Lexicon PCM80 On Fire!

LPT45 Power Supply

Overview One of the downsides of owning vintage synths and FX’s from the 1980’s is that there is a risk of power supply failure, with capacitors emitting magic smoke or worse still bursting into flames. I bought an Emulator I many years ago for just £50 because when we switched it on it created a huge plume of smoke as various capacitors failed.

My approach over the last few years has been to refurbish the power supplies as I acquire the item, because they are usually 30 years old. In my new studio I also have a smoke alarm fitted and never leave items powered on overnight. I have fitted 1U Samson Power Strip PS10’s to supply all the gear, this enables me to turn off the power to all the gear quickly and simply.

Blown Capacitor

A Cautionary Tale  I recently installed my PCM80 into the main studio and powered it on, and it worked fine. However 30 minutes later magic smoke came out of the rack and I traced it to the PCM80 power supply and immediately switched it off. Looking at the top of the old switched mode power supply you can just see a capacitor top pushing up, which is a common failure mode for these old units.

But once I had taken out the power supply module you can see the failing capacitor has cause other components on the bottom of the PCB to burn out and worse still the plastic shield between the PSU and chassis has started to melt. Within a few minutes this could have become a major fire with plastic dripping onto the units below and smoke filling the room.

Make sure your studio has a Smoke Alarm!!

Fire Damage!

Lexicon PCM80 PSU Replacement With the PCM80 (1993) Lexicon moved from fully linear to switched mode power supplies. They also added subsequent linear regulators for the analog rails, to ensure low noise. They used a standard third party switching power module, which is easy to replace with a modern version with the same voltages, current supply and fixing holes.

The Artesyn LPT45 is the model to go for, and it can be bought for £50. This is a lot cheaper than sellers on eBay want for a PCM80 PSU, which is simply a LPT45. The service manual states the power rail voltages and current demand, so it was easy to check this was the correct part. PCM80 Max Ratings are:

  • +5V is 5A
  • +15V is 2A
  • -15V is 300mA

The LPT45 delivers 4A on the +5V rail but the consensus is that is sufficient to safely power the PCM80. Lexicon did a great job on the power supply design with carefully designed analog power conditioning, using linear regulators, inductors and electrolytic capacitors. This circuitry looks to be in good condition, as it is not stressed as much as the switched power supply. However I will replace the power capacitors to be safe.

Tufnol Protector

Fitting the LPT45 The new power module is an exact fit, same connections and mounting holes. The only problem I had was the plastic shield had been melted by the power failure. I replaced it with a 1mm piece of Tufnol which provides the correct electrical insulation and is not going to melt or catch on fire.

The LPT45 is grounded to the chassis ground by two of the fixing holes which have earth pads, I double checked the earth continuity from chassis to the LPT45 ground connector to be sure. I returned the PCM80 to its rack and powered up – everything works and no smoke!

Learning Lesson Whilst I have refurbished the linear power supplies of the vintage gear I own, I have left the switched mode power supplies alone. That strategy has now changed, and I am replacing them ASAP. This means replacing the Emax power supply, where I will design a mounting  PCB for the Meanwell RPT-60B, and the Wavestation where an LPT42 may fit (again with a mounting PCB). I will also complete the design of a switched mode power supply and PCB for my Roland MKS-80.

 

Lexicon PCM60 Refurb

Overview Back in 1980’s I could only dream of a Lexicon reverb, slim expensive 1U rack FX’s that lived in Pro recording studios. My first FX unit was (IIRC) an ART reverb which was quickly replaced with an Alesis Quadraverb, which served me well for 10 years in the 1990’s. During 2000/2010 I downsized the studio and had no need for FX, even a TC3000 only lasted a year. New synths around this time tended to have in built FX.

In 2017 I built a new studio space with room for some outboard. I was fortunate enough to buy both a PCM70 and PCM80 from a couple of old recording studios that were closing down, one of them in France. These are the back bone of my reverb setup, along with an old Yamaha REV7, which I first saw in a recording studio in Reigate in the mid 80’s. Gated Reverb – ha!

Whilst the PCM70 and 80 have some great reverbs, they are more useful during mix down, rather than for tracking synths. They stay hooked up the the analog console as outboard. For tracking synths I prefer older Roland SDE delays which sound like refined tape delays, a refurbished Quadraverb or my newly acquired PCM60 reverb.

Lexicon PCM60 The advantage of the 60 is you get two reverb algorithms derived from the legendary Lexicon 224 (Room and Plate) with just 4 time delay settings and on/off low and high EQ. No presets, everything is real time button selection, no deep spaces to get lost in – just rooms. The 60 also has an effects send and return which means you can patch in a delay or EG to further change the sounds.

