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The Yamaha C1 music computer is the daddy of MIDI sequencing from the early 90s..
Released in 1989, it was a stupid amount of money, but had 8 MIDI OUT ports, SMPTE on-board, and ran Voyetra Sequencer+ software with a full 128 MIDI channels
available.
The machine is CGA, 10Mhz 80286, and came with twin floppies or a 20mb Hard drive.
I have had 4 of them in my time. The first was a USA twin floppy, with a broken screen, my first purchase on eBay back in the 90s.
It exploded one morning when it had 230v shoved into it. I had it booting from floppy and mounting a Zip100 disk. It worked. So what.
The second one i found online in a GOODWILL in the USA. It went missing in shipping, and i got refunded.
The most recent 2 came from the UK eBay. Both 20mb HDD versions.
I have started working on one.
the service manual is here - https://archive.org/details/MusicComputerC1 and here - https://www.lo-tech.co.uk/wiki/Lo-te...er_IDE_Adapter
It's nice, just a little bit useless for some things. Parts list, yes, and layout, yes, and how to take it apart, yes!
C1mobo.jpg
So, right away You need to remove and replace the 9 metallic green 47uf/25v capacitors on the motherboard. They will all have leaked, and will smell of fish.
It will not be easy getting them to come out, prepare for anger. I'll leave that to You to work out. Best of luck.
Around each of these will be damage. You will likely be able to patch the broken traces on the top or underside of the motherboard, except for the ones near
the expansion slot, which are pointless to repair as there are no compatible devices for this slot. So. Don't fret. Making all these tracks good again will be
helped by the layout diagram in the service manual.
C1leakycap.jpg
I went ahead an removed some of the other caps - the 220uf etc., and they were still fine, so, your call on them.
Now, to the issue that will kill your secret plans to revive one: The fuc*ing power supply.
It's a Nichicon, 87P-50(E) ZSNK730HA. Nichicon used to make power supplies in the 1970s and 80s. They appear to have no record of these anywhere. Mine is
fuc*ed. The fan does not come on, and there appears to be only about 150VAC floating about the primary section. I detest early switch mode power supplies, and
i have no luck rebuilding them, apart form the one on my O.G. Arp 2083, which was a doozy.
The service manual has a parts manifest for the PSU, but no diagram, no real details. No, this is best replaced with a known working alternative. Much less
brain damage.
We need to know what voltages to offer the machine.
So, looking from the front of the machine, the white lead with 9 pins connects the PSU with the motherboard. All the devices in the system get their power via
the motherboard.
Yes, you read that right. -24v on pin 6! We know this because that pin is fed by the output pin of a Panasonic AN79M24F Series Regulator. This is a -24V
regulator, capable of pushing about 500ma. This leads to the riser that the screen/top case connects to, and is likely used to power the invertor that drives
the LCD screen backlight. elsewhere in the PSU we find the -12v version of this panasonic part, and this traces to the -12 pin on the bus, and on to a
regulator on the far left of the board that makes -9v. We can also confirm +12v as it's used to power the fan in the PSU. +5v can be traced to the 80287 slot,
and the +5v pin there. So. All voltages are identified
You can go ahead and try to find an off-the-shelf PSU that will do 5,12,-12 and -24v from house voltage, and if you can find one at all/cheap, and it will fit in the
space vacated by the original one, then go for it.
Meanwhile in the real world, there is nothing of the sort available that i can find in a single unit. You need to treat the -24v as it's own problem.
We know from the spec sheets of the -12v and -24 Regulators in the stock PSU that both lines are rated for 500ma, so, a +/-5 and +/-12 PSU like a Mean Well
RPT-60B, is about 35eu new, and it will provide the required 500ma on the -12v line, with 4.4a on the +5v and 2.2a on the +12v line. It's also small enough to
fit in the bay, with about half the space left free, while avoiding the mains input and power switch stuff.
