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Michael Kukat
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We have only one cloud here above the Roßberg at the moment...


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After the rain

Taken some minutes ago. It wasn't much rain but we have wonderful rainbows recently :)

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Moonrise, yesterday evening in Gomaringen, South Germany.
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The Teisco S-100P

Also sold under the Kawai brand as 100P.

A friend recently bought this thing and asked me to check it to make sure everything is okay. I smiled when i heard the price for this 1-VCO presets-only synth, but okay, the current prices for vintage analog synths simply are crazy.

But okay, on the other side, he isn't someone tweaking sounds, he just needs good sounding instruments to make music with. And during the final check i was seriously impressed about this little toy. It sounds so beautiful, likely owed to the VCF, which looks "a bit" familiar. Together with portamento, glissando and aftertouch (yep, aftertouch. 1979!), it's real fun to play on this little synth. By the way - the ARP patent mentioned on the bottom is for exactly this aftertouch feature.

I didn't have much work with this, it's in a great cosmetic shape, i just cleaned it a bit, bent some sliders and switches back to their original shape, cleaned the potentiometers, sliders and switches in the control panel on the left and did some fine adjustments among the keyboard control because the glissando kept switching between 2 steps at the end for some notes. Looks like someone replaced a 741 in it and didn't adjust the offset afterwards. It's in perfect tune again now and the rest of the settings stays untouched, it sounds great as it is.

No leaking capacitors, even the ones in the PSU are still okay, works like on the first day - after more than 35 years. Another proof that electronics started to become crap in the 1980s. The amount of problems with stuff from the 1960s and 1970s is very low compared to the mid 1980s until the end of the century. Not even talking about 21st century crap.

The interesting thing on this is the presets PCB. That's a large array of diodes and resistors, technically spitting out 15 digital control signals and 12 control voltages. If i ever own such a synth, it won't take long to add MIDI in exactly this place. The nice sound of this synth, combined with full editing capability via MIDI, that would be really nice.
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Korg DW-8000 "Version E" maintenance

This is the second time i have this special variant of the Korg DW-8000 on the desk. It's quite rare and even when the sheet of paper that came with it states that it's done by Korg Vertrieb Marburg, it's not a modification invented by Korg.

From the user's perspective, this modification adds an ultra-ugly button (named "Enter" for no obvious reason) and a LED to the front panel. There also is an input at the rear to feed external signals into the DW-8000's digital delay.
The button toggles the state of the LED and internally switches between 2 banks of wave ROMs and program RAM. This time there was a bit more work necessary to keep this nice oldie alive for hopefully some more decades, so i used that time to have a closer look at this modification.

It didn't take long to find out everything about it:
- The button, together with 2 inverters of the 4049 plus some resistors and capacitors, provides the toggle function. The circuit also makes sure it powers up "off", but can also power up "on", if the button is hold during power up.
- The 7432 and more inverters of the 4049 plus some wires from the main board generate the select signals for the 2 6116 SRAMs and the 2 banks of wave ROMs
- The new waves are on a separate PCB, in a bunch of 27256s, which plugs into the place where one of the 4 original wave ROMs was, this wave ROM moved to the new PCB also, a new 74139 is there for the select signals, one main board trace (or better IC pin) is cut to support this
- The battery back up control for the second 6116 replicates the circuitry of the main board, which is still used (after cutting another trace) for the first 6116

So all in all, this doesn't look very nice and obviously, this modification never had a cable tie or anything else to keep the "RAM board" in place, so a common problem is that it falls out of the socket. And if you want to replace the battery, you need to pull it off anyway and lose all your sounds if you didn't back them up. Maybe this is the reason why the factory presets for this modification seem to be totally unobtainable. Not sure how many synth techs care about backing up RAM contents on machines they have for repair, and many musicians also might not care too much about maintaining backups for all their synths. But at least i'm not guilty for the loss of the sounds, they were already gone and the memory was filled with garbage, crashing the machine, which was the main reason why a friend asked me to have a look at it.

The modification has been invented by a company named "PA-Decoder", which is out of business since a long time and made similar modifications for other synths also. The PCBs and the soldering is very much hobbyist quality and all in all, i decided to clean up all this mess to improve reliability. I wondered why they didn't it the way i did it now in the first place, but then i had a look at a 1988 electronics catalogue. The 27512 necessary for this was 37 DM back then, the 27256 13 DM. And this thing is from 1985, the difference might be even bigger then. Or maybe 27512s were not even available back then?