It took me a few years to find one, and its not a perfect example by any means. But I finally have a PCM60 which I use with my “Big Moog”, its patched into the 984 Matrix Mixer, whilst the PCM60 effects loop goes of to a SDE1000 Digital Delay. I prefer to print sounds and FX on the way into my DAW, rather than in post production.

PSU Recap

Refurbishment Outside the PCM60 needed a clean, and there is writing underneath the buttons where someone has recorded their patch settings. Unfortunately this permanent ink will not come off and is embedded in the now faded blue part of the panel. I will have to live with this, unless I can find a better panel in the future.

Electronically the PCM60 works well with only two issues; The input level pot is worn and jumps to maximum causing a lot of distortion as the input stage is overloaded. Fortunately a similar pot is still available from Mouser, so I replaced it. It is not a perfect match; the pin out is further forward and the shaft a slightly smaller diameter. The knob is also a very tight fit, but it works.

The second issue is that one of the signal level indicator LED’s is not working. I suspect this is a problem with the LM3915 driver chip which is socketed, so it was easy for me to replace it. However the problem was a LED failure, so I replaced all the green LED’s, as the modern LED’s have a slightly different colour. Its easy to remove the LED PCB from the front panel and swap the LED’s.

The Lexicon components are high quality and the PCB layout is excellent. The power supply capacitors date back to 1984, so I have replaced them with new Panasonic high quality versions. I am pleased with the sound and noise floor, so I haven’t made any Op Amp changes which would be; FET input and output S&H to AD823,  Bipolar input/output to LM4562.

Outcomes The PCM60 is very well engineered, cheaper and rarer than the well loved PCM70, with two sets of sound that are very nice for vocals and drums. I use it with shorter percussive synthesizers sounds rather than for big ambient pads, which need longer reverb times from my PCM70 and 80.

There is a set of version 2 ROM’s that replace the Plate reverb with an Inverse Room, which was popular back in the 1980’s, but rather a cliché now. The V1.0 ROM’s are 24-pin 2732’s and the V2.0 is 28-pin 2764, they can be kludged together and manually switched but the Inverse Room is not worth the bother and cost.

 

Roland SDE1000 Repair

Roland SDE1000

Overview I bought a broken Roland SDE1000 Digital Delay in November 2020 for just £40, but with the known fault of it not powering on. I already have a mint and boxed SDE1000 which I find to be a fantastic delay unit for using with analog mono synths. The plan is to repair this one and use it with my “Big Moog”, instead of the Revox A77 tape delays that Klaus used.

This particular SDE1000 was manufactured in March 1985. This was two years before I rekindled my interest in synths and a secondhand ARP Odyssey Mk3.  Although the Roland was a lot cheaper than studio FX at the time, it was an expensive luxury for me at the time.

The Roland SDE-1000 was one of the Japanese company’s first effects unit, launched in July 1983 at £399 alongside the more powerful “studio version” SDE3000 which was double the price. The delay unit is quick & simple to use, with a very straightforward front panel & interface.  Sound quality is surprisingly good with a smooth, very analogue sound. This is in part due to the companding circuits to get the analog data into just 12-bits.

Maximum delay time is 375ms in standard mode (750 ms in x2 mode) and 605/1210 ms using the x1.5 rear panel control.  The sound of the SDE in X2 mode is quite reminiscent of a slow tape delay, and increasing feedback results in a gradually decaying, dulling repeat – again, like tape.

Delay time is displayed on a 4-digit blue fluorescent display with an Up – Down rocker switch to alter delay settings. The LFO has speed & depth controls, which can give deep chorusing effects or a gently shifting delay with phasing.  There are only 4 memory presets and no MIDI but the SDE1000 was a sales success with over 7,000 made, and it remained popular before Alesis entered the market with custom DSP chips.

SDE1000 Advert

Technology The SDE1000 is an early digital delay which uses a Gate Array chip as the main controller rather than a DSP chip, and a 12-bit R2R DAC rather than a dedicated DAC chip. The microprocessor is the familiar 8049 which Roland used in many products during the early 1980’s. The analog signal is compressed into a 12 bit data word with three 64k bit RAM chips used to store the digital data.

Roland used good quality NE5532 Op Amps in the output circuits and a dual transistor input buffer

Changes The SDE100 went through a number of circuit changes in 1983 to improve the headroom and HF response. They are documented in the service manual. This particular unit in from 1985 so it has these changes implemented and a V3 PCB which is not mentioned in the service manual.