Making -24v can be done 2 ways. Add in a second PSU just doing the 24v, and reverse the polarity on the output - THIS ONE looks nice - or, You can just 'buck convert' from the 12/5v PSU, with a "TRACOPOWER TEN 40E DC-DC Converter, ±24V dc/ 833mA Output, 9 → 18 V dc Input, 40W" DC-DC convertor, Mfr. Part No.:
TEN 40-1225E. It's not cheap - about 60euro, but i have used these in RF-sensitive equipment, and they are invisible when correctly deployed. This will accept 12v from Your basic PSU and bump it up to +/-24v at up to 866ma. You need to pay attention to the application notes for this unit,
as it needs a little work to make it interference-proof: http://www.tracopower.com/overview/ten40e - basically a couple of caps and a dual inductor need to be used to avoid it being a
source of random buzzing noises in your studio. No big deal. The Dual Inductor TCK-177 they spec is a touch pricey, and always in short supply, but you can try an alternative
with almost the same ratings: The KEMET 500 μH 15 A Common Mode Choke 8mΩ Mfr. Part No.:
SC-15-05J - this is basically a dual coil inductor, and is very close to the one mentioned by TRACO in their notes, and available in small numbers.
You can of coarse just use The TEN 40E straight, with no noise suppression if that suits You. I would not though. If You have come this far, do it right. These things (especially the many you will find on Amazon) are 'square wave PWM choppers' and generate nasty electrical noise while doing their jobs. The less You pay, the more noise/buzz/crackle You will endure, and the more risk of burning your shack down.
So, total price for a NEW power supply made this way is about 90euro, less, if like me, you had a +/-5v,+/-12v PSU lying about. I have a few actually, as
my Emulator IV was eating them for a while, until i worked out it was the Molex connectors that sucked, and the Flash RAM stick needed cleaning and
re-seating.. DOH!
Also, You can try just ignoring the -24v if You intend using the C1 with an external display. The output is CGA, 640. You can find a convertor to make this VGA
here: https://www.aliexpress.com/item/33059176013.html about 40euro landed. Just set the dipswitches at the rear to enable the external display and work away.
So, this is a W.I.P. for me.
Caps are done, tracks all repaired - next is power supply build - i have the Basic 5/12/-12 unit, waiting for the Traco +/-24v device, then We can see if I am wasting my time on this unit.
Released in 1989, it was a stupid amount of money, but had 8 MIDI OUT ports, SMPTE on-board, and ran Voyetra Sequencer+ software with a full 128 MIDI channels
available.
The machine is CGA, 10Mhz 80286, and came with twin floppies or a 20mb Hard drive.
I have had 4 of them in my time. The first was a USA twin floppy, with a broken screen, my first purchase on eBay back in the 90s.
It exploded one morning when it had 230v shoved into it. I had it booting from floppy and mounting a Zip100 disk. It worked. So what.
The second one i found online in a GOODWILL in the USA. It went missing in shipping, and i got refunded.
The most recent 2 came from the UK eBay. Both 20mb HDD versions.
I have started working on one.
the service manual is here - https://archive.org/details/MusicComputerC1 and here - https://www.lo-tech.co.uk/wiki/Lo-te...er_IDE_Adapter
It's nice, just a little bit useless for some things. Parts list, yes, and layout, yes, and how to take it apart, yes!
C1mobo.jpg
So, right away You need to remove and replace the 9 metallic green 47uf/25v capacitors on the motherboard. They will all have leaked, and will smell of fish.
It will not be easy getting them to come out, prepare for anger. I'll leave that to You to work out. Best of luck.
Around each of these will be damage. You will likely be able to patch the broken traces on the top or underside of the motherboard, except for the ones near
the expansion slot, which are pointless to repair as there are no compatible devices for this slot. So. Don't fret. Making all these tracks good again will be
helped by the layout diagram in the service manual.
C1leakycap.jpg
I went ahead an removed some of the other caps - the 220uf etc., and they were still fine, so, your call on them.
Now, to the issue that will kill your secret plans to revive one: The fuc*ing power supply.
It's a Nichicon, 87P-50(E) ZSNK730HA. Nichicon used to make power supplies in the 1970s and 80s. They appear to have no record of these anywhere. Mine is
fuc*ed. The fan does not come on, and there appears to be only about 150VAC floating about the primary section. I detest early switch mode power supplies, and
i have no luck rebuilding them, apart form the one on my O.G. Arp 2083, which was a doozy.
