Lowrey Micro Genie V-100
Polyphonic Preset Synth / Portable Organ
The Lowrey Micro Genie V-100 is a portable keyboard introduced in 1982 and produced until 1987 (the latter date according to usedprice.com). Other members of the Micro Genie series include the V-60, V-101 (very similar except for cosmetic changes), V-105, V-125, and so on, all of which are basically modified JVC KB-series instruments (as will be explained shortly). This article was originally posted on my old website "JCS", but since then, I've largely re-written it, added more information, and increased the image thumbnail quality.
The V-100 is not really a Lowrey instrument. Rather, it was made by the Victor Company of Japan (i.e. JVC), being a rebranded version of the JVC KB-500 with only slight modifications. Cosmetic differences include changes to the text wording (e.g. the "Mach 3" sequencer section was originally called "Compucorder"), and different plastic colors (e.g. the black side pieces of the top case were white on the KB-500, and the preset buttons were changed to red from the KB-500's blue). Functionally speaking, there might be a difference in the way the accompaniment recognizes chord fingerings, but I'm not sure—I've only read it. I don't know of any other differences. Also, besides the V-100, Lowrey marketed at least eight other keyboards modified from JVC KB-series instruments—see here for a list.
Now for a bit of semantics. Lowrey called the V-100 a "portable organ". I don't find this to be a good description, given that it is preset-based, with only two "organ" voices, neither of which are especially exciting. The focus is clearly not on generating organ sounds. Of course, both home and portable organs of the time also usually had some preset, auto-accompaniment, and rhythm functions built in, but these were auxiliary to the generation of versatile organ sounds (by selectively combining different registers/stops, adding vibrato, and so on).
More accurately, the V-100 is a polyphonic preset-based synthesizer, with rhythm and auto-accompaniment features. There are 10 presets selectable by pop-out buttons, which can be combined (sort of) if you release the buttons simultaneously. Synthesis is digitally-controlled "semi-analog": generation of the basic pitched tones is done by a custom JVC "programmable tone synthesizer" chip (which uses both analog and digital circuitry, as will be explained), controlled by a microcontroller. External analog circuitry filters and shapes these basic signals into the various preset voices, as well as the music-chord/genie, arpeggio, and bass signals. As well, there are analog drum sound generator circuits (made with simple op-amps, gates, and discrete transistors), which are triggered by the same microcontroller system that controls the synth chip. More on all this in the "Hardware" section below.
Since it was not available online, I purchased a copy of the service manual on eBay (which turned out to have water damage) and scanned it. The high-quality scan can be downloaded here, and a compressed version here. This manual is extremely detailed and well-written, giving pretty good descriptions of every circuit, a block diagram, full schematics (very well drawn), and so on.
This instrument took some time to fix, due to its poor physical condition, and the use of a bad batch of electrolytic capacitors. Every fault was basically mechanical—no interesting electronic diagnostics this time, I'm afraid.
To give some background, this V-100 was picked up in April 2015 at Lazaro's Music (the best shop in Edmonton for vintage equipment), where it had been stored almost inaccessible among a pile of other things. I had passed it over at least three times before, thinking it was another modern cheap plastic digital unit—with its plain black plastic case, it does look the part from a distance. However, upon closer inspection, I realized it was an older semi-analog instrument. After testing it and noting multiple problems, I negotiated a reasonable price, and took it home (on the city bus, yet nobody seemed to notice!) These initial problems were:
As well, the original stand was (and still is) missing, which would have attached to the eight threaded mounting points in the bottom. Two other parts are also missing: the transparent plastic music stand / dust cover, and the battery cover. I am still looking for these, so if you have spares, please contact me. But of course, they are not necessary, given that I have other stands, don't use it with batteries, and don't usually read music. In any case, here are pictures of the instrument pre-repair:
The first things repaired were the non-sounding keys, all caused by dirty keyswitch contacts. I started by dissassembling the instrument to the point of removing the keyswitch board, called the "MKM Ass'y." It is an unusual design of the transitional '80s: a rubber dome-switch keyboard where each switch is a discrete component, similar to a 12 x 12 mm tactile switch. As you may know, dome switch keyboards usually use a board (sometimes split) with the contacts printed directly on the board, and rubber/silicone membranes with many integrated domes. Of course, this makes the parts more specialized (resulting in poorer parts availability), and the integration means that if one section fails, then the whole thing may require replacement (unless you can "graft" on new domes, or new PCB contacts, for example).