The Repair This SDE1000 is in reasonably good external condition and a sound interior, which has possibly had a small amount of repair work (like the rear pot for time adjustment). It is a robust and reliable design, so I am not expecting chip failure but a power supply problem.

The power supply provides many different voltage rails;

  • +/-15V rails for the analog circuits using a discrete voltage regulator
  • +5V for the digital chips using a 7805
  • +12V rail (7812) for the front panel LED level indicators
  • +12V for the DAC voltage reference
  • +20V for the LCD driver chips
  • +1.7V for the LCD itself

Any part of these circuits could be where the short circuit is, so this is going to take some time! I checked the X2 safety capacitor on the mains side of the transformer and it was ok but I have replaced it. I disconnected the power connectors until I was left with the +1.7V rail which was the source of a short circuit.

I disconnected the LCD and switch PCB from the main PCB to eliminate it as a source of a short, however there was an additional short in the 15V rails. In the end I replaced the W02 regulators and power diodes, all the power supply capacitors, power transistors and power capacitors. Even though none tested as failed, this complete overhaul solved the problem and the SDE1000 powered up perfectly and works a treat.

Sounds The original factory SDE1000 presets, which can be overwritten, are:

  • Long Delay: 750ms with feedback and light modulation
  • Doubler: 30ms delay with feedback and no modulation
  • Chorus: 50ms of delay with light modulation and feedback
  • Flanger: 15ms of delay with deep modulation

The sound quality does deteriorate when in x2 mode with a limited bandwidth of just 8kHz. So I keep the delay in x1 mode with the rear trimmer set to 1x or 1.3x.

Outcomes A nice warm digital delay line for £40 and another £40 on component replacements, that will maintain the SDE1000 for another 35 years! I replaced the original old battery while I had the delay apart and I will re-calibrate using the notes in the service manual before it finally goes in the studio. The slight change in power supply voltage rails may not be exactly as it came in the factory back in 1985.

Alesis DataDisk Refurb

Alesis DataDisk

Overview I picked up an Alesis DataDisk in May 2020 for £25, so I  can store and retrieve SysEx data from my hardware synths rather than having to power the computer on and use software. The 1U rack  connects up to my MIDI hub and uses a 3.5″ floppy diskette to store 800 KB of data.

The DataDisk was launched in late 1989 at a rather steep £299, but was quite popular for musicians touring and wanting to restore all their patches across multiple synthesizers. In the studio an Atari 520 was more effective with the right software, and that is what I used in 1990. The high cost of the DataDisk put me off buying one, until now!

Recap Complete

Refurb The DataDisk looks like an x-hire unit; connections have been hot glued and there is lots of wear to the casing and buttons. All the casing screws needed replacing with new ones, and the LCD mount has broken. It also needed a 9V external power supply, which is the same as used with the Quadraverb with a 4-pin plug, bought from eBay. I replaced the 16×2 LCD with a new OLED display and glued the mounting back together (two parts were broken) and unglued the ribbon cable.

The original LCD is 16×2 characters with 14 pins, here is the Quadraverb schematic which uses the same LCD. Note that there is no contrast potentiometer but a fixed contrast voltage of -0.6V at Pin 3. Pin 2 is the main GND connection and pin 5 is set low to enable write to the display. Pin 4 is the mode control for either data or an instruction and Pin 1 the +5V.

New OLED Display

I have fitted a new blue character OLED display, the Winstar WEH001602DBPP5BN which is available from Rapid Electronics. It has the same 14-pin connector and PCB size and is a drop in fit as Pin 3 is Not Connected. There is no contrast needed on an OLED display. To be extra safe the cable to pin 3 can be cut or the diode and resistor removed from the main PCB.  The new OLED fits on the same plastic mount but is thinner than the original and therefore the front of the OLED is set back 5mm from the bezel.

The three large 4700uF 25V axial electrolytic capacitors were replaced in the power supply along with 3x 4.7uF 50V and one 100uF 16V capacitor. The OS is 2.10 and does not need upgrading. There was no floppy drive in the unit, so I tried my spare diskette drive but it was not compatible, and I don’t want to hack one. There is not much space in the case left free for the diskette cable at the rear of the drive but there is plenty of room for a Gotek drive.

