Vintage 70's Midas Channel Strip Problem PRO5A

[RoadrunnerOZ]

Yeah - should be fine - it’s just a ground wire for the plate by the look. Just make sure that wire is out of the way and can’t short anything out. However this is where you need to get yourself some test gear - signal generator and scope - and start with injecting some signal and probing the path from the back plate assembly with a scope - there’s not much there but there could be a break in the wiring from the back bracket sub assembly XLR to the board with R1 to R5 and L1 and L2 or from that board to the transformer (the transformer needs to be checked for continuity on both input and output), then mic/line switch and wiring, if the switch is open circuit = no sound - the switch centre pole is a good place to inject signal. You can’t go much further without the basic gear and also a soldering iron or the assistance of someone with the gear and ability to trace the schematics. If you have the knowledge and basic skills yourself and can get the gear to do it yourself it costs less to buy the test and service basics than paying a tech for an outcall that is costing by the hour. Have you checked your extender cable on another channel card or tried this board back in the desk without the extender? If not I’d do so.

 

[telehumbucker]

Yeah - should be fine - it’s just a ground wire for the plate by the look. Just make sure that wire is out of the way and can’t short anything out. However this is where you need to get yourself some test gear - signal generator and scope - and start with injecting some signal and probing the path from the back plate assembly with a scope - there’s not much there but there could be a break in the wiring from the back bracket sub assembly XLR to the board with R1 to R5 and L1 and L2 or from that board to the transformer (the transformer needs to be checked for continuity on both input and output), then mic/line switch and wiring, if the switch is open circuit = no sound - the switch centre pole is a good place to inject signal. You can’t go much further without the basic gear and also a soldering iron or the assistance of someone with the gear and ability to trace the schematics. If you have the knowledge and basic skills yourself and can get the gear to do it yourself it costs less to buy the test and service basics than paying a tech for an outcall that is costing by the hour. Have you checked your extender cable on another channel card or tried this board back in the desk without the extender? If not I’d do so.

Thanks for all your info, help. I had a tech in here and the transformer is fine....he narrowed it down to the input section.....As others here suggested, he recommended I start doing continuity on the wires in that section. After a couple of wires tested o.k., a wire that connects to the mic/line switch appeared to be disconnected under the blue sleeve. When I pulled back the sleeve the wire was detached as shown in the picture - the red wire. Hopefully that is the issue. I haven't soldered it back yet, as I am getting the equipment needed to do so. Also, a couple of wires on the transformer came detached in the process of testing, so need to resolder those also. Where can I find something like, a modern equivalent, to the blue rubber sleeves that protect the wires at the solder joints. The wires measure about .1mm diameter, and the smallest sleeve in the USA i've been able to find are 1/8" interior diameter. I assume they are available somewhere, just haven't yet found a source.....

 

[NoisyIndividual]

They used to be called Hellerman sleeves, they come in many different sizes.
Now you will find them as Hellermantyton sleeves pretty much everywhere.
I still use them to wire XLR's, as I have lots of them left.
You need to buy them by the 100, but to be honest you may as well just get a metre length of heatshrink tubing instead for the small amount you need.

This should add some level of strain relief between solid pin and flexible wire, and will also guard against stray strands of unsoldered wire shorting between adjacent pins, which is what the Hellerman sleeves are designed to do, but on more of an industrial scale than heatshrink.

The Hellerman sleeves also really benefit from Hellerman lubricant and the appropriate spreading tool to apply them easily, as they are really quite tacky by design.
Heatshrink is much easier to use, and doesn't require a tool or lubricant, just some hot air.
Some people use cigarette lighters but I don't think I would stoop so low.

 

[telehumbucker]

The used to be called Hellerman sleeves, they come in many different sizes.
Now you will find them as Hellermantyton sleeves pretty much everywhere.
I still use them to wire XLR's, as I have lots of them left.
You need to buy them by the 100, but to be honest you may as well just get a metre length of heatshrink tubing instead for the small amount you need.

This should add some level of strain relief between solid pin and flexible wire, and will also guard against stray strands of unsoldered wire shorting between adjacent pins, which is what the Hellerman sleeves are designed to do, but on more of an industrial scale than heatshrink.

The Hellerman sleeves also really benefit from Hellerman lubricant and the appropriate spreading tool to apply them easily, as they are really quite tacky by design. Heatshrink is much easier to use and not tacky at all.

Thanks. Sound like heat shrink is the way to go.

 

[NoisyIndividual]

Unless you need to do this sort of thing, then yes.

 

[RoadrunnerOZ]

Thanks for all your info, help. I had a tech in here and the transformer is fine....he narrowed it down to the input section.....As others here suggested, he recommended I start doing continuity on the wires in that section. After a couple of wires tested o.k., a wire that connects to the mic/line switch appeared to be disconnected under the blue sleeve. When I pulled back the sleeve the wire was detached as shown in the picture - the red wire. Hopefully that is the issue. I haven't soldered it back yet, as I am getting the equipment needed to do so. Also, a couple of wires on the transformer came detached in the process of testing, so need to resolder those also. Where can I find something like, a modern equivalent, to the blue rubber sleeves that protect the wires at the solder joints. The wires measure about .1mm diameter, and the smallest sleeve in the USA i've been able to find are 1/8" interior diameter. I assume they are available somewhere, just haven't yet found a source.....