So, although I appreciate the discrete dome switches because they are individually replaceable, I have not found a source of replacements. And indeed, I did not have to replace any, since they can be cleaned. While the contacts cannot be directly cleaned without surgically removing the domes, they can be "indirectly" cleaned by applying spray contact cleaner to every switch along the edges of the domes, so that it seeps onto the contacts inside, and then massaging the domes for about a minute each. With four fingers, four can be massaged at a time. On my unit, this process fixed all but one especially dirty switch, which I had to re-clean and re-massage. I should also mention that when I did this back in 2015, MG Chemicals' contact cleaner with silicone was used, but today I would instead use MG Chemicals Electrosolve, which is nearly the same except without silicone (which is unnecessary in this case). All keys still work perfectly as of January 2019.
A fellow in Ukraine known as T-150 (who also provided the tone generator chip datasheet for the Kawai KMA-37) sent me the photo below, showing the inside of a dome switch. It appears that the dome itself has a carbon-infused disc as expected, but the fixed contacts are small metal dimples, rather than the usual printed carbon traces. This probably explains why the switches age the way they do — the metal contact surface (which I'm guessing is silver, nickel, or some alloy) oxidizes, whereas the usual carbon contacts do not oxidize, though they can become contaminated, causing similar contact issues.
I also cleaned all of the switches, first with contact cleaner with silicone (in 2015), and again with Electrosolve (in late 2018). While this helps in the short term, each time they have returned to being intermittent/scratchy (especially the preset switches, probably indicating physical wear besides dirtiness), and I haven't found suitable replacements. Lowrey gives the part number of the effect & preset switch assembly as 460-034836-000 in the SM, which brings no useful search results. Oh well, they are still usable.
As for the two sideways keys, broken plastic at the pivot points near the back was the cause. Thankfully, the snapped-off chunks were still inside the instrument! Another key—the D directly beside the broken D#—was just starting to crack at the same point, so this was also repaired in the same way. In order to remove the keys, the entire keyboard assembly had to be removed from the rest of the case, by means of removing various screws. I was able to figure it out on my own, but there are instructions in the service manual if you have difficulty. Here are the C and D keys prior to repair:
A little bit of thin cyanoacrylate glue did the trick.
Having the keyboard disassembled made for a good opportunity to clean the filthy keys and keybed.
Another plastic repair was this broken mounting post, which was one of four attaching the back of the metal keyboard frame to the top plastic piece. This was also repaired with cyanoacrylate glue, once the keyboard assembly had been reattached to the top section.
At this point, the instrument was completely functional, but...
Every 220µF 10V and 10µF 25V electrolytic capacitor had corrosion on one or both leads, due to leakage of the electrolyte. The others of the same series but different values (such as 1µF, 100µF, and 470µF) were all fine. Clearly, these specific values were of a batch with failure-prone rubber seals. If left longer, the electrolyte would've dissolved solder joints and PCB pads, causing functional issues, as I have seen on another device (a Technics SH-8010 equalizer from the same era). Based on the logo, these are Matsushita / Panasonic capacitors, though I'm not sure what the "CE" signifies—I don't think it is the series. In any case, I decided to replace all of the leaky types, which was pretty straightforward; eleven 10µF and eleven 220µF capacitors were replaced, as shown below.
One final note, and that is that initially, I thought the Mach III sequencing/"recording" feature was not working, since I could not get any of the LEDs to respond no matter what I pressed. Only after I received a copy of the service manual did I figure out how this works. Page 8 indicates that the instrument must be in Music Chord mode and with the Auto Start switch pressed, with the rhythm running, and then you can press the Record button, making the record light and one of the channel lights turn on, select the channel, and then play the chord progression and have it recorded.
Let's start with the bottom, on which there is not a whole lot to see. First, notice the eight threaded metal inserts for mounting the unit to the long-gone original stand. Then notice the battery compartment, the cover of which is also long gone. It takes eight D cells, which the service manual states will last only 3 hours at full volume! Note as well that Lowrey made no attempt to hide JVC as the true manufacturer—it is printed right on the label.