In the Studio I use the DataDisk with my MIDI polysynths to save and restore patch banks; the Wavestation, OB-6, XTk and D-05 using the iConnectivity MIO as the MIDI hub. All these synthesizers can initiate a SysEx dump of patch data, which the DataDisk simply listens for and then reads the data stream and puts it on the diskette. The DataDisk cannot handshake with my MKS-80, so I use the my MC-300 with the MFB-500 Bulk Librarian software which works perfectly.

The DataDisk can also initiate a SysEx Dump request, provided the Manufacturer and Device ID’s are known by the DataDisk software. You simply select these two parameters from the display, however the OS has not had an update for 30 years, and there is no free form editing of the Device ID which would be very useful – see below.

Storage Limitations the DataDisk is limited to 764 KB of patch data storage and a maximum of 53 files. In 1991 the storage limitation was not significant (a D-50 Patch Bank is 36 KB, the Wavestation is 64 KB and the XTk is 70 KB) but today synthesizers can generate much larger SysEx files, such as the OB-6 at 576 KB! Large SysEx files generated by fast PC’s may overwhelm the old synth processors, so I use pauses when sending to the Wavestation. The DataDisk uses a slow processor my today’s standards and therefore should not overwhelm the synths with SysEx, but maybe new synths will overwhelm the DataDisk, we will see!

Gotek Drive Setup It is easy to fit a Gotek drive and here is the setup, you need to customize the firmware:

  • Track Type: MFM, Two sides floppy, GAP3 auto GAP3
  • 80 Tracks, Sector IC Start: 1, Sectors size: 1024, 5 sectors per track
  • RPM: 300,  Bitrate: 250,000, Total sector: 800, Total size: 819200
  • HFE file interface mode: Auto (IBM PC 720kB)
  • Shugart device
  • Hardware Jumper settings: MO and ID0

File Naming The DataDisk reads the inbound MIDI SysEx message and extracts both the Manufacturer and Product ID’s. The Manufacturer ID is either one or three bytes with the DataDisk capable of recognizing the big manufacturers from the 1980’s using a single byte;

  • Sequential 01H
  • Roland is 41H
  • Korg is 42H
  • Waldorf is 3EH
  • Behringer is 00H 20H 32H

The DataDisk is over 25 years old and therefore has not kept up with more recently issued manufacturer ID’s in its ROM based look up table> If the manufacturer ID is not recognized the default is xxH. The Device ID’s are also a problem, as these single byte numbers correspond to a product name which the manufacturer has determined. Once again a look up table is needed and the DataDisk is stuck in 1991!

The DataDisk names the files with 3 set of characters:

  • XXXXXX is the manufacturers name
  • YYYYYY is the product model name
  • ZZZZZZZZ is the name of the file and can be edited

I may extract the ROM code and do an update if there is room in the ROM.

SQ Display

SQ Upgrade Alesis updated the DataDisk to a new SQ model in the Autumn of 1990 with a new firmware version 2.0 (and higher price of £349). SQ stands for SeQuencer as the upgrade enables the DataDisk to record and playback MIDI sequences, with the usual store and retrieval to floppy disk using DS/DD diskettes. MIDI sequences from a keyboard or a MIDI sequencer (like my Roland MC-300) can be recorded and then played back locked to the MIDI clock.

Sequence recording also allows SysEx to be recorded and played back with pauses, which is often how long data streams are managed.  MIDI data is recorded and played back in real time from the diskette with no copying to internal RAM, so there is no lag between hitting MIDI start and the notes being generated, this made the DataDisk as an attractive MIDI song player for live bands.

Buttons These are touch sensitive (multi-speed) versions and not the usual single click momentary buttons, therefore the best I can do is clean the surface of the buttons, and even polish them, but the damaged ones remained pale. A common issue with these buttons after 30 years of UV light.

Inside the DataDisk

Technical Bits  The DataDisk is based on an Intel 8031 microprocessor running at 12 MHz which does all the MIDI handling, front panel scanning and disk access work. It loads the OS from a 27C256 EPROM (32 KB)and uses 32 KB of static RAM as a work area. There is no battery as the RAM is only used during operation and no data needs to be saved across power downs.

A Sony MPF11W-10WP 3.5″ DS/DD diskette drive was used in the DataDisk, which can now be replaced with a Gotek drive – see above. Some hardware bugs were sorted out in the DataDisk manufacturing life, some to do with MIDI timing and signal levels. Mine has a few kludges.

OS Versions The latest OS versions are 1.03 (non SQ) and 2.10 (SQ) and there are many versions below this final numbers, so its well worth getting 2.10 which cures all the known bugs. It was released in November 1991. The service manual explains the version history and bugs, the OS EPROM is available on eBay.

 

 

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