Try here - they have black, blue, red, pink:

https://au.element14.com/w/c/cable-...r=1.2mm&product-range=helsyn-h&packaging=pack

 

[RoadrunnerOZ]

It sounds like the wiring is ageing and starting to rot at the joins - the corrosion starts where the solder ends and the wire starts before it goes into its insulation, the rubber sleeves basically hide the problem - you need to give the wires a firm gentle tug, enough that the rubber outer sleeve is not masking the disconnect.

The sleeves I posted above are slide on - you push them back up the wire before soldering but you shouldn’t be missing any sleeves anyway unless they’ve perished.

On looking at the photo these appear to be larger diameter than the wire - they may be the 1.5 or 2mm ones. If you have a digital caliper you can measure the outer diameter of the tube while it’s shape is supported by the wire inside - and then the tube wall thickness with one of the tubes off the wire - subtract 2 x wall thickness from the OD to get ID. It’s almost impossible to measure the internal diameter of a flexible tube that small and even if you got the tips inside the shape would distend and give a false diameter reading.

https://au.element14.com/w/c/cable-...5mm|2mm&product-range=helsyn-h&packaging=pack

 

[NoisyIndividual]

Hellerman sleeves are an interference fit.
You need to stretch them open before/whilst sliding them onto the soldered pin, where they then close back up and grip well.
You can get away with just pushing them on if your pin and solder have no spiky bits sticking out preventing this.

Which is really why you need at least the lubricant and preferably the stretching tool to apply them in large numbers quickly.

If they aren't tight they will just fall off.

 

[RoadrunnerOZ]

I used to have the stretching tool and sets of sleeves but I’ve since replaced all that with heatshrink years ago. The tool has three tapered prongs that slide inside the tube - you then have to poke the wire through the tube from behind with it expandedand with the tool slid back up the wire, solder the wire, bring the tool with opened jaws over the soldered terminal then slide the tool out of the sleeve. This was a major pain in the butt - in dense wiring you can’t manoeuvre the tool especially if all the boards are mounted surrounding the termination points.
There were also sleeves used that were sized slightly larger than the wire but smaller than the terminal post and relied on neat soldering - these were just slid over the terminal with a bit of force.
Personally I’d go with heatshrink and use an air heat gun set to low temperature - you pre-prep all the wires with shrink at once, solder them all and lastly hit them with the heat gun.
A lot of this assembly sleeving was done as part of the assembly process with the unit in a fairly dismantled state - you don’t want to pull the whole thing apart just to re-sleeve a few wires using a tool like that.
The tool itself is also expensive:
https://au.element14.com/hellermann...ves-3-sizes/dp/151080?st=hellermanntyton tool

 

[NoisyIndividual]

I still use my 3 pronged tool to put Hellerman sleeves over the end of mic cable to secure the green silicone sleeving I put over the ground wire.
It's quicker than having to use a heat gun afterwards on heat shrink, and the result is bullet proof.

 

[RoadrunnerOZ]

Yeah if the sleeve slides over the terminals without having to use the tool you’re cool - you just use the tool to get them on the wire, but when the terminal is much larger than the wire you have to either carry the sleeve over the terminal with the tool or push like hell to get the tube over. The problem I’ve found with these is they usually don’t fully engage the wire insulation surface leaving room for wire ends cracking off inside. This occurs where the sleeve tube has to leave the terminal and engage the wire insulation - there is a small gap whereas heatshrink fully engages and forms a strong part of the hold-in-place mechanism as it also shrinks very slightly longitudinally. For more flexible sleeving I use medical grade silicone heatshrink - this handles from -60 degC to +200 - heat gun takes 15 - 30sec.
I still do like the Hellermann but I use heatshrink for convenience.

 

[NoisyIndividual]

I used to wire DSUBs with Hellerman sleeves, much like the photo I posted, but pushing that onto the pins, as you say, can be a pain if you don't get every solder connection perfect first. Lubricant is a must to do that.
Now I use heat shrink, but it doesn't stick as well.

 

[NoisyIndividual]

The lubricant also seemed to help with the bonding process. Maybe it is this that sends the sleeves crusty some 30 years later?

 

[RoadrunnerOZ]

The lubricant also seemed to help with the bonding process. Maybe it is this that sends the sleeves crusty some 30 years later?

I’d say so - it’s a petrochemical lubricant from those days and that causes rubber to harden - happens a lot in old cars with their oil lines, even the best of them. A lot of heatshrinks now have a sealant adhesive internally - these for outdoor wet and marine environments but to be honest, once you trim back the wires, put a new sleeve over whether heatshrink or rubberised tubing you’re good for another 30 - 40 years. The sleeve is to maintain a strong flexible coupling that theoretically protects the copper wires from breaking off during servicing. I’ve had a lot of gear in for servicing that has had wires hanging by a couple of strands of copper. I like the silicone high grade stuff as it has a memory as well as clinging firmly to the wire’s insulation jacket and being flexible. If you shift a loom to a new position you just reheat the shrink sleeves on the multi pin connector and it’ll stay there.

 

[transient]

See this thread for further comments about Hellerman sleeving:

https://groupdiy.com/threads/hellerman-sleeves-turning-to-goo.78246/post-999897https://groupdiy.com/threads/hellerman-sleeves-turning-to-goo.78246/post-1000058
I have seen solder joints that seem to have been attacked by the degrading sleeving, turning the solder to a crumbly mess.

I used to drive a Midas console back in the seventies when they were all hand-built - like this one.