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.