Micro-synth, mega-exasperation

[Mark Hammer]

A buddy  asked me to repair his older Micro-synth some 2 years ago.  With some very gracious help from Stephen Giles, I got it working.  Had to install a new CA3094 and 4558 to replace two chips that were fried. But got the beast up and running....on the bench.  Try to package it up again to stuff into the enclosure and no dice.  I let it sit for a year and a half out of frustration. 

Now, the fellow is coming over next week to pick it up, so it's time to bite the bullet and get it functional.  I set it up on the bench, discover a fractured wire, fix that, and bingo, sweet grindy wah sweeps once again.  Fold the two boards over and attempt to re-install into the chassis and once again it doesn't work.

The board with all the slider pots is connected to the board with all the electronics by 12 solid-core wires that have the nasty habit of fracturing when you have to bend them to fi the two boards into the box on top of each other.  Driving me absolutely nuts.  It feels like I'm going to have to replace every single piece of solid-core wire with stranded stuff, just to be able to wiggle things back into place.

Anybody else have experience with the insides of these things that can provide some advice, other than "Don't give up"?

[Gus]

I have had issues with solid wire in older effects
I think the best thing to do is replace all of the solid wire

[MikeA]

Hey Mark, I worked for a telecom for 25 years where solid core CU was the norm for wiring backplanes (30 ga) and distributing frames (22-24 ga.)  Fatigue in solid wire is a function of the number of times it's bent, and the bend radius (radii?)  If you can pre-bend once with the largest possible radius and not re-bend during assembly, you'll have the best chance of avoiding a complete rewire.   

[amptramp]

If the wiring has regular spacing, you may be able to use a board connector on each board so they can plug in together.  Board connectors have their own reliability issues but this is usually addressed by contact cleaner, not replacement.  There are ribbon cables that can be useful as they are meant to be bent into all sorts of shapes and some of them come with terminated ends so you can just solder them into the board.  Some of them are solid conductor but many are stranded but you don't have to deal with the strands if they are terminated in a pin header.

If you want to stick with individual wires, the smaller the gauge, the less stress you put on the wire from flexing.  If you bend a wire, there is an inner part of the bend that compresses and an outer part of the bend that stretches and the smaller the gauge, the less the stress.

[Mark Hammer]

Sadly, fairly irregular spacing.  And the solder joints....some are huge.  Some of the older EHX and MXR devices, man.  Sometimes you had to wonder if they weren't made to stick in the trunk and provide better wheel traction in the snow.  Just gobs and gobs of solder.

[Mark Hammer]

Well, I replaced every last bit of solid-core wire with stranded wire, and that seems to have fixed the problem as near as I can tell.

For all of its various virtues, one of the inherent flaws of solid core is that if it gets bent too much AND the insulating covering is hardy enough, the wire can fracture inside but you can't necessarily see it from outside.

[StephenGiles]

Only just seen this thread Mark, I think you've done the right thing. I had the same problem with the 2 units I was given at EH UK (as non-repairable!!) almost 40 years ago, every time I tried to bend over the slider board another wire would break free. I eventually sold both units to a collector who didn't care if they worked or not - although they both did at time of sale!

[Kevin Mitchell]

Well, I replaced every last bit of solid-core wire with stranded wire, and that seems to have fixed the problem as near as I can tell.

Ehh I've been neglecting to do the same thing. Every time I handle the circuit one of the damn wires break. Though sadly that's likely not the main culprit for my unrepaired micro synthesizer 

[puppiesonacid]

hey Kevin, hows the MS project going?

[Kevin Mitchell]

hey Kevin, hows the MS project going?

PM'd

[StephenGiles]

A Happy New Year to everyone!

I'm looking at the EH Microsynth drawing dated September 26 1996.

What if the peak follower output at junction of D3 and pin 6 of IC5B, which it states is between 0v and -7v depending on signal, is connected via a suitable resistor to the wiper of the start frequency pot, where the voltage would normally be set between 0v and -ve. Would this clamp the max voltage at the start frequency pot wiper to that of the leading edge voltage of the peak follower, or if not how could this be done? The object of this being to allow the initial peak of the filter sweep to follow strength of the input signal!!

I'm convinced there is a simple solution, but I can't nail it!