from roland and I hope you'll join me by subscribing to my other video so you can see inside other rare and interesting synthesizers this has been synth Jay sir from synth chaser calm thanks for watching have a great day you