Bad contacts in 25 year old mixing console

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fripholm

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I currently have a 1992 Allen&Heath GL3 on the bench for repair that is used as a FOH console. Despite its age and environmental abuse (for at least 10 years, the room its in is full of people on an almost daily basis) there are just a few minor niggles with this mixer.

Apart from a broken solder joint for phantom power in channel #9, everything else that is not working right can be attributed to bad contacts in the 26-way ribbon cable that is inter-connecting the channel modules. The cable itself is fine but on a number of channels/groups no current flows between cable and board connector - most of the time it's just one single pin that doesn't work.

One small wiggle on the connector and everything works again - but how long before something else fails...

What can be done to reliably make the connectors conduct, any ideas?

 
Often in gear this old, the contacts of both the plug and the socket will tarnish which can cause intermittent connections. The answer is to remove the tarnish but the question is how to do it. The contacts in ribbon cables are not exactly accessible. If the headers are not shrouded you may be able to clean them with a fine wire brush. The ideal solution for the ribbon itself is to replace it.

Cheers

Ian
 
I will second the suggestion to replace the ribbon cable if possible. Have you asked Allen and Heath about the possibility of sourcing a replacement? 

If it's a common problem they may have already made up a batch, if not they may have alternate advice.

JR

 
Yes - you need to replace the ribbon cable assembly - and clean the header pins on the pcb as best able to remove oxidisation.
Is it a simple ribbon cable or is there anything complicated about it ?
Assuming it's standard 1.27mm pitch tibbon cable (IDC connectors on 2.54mm - 0.1 inch pitch) then it's possible to make one up being careful with a bench vice if you don't have proper tooling. Or a local 'wiring shop' should be able to make it up at not too great a cost if you supply the technical info.
 
When properly fabbed insulation displacement ribbon cables can make reliable connections, but I have seen too many faulty ribbon cables from commercial fabs to encourage DIY.

The tooling and machinery for making ribbon cable require adjustment and maintenance to be problem free.

Good luck.

A good cleaning***  might help.

JR

**** I recently repaired my old neighbor's mobility scooter when a connector underneath it was dirty.  It was a serious commercial shrouded locking multi-pin connector, but over the years of exposure to the elements became intermittent (open circuit).  Some isopropyl alcohol and a toothbrush got it happy again. 

I've also restored some balky tact switches in my coffee roaster control panel by soaking them in isopropyl . This was meant to be a temporary fix, but still working like new months later.
 
JohnRoberts said:
When properly fabbed insulation displacement ribbon cables can make reliable connections, but I have seen too many faulty ribbon cables from commercial fabs to encourage DIY.

The tooling and machinery for making ribbon cable require adjustment and maintenance to be problem free.

Good luck.

A good cleaning***  might help.

JR

**** I recently repaired my old neighbor's mobility scooter when a connector underneath it was dirty.  It was a serious commercial shrouded locking multi-pin connector, but over the years of exposure to the elements became intermittent (open circuit).  Some isopropyl alcohol and a toothbrush got it happy again. 

I've also restored some balky tact switches in my coffee roaster control panel by soaking them in isopropyl . This was meant to be a temporary fix, but still working like new months later.

It seems I've had more joy with 'DIY' IDC cables than yourself. But it does take practice and attention to detail.
Where we do them at my work I did the drawings and prototypes but a member of the production staff turn out the 'real' ones.
It's quite low volume for industrial analysis instruments so that helps with the attention to detail I think.
Having said that I'd still rather use a good supplier with the production tooling - properly calibrated / maintained of course - but we've brought costs in house where possible as it makes more csense commercially in this instance.
I'll also add in that it's very adviseable to use a cable connector with an effective strain relief - some connectors don't have this.

Out of interest - was the mobility scooter connector in 'gel' - automotive style - to protect it ? I know that these can eventually dry out and give problems.
IPA (as in Ispopropyl Alcohol - not India Pale Ale  :) is my favourite cleaning thing - non corrosive to skin (the worst itwill do is dry it out) and residue free - just don't drink it !
I usually think of IPA to degrease and Caig DeOxit to get rid of oxidisation - though I know some people reckon DeOxit can give issues with residue in the long term...
 
Newmarket said:
It seems I've had more joy with 'DIY' IDC cables than yourself. But it does take practice and attention to detail.
Where we do them at my work I did the drawings and prototypes but a member of the production staff turn out the 'real' ones.
It's quite low volume for industrial analysis instruments so that helps with the attention to detail I think.
Having said that I'd still rather use a good supplier with the production tooling - properly calibrated / maintained of course - but we've brought costs in house where possible as it makes more csense commercially in this instance.
I'll also add in that it's very adviseable to use a cable connector with an effective strain relief - some connectors don't have this.
I just do not encourage this for casual DIY
Out of interest - was the mobility scooter connector in 'gel' - automotive style - to protect it ? I know that these can eventually dry out and give problems.
There was no evidence of gel.... but plenty dust and dirt...  The connector looked like a healthy current multi pin molex or similar, but was apparently not completely sealed from environment. It was feeding the brake solenoid (brake is automatically engaged when throttle is idled). The scooter has a smart microprocessor self-diagnostic code that declared the brake connection was not found. Later models had a microswitch to detect if mechanical clutch is engaged in this same multi-pin cable but this older model has no micro switch. Lots of guesswork making repairs from a newer service manual (I found on the WWW).