Anyway, we have 2017 now and i have lots of old EPROMs, the most of them are 27512. And i also have 6264 low power variants. And i wanted to have all the wave ROM contents for my archive anyway, so i unsoldered the 3 remaining wave ROMs also, read their contents, had to unsolder the 4 EPROMs from the expansion board because there was something wrong that kept me from reading them with the whole board, but at the end, i had all the 8 wave ROM images and could glue them together into 4 new 27512s. Pin 1 of their places on the main board was not connected, so i didn't need to cut a trace but just create a new one. After replacing the battery with a CR2032 holder, i even got a free hole where i could bring my new address line to the upper side of the main board, where it joins an address line of the SRAM. Some wire origami patched the pinout of the SRAM to fit into the 6116 socket, and i even have another address line free to add another 2 banks. But for now, only half of the 6264 is used.

As i removed the control board completely, i had to replicate the toggle button functionality. I had no 4049 around (okay, one from 1975 :), so i experimented a bit and came to a simple circuit using MOSFETs for this, that ended on a small piece of veroboard. After i put everything together, i was a bit confused that this thing reliably starts up in the "on" position instead of "off" and needed a moment to realize whats going on there. I assume, the 5V rises too slow, so the circuit doesn't work as intended, not giving enough voltage through the LED plus resistor for a clean power-up. I just added another 4.7K resistor between left transistor's D and the +5V and everything worked as expected.

Besides this modification stuff, i upgraded the OS, it was a very early machine with version 9, now it has the last version 12, and i removed some rust and dirt.

By the way - i assume Enter buttons were a special offer at that time, because there really is no other reason to label a bank switch button this way :)
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They make different synthesizers over there in Russia...

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Sunday hardware puzzle - DEC RWZ01-AA

Since more than a decade, i have two of those drives around. And lots of MO disks from the times where i had a HP 200t MO library at home. So i wanted to check those drives and play a bit with them.

Just powering them up and inserting a medium wasn't very successful, so i did some minor work on the mechanics a while ago already. Still no success in detecting the medium.

Since yesterday evening, i wanted to have a second look and finally repair those drives. After replacing a leaking SMD capacitor and carefully analyzing what the problem could be, my assumption was that this one doesn't "see" the medium because it spins up and down again, repeating this for several times. More success with the other drive, i could even read some data there with 128KB/s already (should be a bit more, like 680KB/s) but it also is very unstable.

But back to this one. I also noticed a light "smell of current", something seems to get warm in there. So i complete disassembled it. And i really mean completely, because i wanted to clean and lubricate the mechanics for the optical head and the optics itself. And down to the (nearly) deepest level into this, i found the root cause of the problem and maybe also the source of the smell - the tracking coils are fried.

Too bad, but this one is a write-off :( I hope, i have more luck with the other one, will check if the lens still moves freely there, otherwise, i can just put it back together and throw it into the attic. Need to find a way to erase all the media i have before giving them away then.

But while i have it disassembled that far, i can also do the rest and have a closer look at what's underneath all those covers around the optical head. First, we've seen the lens assembly. This is very similar to what you find in a CD player, a lens that can be moved up and down for focusing and horizontally for tracking. Today's CD player mechanics for this are a bit simpler, but here you can clearly see how it works. The large coil around the lens is for focusing and can lift the whole thing within the lens assembly. The two burned coils are there for tracking and can rotate the part within the assembly. This is not an exact linear motion of the head, but totally enough for the purpose.

This lens assembly sits on the optical head with the lens floating above a prism, that is also visible in the photos. I didn't dive deeper into this but you can see 2 photodetectors, maybe one is for focus/tracking and the other for reading data, i don't know exactly. The laser is hidden, you just see the small board where i assume it. And then, there is not just a large amount of electronics within the head, but also many, many trimpots. If this thing ever goes out of adjustment, it might be very hard to get it back to working condition. In the same way, it might also be a problem to replace parts of the head - like this lens assembly that needs replacement. And then, this lens assembly also needs adjustment, at least it can moved on the optical head.

The rest of the unit is not so spectacular, the load mechanics are interesting because there are two levers to open the medium shutter, which can only move in one direction. One is for side A, one for side B. On top of this, there is the large rotatable magnet that's responsible for writing to the medium, it flips very small magnets in the medium if that area is heated up by the laser.

On top and bottom there are 2 PCBs controlling all the mechanics and providing a semi-dumb modified ESDI interface. The SCSI interface available at the rear of the unit comes from a third board, which is the ESDI controller of the whole unit.

Sorry for the totally unsorted photos, but the photo upload in the new, ultra-crappy, annoying, unusable g+ interface is the most stinking bullshit that could happen to g+. Trying to sort them after posting or at least adding come comments.
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Moonrise in Gomaringen, South Germany

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Carpenter Bee

while having a closer look at the clouds out there, i found something more interesting :)

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Yesterday's full moon rising

I saw this by chance yesterday evening when i passed the patio door and was quick enough to grab the camera and the 300mm lens.
I miss most of those moments or don't get the camera ready quick enough, but this time it worked fine :)
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