EMS synthi Hi-Fli repair

[bsoncini]

My friend just got his hands on one of these and it works but sounds pretty bad.  Asked me to take a look at it to see if I could get it working better.  Thought you guys might enjoy the pics of how big this beast is.  To learn more about the product.  http://www.gilmourish.com/?page_id=77.  Apparently designed by a guy who designed a lot of electro harmonix pedals.  I have no idea where to start.  I'm guessing recapping the whole thing

My hand on it is a reference for how big it is



Look at all those diodes

[somnif]

Are those all diodes there on the left? 

[bsoncini]

Are those all diodes there on the left? 

yes. all 1n4148s

also 9 ca3080.  lots of compressors to be made if in the end this thing is not fixable

[Marshall Arts]

Be very, very careful:

https://reverb.com/ca/item/1567718-original-ems-synthi-hi-fli-analog-guitar-synth-effects-ultra-rare-exc-vtg-cond

There is no "cannot fix it" at that price point. 

[bsoncini]

Be very, very careful:

https://reverb.com/ca/item/1567718-original-ems-synthi-hi-fli-analog-guitar-synth-effects-ultra-rare-exc-vtg-cond

There is no "cannot fix it" at that price point. 

Holy sh*t

[somnif]

http://jbemond.free.fr/SDIY/EMS/EMS_Hifli.pdf

Circuit notes and schematic if you want to poke around. Scan quality sucks, unfortunately, but its something to work from.

More discussion: https://www.diystompboxes.com/smfforum/index.php?topic=94294.0
And more still: https://www.diystompboxes.com/smfforum/index.php?topic=73726.0

[bsoncini]

http://jbemond.free.fr/SDIY/EMS/EMS_Hifli.pdf

Circuit notes and schematic if you want to poke around. Scan quality sucks, unfortunately, but its something to work from.

More discussion: https://www.diystompboxes.com/smfforum/index.php?topic=94294.0
And more still: https://www.diystompboxes.com/smfforum/index.php?topic=73726.0

thanks.  that'll be helpfull.  over 200 diodes in the phaser part of the pedal!

According to slacker from diystompboxes
"The phaser is the same basic design as things like the Phase 45 and Phase 90, but instead of using JFets as voltage controlled resistors it used the string of diodes instead.
The way the diodes act as a voltage controlled resistor is something like this, each diode drops about 0.6 volts across it and this is near enough constant for different currents. Mr Ohm tells us V = IR so if V is constant then as I increases R must decrease, so the resistance of the string of diodes is inversely proportional to the current through it, so by varying the current you vary the resistance.
This is used in a number of synth designs, like the Steiner Synthacon filter, the classic Moog filter does essentially the same thing but with transistors instead of diodes. In diystompbox land Tim Escobedo's Quick and Dirty VCFs use the same trick."

[PMowdes]

Holy shit, I'd love to trace this.  I have a set of documents which might be helpful, they include the schematics but the quality is too poor to make sense of for a reliable read.

[somnif]

I just realized it has a "Meow" setting.

...I love this.

[bsoncini]

Holy shit, I'd love to trace this.  I have a set of documents which might be helpful, they include the schematics but the quality is too poor to make sense of for a reliable read.

I think sonic posted that schematic. It's kinda hard to read in parts.

Maybe we can figure something out. My friend is not in desperate need to get it back as soon as possible. All the faders are broken so I need to figure how to replace them. But they work sliding empty with a screw driver.

The fuzz and octave down parts work and sound pretty great.

Kinda weird with the foot pedal. It's not like an expression pedal. You can program to turn effects on or off in the up and down positions.

[PMowdes]

Holy shit, I'd love to trace this.  I have a set of documents which might be helpful, they include the schematics but the quality is too poor to make sense of for a reliable read.

I think sonic posted that schematic. It's kinda hard to read in parts.

Maybe we can figure something out. My friend is not in desperate need to get it back as soon as possible. All the faders are broken so I need to figure how to replace them. But they work sliding empty with a screw driver.

The fuzz and octave down parts work and sound pretty great.

Kinda weird with the foot pedal. It's not like an expression pedal. You can program to turn effects on or off in the up and down positions.

Yeah that document has been around a while,. Dino and I talked about buying one to trace it.

Some decent photos would be a great place to start.  Are the boards all soldered together on those headers?

[bsoncini]

Yeah. The headers are soldered in. But there are no components hidden on the board below. All the pots, faders and switches are on the other side of that board.

I can take as many pics as you want

[Scruffie]

Welp, I repaired an A/DA Harmony Synth *rolls up sleeves* (hard not to brag on that one  )

David Cockerell design I believe, if you're studying sections the V1 small stone and V1 micro synth will probably be handy references.

Given the size and age, a full electro recap is probably a very good port of call and a full set of voltages of all the CA3080 with all the sliders up and all of them down... probably best to number them in an image file.

Edit: And static voltages of any other op amp or whatever chips are in there.

[PMowdes2]

Yeah. The headers are soldered in. But there are no components hidden on the board below. All the pots, faders and switches are on the other side of that board.

I can take as many pics as you want

If you have to take the boards apart to get to the bits you need to repair then a colour photocopy of the top and bottom of each board would be incredibly useful, we could flip the images and superimposed them to get a better idea of the topology.

[digi2t]

This one is on my bucket list. Having cheated death once already, I say that in the most sincere way. This needs to be traced proper. Somebody please trace this before I die. Again.