Connector was pretty robust but many years hanging underneath the scooter (being used outdoors) took it's toll. 
IPA (as in Ispopropyl Alcohol - not India Pale Ale  :) is my favourite cleaning thing - non corrosive to skin (the worst it will do is dry it out) and residue free - just don't drink it !
I don't drink either one (I prefer a hearty dark stout).
I usually think of IPA to degrease and Caig DeOxit to get rid of oxidisation - though I know some people reckon DeOxit can give issues with residue in the long term...
Rubbing alcohol and q-tips  is all I had in my bathroom cabinet.  Glad it worked...and I was able to get my 89 YO neighbor mobile again, on the cheap***.

JR

*** This is the third time I have repaired this same scooter.

1- was the battery charger not charging, and I had to reverse engineer the circuit to find a faulty resistor. I never encountered a 1/4w resistor that failed like that before, but it was cheap chinese crap, too cheap to keep working. The repair cost me a couple cent resistor, not counting my free labor.

2- next fix was after he left it out in the rain, and rainwater mixed with dirt to corrupt some electrical connections going into the smart microprocessor. It thought the forward/back control was not centered, but actually conductive mud was altering the electrical circuit. Again a zero cost repair, aided by rubbing alcohol, not counting my free labor.

3- most recent repair was made harder by my neighbor's attempt to fix it himself. At his age he is not as handy as he thinks he is and I found wires cut and reconnected incorrectly. Luckily the design is pretty robust, and nothing was blown up. I was able to finally suss out where all the random wires were supposed to connect.  I rather strongly advised him to just call me next time and never try to repair it himself  again.
 
Thanks guys for the suggestions!

JohnRoberts said:
I will second the suggestion to replace the ribbon cable if possible. Have you asked Allen and Heath about the possibility of sourcing a replacement? 

If it's a common problem they may have already made up a batch, if not they may have alternate advice.

JR

Having successfully DIYed ribbon cables before, I might try that first. I already have the proper tooling and materials for this job. If all else fails, I'll ask Allen & Heath about a replacement.
 
JohnRoberts said:
**** I recently repaired my old neighbor's mobility scooter when a connector underneath it was dirty.  It was a serious commercial shrouded locking multi-pin connector, but over the years of exposure to the elements became intermittent (open circuit).  Some isopropyl alcohol and a toothbrush got it happy again. 

Connectors like the one you describe, just love being packed with lithium soap white grease after cleaning. Excellent at excluding moisture, Used on boat trailer wheel bearings, as they do spend some time underwater.

Ford used it in the past to pack the bulkhead connector under the hood where the motor wiring harness connects at the firewall. Lubriplate is a common brand.

Gene

 

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Gene Pink said:
Connectors like the one you describe, just love being packed with lithium soap white grease after cleaning. Excellent at excluding moisture, Used on boat trailer wheel bearings, as they do spend some time underwater.

Ford used it in the past to pack the bulkhead connector under the hood where the motor wiring harness connects at the firewall. Lubriplate is a common brand.

Gene
I am a little nervous about using something called lithium soap grease, but if it happens again I will probably tape it up to seal it better....  at 89 YO I don't expect to be fixing it many more times.

Thanx for the tip I will research it (next time).

JR
 
JohnRoberts said:
I am a little nervous about using something called lithium soap grease, but if it happens again I will probably tape it up to seal it better....  at 89 YO I don't expect to be fixing it many more times.

Thanx for the tip I will research it (next time).

JR

Folks are living longer these days.  My grandmother made it to 102, still walking and cracking jokes.  Anyhow, I hope you have a neighbor just as kind and helpful when you reach the age where you can't solder!
 
> nervous about using something called lithium soap grease

"Grease" is oil and a soap (salt of a fatty acid, not hand-soap).
https://en.wikipedia.org/wiki/Lithium_soap
https://en.wikipedia.org/wiki/Grease_(lubricant)
https://en.wikipedia.org/wiki/Soap

Lubriplate is general mechanical lubrication. I had a Ford which had to have "dielectric grease" on its connectors or they would crap-out. Dielectric grease is a standard car-store item. I don't know how much crossover there is with "white grease" like Lubriplate.
 
fripholm said:
Thanks guys for the suggestions!

Having successfully DIYed ribbon cables before, I might try that first. I already have the proper tooling and materials for this job. If all else fails, I'll ask Allen & Heath about a replacement.

Let us know how it turned out. I got the same desk in a few days ago, with the very same ribbon wire problem.
 
PRR said:
> nervous about using something called lithium soap grease

"Grease" is oil and a soap (salt of a fatty acid, not hand-soap).
https://en.wikipedia.org/wiki/Lithium_soap
https://en.wikipedia.org/wiki/Grease_(lubricant)
https://en.wikipedia.org/wiki/Soap

Lubriplate is general mechanical lubrication. I had a Ford which had to have "dielectric grease" on its connectors or they would crap-out. Dielectric grease is a standard car-store item. I don't know how much crossover there is with "white grease" like Lubriplate.
I vaguely recall using lubriplate when rebuilding motors on bearings and the like to provide lubrication until oil pressure comes up (I think).  I also recall a questionable oil additive (STP?) that was used on bearings for dry starts. 

A dielectric grease sounds more electrical.  I can appreciate the merit to keeping water and dust out. If/when it fails again.

Thanx

JR
 
jensenmann said:
Let us know how it turned out. I got the same desk in a few days ago, with the very same ribbon wire problem.

It worked great!

Unfortunately I was thrown back a bit by a blown resistor for supply filtering in the left master channel, because I tried to turn the console on - still with parts of the old cable installed - stupid me! However, it was an easy fix...  ::)

To clean all the board connectors, I used a fine rotary wire brush mounted on a dremel and contact cleaner/spray before I installed my home made ribbon cable. After that I've checked the routing of all the channels to all groups/auxes etc and everything seems to work fine now - and the left master module, too  ;)

 
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