All posts by admin

other

Dynacord Echocord S62 and S65

It must be Echo season,  I have now 5 tape echos in for repair. Dynacord Echocord Super 65 was not working at all, however it was in incredibly good shape otherwise I don’t think this particular piece done many active hours because there wasn’t a lot of wear on the original heads and everything was in perfect order except the motor which clearly had some moisture induced damage. Shaft was rusted in the bearing but I managed to free this up, clean and lubricate.

I had the pinch roller refurbished, cleaned the heads and made a new loop out of master BASF tape, but I struggled to get this rolling, it wouldn’t spin on adagio and even on presto setting it would stop eventually. I was puzzled for quite a bit and learned several lessons.

1) master tape is no good for echo loops, it is too thick, abrasive and sticks to the brass heads.

2) Brasso polish is great for refurbishing worn tape head surface, it made it roll with much less resistance

3) tension settings and pinch roller pressure settings are extremely important, even a slightest tweak makes whole lot of difference to the overall ability to spin freely, especially at low speeds

With mechanical problems out of the way it was time to check electrolytic caps and they were generally OK with exception of the main PSU filtration. Non functional Magic Eye indicator was caused by faulty diode as well as faulty EM84 itself.

Main issue was the combined pot / pull switch which had to be taken apart cleaned and reassembled Echo is working flawlessly since.

I have also replaced burnt light bulbs illuminating the  selector switches. It’s a beauty to behold

 

I expected the Super 62 to be easier to repair because Nachhall function was working and the only missing bit was the Echo functionality…. I couldn’t be more wrong. This piece gave me proper headache to repair and countless hours of head scratching.

Capacitors were generally in really poor state, all the Electrolytics were measuring very high ESR and even several of the ceramic caps had problems. I rarely ever see ceramics to be the problem but these wax sealed units probably somehow soaked up moisture and became partly conductive which resulted in valve self oscillations.

I have eventually decided to do complete recap.  This was especially surprising because just 3 years younger unit S65 was nearly perfect in this regard.

After the recap this unit was still only partly functional but substantially quieter. There was remaining issue with insufficient voltage on the erase head. Problem was eliminated by replacement of ECC82 with new known good example. After proper cleanup of the combined Pot/Switch I could hear faint echo coming through on Echo 2 settings but not so on 1 or 3. I measured the selector switch and had to de-solder entire board and take the selector switch cluster apart and clean thoroughly.

Now I was at the point where I really didn’t know what to do, it appeared as if there was a bad valve socket for the Ecc83 acting as a playback head amplifier I could hear clearly when I tapped one of the heads with screwdriver but only faintly when I did the same with the other.

The root cause of the problem ended up being bad playback head, after desoldering it one of them measured 1kOhm but the other was open circuit so when I was tapping the bad head what I was hearing was just a cross talk from the other head!

At the moment I’m facing challenge with sourcing replacement playback head and may have to have it custom manufactured which would sadly result in already largely uneconomical repair to become entirely uneconomical. Nearly 40 hours of time in total and it’s still not running. I hope there is some spare head lying about.

 

 

 

 

mixing desks

Fender M12

I never knew Fender did mixing desks but then out of the blue this one had to be saved from going to the scrapyard.

There were several issues

  1. PSU had a toast rectifier diode and burnt out stabilizer. I could tell there was somebody in there before me and added various modifications. One of them was extra huge electrolytic cap to get rid of the PSU induced hum. Thing is, PSU hum was there due to dried out electrolytic capacitors with massive dielectric losses so while this modification removed the unneeded hum the ever increasing load on the transformer and rectifier diodes eventually led to the diode failure and associated chain events.
  2. one of the meter  module opamps were toast and presented beautiful smelly smoke following the power up
  3.  few of the channels had a bad solder joints
  4. one of the channels had a bad OPAmp

When tackling vintage console the main question is that of economical feasibility of the repair

If things are to be done properly, every switch and pot taken apart cleaned and lubricated, every dried out cap replaced it takes enormous amount of time which will be worth several times the price of the console itself

With everybody moving to digital nowadays , there are high end analog consoles available for unbelievably low prices