The service manual has a parts manifest for the PSU, but no diagram, no real details. No, this is best replaced with a known working alternative. Much less
brain damage.
We need to know what voltages to offer the machine.
So, looking from the front of the machine, the white lead with 9 pins connects the PSU with the motherboard. All the devices in the system get their power via
the motherboard.
From left to right, pin 9 to pin 1:
COM +12V COM -24V -12V COM COM +5V +5V
COM +12V COM -24V -12V COM COM +5V +5V
Yes, you read that right. -24v on pin 6! We know this because that pin is fed by the output pin of a Panasonic AN79M24F Series Regulator. This is a -24V
regulator, capable of pushing about 500ma. This leads to the riser that the screen/top case connects to, and is likely used to power the invertor that drives
the LCD screen backlight. elsewhere in the PSU we find the -12v version of this panasonic part, and this traces to the -12 pin on the bus, and on to a
regulator on the far left of the board that makes -9v. We can also confirm +12v as it's used to power the fan in the PSU. +5v can be traced to the 80287 slot,
and the +5v pin there. So. All voltages are identified
You can go ahead and try to find an off-the-shelf PSU that will do 5,12,-12 and -24v from house voltage, and if you can find one at all/cheap, and it will fit in the
space vacated by the original one, then go for it.
Meanwhile in the real world, there is nothing of the sort available that i can find in a single unit. You need to treat the -24v as it's own problem.
We know from the spec sheets of the -12v and -24 Regulators in the stock PSU that both lines are rated for 500ma, so, a +/-5 and +/-12 PSU like a Mean Well
RPT-60B, is about 35eu new, and it will provide the required 500ma on the -12v line, with 4.4a on the +5v and 2.2a on the +12v line. It's also small enough to
fit in the bay, with about half the space left free, while avoiding the mains input and power switch stuff.
Making -24v can be done 2 ways. Add in a second PSU just doing the 24v, and reverse the polarity on the output - THIS ONE looks nice - or, You can just 'buck convert' from the 12/5v PSU, with a "TRACOPOWER TEN 40E DC-DC Converter, ±24V dc/ 833mA Output, 9 → 18 V dc Input, 40W" DC-DC convertor, Mfr. Part No.:
TEN 40-1225E. It's not cheap - about 60euro, but i have used these in RF-sensitive equipment, and they are invisible when correctly deployed. This will accept 12v from Your basic PSU and bump it up to +/-24v at up to 866ma. You need to pay attention to the application notes for this unit,
as it needs a little work to make it interference-proof: http://www.tracopower.com/overview/ten40e - basically a couple of caps and a dual inductor need to be used to avoid it being a
source of random buzzing noises in your studio. No big deal. The Dual Inductor TCK-177 they spec is a touch pricey, and always in short supply, but you can try an alternative
with almost the same ratings: The KEMET 500 μH 15 A Common Mode Choke 8mΩ Mfr. Part No.:
SC-15-05J - this is basically a dual coil inductor, and is very close to the one mentioned by TRACO in their notes, and available in small numbers.
You can of coarse just use The TEN 40E straight, with no noise suppression if that suits You. I would not though. If You have come this far, do it right. These things (especially the many you will find on Amazon) are 'square wave PWM choppers' and generate nasty electrical noise while doing their jobs. The less You pay, the more noise/buzz/crackle You will endure, and the more risk of burning your shack down.
So, total price for a NEW power supply made this way is about 90euro, less, if like me, you had a +/-5v,+/-12v PSU lying about. I have a few actually, as
my Emulator IV was eating them for a while, until i worked out it was the Molex connectors that sucked, and the Flash RAM stick needed cleaning and
re-seating.. DOH!
Also, You can try just ignoring the -24v if You intend using the C1 with an external display. The output is CGA, 640. You can find a convertor to make this VGA
here: https://www.aliexpress.com/item/33059176013.html about 40euro landed. Just set the dipswitches at the rear to enable the external display and work away.
So, this is a W.I.P. for me.
Caps are done, tracks all repaired - next is power supply build - i have the Basic 5/12/-12 unit, waiting for the Traco +/-24v device, then We can see if I am wasting my time on this unit.
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