Opening it up can be done by the removal of 13 screws on the bottom, instructions for which are in the service manual. The top and bottom halves are then joined only by three cables towards the back, which connect the "Rectifier" board in the bottom to the "Regulator" board in the top. Unless you have a large workspace where the bottom piece will not get in the way, it's best to disconnect these when power is not necessary. Conveniently, there are hand-written numbers on the plugs which match to the socket references. The bottom half doesn't have much mounted to it except for the power supply circuitry and a foil-coated-cardboard ground shield:
Everything else is mounted to the top half. Unlike the largely hollow keyboards of today (e.g. the Yamaha PSR-E413), this unit has almost every bit of free space filled. It containts a remarkable amount of electronics for its size, with 13 circuit boards in total. The two largest and most obvious boards are the "Central Processing System" and "Quality Control" boards (as called in the SM); on the actual boards, they are marked as the "D1 Ass'y" and "AN Ass'y" respectively. These are mounted on a metal bracket on a hinge, which can be moved upwards 90 degrees into servicing position after the removal of four screws.
Another large and obvious board is mounted directly on the top case towards the back. This is Board 3, the "Rhythm Instrumentation" or "RH Ass'y" board.
As for electronics, the V-100 uses an interesting mix of analog and digital circuitry. Virtually all functions capable of being implemented with ICs are done with such. There are three LSI chips, which are a microcontroller (MCU), RAM & I/O chip, and a custom JVC tone generator chip. The rest are mostly 4000 series CMOS logic and various linears (4558 dual op-amp, MN3204 bucket-brigade device, LA4125T power amp, etc.) typical of early 80s designs. All components are through-hole, with all boards being single-sided and made of phenolic paper. Anyway, before continuing, have a look at the block diagram, as presented on page 18 in the service manual:
The MCU chip is an OKI MSM80C49-21RS, which is a CMOS version of the Intel 8049 with 2048 bytes of mask ROM and 128 bytes of RAM. This is supported by an OKI MSM81C55RS (i.e. 81C55), which contains 256 bytes of RAM as well as some I/O circuitry. These do much less than the computer systems in modern digital keyboards, which typically are responsible for the entirety of tone generation through DSP software and prerecorded samples. Rather, in this case, these chips are used for interpreting the keyboard input and some switch settings, triggering the rhythm generating circuits and beat LEDs, providing the Mach III sequencer functionality, and controlling the tone generator chip.
Speaking of which, all sounds except the rhythm and the noise in the flute voice are generated by the 42-pin "Programmable Tone Synthesizer" chip: the JVC VC4050BL shown below, or VC4050BH as specified in the SM. It is the only socketed chip in the unit. It has a basic description on page 12 of the SM, but this is not complete and has some errors / confusing aspects, so I will try to give a better explanation. To start with, the chip contains ten programmable frequency dividers, which divide the 1MHz master oscillator (generated externally) down into the desired pitches, controlled digitally by the MCU. One divider is always allocated to the bass, and another to the arpeggio. The remaining eight are split between the accompaniment chords and the preset voice. In "full keyboard" mode, all eight go to the preset notes. In "genie" mode, four go to the chord notes, and four to the preset notes. In "music chord" mode, only three go to chord notes, while five go to preset notes. The signals from these eight dividers, which I will call the "main" dividers, are further divided to give four octaves (i.e. "footages") of squarewaves: 2', 4', 8', and 16'.
This is where things become uncertain, due to the incomplete description and lack of other information on the chip; however, after some thought, I believe I've figured out how it works. From here, the divided squarewaves are probably combined using appropriate logic circuits to give discrete-time digital approximations of triangle waves (in 4', 8', and 16' footages) and sawtooth waves (in 8' and 16' footages) to serve as basic tones from which the preset voices are formed. These digital signals are fed to internal digital-to-analog converters, which output "stepped" triangle and sawtooth waveforms, as shown on page 40 of the SM, and reproduced below. Note that the steps are as long as a half-cycle of the 2' squarewave, as expected from the design described. Similar techniques are most likely used to generate the chord (8' sawtooth, not triangle as stated on p. 12), arpeggio (4' square, not 8' as stated on p. 21), and bass (8' pulse) waveforms. Note that as also shown on page 40, the bass waveform is a pulsewave of roughly 80% duty cycle, rather than a plain squarewave.
Then, these analog signals are fed to amplifiers with controllable gain. To be specific, these signals include nine footages (2', 4', 8', and 16' squarewaves; 8' and 16' sawtooths; and 4', 8', and 16' triangles) for each of the eight "main" dividers, one footage (4' square) for the arpeggio divider, and two footages (8' and 16' pulse) for the bass divider. As well, one footage (8' sawtooth) is present for each of the four chord notes, but these are probably just from the "main" dividers' 8' sawtooths, simply switched over to the "chord" signal path. As well, while I don't know the exact arrangment of amplifiers, I'm guessing that there must be one amplifier for each footage of each "preset note", giving 9 × 8 = 72 amplifiers (this is the only way I can think of to have both independent footages and separate envelopes for the eight preset notes). Then, one amplifier for the chords (which would take in the summation of 3 or 4 notes, depending on the chord mode), one for the arpeggio, and one for the bass.