However it was decided to rescue this vintage piece and 2 weeks of cleaning have begun

I stripped every channel, carefully opened every single pot and cleaned using three stage process First I remove the coarse debris with compressed air, clean all the contacts and pot track with Kontakt 60 contact cleaner, wash it down with Kontakt WL and finally lubricate with Kontakt 61 fader lubricant

Nylon scratch brushes were particularly handy in this effort

This before / after picture of the slider pot shows the difference thorough cleaning can make, all of the sulfides dust dried out grease are removed and surface freshly lubricated

Difference it made to the feel of the slider pots was quite eye opening

The end result is reliable vintage mono mixer with fairly high noise bed but it’s nice analog noise, nothing particularly irritating

 

Organs / Synthesizers

Antares 2 – Kolafon

Antares 2 is a rare breed. This Synth was developed in Czechoslovakia in 1979 by VURT (Research Institute of Broadcast and Television) and only few prototypes were ever made. There was one small batch manufactured (<10 pieces) before the project was finally retired.

There were few issues with this particular piece. Mechanical problem with one of the keys and associated damage around the key J wires.

Major problem were the capacitors. I had to replace both the dried up electrolytic caps as well as metalised paper caps and ceramic caps which absorb moisture over time. Following the  cleanup of all the pots and switches as well as full recap Antares sprung back to life.

I’m giving special credit to the mechanical construction of this piece, all the electronics apart of keyboard itself are in one metal enclosure. This can be tilted upwards to allow for better access to the controls.

More pictures are little history in Czech language can be found here.

http://czechkeys.blog.cz/0912/syntetizer-antares-ii

All the electronics are in 5 modules and use gold plated high quality connectors. The entire PCB section can be also tilted and secured in place using thumb screws allowing full access to all the components.

Real joy to work on.

Amps / Preamps

Trace Elliot GP 11

This preamp was humming and some of the graphical sliders worked as a noise generators rather then equalizer.  Also the two momentary switches were bad. I couldn’t find the exact momentary switch so i had to modify the switch cap slighty to fit modern replacements.

Re-cap and upgrade of main filter cap from 2200uF to 15000uF resolved all the PSU induced hum and one of the transistors in the graphical equalizer actually had a small crater where the silicon chip used to be inside of the plastic casing. It was interesting that the transistor was still working-ish but it was acting as a noise generator.

Organs / Synthesizers

Vermona E-Piano

E-Piano was a bit more complicated repair compared to the Vermona string synth. PSU had dried up filter electrolytics and one of the earth wires fell off.

Following a pot cleanup all was working well except tremolo.

See the unusual but very reliable slider pot

I noticed some of the electrolytic caps were getting warm due to ESR. After the replacement piano was quieter with less strain on the PSU however the tremolo generator still wasn’t oscillating.

Both of the transistors were OK, all the surrounding resistors as well, electrolytes were replaced so the only culprit left were the foil capacitors and indeed once replaced by small electrolytic caps (the only 470nF I had in my spares drawer) tremolo sprung to life. I managed to later replace electrolytics with foil polypropylene condensers and tremolo was much nicer and more stable sounding afterwards.

Organs / Synthesizers

Korg Poly 61

This Synth came to me following a damage suffered during transport. Joystick was loose /broken and it wouldn’t turn on or even when it turned on it would just display nonsense and wouldn’t react to any of the presets.

The core of the issue was a semi shorted battery and the spring clip from the joystick wedged under one of the PCB’s causing short of some sort.

With battery and the offending spring clip removed all sprung to life and worked just fine when presets were loaded.

I managed to glue the joystick together, but I sourced replacement module in the meantime.

 

Organs / Synthesizers

Vermona Piano Strings

 

Vintage synth from Eastern Germany, you can smell the communist era inside of it. Very typical earthy smell of brown PCB boards. All it needed to bring back to life was thorough cleanup of all the keyboard contacts and slider pots.  After an hour and a half with compressed air and IPA it’s back in business.

Slider pots are actually very good design, fully open accessible and designed to be cleaned, sadly I forgot to take picture.

The way this one sound is just pure filth, it’s harsh…….