These amplifiers are controlled by envelope generators, 11 in total, with external capacitors and control voltages that determine how they behave. The bass, arpeggio, and chords each have one envelope generator, and the remaining eight are for the eight preset notes. There are three important control lines: the "percussion sustain enable" line, the "percussion snub control" line, and the "sustain" line. The percussion sustain enable line enables or disables the envelope decay— it is enabled only on the Piano, Hawaiian Guitar, Harpsichord, and Vibraphone voices, as expected (see page 22). Interestingly, this is controlled digitally through the MCU, as there is no analog control voltage (CV) input; yet, the "percussion snub control" line does have a CV input, and is enabled on the Piano and Harpsichord voices, causing a faster envelope decay. Lastly, the "sustain" line goes to a CV input on the chip, and has short, medium, and long states depending on the selected preset and the sustain button.
Finally, the signals from the amplifiers are summed to their respective footage outputs (e.g. all eight 2' squarewave outputs get summed to pin 42), and go on to be filtered and otherwise processed by external analog circuitry. This ends my description of the tone generator chip—if you have any comments (an especially if you have any datasheet or other info on the chip), please let me know. I emailed JVC to see if they have anything, and they responded in the negative.
The rest of the circuits have good descriptions (or at least the schematics are easy to read) in the SM, so I won't try to explain them here. Check out the vibrato circuits if you get a chance. As well, the rhythm sounds are generated completely seperately from the tone generator chip, with circuits using discrete transistors and op-amp ICs as the active components. This is done on the "RH Ass'y" board shown previously.
I should also point out that while the MSM81C55RS (or equivalent) is still relatively easy to source (being a common non-programmable RAM and I/O chip), the MSM80C49-21RS and VC4050BL chips are virtually impossible to find except inside these instruments, which themselves are now rare. This is because these two chips are custom devices with low production; the MCU might only have been used in this exact model, while the synthesizer chip was probably used only in a few models of JVC keyboards. Even if you source another variant of the 8049 MCU, it will be useless, since it won't have the correct mask ROM. [see insertion below] And JVC's custom tone generator chip is so obscure, I can find absolutely nothing online—no datasheet, and none for sale. Thus, like in all cases where low-volume and programmable ICs are used, the repairability of this instrument is severely limited in the event that either of these chips fail. This is why I prefer discrete designs, or those that use solely common non-programmable ICs. Also, going back to the mask ROM of the MCU, considering that it determines how the chord fingerings work, it would be interesting to know if the KB-500's MCU is truly a different type. If you know, please contact me.
With the help of T-150, I received this interesting information from C. O. Windler of Tablehooters fame. He owns the more advanced JVC KB-700, and provides some info about it, and his sadly unsuccessful efforts trying to dump the ROM of the 8049 CPU. Most importantly, he points out that an 8749 processor (ideally a CMOS version, which I'm not sure exists) should be a drop-in replacement of the 80C49 if programmed with the correctly-dumped ROM data. In his words:
So, if Mr. Windler ever manages to dump the KB-700's data, I will try a similar process on my V-100 CPU (which will have to be desoldered, unlike the KB-700). The challenge is figuring out how test mode works, since the OKI chip apparently does not go into test mode like a real Intel chip. I bet it has a test mode (for checking the mask ROM during manufacture), but more info is needed.
Also, I've added a link to the JVC KB-700 service manual (also thanks to T-150 for finding this), for comparison to the KB-500 / Lowrey V-100. The text descriptions are less detailed than Lowrey's manual, but it still gives full schematics and other useful diagrams and parts lists.
One last interesting thing to note: near the tone synthesizer chip is a 0.047F (i.e. 47,000µF) capacitor that is used to retain the contents of RAM for "up to fourteen days with the organ power turned off," according to the SM. This is the earliest example I've found of a supercapacitor used for memory backup, especially given that mass production of supercapacitors began around 1978—see the History section on Wikipedia's supercapacitor article.
Like many keyboards of the 80s and beyond, the V-100 has a large variety of sounds it can produce. It would take a lot of text to describe all of them, and it would be ambiguous no matter what, so I will skip the description this time. There are already some videos and sound samples of the keyboard online, including on the KB-500 page of the website dedicated to JVC keyboards, a link to which is at the bottom.
|If you notice any errors or have additional information that you would like to add, please contact me!|